BIOLOGICAL MOLECULES

• Carbohydrates are molecules which consist only of carbon, hydrogen and oxygen and are long chains of sugar units called saccharides.
• There are three types of saccharides: monosaccharides, disaccharides and polysaccharides.
• Monosaccharides can join together to form disaccharides and polysaccharides by glycosidic bonds which are formed in condensation reactions.
• Glucose is a monosaccharide containing six carbon atoms in each molecule and is the main substrate for respiration.
• Ribose is a monosaccharide containing five carbon atoms and is a pentose sugar and a component of RNA.
• DNA contains an isomer of ribose called deoxyribose, which lacks the OH group on the second carbon of the sugar ring.
• Maltose is a disaccharide formed by condensation of two glucose molecules.
• Sucrose is a disaccharide formed by condensation of glucose & fructose.
• Lactose is a disaccharide formed by condensation of glucose & galactose.
• Glycogen is the main energy storage molecule in animals and is formed from many molecules of alpha glucose joined together by 1, 4 and 1, 6 glycosidic bonds.
• Starch stores energy in plants and it is a mixture of two polysaccharides called amylose and amylopectin.
• Amylose is an unbranched chain of glucose molecules joined by 1, 4 glycosidic bonds, making it a very compact molecule meaning it can store a lot of energy.
• Amylopectin is made up of glucose molecules joined by 1,4 and 1,6 glycosidic bonds, making it a branched molecule.
• Inorganic ions occur in solution in the cytoplasm and body fluid of organisms, including nitrate ions required for DNA and amino acids, calcium ions needed to form calcium pectate for the middle lamellae in plants, phosphate ions required to make ADP and ATP, and DNA and RNA, and magnesium ions needed to produce chlorophyll.
• Inhibition may be reversible or irreversible.
• Water has a high specific heat capacity, minimising temperature fluctuations and allowing organisms in rivers and lakes to survive in different seasons.
• Water has a relatively large latent heat of vaporisation, providing a cooling effect with little water loss.
• There are two categories of inhibition: competitive inhibition, where an inhibitor molecule competes with the substrate for binding to the active site of the enzyme, and non-competitive inhibition, where an inhibitor binds to a different part of the enzyme and changes the shape of the enzyme.
• Water molecules stick together due to cohesion and can adhere to the sides of tube-like cells due to adhesion.
• Temperature increases the rate of reaction up to the optimum temperature, after which the rate of reaction decreases as enzymes become denatured.
• Substrate concentration increases the rate of reaction up to a certain point, after which the rate of reaction no longer increases as enzyme concentration becomes the limiting factor.
• Inhibitors are substances which stop the enzyme from binding to its substrate, controlling the progress of a reaction.
• The maximum density of water is at 4 degrees Celsius, meaning that ice is less dense than water as the water molecules are spread out and fixed in place, increasing the chance of survival of organisms in large bodies of water as it prevents them from freezing when temperatures decrease.
• Water is a polar solvent in which many metabolic reactions occur.
• Water is a polar molecule due to uneven distribution of charge within the molecule, making it possible for ionic substances like NaCl to dissolve in water.
• Cellulose is a component of cell walls in plants and is composed of long, unbranched chains of beta glucose monomers which are joined by 1,4 glycosidic bonds.
• Microfibres and microfibrils are strong threads which are made of long cellulose chains joined together by hydrogen bonds and they provide structural support in plant cells.
• Lipids are biological molecules which are only soluble in organic solvents such as alcohols.
• Saturated lipids such as those found in animal fats only contain carbon-carbon single bonds.
• The primary structure of a protein is the linear sequence of amino acids in the polypeptide chain, held together by peptide bonds.
• The tertiary structure of a protein is the 3D folding of the secondary structure into a complex shape, determined by the type of bonding present, such as hydrogen bonding, ionic bonding (salt bridges, form between oppositely charged groups on the R groups) and disulphide bridges (covalent bonds between sulphur atoms in cysteine).
• Proteins can be fibrous or globular.
• Lipids are waterproof because the fat tail is hydrophobic.
• Triglycerides are lipids made of one molecule of glycerol and three fatty acids joined by ester bonds formed in condensation reactions.
• Unsaturated lipids which can be found in plants contain carbon-carbon double bonds and melt at lower temperatures than saturated fats.
• In phospholipids, one of the fatty acids of a triglyceride is substituted by a phosphate-containing group.
• Fatty acid chains in triglycerides can vary in length and have different types of carbon-carbon bonds: C-C single bonds and C-C double bonds.
• Lipids are very compact, have better gram-for-gram energy release than carbohydrates or proteins because more C-O bonds are hydrolysed, are non-polar and insoluble in water, therefore they are good for storage, and provide thermal insulation.
• The quaternary structure of a protein is the 3D arrangement of more than one polypeptide.
• Saturated lipids are more compact as the molecules can pack closer together because there are no kinks in the carbon chain.