Mutations

Question 1

what is a frame shift

Answer 1

change resulting in misreading of all nucleotides downstream, usually resulting in a truncated non-functional protein

Question 2

what type of mutations cause a frame shift and explain them

Answer 2

deletion - the removal of 1 or more bases resulting in a frame shift

addition - the adding of one or more bases resulting in a frame shift

duplication - where one or more bases is repeated causing a frame shift

Question 3

what type of mutations don’t cause a frame shift and explain them

Answer 3

inversion - a sequence of bases is reversed e.g. TAGCAGCT becomes TCGACGAT

translocation - a sequence of bases is moved from one location in the DNA molecule to another part of the genome

substitution - the replacement of one or more bases by one or more different bases

Question 4

why can a functioning protein still be formed after substitution

Answer 4

• the DNA code is degenerate meaning that an amino acid can be coded by more than 1 base triplet
• the mutation could have occured in an intron which doesn’t code for proteins
• the mutation doesn’t affect the shape of the tertiary structure in a way that affects the function of the protein

Question 5

How is the structure of DNA related to its function (6)

Answer 5

sugar-phosphate backbone gives strength

coiling gives compact shape

long molecule stores large amount of information

double stranded so replication can happen semi-conservatively

chains held together by weak hydrogen bonds; chains can split for replication / transcription

base sequence allows information to be stored

Question 6

how can a mutation in the DNA result in a non-functional enzyme

Answer 6

• change in DNA base sequence leading to change in amino acid sequence
• change in hydrogen / ionic / disulphide bonds leading to change in the tertiary structure and therefore active site
• substrate not complementary and therefore no more
  enzyme-substrate complexes can form