This document discusses lipids and membranes. It describes the basic structures of lipids like fatty acids, glycerophospholipids, sphingolipids, and cholesterol. These lipids can assemble into structures like micelles and bilayers in aqueous environments due to their amphipathic nature. Bilayers allow for the formation of cell membranes. Membranes contain proteins that can be integral, peripheral, or lipid-anchored. Lipid composition and proteins influence membrane properties like fluidity.
This document discusses the structure and functions of membrane lipids. It describes the main types of membrane lipids - glycerophospholipids, sphingolipids, glycosphingolipids, and cholesterol. It explains the structures of these lipids, including their polar head groups and non-polar hydrocarbon tails which allow them to form lipid bilayers. The document also summarizes how membrane lipids contribute to membrane fluidity and permeability, noting how cholesterol and unsaturated fatty acids influence fluidity and prevent crystallization.
The document summarizes key biological molecules and their structures and functions. It discusses monomers that make up carbohydrates like monosaccharides, disaccharides, and polysaccharides. It then explains lipids, made of triglycerides, and proteins, composed of amino acid chains that fold into primary, secondary, tertiary, and quaternary structures. It also briefly mentions the roles of water and inorganic ions in living organisms.
Lipids have a hydrophobic nature due to hydrocarbon chains. They are insoluble in water but soluble in nonpolar solvents. Major lipids include fatty acids, triacylglycerols, phospholipids, cholesterol, and steroid hormones. Fatty acids are used for energy storage and membrane components. Triacylglycerols store fatty acids as an energy source. Phospholipids are major membrane components. Cholesterol is important for membrane structure and steroid hormone synthesis. Lipids are digested into fatty acids and monoacylglycerols then absorbed into intestinal cells to form chylomicrons which transport lipids through lymph and blood.
This document discusses lipids and their classification and functions. It describes the main categories of lipids including fatty acids, glycerolipids, glycerophospholipids, sphingolipids, sterol lipids, prenol lipids, and saccharolipids. Key points include that fatty acids are the basic building blocks of lipids and can be saturated or unsaturated. Glycerolipids like triglycerides function in energy storage. Glycerophospholipids make up the lipid bilayer of cells. Sphingolipids contain sphingoid bases and include cerebrosides and gangliosides. Cholesterol is an important sterol lipid that structures membranes. Imbalances in lipid metabolism can lead to
Compound lipids contain additional substances like phosphorus, carbohydrates or proteins in addition to fatty acids and alcohols. Phospholipids are important compound lipids that contain phosphoric acid and make up cell membranes. They are classified as glycerophospholipids containing glycerol or sphingophospholipids containing sphingosine. Glycolipids contain carbohydrate residues and sphingosine. Lipoproteins combine lipids and proteins and transport lipids in the bloodstream, classified by density.
Phospholipids are major constituents of cell membranes and are composed of a glycerol backbone with two fatty acid chains and a phosphate-containing polar head group. There are two main types of phospholipids: glycerophospholipids, which have a glycerol backbone, and sphingolipids, which have a sphingosine backbone. These amphipathic phospholipids spontaneously form bilayers that serve as permeability barriers enclosing cells and organelles. Common phospholipids include phosphatidylcholine, phosphatidylethanolamine, sphingomyelin, and phosphatidylinositol, which each have different head groups that influence their roles in cell signaling and structure.
This document discusses the structure and composition of bio-membranes. It states that bio-membranes are composed primarily of phospholipids that spontaneously form a bilayer structure. The phospholipids are amphipathic, with a hydrophobic tail and hydrophilic head. This allows the tails to interact at the membrane interior, separating the hydrophilic exterior into cytosolic and extracytosolic leaflets. Membranes also contain proteins and sterols that modulate membrane properties and functions. Integral membrane proteins span the bilayer, while peripheral proteins are attached to surfaces.
This document discusses the structure and functions of membrane lipids. It describes the main types of membrane lipids - glycerophospholipids, sphingolipids, glycosphingolipids, and cholesterol. It explains the structures of these lipids, including their polar head groups and non-polar hydrocarbon tails which allow them to form lipid bilayers. The document also summarizes how membrane lipids contribute to membrane fluidity and permeability, noting how cholesterol and unsaturated fatty acids influence fluidity and prevent crystallization.
The document summarizes key biological molecules and their structures and functions. It discusses monomers that make up carbohydrates like monosaccharides, disaccharides, and polysaccharides. It then explains lipids, made of triglycerides, and proteins, composed of amino acid chains that fold into primary, secondary, tertiary, and quaternary structures. It also briefly mentions the roles of water and inorganic ions in living organisms.
Lipids have a hydrophobic nature due to hydrocarbon chains. They are insoluble in water but soluble in nonpolar solvents. Major lipids include fatty acids, triacylglycerols, phospholipids, cholesterol, and steroid hormones. Fatty acids are used for energy storage and membrane components. Triacylglycerols store fatty acids as an energy source. Phospholipids are major membrane components. Cholesterol is important for membrane structure and steroid hormone synthesis. Lipids are digested into fatty acids and monoacylglycerols then absorbed into intestinal cells to form chylomicrons which transport lipids through lymph and blood.
This document discusses lipids and their classification and functions. It describes the main categories of lipids including fatty acids, glycerolipids, glycerophospholipids, sphingolipids, sterol lipids, prenol lipids, and saccharolipids. Key points include that fatty acids are the basic building blocks of lipids and can be saturated or unsaturated. Glycerolipids like triglycerides function in energy storage. Glycerophospholipids make up the lipid bilayer of cells. Sphingolipids contain sphingoid bases and include cerebrosides and gangliosides. Cholesterol is an important sterol lipid that structures membranes. Imbalances in lipid metabolism can lead to
Compound lipids contain additional substances like phosphorus, carbohydrates or proteins in addition to fatty acids and alcohols. Phospholipids are important compound lipids that contain phosphoric acid and make up cell membranes. They are classified as glycerophospholipids containing glycerol or sphingophospholipids containing sphingosine. Glycolipids contain carbohydrate residues and sphingosine. Lipoproteins combine lipids and proteins and transport lipids in the bloodstream, classified by density.
Phospholipids are major constituents of cell membranes and are composed of a glycerol backbone with two fatty acid chains and a phosphate-containing polar head group. There are two main types of phospholipids: glycerophospholipids, which have a glycerol backbone, and sphingolipids, which have a sphingosine backbone. These amphipathic phospholipids spontaneously form bilayers that serve as permeability barriers enclosing cells and organelles. Common phospholipids include phosphatidylcholine, phosphatidylethanolamine, sphingomyelin, and phosphatidylinositol, which each have different head groups that influence their roles in cell signaling and structure.
This document discusses the structure and composition of bio-membranes. It states that bio-membranes are composed primarily of phospholipids that spontaneously form a bilayer structure. The phospholipids are amphipathic, with a hydrophobic tail and hydrophilic head. This allows the tails to interact at the membrane interior, separating the hydrophilic exterior into cytosolic and extracytosolic leaflets. Membranes also contain proteins and sterols that modulate membrane properties and functions. Integral membrane proteins span the bilayer, while peripheral proteins are attached to surfaces.
Monosaccharides are simple sugars that can be classified based on their number of carbons as trioses, tetroses, pentoses, or hexoses. Disaccharides consist of two monosaccharides linked together, while oligosaccharides have a few monosaccharides linked together. Polysaccharides are long chains of monosaccharide or disaccharide units that serve as energy storage molecules in plants and animals.
1. Phospholipids are a class of lipids that contain phosphate groups and include glycerophospholipids and sphingophospholipids.
2. Glycerophospholipids have a glycerol backbone with fatty acids attached via ester bonds to carbons 1 and 2 and a phosphate-containing polar head group attached at carbon 3.
3. Sphingophospholipids are similar but contain a sphingosine backbone instead of glycerol.
Lipids are hydrophobic molecules that include fatty acids, triglycerides, phospholipids, sphingolipids, and sterols. They serve important structural and metabolic roles in the body. Fatty acids are used for energy storage and signaling molecules. Triglycerides store fatty acids in adipose tissue. Phospholipids and sphingolipids are major components of cell membranes. Sterols like cholesterol are important membrane components and steroid hormones modulate physiological activity.
The document discusses the importance of carbon in biological molecules. Carbon atoms can form up to four bonds and bonds between carbon atoms are very strong. This versatility allows carbon to form the core structures of organic molecules. The document then provides examples of important functional groups containing carbon that confer properties like reactivity and polarity to molecules. These include hydroxyl, amine, carboxyl, methyl and phosphate groups.
Carbohydrates are one of the major classes of biological molecules and are the most abundant. They have many important functions including energy storage, structural components, and cell signaling. Carbohydrates exist as monomers, dimers, oligomers, and polymers. Monosaccharides like glucose and fructose are the simplest units and exist as open chains or rings. Isomers have the same molecular formula but different structures. Cyclization of monosaccharides forms rings called pyranoses and furanoses. The document defines important carbohydrate terms and classifications.
This tackles the topic on Lipids, generally. This include its uses, structures, metabolism and Chemical reactions involved with it.
This is a great help for learners in Junior High School, senior high school and those who are majoring in Science.
1. Carbohydrates are organic compounds made of carbon, hydrogen, and oxygen. They include sugars, starches, and fibers and serve important functions in the body.
2. The document discusses the classification of carbohydrates into monosaccharides, oligosaccharides, and polysaccharides. Important monosaccharides include glucose, fructose, and galactose. Disaccharides include sucrose, lactose, and maltose.
3. Polysaccharides are high molecular weight carbohydrates and include starch, glycogen, and cellulose. Starch is made of amylose and amylopectin and is an important storage carbohydrate in plants.
This document provides an overview of the four main types of biological macromolecules: carbohydrates, proteins, lipids, and nucleic acids. It describes the general characteristics and structures of carbohydrates including monosaccharides like glucose, disaccharides, and polysaccharides. For proteins, it discusses the building blocks of amino acids and different protein structures like keratin, silk, and collagen. For lipids, it defines triglycerides, phospholipids, fatty acids and cell membranes. The document aims to distinguish between each macromolecule and relate their structures to properties.
This document discusses lipids, including their structure, classification, functions and metabolism. It begins by outlining the learning objectives which are to understand the structure and composition of lipids, the pathways of fatty acid oxidation and ketogenesis, and lipid synthesis, transport and metabolism. It then defines lipids and classifies them as simple (fats, waxes) or complex (phospholipids, glycolipids). Key aspects of fatty acid chemistry and essential fatty acids are explained. The roles of the major lipids like triacylglycerols and phospholipids are described. Finally, it outlines the digestion and absorption of lipids in the stomach, small intestine and role of enzymes.
This document summarizes key information about carbohydrates. It defines carbohydrates and discusses their classification including monosaccharides, disaccharides, oligosaccharides, and polysaccharides. It describes important monosaccharides like glucose and fructose and how they can form cyclic structures. It also discusses glycosidic bond formation and several important polysaccharides like starch, glycogen, and cellulose.
Lipids are non-polar compounds that include fatty acids, triglycerides, phospholipids, and sterols. They function in energy storage, cell membrane structure, insulation, and hormone production. Fatty acids are the building blocks of lipids and contain long hydrocarbon chains with a carboxyl group at one end. Saturated fatty acids contain only single bonds while unsaturated have one or more double bonds. Phospholipids like phosphatidylcholine are amphipathic and form bilayers that make up cell membranes. Membrane lipids also include cholesterol and sphingolipids such as sphingomyelin and cerebrosides.
Carbohydrates are organic compounds that serve as a primary energy source. They can be classified as monosaccharides, disaccharides, oligosaccharides, or polysaccharides depending on their structure. The three most common disaccharides are maltose, lactose, and sucrose. Polysaccharides include glycogen, starch, and cellulose. Glycogen functions as energy storage in animals, while cellulose provides structure to plant cell walls. Carbohydrates play important structural and functional roles throughout biology.
Membranes are composed of lipids and proteins that form a bilayer. This structure allows membranes to compartmentalize cells and organelles while regulating the transport of substances. Lipids are the main structural component and include fatty acids, glycerol, and phospholipids. Fatty acids esterify to glycerol to form simple lipids like triglycerides, which function as energy stores. More complex lipids contain additional groups like phosphate and incorporate into membranes. Membranes use the asymmetric lipid bilayer to control permeability through passive diffusion and active transporters.
Membranes are organized assemblies of lipids and proteins that form compartments and regulate transport of substances into and out of cells. Lipids are classified as simple, complex, or derived and include fatty acids, glycerolipids, glycerophospholipids, sphingolipids, and sterols. Membranes have a fluid lipid bilayer structure that forms a selective permeability barrier. Transmembrane proteins embedded in the bilayer facilitate transport and cell signaling.
This document provides an overview of lipids, including their classification. It discusses simple lipids like triglycerides and waxes, as well as complex lipids including phospholipids, glycolipids, and derived lipids like steroids. Phospholipids are important structural components of cell membranes and are involved in many cellular processes. Glycolipids contain carbohydrates and function in cell interactions and as receptors. Cholesterol is a prevalent steroid that is a component of cell membranes and precursor to other important steroids. In summary, the document classifies and describes the structures and functions of the major classes of lipids in biological systems.
Lipids are non-polar compounds that function in energy storage, cell membrane structure, and as precursors to hormones. Most lipids are fatty acids or fatty acid esters. Membrane lipids include phospholipids, sphingolipids, and sterols. Phospholipids have a glycerol backbone, with fatty acids attached via ester bonds and a phosphate-linked polar head group. Sphingolipids are derived from sphingosine and include ceramides, sphingomyelins, and glycosphingolipids. Cholesterol is an important membrane component. Lipid composition influences membrane structure and properties.
Carbohydrates are one of the four major macromolecules and are the most abundant organic molecules in nature. They contain carbon, hydrogen, and oxygen. Carbohydrates have many functions including energy storage, structural components, and cell signaling. They can be classified as monosaccharides, disaccharides, oligosaccharides, or polysaccharides depending on the number of sugar units. Common monosaccharides include glucose, fructose, and galactose. Polysaccharides serve important structural and storage roles. Carbohydrates are broken down into monosaccharides through digestion before being absorbed.
The document provides information on the structure and functions of the plasma membrane and gap junctions. It discusses the fluid mosaic model of the plasma membrane and describes the key components of membranes, including phospholipids, cholesterol, and integral and peripheral proteins. It outlines several functions of the plasma membrane, such as forming a selective barrier and anchoring the cytoskeleton. Transport mechanisms like transport proteins are also summarized.
This document discusses lipids, which are concentrated energy molecules that serve several functions in biology. Lipids include fats, oils, waxes, and hormones. They are used for energy storage and provide twice the energy of carbohydrates. Lipids also make up cell membranes and help cushion and insulate organs. Saturated fats from animals are solid at room temperature and contribute to heart disease, while unsaturated fats from plants and fish are liquid and are a healthier choice. Cell membranes contain phospholipids that form a barrier for the cell, with hydrophilic heads on the outside and hydrophobic tails on the inside.
The document discusses the evolution of cell membranes from early RNA molecules clinging to clay particles to the modern fluid mosaic model. Key events include the formation of lipid bilayers that separated internal and external chemistry, allowing more efficient reactions. Experiments showed lipids spontaneously forming enclosed compartments and lipid bilayers with integral membrane proteins that gave membranes a mosaic-like structure. The fluid mosaic model proposes membranes are fluid with lipids and proteins able to diffuse freely within the plane of the bilayer. Transport proteins like channels and carriers allow selective permeability while pumps use ATP to transport molecules against gradients.
Monosaccharides are simple sugars that can be classified based on their number of carbons as trioses, tetroses, pentoses, or hexoses. Disaccharides consist of two monosaccharides linked together, while oligosaccharides have a few monosaccharides linked together. Polysaccharides are long chains of monosaccharide or disaccharide units that serve as energy storage molecules in plants and animals.
1. Phospholipids are a class of lipids that contain phosphate groups and include glycerophospholipids and sphingophospholipids.
2. Glycerophospholipids have a glycerol backbone with fatty acids attached via ester bonds to carbons 1 and 2 and a phosphate-containing polar head group attached at carbon 3.
3. Sphingophospholipids are similar but contain a sphingosine backbone instead of glycerol.
Lipids are hydrophobic molecules that include fatty acids, triglycerides, phospholipids, sphingolipids, and sterols. They serve important structural and metabolic roles in the body. Fatty acids are used for energy storage and signaling molecules. Triglycerides store fatty acids in adipose tissue. Phospholipids and sphingolipids are major components of cell membranes. Sterols like cholesterol are important membrane components and steroid hormones modulate physiological activity.
The document discusses the importance of carbon in biological molecules. Carbon atoms can form up to four bonds and bonds between carbon atoms are very strong. This versatility allows carbon to form the core structures of organic molecules. The document then provides examples of important functional groups containing carbon that confer properties like reactivity and polarity to molecules. These include hydroxyl, amine, carboxyl, methyl and phosphate groups.
Carbohydrates are one of the major classes of biological molecules and are the most abundant. They have many important functions including energy storage, structural components, and cell signaling. Carbohydrates exist as monomers, dimers, oligomers, and polymers. Monosaccharides like glucose and fructose are the simplest units and exist as open chains or rings. Isomers have the same molecular formula but different structures. Cyclization of monosaccharides forms rings called pyranoses and furanoses. The document defines important carbohydrate terms and classifications.
This tackles the topic on Lipids, generally. This include its uses, structures, metabolism and Chemical reactions involved with it.
This is a great help for learners in Junior High School, senior high school and those who are majoring in Science.
1. Carbohydrates are organic compounds made of carbon, hydrogen, and oxygen. They include sugars, starches, and fibers and serve important functions in the body.
2. The document discusses the classification of carbohydrates into monosaccharides, oligosaccharides, and polysaccharides. Important monosaccharides include glucose, fructose, and galactose. Disaccharides include sucrose, lactose, and maltose.
3. Polysaccharides are high molecular weight carbohydrates and include starch, glycogen, and cellulose. Starch is made of amylose and amylopectin and is an important storage carbohydrate in plants.
This document provides an overview of the four main types of biological macromolecules: carbohydrates, proteins, lipids, and nucleic acids. It describes the general characteristics and structures of carbohydrates including monosaccharides like glucose, disaccharides, and polysaccharides. For proteins, it discusses the building blocks of amino acids and different protein structures like keratin, silk, and collagen. For lipids, it defines triglycerides, phospholipids, fatty acids and cell membranes. The document aims to distinguish between each macromolecule and relate their structures to properties.
This document discusses lipids, including their structure, classification, functions and metabolism. It begins by outlining the learning objectives which are to understand the structure and composition of lipids, the pathways of fatty acid oxidation and ketogenesis, and lipid synthesis, transport and metabolism. It then defines lipids and classifies them as simple (fats, waxes) or complex (phospholipids, glycolipids). Key aspects of fatty acid chemistry and essential fatty acids are explained. The roles of the major lipids like triacylglycerols and phospholipids are described. Finally, it outlines the digestion and absorption of lipids in the stomach, small intestine and role of enzymes.
This document summarizes key information about carbohydrates. It defines carbohydrates and discusses their classification including monosaccharides, disaccharides, oligosaccharides, and polysaccharides. It describes important monosaccharides like glucose and fructose and how they can form cyclic structures. It also discusses glycosidic bond formation and several important polysaccharides like starch, glycogen, and cellulose.
Lipids are non-polar compounds that include fatty acids, triglycerides, phospholipids, and sterols. They function in energy storage, cell membrane structure, insulation, and hormone production. Fatty acids are the building blocks of lipids and contain long hydrocarbon chains with a carboxyl group at one end. Saturated fatty acids contain only single bonds while unsaturated have one or more double bonds. Phospholipids like phosphatidylcholine are amphipathic and form bilayers that make up cell membranes. Membrane lipids also include cholesterol and sphingolipids such as sphingomyelin and cerebrosides.
Carbohydrates are organic compounds that serve as a primary energy source. They can be classified as monosaccharides, disaccharides, oligosaccharides, or polysaccharides depending on their structure. The three most common disaccharides are maltose, lactose, and sucrose. Polysaccharides include glycogen, starch, and cellulose. Glycogen functions as energy storage in animals, while cellulose provides structure to plant cell walls. Carbohydrates play important structural and functional roles throughout biology.
Membranes are composed of lipids and proteins that form a bilayer. This structure allows membranes to compartmentalize cells and organelles while regulating the transport of substances. Lipids are the main structural component and include fatty acids, glycerol, and phospholipids. Fatty acids esterify to glycerol to form simple lipids like triglycerides, which function as energy stores. More complex lipids contain additional groups like phosphate and incorporate into membranes. Membranes use the asymmetric lipid bilayer to control permeability through passive diffusion and active transporters.
Membranes are organized assemblies of lipids and proteins that form compartments and regulate transport of substances into and out of cells. Lipids are classified as simple, complex, or derived and include fatty acids, glycerolipids, glycerophospholipids, sphingolipids, and sterols. Membranes have a fluid lipid bilayer structure that forms a selective permeability barrier. Transmembrane proteins embedded in the bilayer facilitate transport and cell signaling.
This document provides an overview of lipids, including their classification. It discusses simple lipids like triglycerides and waxes, as well as complex lipids including phospholipids, glycolipids, and derived lipids like steroids. Phospholipids are important structural components of cell membranes and are involved in many cellular processes. Glycolipids contain carbohydrates and function in cell interactions and as receptors. Cholesterol is a prevalent steroid that is a component of cell membranes and precursor to other important steroids. In summary, the document classifies and describes the structures and functions of the major classes of lipids in biological systems.
Lipids are non-polar compounds that function in energy storage, cell membrane structure, and as precursors to hormones. Most lipids are fatty acids or fatty acid esters. Membrane lipids include phospholipids, sphingolipids, and sterols. Phospholipids have a glycerol backbone, with fatty acids attached via ester bonds and a phosphate-linked polar head group. Sphingolipids are derived from sphingosine and include ceramides, sphingomyelins, and glycosphingolipids. Cholesterol is an important membrane component. Lipid composition influences membrane structure and properties.
Carbohydrates are one of the four major macromolecules and are the most abundant organic molecules in nature. They contain carbon, hydrogen, and oxygen. Carbohydrates have many functions including energy storage, structural components, and cell signaling. They can be classified as monosaccharides, disaccharides, oligosaccharides, or polysaccharides depending on the number of sugar units. Common monosaccharides include glucose, fructose, and galactose. Polysaccharides serve important structural and storage roles. Carbohydrates are broken down into monosaccharides through digestion before being absorbed.
The document provides information on the structure and functions of the plasma membrane and gap junctions. It discusses the fluid mosaic model of the plasma membrane and describes the key components of membranes, including phospholipids, cholesterol, and integral and peripheral proteins. It outlines several functions of the plasma membrane, such as forming a selective barrier and anchoring the cytoskeleton. Transport mechanisms like transport proteins are also summarized.
This document discusses lipids, which are concentrated energy molecules that serve several functions in biology. Lipids include fats, oils, waxes, and hormones. They are used for energy storage and provide twice the energy of carbohydrates. Lipids also make up cell membranes and help cushion and insulate organs. Saturated fats from animals are solid at room temperature and contribute to heart disease, while unsaturated fats from plants and fish are liquid and are a healthier choice. Cell membranes contain phospholipids that form a barrier for the cell, with hydrophilic heads on the outside and hydrophobic tails on the inside.
The document discusses the evolution of cell membranes from early RNA molecules clinging to clay particles to the modern fluid mosaic model. Key events include the formation of lipid bilayers that separated internal and external chemistry, allowing more efficient reactions. Experiments showed lipids spontaneously forming enclosed compartments and lipid bilayers with integral membrane proteins that gave membranes a mosaic-like structure. The fluid mosaic model proposes membranes are fluid with lipids and proteins able to diffuse freely within the plane of the bilayer. Transport proteins like channels and carriers allow selective permeability while pumps use ATP to transport molecules against gradients.
This document provides information about lipids and fatty acids. It defines lipids as biomolecules that contain fatty acids or a steroid nucleus and are soluble in organic solvents but not water. There are different types of lipids containing fatty acids, including waxes, fats and oils (triacylglycerols), glycerophospholipids, and prostaglandins. Fatty acids are long-chain carboxylic acids that can be saturated or unsaturated. Fats and oils are esters of glycerol and three fatty acids called triacylglycerols. Unsaturated fatty acids have kinks that prevent close packing, giving oils and unsaturated fats lower melting points than saturated fats. Hydrogen
The octapeptide contains the amino acids A, C, D, G, L, M, S. Enzyme digestion and mass spectrometry identify the fragments D-C-M, A-S, C-M-A, S-G-A, and L-D. This information determines the primary structure is L-A-G-S-D-C-M-A. Secondary structure is based on bond rotations forming elements like alpha helices and beta pleated sheets. Tertiary structure describes the overall shape from peptide chain folding while quaternary structure involves interactions of multiple protein subunits.
This chapter discusses protein therapeutics including recombinant proteins and monoclonal antibodies. It provides examples of recombinant proteins approved for human use to treat disorders like hemophilia, diabetes, and cystic fibrosis. The chapter outlines different expression systems used to produce recombinant proteins, including bacteria, yeast, insect, and mammalian cells. It also describes the structure of antibodies and the development of monoclonal antibodies as therapeutic agents, from mouse antibodies to humanized antibodies to reduce immunogenicity.
Proteins are made up of chains of amino acids and are essential to many bodily functions. Amino acids link together through peptide bonds and proteins fold into complex three-dimensional shapes that determine their specific roles. Both insufficient and excessive protein intake can be harmful, so a balanced diet containing moderate protein is recommended.
This document provides an overview of amino acids, peptides, and proteins. It discusses the 20 standard amino acids, including their structures, properties, and classifications. Peptide bond formation between amino acids is described. Peptides are defined as short chains of amino acids, with examples of peptide functions. Proteins are introduced as longer polymers made up of amino acids that may also contain cofactors or modifications. The learning goals cover the key aspects of amino acid and peptide structures and properties.
Protein folding is the process by which a protein goes from an unfolded state to its biologically active three-dimensional structure. It is important to understand protein folding to help predict protein structures from sequence alone and to understand diseases caused by protein misfolding. Proteins typically fold through progressive formation of native-like structures rather than through a random search. Molecular chaperones help other proteins fold within cells. Misfolded proteins can form amyloid fibrils associated with diseases. Computational methods aim to predict protein structures from sequence using fragment libraries and modeling protein energy landscapes. Protein design techniques aim to computationally modify protein sequences to achieve desired stabilities, functions, and binding properties.
This document discusses protein classification and structure. It defines protein classification as grouping proteins based on structure, function or size. Proteins can have domains and subunits. They come in globular, fibrous, and other shapes. Proteins are linked within and between polypeptide chains using covalent bonds. Proteins bind other molecules specifically through interactions like ionic bonds. Binding allows proteins to regulate activity and form complexes with other molecules like opsins.
Heat shock proteins (HSPs) help other proteins properly fold and function. HSP90 and HSP70 are molecular chaperones that work sequentially to fold proteins in the cytoplasm. Misfolded proteins can cause disease. HSP90 helps buffer hidden genetic variations but under stress these variations are expressed and can lead to morphological changes. HSP90 is highly conserved across species and plays a role in evolution by allowing traits to change in response to stress. Current research studies HSP90 to better understand protein misfolding diseases.
1. Enzymes are biological catalysts that lower the activation energy of reactions and increase reaction rates. They are often proteins that contain cofactors.
2. Enzymes are classified based on the type of reaction they catalyze, such as oxidation-reduction, hydrolysis, or transfer of chemical groups. Common enzyme names end in "-ase".
3. The lock and key model describes how enzymes bind specifically to substrates in their active sites to form enzyme-substrate complexes. In the induced fit model, the enzyme structure changes to better fit the substrate.
Protein structures are classified to generate overviews of structure types and detect evolutionary relationships. Major classification schemes include SCOP, CATH, and FSSP. SCOP classifies proteins into classes, folds, superfamilies, and families based on structural and sequence similarities. CATH also uses a hierarchical system of classes, architectures, topologies, and superfamilies. FSSP provides fully automated and updated structural alignments and classifications.
This document discusses proteins from a chemist's perspective. It describes how proteins are made of amino acids, with 20 standard types but only 9 being essential. The unique side groups of each amino acid determine their individual properties. Protein structure and function depend on the specific amino acid sequence. Amino acids are linked through peptide bonds to form proteins. The document also covers protein digestion and roles of proteins in the body.
This document discusses protein structure and synthesis. It begins by describing the primary, secondary, tertiary, and quaternary structures of proteins. This includes the structures of alpha helices, beta sheets, turns, and domains. It then discusses protein translation, noting that proteins begin folding as they emerge from the ribosome in a co-translational manner. The final section discusses protein folding and some of the challenges of the folding process.
The document discusses heat shock proteins (Hsps), Hsp90 inhibitors, and protein degradation. It provides background on protein degradation mechanisms and heat shock proteins. Hsp90 plays a key role in cancer cell survival by regulating oncogenic signaling proteins. Hsp90 inhibitors like geldanamycin and 17-AAG bind Hsp90's ATP binding site, altering its function and inducing degradation of client proteins, stopping cancer cell growth. The paper found that tumor Hsp90 exclusively exists in active multichaperone complexes, conferring higher binding affinity for 17-AAG compared to normal cell Hsp90. This activated conformation in tumor cells represents a unique drug target.
This document summarizes protein therapeutics and provides a pharmacological classification. It notes that the human genome contains 25,000-40,000 genes that can undergo alternative splicing and post-translational modifications, resulting in a very high number of functionally distinct proteins. Protein therapeutics are classified into 4 groups based on their function: group I includes proteins with enzymatic or regulatory activity, group II targets specific molecules or organisms, group III are protein vaccines, and group IV are protein diagnostics. The document outlines some advantages of protein therapeutics but also challenges including solubility, immune response, stability, and costs.
1. Proteins are made up of amino acids and take on specific three-dimensional structures that dictate their function. Determining a protein's structure is important for understanding its role in biological processes.
2. There are several methods for determining and predicting protein structure, including X-ray crystallography, NMR, and computational methods like homology modeling or ab initio structure prediction.
3. Protein structure is hierarchical, ranging from secondary structure like alpha helices and beta sheets to the overall fold classified in databases like SCOP and CATH. Predicting secondary structure is easier than predicting a protein's full three-dimensional structure.
Amino acids are organic compounds that contain an amino group and a carboxyl group. There are 20 different amino acids that serve as the building blocks of proteins. Amino acids link together through peptide bonds to form polypeptide chains that fold into complex three-dimensional protein structures. Proteins serve essential functions and 10 of the 20 amino acids must be obtained through diet as humans cannot synthesize them. Common protein tests identify the presence of proteins using reactions that detect peptide bonds, amino acid side chains, or disulfide bridges.
- Proteins are made up of amino acids, which are the building blocks. There are 20 different amino acids, some are essential and must be obtained through diet.
- The specific sequence of amino acids determines the 3D shape of a protein and its function. Denaturation occurs when proteins lose their shape due to heat, acid, etc.
- Proteins serve many important functions in the body including structure, enzymes, transport, hormones, antibodies, and more. An inadequate intake can result in the body breaking down its own proteins to obtain energy.
This document summarizes different classes of proteolytic enzymes (proteases) including serine, cysteine, aspartic acid, and metallo proteases. It describes their catalytic mechanisms and examples of each class. Key points are that serine proteases use a catalytic triad of serine, histidine, and aspartate residues in their mechanisms, while cysteine proteases employ a catalytic cysteine and histidine. Aspartic and metallo proteases also have distinct catalytic residues and mechanisms. The roles of proteases in digestion, lysosomes, and other cellular processes are overviewed.
The best massage spa Ajman is Chandrima Spa Ajman, which was founded in 2023 and is exclusively for men 24 hours a day. As of right now, our parent firm has been providing massage services to over 50,000+ clients in Ajman for the past 10 years. It has about 8+ branches. This demonstrates that Chandrima Spa Ajman is among the most reasonably priced spas in Ajman and the ideal place to unwind and rejuvenate. We provide a wide range of Spa massage treatments, including Indian, Pakistani, Kerala, Malayali, and body-to-body massages. Numerous massage techniques are available, including deep tissue, Swedish, Thai, Russian, and hot stone massages. Our massage therapists produce genuinely unique treatments that generate a revitalized sense of inner serenely by fusing modern techniques, the cleanest natural substances, and traditional holistic therapists.
TEST BANK For Accounting Information Systems, 3rd Edition by Vernon Richardso...rightmanforbloodline
TEST BANK For Accounting Information Systems, 3rd Edition by Vernon Richardson, Verified Chapters 1 - 18, Complete Newest Version
TEST BANK For Accounting Information Systems, 3rd Edition by Vernon Richardson, Verified Chapters 1 - 18, Complete Newest Version
TEST BANK For Accounting Information Systems, 3rd Edition by Vernon Richardson, Verified Chapters 1 - 18, Complete Newest Version
Healthy Eating Habits:
Understanding Nutrition Labels: Teaches how to read and interpret food labels, focusing on serving sizes, calorie intake, and nutrients to limit or include.
Tips for Healthy Eating: Offers practical advice such as incorporating a variety of foods, practicing moderation, staying hydrated, and eating mindfully.
Benefits of Regular Exercise:
Physical Benefits: Discusses how exercise aids in weight management, muscle and bone health, cardiovascular health, and flexibility.
Mental Benefits: Explains the psychological advantages, including stress reduction, improved mood, and better sleep.
Tips for Staying Active:
Encourages consistency, variety in exercises, setting realistic goals, and finding enjoyable activities to maintain motivation.
Maintaining a Balanced Lifestyle:
Integrating Nutrition and Exercise: Suggests meal planning and incorporating physical activity into daily routines.
Monitoring Progress: Recommends tracking food intake and exercise, regular health check-ups, and provides tips for achieving balance, such as getting sufficient sleep, managing stress, and staying socially active.
International Cancer Survivors Day is celebrated during June, placing the spotlight not only on cancer survivors, but also their caregivers.
CANSA has compiled a list of tips and guidelines of support:
https://cansa.org.za/who-cares-for-cancer-patients-caregivers/
LGBTQ+ Adults: Unique Opportunities and Inclusive Approaches to CareVITASAuthor
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2. Lipids are non-polar (hydrophobic) compounds,
soluble in organic solvents.
Most membrane lipids are amphipathic, having a
non-polar end and a polar end.
Fatty acids consist of a hydrocarbon chain with a
carboxylic acid at one end.
A 16-C fatty acid: CH3(CH2)14-COO-
Non-polar polar
A 16-C fatty acid with one cis double bond between
C atoms 9-10 may be represented as 16:1 cis D9.
3. Some fatty acids and their common names:
14:0 myristic acid; 16:0 palmitic acid; 18:0 stearic acid;
18:1 cisD9 oleic acid
18:2 cisD9,12 linoleic acid
18:3 cisD9,12,15 a-linonenic acid
20:4 cisD5,8,11,14 arachidonic acid
20:5 cisD5,8,11,14,17 eicosapentaenoic acid (an omega-3)
Double bonds in fatty
acids usually have the
cis configuration.
Most naturally
occurring fatty acids
have an even number
of carbon atoms.
C
O
O
1
2
3
4
a
fatty acid with a cis-D9
double bond
4. There is free rotation about C-C bonds in the fatty acid
hydrocarbon, except where there is a double bond.
Each cis double bond causes a kink in the chain.
Rotation about other C-C bonds would permit a more
linear structure than shown, but there would be a kink.
C
O
O
1
2
3
4
a
fatty acid with a cis-D9
double bond
5. Glycerophospholipids
Glycerophospholipids
(phosphoglycerides), are common
constituents of cellular membranes.
They have a glycerol backbone.
Hydroxyls at C1 & C2 are esterified
to fatty acids.
C OH
H
CH2OH
CH2OH
glycerol
An ester forms
when a hydroxyl
reacts with a
carboxylic acid,
with loss of H2O.
Formation of an ester:
O O
R'OH + HO-C-R" R'-O-C-R'' + H2O
6. Phosphatidate
In phosphatidate:
fatty acids are esterified to hydroxyls on C1 & C2
the C3 hydroxyl is esterified to Pi.
O P O
O
O
H2C
CH
H2C
O
C
R1
O O C
O
R2
phosphatidate
7. In most glycerophospholipids (phosphoglycerides),
Pi is in turn esterified to OH of a polar head group (X):
e.g., serine, choline, ethanolamine, glycerol, or inositol.
The 2 fatty acids tend to be non-identical. They may differ
in length and/or the presence/absence of double bonds.
O P O
O
O
H2C
CH
H2C
O
C
R1
O O C
O
R2
X
glycerophospholipid
8. Phosphatidylinositol, with inositol as polar head group,
is one glycerophospholipid.
In addition to being a membrane lipid,
phosphatidylinositol has roles in cell signaling.
O P
O
O
H2C
CH
H2C
O
C
R1
O O C
O
R2
OH
H
OH
H
H
OH
H
OH
H
O
H OH
phosphatidyl-
inositol
9. Phosphatidylcholine, with choline as polar head
group, is another glycerophospholipid.
It is a common membrane lipid.
O P O
O
O
H2C
CH
H2C
O
C
R1
O O C
O
R2
CH2 CH2 N CH3
CH3
CH3
+
phosphatidylcholine
10. polar
non-polar
"kink" due to
double bond
O P O
O
O
H2C
CH
H2C
O
C
R1
O O C
O
R2
X
glycerophospholipid
Each glycerophospholipid
includes
a polar region:
glycerol, carbonyl O
of fatty acids, Pi, & the
polar head group (X)
non-polar hydrocarbon
tails of fatty acids (R1, R2).
11. Sphingosine may be reversibly
phosphorylated to produce the signal
molecule sphingosine-1-phosphate.
Other derivatives of sphingosine are
commonly found as constituents of
biological membranes.
H2C
H
C
OH
CH
N+ CH
C
CH2
CH3
H
H3
OH
( )12
sphingosine
Sphingolipids are derivatives of
the lipid sphingosine, which has a
long hydrocarbon tail, and a polar
domain that includes an amino group.
sphingosine-1-P
H2C
H
C
O
CH
N+
CH
C
CH2
CH3
H
H3
OH
( )12
P O
O
O
12. In the more complex sphingolipids,
a polar “head group" is esterified
to the terminal hydroxyl of the
sphingosine moiety of the ceramide.
H2C
H
C
OH
CH
N+ CH
C
CH2
CH3
H
H3
OH
( )12
sphingosine
H2C
H
C
OH
CH
NH CH
C
CH2
CH3
H
OH
( )12
C
R
O
ceramide
The amino group of sphingosine can
form an amide bond with a fatty acid
carboxyl, to yield a ceramide.
13. Sphingomyelin, with a phosphocholine head group, is
similar in size and shape to the glycerophospholipid
phosphatidyl choline.
Sphingomyelin has
a phosphocholine or
phosphethanolamine
head group.
Sphingomyelins are
common constituent
of plasma membranes
H2C
H
C
O
CH
NH CH
C
CH2
CH3
H
OH
( )12
C
R
O
P
O O
O
H2
C
H2
C
N
+
CH3
H3C
CH3
Sphingomyelin
phosphocholine
sphingosine
fatty acid
14. head group that is a complex oligosaccharide, including
the acidic sugar derivative sialic acid.
Cerebrosides and gangliosides, collectively called
glycosphingolipids, are commonly found in the outer
leaflet of the plasma membrane bilayer, with their sugar
chains extending out from the cell surface.
cerebroside with
-galactose head group
H2C
H
C CH
NH CH
C
CH2
CH3
OH
C
R
O
OH O
H H
H
OH
H
OH
CH2OH
H
O
H
( )12
A cerebroside is a
sphingolipid
(ceramide) with a
monosaccharide
such as glucose or
galactose as polar
head group.
A ganglioside is a
ceramide with a polar
15. Depending on the lipid, possible molecular arrangements:
Various micelle structures. E.g., a spherical micelle is
a stable configuration for amphipathic lipids with a
conical shape, such as fatty acids.
A bilayer. This is the most stable configuration for
amphipathic lipids with a cylindrical shape, such as
phospholipids.
Bilayer Spherical Micelle
Amphipathic lipids in
association with water form
complexes in which polar
regions are in contact with
water and hydrophobic
regions away from water.
16. liquid crystal crystal
In the liquid crystal state, hydrocarbon chains of
phospholipids are disordered and in constant motion.
At lower temperature, a membrane containing a single
phospholipid type undergoes transition to a crystalline
state in which fatty acid tails are fully extended, packing
is highly ordered, & van der Waals interactions between
adjacent chains are maximal.
Kinks in fatty acid chains, due to cis double bonds,
interfere with packing in the crystalline state, and lower
the phase transition temperature.
Membrane fluidity:
The interior of a lipid bilayer
is normally highly fluid.
17. Cholesterol is largely
hydrophobic.
But it has one polar group,
a hydroxyl, making it
amphipathic.
Cholesterol
HO
Cholesterol, an
important constituent
of cell membranes,
has a rigid ring
system and a short
branched
hydrocarbon tail.
cholesterol
PDB 1N83
18. Cholesterol
in membrane
Cholesterol inserts into bilayer membranes with its
hydroxyl group oriented toward the aqueous phase &
its hydrophobic ring system adjacent to fatty acid
chains of phospholipids.
The OH group of cholesterol forms hydrogen bonds
with polar phospholipid head groups.
Cholesterol
HO
19. But the presence of cholesterol in a phospholipid
membrane interferes with close packing of fatty acid
tails in the crystalline state, and thus inhibits transition
to the crystal state.
Phospholipid membranes with a high concentration of
cholesterol have a fluidity intermediate between the
liquid crystal and crystal states.
Cholesterol
in membrane
Interaction with the relatively rigid
cholesterol decreases the mobility of
hydrocarbon tails of phospholipids.
20. Two strategies by which phase changes of membrane
lipids are avoided:
Cholesterol is abundant in membranes, such as
plasma membranes, that include many lipids with
long-chain saturated fatty acids.
In the absence of cholesterol, such membranes would
crystallize at physiological temperatures.
The inner mitochondrial membrane lacks cholesterol,
but includes many phospholipids whose fatty acids
have one or more double bonds, which lower the
melting point to below physiological temperature.
21. High speed tracking of individual lipid molecules has
shown that lateral movements are constrained within
small membrane domains.
Hopping from one domain to another occurs less
frequently than rapid movements within a domain.
The apparent constraints on lateral movements of lipids
(and proteins) has been attributed to integral membrane
proteins, anchored to the cytoskeleton, functioning as a
picket fence. See the website of the Kusumi laboratory.
Lateral Mobility
Lateral mobility of a lipid,
within the plane of a
membrane, is depicted at
right and in an animation.
22. Flip-flop would require the polar head-group of a lipid to
traverse the hydrophobic core of the membrane.
The two leaflets of a bilayer membrane tend to differ in
their lipid composition.
Flippases catalyze flip-flop in membranes where lipid
synthesis occurs.
Some membranes contain enzymes that actively transport
particular lipids from one monolayer to the other.
Flip Flop
Flip-flop of lipids (from one
half of a bilayer to the other)
is normally very slow.
23. Peripheral proteins are on the membrane surface.
They are water-soluble, with mostly hydrophilic surfaces.
Often peripheral proteins can be dislodged by conditions
that disrupt ionic & H-bond interactions, e.g., extraction
with solutions containing high concentrations of salts,
change of pH, and/or chelators that bind divalent cations.
Membrane
proteins may be
classified as:
peripheral
integral
having a
lipid anchor integral
lipid
anchor
peripheral
lipid bilayer
Membrane
Proteins
24. Many proteins have a modular design, with different
segments of the primary structure folding into domains
with different functions.
Some cytosolic proteins have domains that bind to polar
head groups of lipids that transiently exist in a membrane.
The enzymes that create or degrade these lipids are subject
to signal-mediated regulation, providing a mechanism for
modulating affinity of a protein for a membrane surface.
regulatory catalytic membrane
domain domain binding
hypothetical protein
25. O P
O
O
H2C
CH
H2C
O
C
R1
O O C
O
R2
OH
H
OPO3
2
H
H
OPO3
2
H
OH
H
O
H OH
1 6
5
4
3
2
PIP2
phosphatidylinositol-
4,5-bisphosphate
E.g., pleckstrin homology (PH) domains bind to
phosphorylated derivatives of phosphatidylinositol.
Some PH domains bind PIP2 (PI-4,5-P2).
26. Other pleckstrin homology domains recognize and bind
phosphatidylinositol derivatives with Pi esterified at the
3' OH of inositol. E.g., PI-3-P, PI-3,4-P2, PI-3,4,5-P3.
O P
O
O
H2C
CH
H2C
O
C
R1
O O C
O
R2
OH
H
OH
H
H
OH
H
OPO3
2
H
O
H OH
1 6
5
2
3 4
phosphatidyl-
inositol-
3-phosphate
27. Some proteins bind to membranes via a covalently
attached lipid anchor, that inserts into the bilayer.
A protein may link to the cytosolic surface of the plasma
membrane via a covalently attached fatty acid (e.g.,
palmitate or myristate) or an isoprenoid group.
Palmitate is usually attached via an ester linkage to the
thiol of a cysteine residue.
A protein may be released from plasma membrane to
cytosol via depalmitoylation, hydrolysis of the ester link.
lipid
anchor
membrane
H3C (CH2)14 C
O
S CH2 CH
C
NH
O
palmitate
cysteine
residue
28. An isoprenoid such as a farnesyl
residue, is attached to some proteins
via a thioether linkage to a cysteine thiol.
CH CH2
C
H3C
CH3
CH CH2
C
CH2
CH3
CH CH2 S Protein
C
CH2
CH3
farnesyl residue linked to protein via cysteine S
lipid
anchor
membrane
29. Glycosylphosphatidylinositols (GPI) are complex
glycolipids that attach some proteins to the outer surface
of the plasma membrane.
The linkage is similar to the following, although the
oligosaccharide composition may vary:
protein (C-term.) - phosphoethanolamine – mannose - mannose -
mannose - N-acetylglucosamine – inositol (of PI in membrane)
The protein is tethered some distance out from the
membrane surface by the long oligosaccharide chain.
GPI-linked proteins may be released from the outer
cell surface by phospholipases.
30. Integral proteins have domains that extend into the
hydrocarbon core of the membrane.
Often they span the bilayer.
Intramembrane domains have largely hydrophobic
surfaces, that interact with membrane lipids.
integral
lipid
anchor
peripheral
lipid bilayer
Membrane
Proteins
31. Hydrophobic domains of detergents substitute for
lipids, coating hydrophobic surfaces of integral proteins.
Polar domains of detergents interact with water.
If detergents are removed, purified integral proteins tend
to aggregate & come out of solution. Their hydrophobic
surfaces associate to minimize contact with water.
Amphipathic
detergents are
required for
solubilization of
integral proteins
from membranes.
detergent
solubilization
Protein with
bound detergent
polar
non-polar
membrane
32. Lipid rafts:
Complex sphingolipids tend to separate out from
glycerophospholipids & co-localize with cholesterol in
membrane microdomains called lipid rafts.
Membrane fragments assumed to be lipid rafts are
found to be resistant to detergent solubilization,
which has facilitated their isolation & characterization.
33. Differences in molecular shape may contribute to a
tendency for sphingolipids to separate out from
glycerophospholipids in membrane microdomains.
• Sphingolipids usually lack double bonds in their
fatty acid chains.
• Glycerophospholipids often include at least one
fatty acid that is kinked, due to one or more double
bonds.
• See diagram (in article by J. Santini & coworkers).
Lipid raft domains tend to be thicker than adjacent
membrane areas, in part because the saturated
hydrocarbon chains of sphingolipids are more extended.
34. Hydrogen bonding between the hydroxyl group of
cholesterol and the amide group of sphingomyelin
may in part account for the observed affinity of
cholesterol for sphingomyelin in raft domains.
H2C
H
C
O
CH
NH CH
C
CH2
CH3
H
OH
( )12
C
R
O
P
O O
O
H2
C
H2
C
N
+
CH3
H3C
CH3
Sphingomyelin
phosphocholine
sphingosine
fatty acid
Cholesterol
HO
35. Proteins involved in cell signaling often associate
with lipid raft domains.
• Otherwise soluble signal proteins often assemble in
complexes at the cytosolic surface of the plasma
membrane in part via insertion of attached fatty acyl
or isoprenoid lipid anchors into raft domains.
• Integral proteins may concentrate in raft domains via
interactions with raft lipids or with other raft proteins.
• Some raft domains contain derivatives of
phosphatidylinositol that bind signal proteins with
pleckstrin homology domains.
36. Caveolin is a protein associated with the cytosolic leaflet
of the plasma membrane in caveolae.
Caveolin interacts with cholesterol and self-associates
as oligomers that may contribute to deforming the
membrane to create the unique morphology of caveolae.
Electron micrograph & information about caveolae
(home page of Deborah Brown at SUNY Stony Brook).
Diagram & information about lipid rafts
(website of Maciver lab at University of Edinburgh).
caveolae
cytosol
Caveolae are invaginated lipid
raft domains of the plasma
membrane that have roles in cell
signaling and membrane
internalization.
37. A membrane-spanning a-helix is
the most common structural motif
found in integral proteins.
membrane
N
C
Integral protein structure
Atomic-resolution structures have been determined
for a small (but growing) number of integral membrane
proteins.
Integral proteins are difficult to crystallize for X-ray
analysis.
Because of their hydrophobic
transmembrane domains,
detergents must be present
during crystallization.
38. In an a-helix, amino acid R-groups protrude out from the
helically coiled polypeptide backbone.
The largely hydrophobic R-groups of a membrane-
spanning a-helix contact the hydrophobic membrane core,
while the more polar peptide backbone is buried.
Colors: C N O R-group (H atoms not shown).
a-helix
R-groups in magenta
39. Particular amino acids tend to occur at different
positions relative to the surface or interior of the bilayer
in transmembrane segments of integral proteins.
Residues with aliphatic side-chains (leucine, isoleucine,
alanine, valine) predominate in the middle of the bilayer.
H3N+
C COO
CH3
H
H3N+
C COO
CH CH3
CH2
CH3
H
H3N+
C COO
CH2
CH CH3
CH3
H
H3N+
C COO
CH CH3
CH3
H
alanine (Ala, A) isoleucine (Ile, I) leucine (Leu, L) valine (Val, V)
amino acids: non-polar aliphatic R-groups
40. It has been suggested that the polar character of the
tryptophan amide group and the tyrosine hydroxyl, along
with their hydrophobic ring structures, suit them for
localization at the polar/apolar interface.
tryptophan tyrosine
H2N C COO
CH2
HN
H
H3N+
C COO
CH2
OH
H
Tyrosine and
tryptophan are
common near the
membrane surface.
41. Lysine & arginine are often at the lipid/water interface,
with the positively charged groups at the ends of their
aliphatic side chains extending toward the polar
membrane surface.
H3N+
C COO
CH2
CH2
CH2
NH
C
NH2
NH2
H
H3N+
C COO
CH2
CH2
CH2
CH2
NH3
H
lysine arginine
42. Cytochrome oxidase is an integral protein whose intra-
membrane domains are mainly transmembrane a-helices.
Explore with Chime the a-helix colored green at far left.
membrane
Cytochrome oxidase dimer (PDB file 1OCC)
43. A 20-amino acid a-helix just spans a lipid bilayer.
Hydropathy plots are used to search for 20-amino
acid stretches of hydrophobic amino acids in the
primary sequence of a protein for which a crystal
structure is not available.
Putative hydrophobic transmembrane a-helices have
been identified this way in many membrane proteins.
Hydropathy plots alone are not conclusive.
Protein topology studies are used to test the
transmembrane distribution of protein domains
predicted by hydropathy plots.
44. If a hydropathy plot indicates one 20-amino acid
hydrophobic stretch (1 putative transmembrane a-helix),
topology studies are expected to confirm location of
N & C termini on opposite sides of membrane.
If two transmembrane a-helices are predicted, N & C
termini should be on the same side. The segment
between the a-helices should be on the other side.
N
C
membrane
N
C
45. Transmembrane topology is tested with impermeant
probes, added on one side of a membrane. For example:
Protease enzymes. Degradation a protein segment
indicates exposure to the aqueous phase on the side of
the membrane to which a protease is added.
Monoclonal antibodies raised to peptides equivalent
to individual segments of the protein. Binding
indicates surface exposure of a protein segment on the
side to which the Ab is added.
Such studies have shown that all copies of a given type of
integral protein have the same orientation relative to the
membrane. Flip-flop of integral proteins does not occur.
46. An a-helix lining a water-filled channel might have
polar amino acid R-groups facing the lumen, & non-polar
R-groups facing lipids or other hydrophobic a-helices.
Such mixed polarity would prevent detection by a
hydropathy plot.
A “helical
wheel” looks
down the axis
of an a-helix,
projecting side-
chains onto a
plane.
Simplified helical wheel diagram of four
a-helices lining the lumen of an ion channel.
Polar amino acid R-group
Non-polar amino acid R-group
47. Porin -barrel
While transmembrane a-
helices are the most common
structural motif for integral
proteins, a family of bacterial
outer envelope channel
proteins called porins have
instead barrel structures.
A barrel is a sheet rolled
up to form a cylindrical pore.
At right is shown one channel
of a trimeric porin complex.
Porin Monomer
PDB 1AOS
48. In a -sheet, amino acid R-groups alternately point above
& below the sheet.
Much of porin primary structure consists of alternating
polar & non-polar amino acids.
• Polar residues face the aqueous lumen.
• Non-polar residues are in contact with membrane lipids.
Explore an example of a bacterial porin with Chime.
polar R group, non-polar R group