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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

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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

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

Formed by condensation reaction

Peptide bond forms between the N and C

Water is produced as a result

The amino acid sequence
  • Determined by the gene that codes for a polypeptide
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
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
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
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
Globular proteins folded into 3D shapes e.g haemoglobin, enzymes
  • Fibrous have a linear 3D shape and are insouble e.g. collagen, keratin
Bond between Carbon 1 and Carbon 4 of an adjacent glucose molecule, water is produced as a result
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

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
Substance in test tube
  • Add biuret (copper sulfate and sodium hydroxide)
  • Positive = lilac
  • Negative = stays blue
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
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
Place substance on a tile
  • Add yellow iodine
  • Positive = blue/black
  • Negative = stays yellow
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
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)