Gene mutations

Question 1

what is a substitution mutation?

Answer 1

one nucleotide base is affected (one substituted for another) so tend to have less severe affects

Question 2

whats a deletion mutation?

Answer 2

these mutations cause frame shifts, which have more severe affects. they change the codon reading frame.

Question 3

what are the three types of substitution mutations?

Answer 3

• Silent mutations
• Mis-sense mutations
• Nonsense mutations

Question 4

define gene mutation

Answer 4

any change to one or more nucleotide bases, or a change in the sequence of bases. it alters the triplet code (s) and therefore the amino acid (s) it codes for.

Question 5

what is a silent mutation?

Answer 5

Since there are degenerate codes, a change of one base in a codon could still code for the same amino acid, therefore making no overall difference. hence why it is called a silent mutation.

Question 6

what is a mis-sense mutation?

Answer 6

sometimes a substitution mutation will cause a different amino acid to be called, therefore the proteins tertiary structure would be changed. Eg, this could cause an enzymes active site to change shape.

Question 7

what is a nonsense mutation?

Answer 7

when a substitution mutation means that a stop codon is coded for, ending translation and producing a shorter polypeptide chain.

Question 8

what is a mutagenic agent?

Answer 8

something that can speed up the frequency of mutations
eg. carcinogenics

Question 9

give some examples of a mutagenic agent

Answer 9

X-rays, UV rays, beta, gamma, alpha, radioactive sources, Benzene, tar in cigarette smoke, mustard gas

Question 10

what are chromosome mutations caused by?

Answer 10

non-disjunction, where homologous chromosomes do not separate in meiosis

Question 11

what are the two ways non-disjunction can occur, describe each

Answer 11

• changes in whole sets of chromosomes occur when organisms have three or more sets of chromosomes rather than the usual two, it is caused by total non-disjunction. This condition is called polyploidy and occurs mostly in plants.
• changes in the number of individual chromosomes sometimes individual homologous pairs of chromosomes fail to separate during meiosis, this is known as non-disjunction and usually results in a gamete having either one more or one less chromosomes

Question 12

how do you answer a question which asks how a mutation causes a change in protein structure?

Answer 12

• change in DNA base sequence which causes…
• change in amino acid sequence (primary structure) which causes…
• change in the tertiary structure, change to the hydrogen/ionic/disulphide bonds

Question 13

what would happen if a mutation occurred in an intron?

Answer 13

there would be no effect on the amino acid sequence/protein structure since introns are non-coding sequences and are spliced out of the pre-mRNA before it becomes mRNA