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Biology - AS Level - 10.1 - Biological Molecules - .2 - Proteins


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3 Structural proteins and their functions:
collagen (bone, cartilage, tendon)
keratin (hair, nails, rhino horn)
actin (muscle)
pepsin, amylase, carbohydrase, bromilase, protease, lipase (+>10 000 others)
Transport (2):
haemoglobin (oxygen), transferrin (iron)
EG Na+ K+ pump in cell membranes
Motors (2):
eg. myosin (muscle), kinesin (cilia)
Hormones (8):
estrogen, testosterone, LH, FSH, ADH, glucagon, insulin.
Rhodopsin (light receptor in retina)
eg immunoglobulins
Storage (2):
eg albumins (egg white pure) in eggs and blood, caesin in milk
Blood clotting (2):
eg thrombin, fibrin
glycoproteins in synovial fluid.
(organic poisons) e.g. diptheria toxin
e.g. glycoproteins in arctic flea
type of protein with CH chain - antenna - sensor
All proteins contain 4 elements:
nitrogen, oxygen, carbon and hydrogen.
amino acids are:
the basic units (monomers) of proteins
basic structure of an amino acid:
NCC spine
2 Hs bonded to N
R above and H below middleC
x2bondto O above right C and bond to OH below


H2N, C, COOH, R above and H below middle C
NH2 group is the...
amino group (in chemistry, the naming group)
COOH group is the...
carboxyl group
R group...
varies between different amino acids. 20 R groups so 20 different amino acids.
Glycine structure:
H for R group.
7 R groups:
Simple (5), Basic (5), hydroxyl (2, end with OH), acidic (2, end with C bonded to O and x2 bonded to O- (extra proton)), sulphur (2, contain sulphur), ringed (3, all ringed but not only ringed amino acids) and cyclic (proline).
What bond joins two amino acids together?
Peptide bond. OH from bottom right of left mol and H from bottom left of right mol make water, C and N bond. The line between is peptide bond (glycosidic is when oxygen is left behind). NCCNCC is the pattern for di and poly spines.
Primary Protein structure:
1. Final configuration depends on the primary struct. - The Primary Structure is the number, type and sequence of amino acids in the chain. There are specific interations between different parts of the chain which give a final 3-dimensional shape of the protein.
Secondary Protein Structure:
H-bonds form between a.a.s in the cahin. Between O atoms of the COOH group (delta-) and Hs of the NH2 groups (delta+). When the groups are v close together they attract. This folds or coils the chain giving rise to the 2ndary structure. 2nd structs include the alpha-helix and the beta-pleated sheet.
Due to backbone interactions and is thus largely independant of primary sequence.
Tertiary Protein Structure:
2ndary structure may then fold and coil forming the 3ry structure. This is held in a specific 3-d shape by electrostatic interaction (between rs with quite strong +/- charges) and disulphide bridges (covalent S-S bonds between 2 cysteine amino acids, which are strong).
Due to side chain interactions - thus depends on the amino acid sequence.
Quaternary protein structure:
Found in prots containing more than one polypeptide chain - simply means how the different polypeptide chains are arranged together. Individual chains are usually globular, but can arrange themselves into a variety of 4ry structs eg haemoglobin, immunoglobulins, actin and tubulin.
Haemoglobin structure:
4 globular subunits arranged in a tetrahedral structure. Each sub contains one FE atom and can bind 1 O2 mol.
Immunoglobulin structure:
Proteins that make antibodies. 4 polypep chains in a y-shape. Held together via sulphide bridges. This shape allows antibodies to link antigens together, causing them to clump.
Actin structure:
One of prots found in muscles. Consists of many globular subunits arranged in a 2 helix to form long filaments.
Tubulin structure:
globular prot that polymerises to form hollow tubes called microtubules. These form part of the cytoskeleton and make cilia and flagella move.
Fibrous proteins:
Long chains of aas which are folded into a helix. Sometimes can be several polypep chains together. Can join to form long fibres. Insoluble (ext. R-groups are non-polar.) Provide strenght and flexibility - structural. Eg. keratin, collagen.
Keratin alpha-helix is basically a secondary structure. Microfibril (1 mol k is made of 3 a-helices). Hair fibre, macrofibril, microfibril.
Hair made up of many keratin molecules which form fibers.
Protein test:
To test for protein in solution add Biuret reagent (alkaline copper sulphate). If protein is present the solution turns purple.
What causes the 2ndary strucutre to differ in length from the primary?
H bonds form between O atoms of Cooh groups and H atoms of NH2 groups, causing the chain to fold or coil.
Explain what is meant by the tertiary structure of a protein?
The way in which the whole molecule is folded or the way it forms a globular shape.
Heating may affect the tertiary structure of a protein. Explain why.
It causes the bonds which hold the tertiary structure together to break. The shape is no longer maintained / The protein is denatured.
What is meant by a receptor molecule?
A molecule in which another molecule can fit
Explain how it's tertiary structure might allow a protein molecule to act as a receptor molecule
The tertiary strucutre gives the receptor a particular shape, which provides the site into which another molecule can fit.
Why electron can see protein but not light.
The fibrils are thin / close together. The electron has a greater resolution than a alight microscope.
Hydrolysis of protein -
into amino acids. The reaction involves the addition of water.
Suggest how a change in the structure of a protein could make it resistant to the action of protein - digesting enzymes.
A change in the secondary structure would change the shape of the PrP molecule. No longer fits the active site of the enzyme.
Biuret test in detial:
Add 10 drops of each Biuret reagent (A and B) to a small sample of the protein. Shake the mixture. If it turns lilac protein is present.
Amino acid structure:
NCC, two Hbonds N, RaboveHbelow middle C, C 2bondO bondOH

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