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
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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
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
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
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)