8.1 Alteration of the sequence of bases in DNA can alter the structure of proteins

Question 1

What are gene mutations?

Answer 1

• Change in base sequence of DNA
• Can arise spontaneously during DNA replication, during interphase of the cell cycle

Question 2

What is a substitution mutation?

Answer 2

• Formation of stop codon translations terminated early
• Codon for a different amino acid - shape of protein changed. Eg/ active site of enzyme no longer fits to make enzyme substrate complex
• Different codon but no change in amino acid - no effect on final protein
• No change due to degenerate nature of genetic code
• 1 triplet/codon change -> 1 amino acid change

Question 3

What is a deletion mutation?

Answer 3

Causes frame shift -> amino acid sequence changes
If multiple of 3 bases lost - no frameshift, but missing triplets/codons -> missing amino acids

Question 4

What is an addition mutation?

Answer 4

• Can cause frame shift -> triplets/codons change downstream of mutation -> amino acid sequence changes
• If 3 bases are added then will not cause a frame shift

Question 5

What is a duplication mutation?

Answer 5

• One or more bases are repeated
• Causes frame shift to the right
  If multiple of 3 bases added - no frameshift, but extra triplets/codons -> extra amino acids

Question 5

What is a duplication mutation?

Answer 5

• One or more bases are repeated
• Causes frame shift to the right
  If multiple of 3 bases added - no frameshift, but extra triplets/codons -> extra amino acids

Question 6

What is an inversion mutation?

Answer 6

• Group of bases become separated from the DNA sequence and rejoin at same position but in the inverse order (back to front)
• That portion of DNA is effected and can alter amino acid sequence
  No frameshift because number of bases stays the same

Question 7

What is a translocation mutation?

Answer 7

• Group of bases move from one chromosome to another
• Often have significant effect on gene expression and abnormal phenotype
  No gain/loss of genetic information

Question 8

What is a translocation mutation?

Answer 8

• Group of bases move from one chromosome to another
• Often have significant effect on gene expression and abnormal phenotype
  No gain/loss of genetic information

Question 9

Why do some mutations not affect the order of amino acids in the polypeptide?

Answer 9

• Some gene mutations (substitution) change only 1 codon
• New codon might still code for same amino acid because genetic code is degenerate (meaning the same amino acid can be coded for by more than one triplet)
• Some gene mutations occur in the introns (non-coding sequences within genes) and therefore won’t affect amino acid sequences

Question 10

Why do some mutations not all affect the order of amino acids in the polypeptide?

Answer 10

• Some gene mutations (substitution) change only 1 codon
• New codon might still code for same amino acid because genetic code is degenerate (meaning the same amino acid can be coded for by more than one triplet)
• Some gene mutations occur in the introns (non-coding sequences within genes) and therefore won’t affect amino acid sequences

Question 11

How can mutations can lead to the production of a non-functional protein/enzyme?

Answer 11

1. Change in base/triplet sequence of DNA/gene
2. Changes sequence of codons on mRNA
3. Changes sequence of amino acids in primary structure of polypeptide
4. Changes position of hydrogen/ionic/disulphide bonds in protein tertiary structure
5. Changes tertiary structure/shape of protein and in the case of enzymes, the active site will change shape
6. In the case of enzymes, the substrate will be unable to bind to active site and form an E-S complex

Question 12

What are the causes of mutation?

Answer 12

• High energy radiation eg/ x-rays, UV rays, gamma rays
• Chemicals eg/ nitrogen dioxide
  Increase in age = increase in mutations