Paper 2 - Inheritance

Question 1

Describe a DNA molecule

Answer 1

• 2 strands coiled to form a double helix
• The strands are linked by a series of paired bases: adenine (A) with thymine
  (T), and cytosine (C) with guanine (G)

Question 2

Describe an RNA molecule

Answer 2

• Single-stranded
• Contains uracil (U) instead of thymine (T)

Question 3

What are the stages of protein synthesis?

Answer 3

Transcription and translation

Question 4

What are the stages of Transcription?

Answer 4

• Section of DNA molecule unwinds and unzips
• Bases are exposed along the template strand
• RNA nucleotides line up along the template strand according to complementary base pairing rules
• RNA nucleotides link together to form mRNA
• mRNA leaves the nucleus through a pore to the cytoplasm
• mRNA goes to the ribosome
• DNA Helix zips up again

Question 5

What are the stages of Translation?

Answer 5

• mRNA binds to the ribosome
• The ‘Start’ codon is always AUG which codes for amino acids methionine to tRNA with complementary UAC anticodon of this tRNA binds to the next codon of mRNA
• A bond forms between methionine and the 2nd amino acid
• The first tRNA is released, ribosomes shift along by one codon and a new tRNA binds etc…
• This continues until the ‘stop’ codon is reached and the protein is released

Question 6

What is the role of mRNA?

Answer 6

• mRNA is a copy of the gene
• mRNA transports RNA nucleotides to the ribosome

Question 7

What is the role of a ribosome?

Answer 7

• To move along the RNA and read 3 bases (1 codon) at a time
• So that the tRNA with the complementary bases will come in and the amino acid will be attached to the tRNA

Question 8

What is the role of tRNA

Answer 8

• To deliver the anticodons that complement the codons on the RNA in the ribosome
• Once bonded, the tRNA gets released

Question 9

What is the role of a codon?

Answer 9

To receive the complementary anticodon from tRNA to form an amino acid

Question 10

What is the role of an anticodon?

Answer 10

To deliver the complementary bases from tRNA to the codon on the RNA to form an amino acid

Question 11

What are the rules of complementary base pairing in DNA?

Answer 11

• Adenine (A) and Thymine (T)
• Cytosine (C) and Guanine (G)

Question 12

What are the rules of complementary base pairing in RNA?

Answer 12

• Adenine (A) and Uracil (U)
• Cytosine (C) and Guanine (G)

Question 13

What is a codon?

Answer 13

A set of 3 bases on the RNA strand

Question 14

What is an anticodon?

Answer 14

A set of 3 bases on the tRNA strand that complement a set of 3 bases on the RNA strand (the codon)

Question 15

What happens when the ribosome reaches the ‘stop’ codon?

Answer 15

• The original gene sequence from the DNA has been fully replicated
• The Protein is released

Question 16

What is codominance?

Answer 16

When both alleles are dominant

Question 17

How can a change in DNA affect the phenotype by altering the sequence of amino acids in a protein?

Answer 17

• Random mutation can change the DNA sequence via duplication, deletion, substitution or inversion
• Creates a new codon so anticodon is no longer complementary
• Codes for and therefore creates incorrect amino acid
• If the amino acid sequence in different, the protein structure will change
• If that protein is an enzyme, the mutation will change the shape of the active site so it will no longer be complementary to the substrate

Question 18

What, if any, effects can genetic mutations have?

Answer 18

Most genetic mutations have no effect on the phenotype, some have a small effect and rarely do they have a significant effect

Question 19

How could the incidence of mutations be increased?

Answer 19

By exposure to :
- Ionising radiation such as, gamma rays, x-rays and UV rays
- Some chemical mutagens such as chemicals in tobacco