Gene Mutation

Question 1

What are the double-ring purines?

Answer 1

Adenine and Guanine

A and G

Question 2

What are the single-ring pyrimidines?

Answer 2

Thymine and Cytosine

T and C

Question 3

What are substitutions?

Answer 3

Changes from one base to different nitrogenous base

Question 4

SUBSTITUTIONS

What are the two types of substitutions?

Answer 4

Transitions

Transversions

Question 5

SUBSTITUTIONS

What are transitions?

Answer 5

Transitions are when you go from a one purine to another purine (A and T) or one pyrimidine to another pyrimidine (C and T)

Question 6

SUBSTITUTIONS

What are transversions?

Answer 6

Tranversion are when you go from a purine to pyrimidine, or from a pyrimidine to a purine.

Question 7

What is a deletion?

Answer 7

The removal of nucleotides from the gene

Question 8

What is an insertion?

Answer 8

The addition of nucleotides to the gene

Question 9

We have a _____ code

Answer 9

We have a triplet code.

Question 10

Since we have a triplet code, insertions are deletions (even of one or two nucleotides) can cause _____.

Answer 10

Since we have a triplet code, insertions are deletions (even of one or two nucleotides) can cause FRAMESHIFTS.

Question 11

What are silent mutations?

Answer 11

Silent mutations - mutations in the DNA within the protein-coding region that do NOT change the amino acid sequence

These mutations have no effect on the protein.

Question 12

What are missense mutations?

Answer 12

Missense mutations - mutations that change the nucleotide and DO cause a change in the amino acids of the protein

Question 13

What are the two types of missense mutations?

Answer 13

Conservative

Non-conservative

Question 14

MISSENSE MUTATIONS

Conservative missense

Answer 14

Conservative missense mutations have the original amino acid replaced with a different amino acid, but one with similar chemical properties.

Conservative changes may have little or no affect on the protein’s function.

Question 15

MISSENSE MUTATIONS

Non-conservative

Answer 15

Non-conservative missense mutations have the original amino acid replaced with an amino acid with very different chemical properties.

These mutations are much more likely to alter the function of the protein.

Question 16

What are nonsense mutations?

Answer 16

Nonsense mutations - mutations in the DNA that result in a premature stop codon being created within the gene

Question 17

What are frameshift mutations?

Answer 17

Frameshift mutations are always deletions or insertions that are not multiples of 3.

Typically either 1 or 2 bases are deleted or added.

Since the genetic codon is read in triplets, these additions or deletions can completely change the amino acid sequence.

Question 18

True or False:

Frameshift mutations usually destroy the protein’s function unless they occur very near the end of the protein.

Answer 18

True - Frameshift mutations usually destroy the protein’s function unless they occur very near the end of the protein.

Question 19

What is the mismatch repair system?

Answer 19

The Mismatch repair system - a system of enzymes that work together to detect mismatched base pairs, remove the incorrect base, and replace it with the correct base, before S phase is completed.

Thus this system usually finds the ‘1 per million’ - mistake that gets past DNA polymerases proof reading ability.

Question 20

Mistakes do happen during DNA replication but proofreading and _____ _____ keep the mistake rate down to one mistake per billion bases.

Answer 20

Mistakes do happen during DNA replication but proofreading and MISMATCH REPAIR keep the mistake rate down to one mistake per billion bases.

Question 21

What is trinucleotide expansion?

Answer 21

Trinucleotide expansion - phenomenon seen for some genes that even normally have many copies of the same amino acid in the protein (and hence many copies of the same triplet codon in the gene); the many copies of the triplet make the region vulnerable to accidentally increasing the number of copies even more

Question 22

When does trinucleotide expansion disease occur?

Answer 22

Trincuclotide expansion diseases occur when the number of copies of the triplet (and hence the number of copies of the amino acid) increases beyond an acceptable, normal range.