Protein Synthesis

Question 1

Define the term exon.

Answer 1

Triplet sequence coding for polypeptide

Question 2

Describe Translation (6)

Answer 2

1. mRNA attaches to ribosomes
2. tRNA anticodons bind to complementary mRNA codons
3. tRNA brings a specific amino acid;
4. Amino acids join by peptide bonds; with use of ATP
5. tRNA released (after amino acid joined to polypeptide);
6. The ribosome moves along the mRNA to form the polypeptide

Question 3

Give two structural differences between a molecule of messenger RNA (mRNA) and a molecule of transfer RNA (tRNA) (5)

Answer 3

1. mRNA does not have hydrogen bonds , tRNA does
2. mRNA is linear , tRNA is cloverleaf;
3. mRNA does not have an amino acid binding site, tRNA does;
4. mRNA has more nucleotides;
5. (Different) mRNAs have different lengths, all tRNAs are similar / same length;
6. mRNA has codons, tRNA has an anticodon;

Question 4

What is an allele?

Answer 4

Different version/base sequence of a gene;

Question 5

Explain how selection occurs in living organisms (6)

Answer 5

1. Variation due to mutation;
2. Different environmental/abiotic/biotic conditions / selection pressures;
3. Selection for different/advantageous, features/characteristics/mutation/ /allele;
4. Differential reproductive success / (selected) organisms survive and reproduce;
5. Leads to change in allele frequency;
6. Occurs over a long period of time;

Question 6

Define degenerate code

Answer 6

More than one codon for one amino acid

Question 7

Explain what the term non-overlapping DNA means

Answer 7

A base from one triplet cannot be used in an adjacent triplet

Question 8

A mutation in a gene coding for an enzyme
could lead to the production of a non-functional enzyme. Explain how (5)

Answer 8

1. Change in DNA base sequence
2. Change in amino acid sequence / primary structure (of enzyme);
3. Change in hydrogen/ionic/ disulphide bonds;
4. Change in the tertiary structure/active site (of enzyme);
5. Substrate not complementary/cannot bind (to enzyme / active site) / no enzyme-substrate complexes form;

Question 9

Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide. Give two reasons why

Answer 9

1. Triplets code for same amino acid
2. Occurs in introns /non-coding sequence;