PIG

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PIG
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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
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• 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

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Describe the structure of an amino acid
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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
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How are peptide bonds formed and broken
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• Formed by condensation reaction
• Peptide bond forms between the N and C
• Water is produced as a result

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What does primary structure mean
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• The amino acid sequence
• Determined by the gene that codes for a
  polypeptide

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What does secondary structure mean
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• 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

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What does tertiary structure mean
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• 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

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Describe haemoglobins tertiary structure
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• 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

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Describe the structure of a collagen molecule
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• 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

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Compare the structure and function of a globular
and fibrous protein
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• Globular proteins folded into 3D shapes e.g
  haemoglobin, enzymes
• Fibrous have a linear 3D shape and are insouble
  e.g. collagen, keratin

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Describe the difference between alpha and beta
glucose
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• Alpha glucose has H above Carbon 1 and OH below
  Carbon 1,
• Beta has the opposite

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Describe a glycosidic bond
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• Bond between Carbon 1 and Carbon 4 of an adjacent
  glucose molecule, water is produced as a result

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Compare and contrast the structure and function
of starch and cellulose
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• 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
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Describe the structure of glycogen
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• Like amylopectin, Carbons 1 and 6 bond, but with
  more branches

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Describe the structure of cholesterol and
steroids
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• 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

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What is the chemical test for protein
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• Substance in test tube
• Add biuret (copper sulfate and sodium hydroxide)
• Positive lilac
• Negative stays blue

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What is the chemical test for reducing sugars
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• 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

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What is the chemical test for non reducing sugars
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• 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

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What is the chemical test for starch
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• Place substance on a tile
• Add yellow iodine
• Positive blue/black
• Negative stays yellow

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What is the chemical test for lipids
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• 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

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Explain how concentration can be determined using
colorimetry
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• 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)