03. The chemical nature of the cell. Ian Anderson (2013) Saint Ignatius College Geelong
Knowledge and skills. Distinguish between organic and inorganic molecules. Describe the roles of biologically important inorganic molecules. Outline the properties of water that are important to life. Describe the basic structures of carbohydrates, lipids, proteins and nucleic acids.
Organic v inorganic molecules.Chemical compounds can be divided into two groups. Organic compounds. Most carbon containing compounds are organic. e.g. methane (CH4) and glucose (C6H12O6). But not all e.g. carbon dioxide(CO2). Therefore our definition: Compounds that contain both carbon and hydrogen Inorganic compounds. All other molecules that do not contain both carbon and hydrogen.
Components of cells.The molecules that make up living organisms can be grouped into five classes Water Carbohydrates Lipids Biomacromolecules Proteins Nucleic acids.
Water. H2O = inorganic compound. Most abundant compound in living organisms Most organisms 70-90% water Humans – females ~50%; males ~60%; newborn babies ~75% Unique properties of water help explain why it is so important to life: Molecules stick together (as a result of H bonding) A good solvent Heat capacity
Biomacromolecules. Very large organic molecules. All are polymers (except lipids). Polymers are made up of many smaller building blocks called monomers. (poly = many; mono = single; mer = segments). The monomers in a polymer are joined by a dehydration (condensation) reaction (where water is released during the reaction). monomer + monomer polymer + H2O (Reverse reaction = hydrolysis reaction)
Carbohydrates. Organic compounds. Most abundant organic compounds in nature. Made up of carbon, hydrogen and oxygen. Energy rich – source of energy for all living organisms. Also important in plants as structural material (cellulose). Exoskeleton of insects (chitin)
Carbohydrates. Basic unit of carbohydrates are the simple sugars – monosaccharides (CnH2nOn) e.g. glucose (C6H12O6). Disaccharides – two monosaccharide sugars joined together (also called simple sugars) e.g. sucrose Polysaccharides – many simple sugars (monomers) joined together to form long chains (polymer). Also called complex carbohydrates. e.g. starch, glycogen, cellulose.
Lipids. General term for fats, oils and waxes. But also include phospholipids, steroids, glycolipids and carotenoids. Composed of carbon, hydrogen and oxygen, but in different proportions to carbohydrates (less oxygen & often contain other elements such as phosphorus and nitrogen). All lipids are hydrophobic and insoluble in water. Lipids are not polymers.
Types of lipids. Triglycerides (fats & oils). Known as simple lipids (composed only of C, H & O, but in different proportions to carbohydrates). Important energy storing molecules. Fats store twice as much energy as the same weight of carbohydrates. Made up of a glycerol molecule and three fatty acid molecules. Fatty acids may be either saturated (no double bonds) or unsaturated (contains double bonds), which is important for determining the fluidity and melting point of the lipid. Fats (which are solid at room temperature) have many more saturated bonds than oils (which are liquid).
Types of lipids. Triglycerides (fats & oils). Source: Enger et al. (2011)
Types of lipids. Phospholipids. Known as complex lipids (also composed of C, H & O, but also other elements such as P & N). Similar in structure to triglycerides, except that one of the three fatty acids attached to glycerol is replaced by a phosphate containing group. Structure results in a hydrophilic, polar head (soluble in water) and a hydrophobic, non-polar tail (insoluble in water). Phospholipids are a major component of cell membranes.
Types of lipids. Phospholipids. Source: Campbell et al. (2011) Source: Enger et al. (2011)
Types of lipids. Steroids. Have a very different structure than other lipids. Four interlocking rings of carbon. Still have large number of carbon-hyrogens, and are non- polar. Important examples include cholesterol, the sex hormones (testosterone, oestrogen and cortisol) and vitamins such as Vitamin D. Waxes. Important role in both plants and animals for their ability to form a waterproof coating.
Proteins. Large molecules made up of amino acids. 20 naturally occurring amino acids. Joined together by peptide bonds (as a result of a hydration reaction). To form a polypeptide. Contain nitrogen, as well as carbon, hydrogen and oxygen (some also contain sulphur, phosphorus and other elements). Proteins are unique to each type of organism.
Proteins. Amino acids (the monomers of proteins). All amino acids share a common structure Amino group. Carboxyl group. Central α (alpha) carbon, and a R group (also called the side chain). Only the R group differs between amino acids.
Protein structure. Proteins are very complex, with four levels of complexity used to describe them. Primary. Secondary. Tertiary. Quaternary.
Protein structure. Primary structure. The sequence of amino acids in the polypeptide chain. The polypeptide chain is the result of dehydration reactions between the carboxyl group of one amino acid and the amino group of another, resulting in peptide bonds. The amino acid sequence determines what three- dimensional shape the protein will have. The specific sequence of amino acids in a polypeptide is controlled by the genetic information of the organism. Source: Enger et al. (2011)
Protein structure. Secondary structure. Hydrogen bonding between the amino groups and the carboxyl groups in a polypeptide can result in α-helices (coils) β-pleated sheets (folds), or random coils (no distinct pattern). Source: Enger et al. (2011)
Protein structure. Tertiary structure. The overall three-dimensional shape of the protein. A polypeptide chain can contain one or more combinations of α-helices and β–pleated sheets, causing the chain to twist, bend and loop. The result is interactions between the various side chains (R groups) of the amino acids, incl Hydrogen bonding, ionic bonding, covalent bonding (e.g. disulphide bridges between two cysteine side chains), hydrophobic interactions, etc. Chaperone proteins (found in cells) help proteins fold into their normal shape.
Protein structure. Tertiary structure. Interactions between the side chains in the tertiary structure of a protein. Source: Campbell et al. (2011) Tertiary structure of a protein. Source: Enger et al. (2011)
Protein structure. Quaternary structure. Two or more polypeptide chains, each with their own tertiary structure, joined together as one functional macomolecule. e.g. Haemoglobin (4 polypeptide chains), insulin (2 polypeptide chains), immunoglobulins (4 polypeptide chains). Source: Enger et al. (2011)
Proteins. Two major types of proteins. Fibrous proteins The secondary structure (either α-helices or β-pleated sheets) forms the dominant structure of the protein (i.e. generally only have primary and secondary structure). Are insoluble in water. Play a structural or supportive role in the body. e.g. keratin, collagen, silk, muscle and ciliary proteins. Globular proteins Are soluble in water. All have tertiary and some have quaternary structure . e.g. enzymes and hormones.
Proteins. Proteins have any different functions, incl. Structural Collagen e.g. collagen, keratin, etc. Regulatory Enzymes e.g. pepsin, catalase, etc. Hormones e.g. insulin, glucagon, etc. Carrier molecules (transport) e.g. Haemoglobin. Source: Reece et al. (2011)
Nucleic acids. The genetic material of all life. Made up of long chains of monomer units called nucleotides. Two types Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA). (We look at these in more detail later, so just an introductory look for now.)
Nucleic acids. Each nucleotide (the monomer) is made up of three parts a sugar a phosphate group, and a nitrogenous base. Source: Walpole et al. (2011)
Nucleic acids - DNA. Double stranded and helical shape (double helix). Sugar and phosphate groups form the backbone of the ladder, while the bases form the steps. The two strands are attached by hydrogen bonds between their bases. Sugar = deoxyribose. Nitrogenous bases = Adenine (A), cytosine (C), guanine (G) and thymine (T).
Nucleic acids - DNA. Source: Raven et al. (2011)
Nucleic acids - RNA. Single stranded. Sugar = ribose. Nitrogenous bases = Adenine (A), cytosine (C), guanine (G) and uracil (U). Three types. Messenger RNA (mRNA) Transfer RNA (tRNA) Ribosomal RNA (rRNA)
Nucleic acids - RNA. Source: Raven et al. (2011)
Other important compounds. Vitamins Organic compounds required by animals in very small (trace) amounts for normal functioning. Essential for many chemical reactions e.g. Vitamin C are components of co-enzymes. Minerals Inorganic ions required by both animal and plant cells. Play a role in metabolic process of cells.