Protein Synthesis

Question 1

Define the term exon.

Answer 1

Base/nucleotide/triplet sequence coding for polypeptide/sequence of amino acids/primary structure

Question 2

Describe transcription in eukaryotes.

Answer 2

1. Hydrogen bonds (between DNA bases) break
2. (Only) one DNA strand acts as a template
3. (Free) RNA nucleotides align by complementary base pairing
4. (In RNA) Uracil base pairs with adenine (on DNA) OR (In RNA) Uracil is used in place of thymine;
5. RNA polymerase joins (adjacent RNA) nucleotides
6. (By) phosphodiester bonds (between adjacent nucleotides)
7. Pre-mRNA is spliced (to form mRNA) OR Introns are removed (to form mRNA)

Question 3

Describe Translation.

Answer 3

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

Question 4

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

Answer 4

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

Question 5

What is an allele?

Answer 5

(Different) version of the same gene.

Question 6

Explain how selection occurs in living organisms.

Answer 6

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 7

Define degenerate code.

Answer 7

More than one codon codes for the same amino acid.

Question 8

Explain what the term non-overlapping DNA means.

Answer 8

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

Question 9

A mutation in a gene coding for an enzyme

could lead to the production of a non-functional enzyme. Explain how.

Answer 9

1. Change in base sequence (of DNA/gene)
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 10

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

Answer 10

1. Triplets code for same amino acid

2. Occurs in introns/non-coding sequence