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)