19.1 Mutations & Variations

Question 1

What’s a mutation

Answer 1

a change in the sequence of bases in DNA.

Question 2

What is the type of point mutation

Answer 2

substitution

Question 3

Why is it called a point mutation

Answer 3

because only one nucleotide will be affected

Question 4

What’s a substitution mutation

Answer 4

when one nucleotide is changed which alters a codon; if the new codon codes for a different amino acid, it will change the primary structure of the final protein.

Question 5

What’s a missense mutation, as a result of substitution

Answer 5

when the new sequence still makes some sense but likely won’t code for the same amino acid.

Question 6

What’s a nonsense mutation, as a result of substitution

Answer 6

when the new sequence makes no sense whatsoever and codes for a stop codon

Question 7

what’s a silent mutation, as a result of substitution

Answer 7

when the sequence still makes sense, can code for the same amino acid, but sometimes code for others.

Question 8

Why is DNA degenerate

Answer 8

because if there is a change to a codon or amino acid, the final amino acid it codes for may be the same, no change will occur

Question 9

What’s a frameshift mutation

Answer 9

when the order of the base sequence is completely changed because of a nucleotide being inserted or deleted.

Question 10

What’s insertion in mutations

Answer 10

When an extra nucleotide is inserted into the base sequence, changing the sequence of the codons after the insertion, therefore, changing the amino acid produced

Question 11

What’s deletion in mutations

Answer 11

When a nucleotide is deleted from the base sequence, messing up the order after the deletion because all nucleotides will be brought back a space, creating different triplet code codons.

Question 12

What are the effects of mutations

Answer 12

1. no effect - no effect on the phenotype because normally functioning proteins are still synthesised
2. damaging - phenotype of organism is negatively affected; can interfere with essential processes, cause cancers etc.
3. beneficial - very rarely are they completely beneficial; for example, some are immune to infection from HIV.

Question 13

What causes mutations

Answer 13

Can occur spontaneously; rate of mutations occurring is increased by MUTAGENS.

Question 14

What is a mutagen

Answer 14

a physical, chemical, biological agent that causes mutations

Question 15

What’s depurination and depyramidination

Answer 15

loss of a purine base and pyrimidine base, respectively

Question 16

What are examples of physical mutagens and how do they work

Answer 16

examples include ionising radiations (x-rays)

break one or both DNA strands, some breaks can be repaired but mutations can occur in the process

Question 17

what are chemical mutagens

Answer 17

example include deaminating agents

chemically alter bases in DNA such as converting cytosine to uracil in DNA, changing base sequence

Question 18

What are biological agents

Answer 18

examples include viruses - viral DNA may insert itself into a genome, changing the sequence;
base analogs - incorporated into DNA in place of the usual bases during replication, changing the base sequence;
alkylating agents - methyl or ethyl groups are attached to bases resulting in the incorrect pairing of bases during replication.

Question 19

What causes genetic disorders

Answer 19

Some mutations can affect whether a protein is actually produced.
If a mutation occurs at the start of a gene, the RNA polymerase can’t bind to it and begin transcription so the code can’t be made.