Protein Structure and Function

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Give an account of protein structure and function
Protein structure
1 Proteins consist of amino acids joined together (in chains) 2 A protein is unique because of the sequence of amino acids 3 The amino acids are joined by strong peptide bonds
4 to produce the primary structure
5 Further (weak) hydrogen bonding between acids
6 produce the secondary and tertiary structures
A maximum of 4 marks can be gained from this section.

Protein function
7 Some proteins are enzymes + named example (eg the digestive enzyme amylase) 8 Some proteins are hormones + named example (eg insulin)
9 Some proteins are antibodies which help the body fight infections 10 Some proteins transport substances + named example (eg haemoglobin) 11 Some proteins provide structure + named example (eg collagen) A maximum of 4 marks can be gained from this section.

Coherence mark (1) is given if sub-headings are used, or points placed correctly in two groups. Relevance mark (1) is deducted if protein synthesis or factors controlling enzyme action are discussed

Give an account of enzyme function under the following headings: (a) the specificity of enzymes; 2
(b) the role of enzymes in biochemical pathways; 4
(c) competitive and non-competitive inhibition of enzymes. 4 (10)

Each numbered point is worth 1 mark. The information in brackets is not a required part of the answer. (a) 1 One enzyme will only react with one type of chemical
2 The chemical an enzyme reacts with is called its substrate 3 The substrate fits into the active site of the enzyme
4 The chemical produced is known as the product
A maximum of 2 marks can be gained from this section.
(b) 5 A biochemical (or metabolic) pathway is a sequence of chemical reactions in which enzymes change one metabolite into another 6 Each stage in the pathway is controlled by a specific enzyme 7 Each enzyme is produced as a result of a gene coding for it 8 If there is a mutation in the gene coding for it, an enzyme may not work properly 9 and the metabolic pathway will be disrupted

10 This is known as an inborn error of metabolism
A maximum of 4 marks can be gained from this section.
(c) 11 Competitive inhibition occurs when the inhibitor competes with the substrate for the active site of the enzyme 12 The competitive inhibitor is a very similar shape to the substrate molecule 13 Competitive inhibition can be reduced by increasing the substrate concentration 14 Non-competitive inhibition occurs when the inhibitor binds to a part of the enzyme other than the active site 15 This permanently changes the shape of the enzyme (including the active site) so that the enzyme is denatured A maximum of 4 marks can be gained from this section.

Give an account of protein synthesis under the following headings: (a) the role of the nucleus; (5)
(b) the role of the cytoplasm. (5)

Each numbered point is worth 1 mark. The information in brackets is not a required part of the answer. (a) 1 DNA (in the nucleus) contains the genetic code (for the particular protein to be synthesised) 2 The DNA acts as a template for the production of mRNA

3 The DNA molecule unzips
4 as the hydrogen bonds between the bases break
5 RNA nucleotides align themselves alongside the DNA molecule 6 The RNA bases are joined to the DNA bases according to the base pair rule: A-U; C-G; G-C; T-A A maximum of 5 marks can be gained from this section.

(b) 7 The mRNA molecule moves out of the cytoplasm and becomes attached to a ribosome 8 tRNA molecules become attached to their specific amino acids (and move to the ribosome) 9 The anticodon (triplet of bases) on the tRNA molecule

10 becomes (temporarily) attached to the complementary codon on the mRNA molecule 11 Peptide bonds form between the amino acids
12 to form a specific polypeptide (protein) molecule
A maximum of 5 marks can be gained from this section.

Give an account of the differences between the anaerobic and aerobic phases of...
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