A membrane protein is a protein molecule that is attached to, or associated with the membrane of a cell or an organelle.
More than half of all proteins interact with membranes.
Introduction
Definition
Chemical composition
Molecular Structure of PM
Bilayel Model
Garter and Grendel s Model
Overton e Model
Fluid Mosaic Model
. Membrane Protein
Transmembrane Protein
Exterinsic Protein
non cytosolic Protein
6. Protein complex in pm.( cell coat)
7. Function of PM
8. Referance
This presentation gives an overview of Lipid Rafts, how it was discovered, its importance and the future research in this area,Feel free to comment and ask any questions
INTRODUCTION
plasma membrane is also known as cell membrane or cytoplasm membrane.
It is the biological membrane, separates interior of the cell from the outside environment.
Selective permeable to Ions and organic molecules.
Its basic function is to protect the cell from its surroundings.
It consists of the phospholipids bilayer with embedded proteins.
Cell membranes are involved in:cell adhesion, ion conductivity and cell signaling and serve as the attachment surface for several extracellular structures.
A membrane protein is a protein molecule that is attached to, or associated with the membrane of a cell or an organelle.
More than half of all proteins interact with membranes.
Introduction
Definition
Chemical composition
Molecular Structure of PM
Bilayel Model
Garter and Grendel s Model
Overton e Model
Fluid Mosaic Model
. Membrane Protein
Transmembrane Protein
Exterinsic Protein
non cytosolic Protein
6. Protein complex in pm.( cell coat)
7. Function of PM
8. Referance
This presentation gives an overview of Lipid Rafts, how it was discovered, its importance and the future research in this area,Feel free to comment and ask any questions
INTRODUCTION
plasma membrane is also known as cell membrane or cytoplasm membrane.
It is the biological membrane, separates interior of the cell from the outside environment.
Selective permeable to Ions and organic molecules.
Its basic function is to protect the cell from its surroundings.
It consists of the phospholipids bilayer with embedded proteins.
Cell membranes are involved in:cell adhesion, ion conductivity and cell signaling and serve as the attachment surface for several extracellular structures.
What is Glycoprotein ?:
Glycoproteins are proteins that contain oligosaccharide chains (glycans) covalently attached to polypeptide side-chains.
This process is known as glycosylation.
The carbohydrate is attached to the protein during the following modifications: Co-translational modification & Post-translational modification.
In proteins that have segments extending extracellularly, the extracellular segments are often glycosylated.
Chaperones are a functionally related group of proteins that assist the covalent folding or unfolding and the assembly or disassembly of other macromolecular structures.
Folding depends upon sequence of Amino Acids not the Composition. Folding starts with the secondary structure and ends at quaternary structure.
Denaturation occur at secondary, tertiary & quaternary level but not at primary level.
. Introduction
2. Cell / Plasma membrane
3. Transport across membrane
Passive transport
a.Osmosis
b. Simple diffusion
c. Facilitated diffusion
Active transport
a. Primary active transport
b. Secondary active transport
Example-
1. Na+/K+ ATPase
2. Ca+ ATPase
3. Proton pump
4. Transport of large molecule by plasma membrane
Endocytosis
Exocytosis
5. Transport of nutrients by membraneprotiens
Channel protein
Carrier proteins
6. Role of membrane Transport
7. Conclusion
8. Reference
Details of cytoskeleton element-microtubule. The Microtubule associated protein-type and function, Treadmilling and dynamic instability, Structure of cilia and flagella
Membrane proteins are proteins that interact with, or are part of, biological membranes. They include integral membrane proteins that are permanently anchored to the membrane and peripheral membrane proteins which are only temporarily attached to the lipid bilayer or to integral proteins.
What is Glycoprotein ?:
Glycoproteins are proteins that contain oligosaccharide chains (glycans) covalently attached to polypeptide side-chains.
This process is known as glycosylation.
The carbohydrate is attached to the protein during the following modifications: Co-translational modification & Post-translational modification.
In proteins that have segments extending extracellularly, the extracellular segments are often glycosylated.
Chaperones are a functionally related group of proteins that assist the covalent folding or unfolding and the assembly or disassembly of other macromolecular structures.
Folding depends upon sequence of Amino Acids not the Composition. Folding starts with the secondary structure and ends at quaternary structure.
Denaturation occur at secondary, tertiary & quaternary level but not at primary level.
. Introduction
2. Cell / Plasma membrane
3. Transport across membrane
Passive transport
a.Osmosis
b. Simple diffusion
c. Facilitated diffusion
Active transport
a. Primary active transport
b. Secondary active transport
Example-
1. Na+/K+ ATPase
2. Ca+ ATPase
3. Proton pump
4. Transport of large molecule by plasma membrane
Endocytosis
Exocytosis
5. Transport of nutrients by membraneprotiens
Channel protein
Carrier proteins
6. Role of membrane Transport
7. Conclusion
8. Reference
Details of cytoskeleton element-microtubule. The Microtubule associated protein-type and function, Treadmilling and dynamic instability, Structure of cilia and flagella
Membrane proteins are proteins that interact with, or are part of, biological membranes. They include integral membrane proteins that are permanently anchored to the membrane and peripheral membrane proteins which are only temporarily attached to the lipid bilayer or to integral proteins.
The aim of this PPT is to take an overview of the ‘membranes’ in cable and membrane structures. Before installation on site a membrane has to go through several stages right from design including the steps as form finding, load analysis and design of fabric geometry. The paper also talks about several shapes and forms a membrane can achieve and the principle behind the design of these shapes. Important aspect of membrane structure is availability of membranes in market. This paper accounts various available covering materials in the market and the criteria have to be considered before their installations on the site. Joinery plays a significant role in attaining the required shape and equilibrium. This PPT takes a review of significant junctions in a membrane structure.
Established in the year 1998 [ www.tensilefabricstructure.com ]As a specialist in designing and building tensile structures, Ekra Decor is involved in every stage upon client selection of combination of architectural fabric structure design and construction.
Structure and function of plasma membrane 2ICHHA PURAK
The presentation consists of 72 slides,describes following heads
DEFINITION : STRUCTURE OF PLASMA MEMBRANE
COMPONENTS OF PLASMA MEMBRANE ( (BIOCHEMICAL PROPERTIES)
LIPID BILAYER
PROTEINS
CARBOHYDRATES
CHOLESTEROL
MODELS EXPLAINING STRUCTURE OF BIO MEMBRANE
FLUID MOSAIC MODEL
MOBILITY OF MEMBRANE
GLYCOCALYX : GLYCOPROTEINS AND GLYCOLIPIDS
TRANSPORT OF IONS AND MOLECULES ACROSS PLASMA MEMBRANE
FUNCTIONS OF PLASMA MEMBRANE
DIVERSITY OF CELL MEMBRANES
SITE OF ATPASE ION CARRIER CHANNELS AND PUMPS-RECEPTORS
The current model of cellular membranes is called PB and J sandwich.pdfbhim1213
The current model of cellular membranes is called PB and J sandwich molecular mosaic fluid
mosaic plasma membrane Which characteristic apply to the phospholipid membrane? It is
primarily a hydrophobic bilayer. Phospholipids are amphipathic Proteins are imbedded within
the phospholipids. The imbedded molecules can move freely within the membrane All are
important characteristics of the Cholesterol molecules in the membrane act to modulate
temperature dependent viscosity and fluidity of the membrane. moderate the effects of a high fat
diet promote fluidity in the membrane. allow for better membrane compaction and integrity.
allow transport across the membrane. One important feature of membranes in the
endomembrane system is that they can move freely from cell to cell. freely bleb off of and then
onto other components of this network. they contain small pieces of independently replicating
DNA. they move from the trans side of the membrane to the cis side. t
Solution
1. Fluid mosaic model.
Fluid mosaic model for plasma membrane proposed by Jonathan Singer and Garth Nicolson is
universally acceoted model for plasma membrane.
2. All are important characteristics.
Phospholipid molecules are hydrophobic and amphipathic. Which means that posess polar head
and non polar tails.
Some of the protien molecules are embedded in the phospholipid layer and these moelcules are
free to move due to fluid nature of plasma membrane.
3. Allows better membrane compaction and integrity.
Cholesterol is an amphipathic molecule like phospholipids. It contains a hydrophilic and a
hydrophobic portion. Cholesterol\'s hydroxyl (OH) group aligns with the phosphate heads of the
phospholipids. The remaining portion of it tucks into the fatty acid portion of the membrane.
Because of the way cholesterol is shaped, part of the steroid ring (the four hydrocarbon rings in
between the hydroxyl group and the hydrocarbon \"tail\") is closely attracted to part of the fatty
acid chain on the nearest phospholipid. This helps slightly immobilize the outer surface of the
membrane and make it less soluble to very small water-soluble molecules that could otherwise
pass through more easily.
4. They contain transport enzymes..
The structure of the cell membrane, the phospholipid layer distinguished to the break down of protein and the lipid layer. Their structural components and the molecular basis of it.
Unit 8 - Information and Communication Technology (Paper I).pdfThiyagu K
This slides describes the basic concepts of ICT, basics of Email, Emerging Technology and Digital Initiatives in Education. This presentations aligns with the UGC Paper I syllabus.
Biological screening of herbal drugs: Introduction and Need for
Phyto-Pharmacological Screening, New Strategies for evaluating
Natural Products, In vitro evaluation techniques for Antioxidants, Antimicrobial and Anticancer drugs. In vivo evaluation techniques
for Anti-inflammatory, Antiulcer, Anticancer, Wound healing, Antidiabetic, Hepatoprotective, Cardio protective, Diuretics and
Antifertility, Toxicity studies as per OECD guidelines
The French Revolution, which began in 1789, was a period of radical social and political upheaval in France. It marked the decline of absolute monarchies, the rise of secular and democratic republics, and the eventual rise of Napoleon Bonaparte. This revolutionary period is crucial in understanding the transition from feudalism to modernity in Europe.
For more information, visit-www.vavaclasses.com
Model Attribute Check Company Auto PropertyCeline George
In Odoo, the multi-company feature allows you to manage multiple companies within a single Odoo database instance. Each company can have its own configurations while still sharing common resources such as products, customers, and suppliers.
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
The Roman Empire A Historical Colossus.pdfkaushalkr1407
The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
Under Augustus, the empire experienced the Pax Romana, a 200-year period of relative peace and stability. Augustus reformed the military, established efficient administrative systems, and initiated grand construction projects. The empire's borders expanded, encompassing territories from Britain to Egypt and from Spain to the Euphrates. Roman legions, renowned for their discipline and engineering prowess, secured and maintained these vast territories, building roads, fortifications, and cities that facilitated control and integration.
The Roman Empire’s society was hierarchical, with a rigid class system. At the top were the patricians, wealthy elites who held significant political power. Below them were the plebeians, free citizens with limited political influence, and the vast numbers of slaves who formed the backbone of the economy. The family unit was central, governed by the paterfamilias, the male head who held absolute authority.
Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
Chapter 3 - Islamic Banking Products and Services.pptx
Membrane structure
1.
2. Thin delicate structures, key function in cell’s most
important functions.
Separates living cell from its enviornment.
Selectively permiable barrier that allows transport of certain
substances and prevents transport of others.
Provides frame work in which components can be
organized.
Site where energy transduced from one form to the other.
Contains receptors which bind specific ligands in the
external space and transfer information to cell’s interior
compartments.
3. Bimolecular layer of amphipatic lipids (phospholipid
bilayer)
2 segments with very different chemical properties.
Polar heads (hydrophilic) face outside and non polar
hydrocarbon tails (hydrophobic) face inside.
5-10nm thick.
Contain phospholipids, proteins and steroid molecules.
Structure called as “FLUID MOSAIC MODEL” and was
devised by S JONATHAN SINGER and GARATH NICHOLSON
of University of California in 1972.
4. A membrane is a MOSAIC
Proteins and other molecules are embedded in a
framework of phospholipids
A membrane is FLUID
Most protein and phospholipid molecules can move
laterally
5.
6.
7. Compartmentalization
Scaffold for biochemical activities
Providing a selectively permeable membrane
Transporting solutes
Responding to external signals (signal
transduction)
Intercellular interaction
Energy transduction
8. Impermeable barrier : passage of only selective
molecules like water and small hydrophilic molecules
Stability : maintained by van der Waals and hydrophobic
interaction, although outer enviornments vary, bilayer has
strength to retain its characteristic architecture
All phospholipid bilayer can spontaneously form
sealed closed compartments: separating the inside
enviornment from the external enviornment
9. Two surfaces of a cellular membrane:
CYTOSOLIC FACE: faces the cytosol.
EXOPLASMIC FACE: faces the exterior enviornment.
In the case of cellular membranes, exoplasmic face is
towards the interior and cytosolic face is towards the
exterior of the organelle. (Exeptions are mitochondria,
chloroplast and nucleous - ENDOSYMBIONT HYPOTHESIS)
10.
11. The ratio of lipid to protein in a membrane varies,
depending on type of cellular membrane, type of
organism and the type of cell.
The components are:
a) Membrane lipids
b) Membrane proteins
c) Membrane carbohydrates
d) Membrane steriods
12. The plasma membrane contains three principal classes of
amphipathic lipids (contain both hydrophobic and hydrophillic
ends)
PHOSPHATE HEAD
(POLAR)
HYDROCARBON TAIL
(NON POLAR)
13.
14.
15. Most abundant lipids.
Derivatives of glycerol 3 phosphate.
Contain a hydrophobic tail composed of 2 fatty acyl chains
esterified to the 2 hydroxyl group in glycerol phosphate
and a polar head attached to phosphate group (fatty acyl
chains can differ in number of carbon they contain and
degree of saturation)
Classified according to nature of head group.
Phosphatidyl choline contains a positively charged choline
head esterified to negatively charged phosphate.
Plasmalogens contain 1 fatty acyl chain attached to C2 of
glycerol by ester linkage and 1 long hydrocarbon chain
attached to C1 of glycerol by ether linkage.
16. At neutral pH, some phosphoglycerides contain no electric
charge (phosphatidyl choline) and some contain net negative
charge (phosphatidyl serine)
Negatively charged phosphate group and hydroxyl group on
head groups interact strongly with water.
17. Derived from amino alcohol Sphingosine.
Long chain fatty acid attached by amide linkage to
sphingosine amino group.
Have phosphate based polar head.
Most abundant sphingolipid – Sphingomyelin- in which
phosphocholine is attached to terminal –OH group of
sphingosene.
Sphingomyelins similar to phosphoglycerides and can form
mixed bilayers with them.
Other sphingolipids are glycolipids.
They constitute 2-10% of total lipid in plasma membrane.
18.
19. Depending on species and cell type carbohydrate concentration
varies from 2-10% by weight.
More than 90% of membrane carbohydrate covalently linked to
proteins to form glycoprotein and rest to lipids to form
glycolipids.
Carbohydrates of cell membrane face outside.
20. Carbohydrates of glycoproteins is present as short, branched
hydrophilic oligosaccharides.
Carbohydrate projections play an important role in mediating
the interactions of a cell with its enviornment and sorting of
membrane proteins to different cellular compartments,
Carbohydrates of the glycolipids of RBC plasma membrane
determine the blood type of a person.
21. Consist of cholesterol and its analogues.
Cholesterol is a 4 ring hydrocarbon.
Although almostt entirely hydrocarbon, it is amphipathic
because its –OH group can interact with water.
Abundant in mammalian cell, but absent in prokaryotes and
plant cells.
About 50-90% of cholesterol in mammalian cells is present
in plasma membrane and associated vesicles.
It is too hydrophobic to form bilayer by its own.
The sterol must interact with phospholipid molecules to be
incorporated into biomolecules.
Key function is its covalent addition to hedgehog protein, a
key signaling molecule in embryonic developement
22. Thermal motion allows lipid molecules to rotate freely
around long axes and also to diffuse laterally within each
leaflet.
Because movements are lateral, fatty acyl chains remain in
hydrophobic interior.
A typical lipid molecule exchange places with its neighbors
in a leaflet about 10^7 times/sec and diffuse several
micrometers /sec at 37˚C.
These diffusions indicate that viscosity of plasma membrane
is 100 times that of water- approx that of olive oil.
A lipid molecule can diffuse the length of a bacteria is 1sec
and that of animal cell in 20secs.
Movement observed by Fluorescence Recovery after
Photobleaching (FRAP) technique.
23. Fluorescence Recovery after Photobleaching (FRAP)
Fluorescence Recovery after photobleaching experiments can
quantify the lateral moovement of proteins and lipids within the
plasma membrane
Label
Bleach
With
laser
Fluoresce
nce
recovery
membrane
protein
Fluorescent
reagent
Bleached area
1 2 3
24. A technique by which two different type of cells can be fused
to produce one cell with common cytoplasm and continuous
plasma membrane.
25. Cells are allowed to fuse with one another making the outer
surface of the cells sticky, so that their plasma membrane
adhere to one another.
In 1970, Larry Frye and Michael Edidin conducted an
experiment where mice cell and human cell were allowed to
fuse and positions of specific proteins were followed once the
membrane had become continuous.
To detect position, antibodies against both cells were prepared
and covalently linked to fluorescent dyes. Antibodies against
mice protein complexes to give green fluorescence and
antibodies against human proteins complexes to give red
fluorescence.
The cells could be located under a fluorescence microscope.
29. Compromises between a completely rigid structure with no
mobility and a completely fluid non viscous liquid without
structural organisation and strength.
Allows interactions to take place in membrane,
Because of fluidity moleculles that interact can come together,
carryout necessary reactions, and move apart.
Key role in membrane assembly.
Many of cell’s basic functions, including cell movement, cell
growth, cell division, formation of intercellular junction,
secretions, and endocytosis, depend on the movement of
membrane components, which is achieved by fluidity.
30. There are differences in relative abundance of phosphoglycerides and
sphingolipids between membranes in ER where phosphoglycerides are
synthesized and in golgi where sphingolipids are synthesized.
1. FLUIDITY
Degree of bilayer fluidity depends on lipid composition, structure of
phospholipid bilayers and temperature.
Saturated fatty acyl chains have greatest tendency to aggregate,
packing tightly together into a gel like state.
Phospholipids with short fatty acyl chains have less surface area, less
van der Waal’s interaction and fluid consistancy.
Cholesterol is important in maintaining appropriate fluidity of natural
membranes.
31. Cholesterol is important in maintaining appropriate fluidity
of natural membranes.
At low cholesterol concentration the steroid ring separates
and disperse phospholipid tails causing the inner regions of
membrane to be more fluid
At concentrations present in plasma membrane, the steroid
rings interact with long hydrophobic tails of phospholipids
and tends to immobilize these lipids and decrease membrane
fluidity.
33. 3. CURVATURE
Curvature of bilayer depends on lipid concentration.
Depends on relative size of polar head and non polar tails of
phospholipids.
Lipids with long tail and large head are cylindrical and
those with small head and long tail are conical.
Result in formation oh highly curved membranes, such as
site of viral budding, microvilli, etc.
34. Asymetry in lipid composition across bilayer.
Although most phospholipids present in both leaflets.
In the plasma membrane of human erythrocytes, sphingomyelin
and phosphatidyl choline are found in exoplasmic leaflet,
phosphatidyl ethanolamine, phosphatidyl serine and
phosphatidyl inositol form more fluid bilayer ; preferentially
located at cytosolic leaflet.
This segregation influence bilayer curvature.
Cholesterol is relatively evenly distributed.
Phospholipases are enzymes that cleave various bonds in
hydrophilic ends of phospholipids.
On addition to external medium, enzymes cannot penetrate
membrane and cleave off the head groups of only those lipids
present in the exoplasmic face.
35. Membrane lipids are not randomly distributed.
Lipids remaining after the extraction of plasma membrane
with non ionic detergent predominantly contain cholesterol
and sphingomyelin.
These found in more ordered, less rigid bilayer; researchers
hypothesized that they form microdomains termed as lipid
rafts, surrounded by other more fluid phospholipids that are
extracted.
Rafts can be destructed by methyl β cyclodextrin that
specifically extracts cholesterol out.
36. By bringing many key proteins to proximity , these lipid
protein complex may facilitate signaling by cell surface
receptors and the subsiquent activation of cytosolic events.
37. Defined by location within or at surface of the membrane.
Proteins associated with particular membrane are responsible
for its distinctive function.
Kind and amount of protein vary depending on subcellular
location and cell type.
eg: inter mitochondrial membrane contain 76% protein,
myelin membrane contain 18% protein.
3 different types of protein:
a) INTEGRAL MEMBRANE PROTEIN
b) LIPID ANCHORED MEMBRANE PROTEIN
c) PERIPHERAL MEMBRANE PROTEIN
38. AKA transmembrane proteins
Span a lipid bilayer and comprises 3 segments.
Cytosolic and exoplasmic face domains have hydrophillic
exterior surface that interact with aqueous solution on the
cytosolic and exoplasmic faces of the membrane.
In contrast the membrane spanning segment contain more
hydrophobic aminoacids whose side chains protrude outward
and interact with the hydrophobic hydrocarbon core.
Membrane spanning segment consist of 1 or more α helices or
multiple β strands.
39.
40. Technique for analyzing cell membrane structures.
In this technique, tissue is frozen and struck with a knife
blade,which fractures the block into two pieces.
Fracture plane often takes path between the two bilayers.
Metals are deposited on exposed surface to form shadowed
replica and viewed under electron microscope.
The fracture goes around the protein particle than cracking it
in half.
Each protein separates with one half of the membrane leaving
a pit behind.
41.
42. Bound covalently to one or more lipid molecules.
Hydrophobic segment embedded in one segment of the
membrane.
Polypeptide chain itself does not enter phospholipid bilayer.
43. Do not directly contact the hydrophobic core of phospholipid
bilayer.
Bound to membrane indirectly by interactions with integral
or lipid anchored protein or directly to lipid head groups.
Can be bound to either cytosolic or exoplasmic face of plasma
membrane.
Cytoskeleton can be loosly associated with cytosolic face by
one or more peripheral proteins.
Such interactions provide support for various cellular
membranes, helping to determine cell shape and much
properties, and 2 way communication between all exterior
and interior faces.
44.
45.
46. α Helix dominate the transmembrane folded structures.
Proteins containing α helix are stably embedded in membranes
because of energetically favorable hydrophobic and van der
Waal’s interaction of hydrophobic side chains in domains with
specific lipid and probably also by ionic interactions with the
polar head groups of phospholipids.
A single α helical domain is sufficient to incorporate an
integral membrane protein into a membrane (membrane
embedded α helix made of continuos segment of hydrophobic
amino acid)
Such an α helix is sufficient to span the hydrocarbon core of
the membrane.
47. 3 proteins with α helical domain:
a) GLYCOPHORIN A
Representative single pass transmembrane protein.
One membrane spanning α helix.
Transmembrane α helix of one glycophorin A polypeptide
associates with corresponding transmembrane helix of other
protein to form coiled coil dimer – common mechanism for
producing dimeric membrane protein and many membrane
protein form oligomers.
48.
49. b) G PROTEIN COUPLED CELL SURFACE RECEPTOR
Multipass transmembrane protein.
Eg: bacteriorhodopsin
50. c) AQUAPORINS
Family of highly conserved proteins that transport water,
glycerol and other hydrophilic molecules through plasma
membrane.
Illustrates several aspects of structure of multipass
transmembrane system.
Tetramers of 4 identical subunits.
Each subunit has 6 membrane spanning α helices, some
transverse membrane at oblique angles.
Has a long transmembrane helix with a bend in the middle,
2 α helix penetrating midway.
51. Protein porin differ from other membrane by structure based
on α helix.
Several type of porin present on outer membrane of Gram –ve
E.coli, mitochondria and chloroplast.
Porins on outer membrane of E.coli enable passage of specific
type of disaccharide, other small molecule, as well as ions of
phosphate.
Amino acid sequence of porins contain non of the long
hydrophobic segments of typical integral proteins.
Porins are trimers of identical subunits, each subunit has 16 β
strands that form a sheet that twist into a barrel shaped
structure with a pore at centre.
52. Porin has hydrophilic interior and hydrophobic exterior,
outward facing side groups on each of the β strands are
hydrophobic and form a nonpolar ribbon like band that
encircles the outside of the barel.
Hydrophobic band interact with fatty acyl groups of membrane
lipids or with other porin monomers.
Side groups facing inside – hydrophillic.
53. Lipid anchored proteins are embedded in bilayer but the
protein itself does not enter the bilayer.
One group of cytosolic proteins are anchored to cytosolic face
of membrane by fatty acyl group covalently attached to N
terminal glycine residue.
Retension of such proteins at membrane by N terminal acyl
anchor is known as acylation.
Second group of proteins are attached to a cystein residue at
or near C terminus.
Some of these anchors are prenyl anchors built from 5C
isoprene units.
54. Proteoglycans are anchored to exoplasmic face by 3rd type of
anchor group glycosylphosphatidylinositol. (GPI anchors)
GPI anchors are glycolipids; they are both necessary and
sufficient for binding protein to the membrane
55. Every type of transmembrane protein has an orientation
callesd as TOPOLOGY.
Cytosolic segments face cytoplasm, exoplasmic segments face
opposite side of membrane.
This assymetry confir different properties on the two
membrane.
Membrane proteins are never been observed to flip-flop
across a membrane, which is energetically unfavourable.
Membrane protein retain assymetric orientation in membrane
during membrane budding and fusion events.
Same segment face cytosolic face and exoplasmic face.
56. Assymetry maintained throughout lifetime of protein.
Transmembrane glycoproteins are located so that
carbohydrate chains are in exoplasmic domain (proteins with
carbohydrate attached to serine, threonine, asparagine.)
Glycolipids in which carbohydrate chain is attached to
glycerol or sphingosine are always located in exoplasmic
domains with carbohydrate chain protruding from membrane
surface.
Both glycoproteins and glycolipids are abundant in plasma
membrane.
As carbohydrate chains of both extend to extracellular space,
they interact with lectins, growth factors and antibodies.
One of the consequences is ABO antigen interaction:
57.
58. Many water soluble enzymes use membrane phospholipids as
substrate and thus bind to membrane surfaces.
Bind to polar head group of phospholipids and carryout
functions.
Phospholipases hydrolyze various bonds in head groups of
phospholipids.
Have important role in degradation and damage of old cell
membrane and are also active components in snake venom.
59. Plasma membrane has dual function- to retain dissolved
contents of the cell and also to allow necessary exchange of
materials in and out of the membrane.
Two means: passively by diffusion, or activly by an energy
coupled transport process.
Two types of movement are;
a. PASSIVE TRANSPORT
b. ACTIVE TRANSPORT
MOVEMENT OF SUBSTANCES ACROSS CELL
MEMBRANE
60. PASSIVE TRANSPORT:
Does not require the expenditure of energy.
a) DIFFUSION
b) OSMOSIS
c) FACILITATED TRANSPORT
i) ION CHANNELS
ii) FACILITATED DIFFUSION
ACTIVE TRANSPORT:
energy coupled transport process.
61. Spontaneous process
Substance moves from its higher concentration to lower
concentration.
Depends on random thermal motion of solutes.
Exergonic process driven by an increase in entropy.
If the substance is an electrolyte, the tendency to diffuse
depends on the ELECTROCHEMICAL GRADIENT.
62. Movement of water molecules from a region of lower solute
concentration to a region of higher solute concentration
through a semipermeable membrane.
Solution with higher solute concentration-hypertonic
Solution with lower solute concentration-hypotonic
Solutions with same solute concentration-isotonic
In hypertonic solution cell shrinks
In hypotonic solution cell swells
In isotonic solution no change
The sweling and shrinking of cells in slightly hypotonic and
hypertonic solution are temporary events.
63.
64.
65.
66. Lipid bilayer highly impermeable to small charged ions like
Na+, K+, Ca²+, Clˉ.
In 1955 Alan Hodgkin and Richard Keyneys proposed that cell
membranes contain ion channels: openings in a membrane that
is specific for ions.
But proof of such a channel was given by Bert Sakmann and
Erwin Neher of Max Planck University.
They developed techniques to monitor ionic current passing
through a single channel.
Accomplished using very fine micropipette-electrode made of
polished glass and the current passing through the membrane
can be measured by maintaining a current across the membrane.
67.
68. Most of the ion channels identified can exist in an open or a
closed confirmation. Such channels are said to be gated. 3
major categories of gated channels are distinguished as:
a) Voltage gated channel: conformational state depends on the
difference in ionic charge on the two sides of the membrane.
b) Ligand gated channels: conformational state depends on the
binding of a specific molecule(ligand) which is usually not the
solute that passes through it. Some gates open on the binding
of ligand on the outer surface of the channel and some open
on binding on the inside.
c) Mechano gated channels: conformational state depends on
mechanical forces that are applied to the membrane.
69. Diffusing substance first binds selectively to a membrane
spanning protein called a facilitative transporter.
Binding of solute to transporter trigger conformational change
in protein, exposing solute to the other surface of the
membrane.
Can facilitate the movement in both directions.
Much like enzymatic reactions; transporters are specific for
solutes, discriminating D and L isomers.
Like enzymes, their activity is regulated.
Glucose transporter is an example for facilitated diffusion.
70.
71. Like facilitated diffusion, active transport depends on integral
membrane protein that selectively bind a particular solute and
move it across the membrane in a process driven by changes
in protein’s conformation.
Movement of solute against concentration gradient requires
the coupled input of energy.
Coupled with exergonic process such as hydrolysis ofATP,
absorbance of light, transport of electrons, or flow of other
substances down their concentration gradient.
Proteins often refered to as ‘pumps’
In 1957 Jens Skou discovered an ATP hydrolysing enzyme in
nerve cell of crab that was only active in the presence of Na+
and K+. The enzyme was called Na+/K+ ATPase or Sodium
Pottasium pump.