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Download Describe How Hydrogen Bonding Occurs
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PIG describe how hydrogen bonding occurs between water molecules, and relate this, and other properties of water, to the roles of water in living organisms • Water is attracted to ions and polar molecules so is a good solvent • High specific heat capacity, so absorbs a lot of thermal energy preventing temperature changes in body • High latent heat, so lots of energy needed before evaporation meaning more heat absorbed by sweat • High cohesion between water molecules to draw water up xylem vessels • Water is reactive, so can be used in hydrolysis • Cannot be compressed so can form a hydrostatic skeleton e.g. earthworms Describe the structure of an amino acid Peptide bonds form between an amine group (NH2) and a carboxylic acid group COOH) R groups project from side of chain Properties are determined by the R group e.g. shape of active site How are peptide bonds formed and broken • Formed by condensation reaction • Peptide bond forms between the N and C • Water is produced as a result What does primary structure mean • The amino acid sequence • Determined by the gene that codes for a polypeptide What does secondary structure mean • The folding of a polypeptide into • Alpha helix or • A beta pleated sheet, a flat sheet that folds back on itself or links to adjacent polypeptides lying parallel to one another What does tertiary structure mean • Further folding of a polypeptide • Hydrogen bonds form anywhere on the polypeptide • Disulphide bonds between sulphur containing R groups (covalent bonds) • Ionic bonds between R groups (positive and negatively attracted to one another) • Hydrophobic interactions Describe haemoglobins tertiary structure • 4 polypeptides in each haemoglobin molecule called alpha and beta globin (2 of each) • In the middle is the haem group that is flat, circular and has an atom if iron in the centre • Each haem group combines loosely with one oxygen molecule • Each haemoglobin can carry four oxygen molecules Describe the structure of a collagen molecule • Fibrous protein • Three polypeptides wound tightly to form a triple helix • Glyceine every third amino acid so it can be wound tightly • Covalent bonds link the helices to make a strong fibre Compare the structure and function of a globular and fibrous protein • Globular proteins folded into 3D shapes e.g haemoglobin, enzymes • Fibrous have a linear 3D shape and are insouble e.g. collagen, keratin Describe the difference between alpha and beta glucose • Alpha glucose has H above Carbon 1 and OH below Carbon 1, • Beta has the opposite Describe a glycosidic bond • Bond between Carbon 1 and Carbon 4 of an adjacent glucose molecule, water is produced as a result Compare and contrast the structure and function of starch and cellulose • Starch: amylose and amylopectin • amylose- energy storage, single unbranched polymer forming a helix, • amylopectin is a branched chain with glycosidic bonds between carbon atoms 1 and 6 • Cellulose: strong for cell walls- polymer of beta glucose, alternate glucose molecules turned through 180 degrees, cellulose forms straight chains Diagram showing rotation Describe the structure of glycogen • Like amylopectin, Carbons 1 and 6 bond, but with more branches Describe the structure of cholesterol and steroids • Cholesterol = a lipid, polar at the OH end, 4 hydrocarbon rings and hydrocarbon tail are no polar, arranged in bilayers similar to a phospholipid • Steroids are made from cholesterol and have a four ring structure What is the chemical test for protein • Substance in test tube • Add biuret (copper sulfate and sodium hydroxide) • Positive = lilac • Negative = stays blue What is the chemical test for reducing sugars • • • • • Benedicts test Solution in test tube Add same vol of blue benedicts solution Heat to 80 degrees Positive = blue to green, then yellow then red with a precipitate • Negative = stays blue What is the chemical test for non reducing sugars • • • • • • • After negative result with benedicts Add hydrochloric acid Boil for a few minutes Add alkali to neutralise acid Carry out benedicts test Positive = blue to yellow then red Negative = stays blue What is the chemical test for starch • • • • Place substance on a tile Add yellow iodine Positive = blue/black Negative = stays yellow What is the chemical test for lipids • Crush material into ethanol • Filter and place ethanol into cold water into another test tube • Discard solid residue, ethanol will float on the water • Positive = white emulsion forms in the water Explain how concentration can be determined using colorimetry • Used to make benedicts quantitative • Colorimeter measures amount of blueness in solution • Light shines through solution and measures either absorbance (light absorbed by solution) or transmission (light that gets through solution)
