DNA mutations- lqc 6a

Question 1

gene mutation

Answer 1

A gene mutation is a change in the base sequence of DNA in a gene.

Question 2

how do mutations arise?

Answer 2

Mutations can arise due to errors in the process of DNA replication , which can happen randomly (by chance). The risk of mutations in DNA occuring can be increased by exposure to ionising radiation or carcinogenic chemicals.

Question 3

substitution mutation

Answer 3

a base has been changed for a different one - changes one DNA triplet in DNA

Question 4

addition mutation

Answer 4

base/s added into the DNA, usually causing a frameshift which changes all subsequent triplets

Question 5

deletion mutation

Answer 5

base/s in the DNA deleted, usually causing a frameshift – changes all subsequent triplets

Question 6

addition or deletion of a base effect on CFTR protein

Answer 6

Causes a frameshift – every DNA triplet after the mutation will change, changing the mRNA codons and the amino acid sequence. The CFTR protein may not be made, especially if the mutation is at the start of the gene

Question 7

substitution of a base effect on CFTR protein

Answer 7

The changed DNA triplet may be transcribed to produce a stop codon (earlier in the mRNA than normal). This results in a shorter polypeptide chain, which may not be able to fold to form a functional CFTR protein.

Question 8

Why might a substitution mutation not change the CFTR protein structure and function?

Answer 8

• Due to the degenerate nature of the genetic code
• The changed mRNA codon may code for the SAME amino acid (especially if it is the third base in a DNA triplet which has been changed)
• The amino acid sequence/ primary structure is unchanged, so the polypeptide folds normally to form a CFTR protein with the normal structure, which can function

Question 9

Distinguish between germ line and somatic mutations.

Answer 9

• Germ line mutations occurs in replicating DNA of ovaries or testes in the creation of ovum or sperm, whereas somatic mutation occur in body cells after conception.
• In germ line mutations the mutation is passed on to offspring and can cause an inherited genetic disorder, whereas in somatic mutation the mutation is not passed on to offspring.