3.8.1 Alterations in base sequence in DNA can alter structure of proteins

Question 1

what is a mutation?

Answer 1

random, spontaneous changes in the sequence of bases in a DNA molecule which affect the sequences of amino acids in polypeptide chains.
Often arise spontaneously during DNA replication

Question 2

what are the three types of ways a mutation can occur?

Answer 2

substitution
deletion
insertion

Question 3

what does degenerate code mean?

Answer 3

different codons code for the same amino acid.

Question 4

what can mutation do to an enzyme?

Answer 4

change the tertiary structure of the active site meaning it is no longer complementary to the substrate - cannot function.

Question 5

what does insertion or deletion of a nucleotide/ nucleotides lead to?

Answer 5

frameshift mutation

Question 6

how many nucleotides code for an amino acid?

Answer 6

3

Question 7

what are the two main causes of mutations?

Answer 7

substitution
deletion

Question 8

what are nonsense mutations?

Answer 8

premature stop codon being coded for. Leads to a premature end of the polypeptide synthesis. Protein cannot function.

Question 9

what is a missense mutation?

Answer 9

the mutation leads to a the substitution of a different amino acid. Can lead to non-functional enzymes.

Question 10

what is a nonsense mutation?

Answer 10

substitution in the sequence of bases that leads to the same amino acid being coded for. There is no negative result on the polypeptide.

Question 11

what is an inversion mutation?

Answer 11

a sequence of bases is reversed (can result in no change as amino acid sequence would stay the same due to degenerate code)

Question 12

what is a duplication mutation?

Answer 12

one or more bases are repeated (can cause a frame shift but can also result in increasing repeating subunits causing genetic diseases. eg. Huntington’s.)

Question 13

what is a translocation mutation?

Answer 13

a sequence of bases is moved from one location in the genome to another, can be movement within the same chromosome or to a different chromosome. Similar to crossing over but with non homologous chromosomes.

Question 14

what name is used for the non coding sections of a gene?

Answer 14

intron

Question 15

during which part of the cell cycle are gene mutations most likely to occur?

Answer 15

S phase

Question 16

why is mutation most likely to take place in the S phase?

Answer 16

the longest stage

Question 17

when can mutations have no effect?

Answer 17

if the same amino acid is coded for
the mutation occurs in introns

Question 18

what external factors can increase the rate of mutations?

Answer 18

UV radiation
ionising radiation ( X rays)
mutagenic chemicals

Question 19

how does UV radiation cause a mutation?

Answer 19

adjacent bases bond instead of bases across the ladder.
this makes a bulge, and the distorted DNA molecule does not function properly

Question 20

how do mutagenic agents cause mutations?

Answer 20

removes the NH2 from cytosine in DNA, changing it to Uracil.

Question 21

what bonds are effected by a mutation in the sequence of amino acids

Answer 21

disulfide bridges
Hydrogen bonds
ionic bonds

Question 22

What are addition and deletion mutations?

Answer 22

where one or more nucleotides (bases) are either inserted or deleted from the DNA sequence.

Question 23

what is a substitution mutation?

Answer 23

Where one nucleotide (base) in the DNA sequence is replaced by another.

Question 24

Which mutations are most likely to have a significant impact and why?

Answer 24

Insertion, deletion, duplication, translocation.
Because they produce a frameshift, meaning the entire amino acid sequence produced will be different.

Question 25

which mutations are less likely to have a significant impact and why?

Answer 25

Substitution, inversion.
Because they only alter one or very few triplets, the amino acid sequence might not be affected due to the degenerate nature of the genetic code.

Question 26

Is a mutation resulting in a change to the amino acid sequence always harmful? why?

Answer 26

No:
may be neutral if the resulting change in protein has no effect on the organism.
Also may be beneficial, which is the basis for evolution and natural selection

Question 27

What is a mutagenic agent? Give examples of this.

Answer 27

Factors that increase the rate of gene mutation. Chemical mutagens such as alcohol and benzene. Ionising radiation such as UV and x-ray.