Genetics : DNA Mutations, Damage, and Repair Mechanisms

Study concepts, example questions & explanations for Genetics

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Example Questions

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Example Question #11 : Dna Mutations, Damage, And Repair Mechanisms

Which method of DNA repair is used to correct damages caused by UV Radiation?

Possible Answers:

mismatch repair

nucleotide excision repair

base excision repair

non-homologous end joint

Correct answer:

nucleotide excision repair

Explanation:

Nucleotide excision repair corrects DNA that turns into pyrimidine dimers. These are usually caused by ultraviolet radiation and result in sizable DNA adducts. 

Example Question #11 : Dna Mutations, Damage, And Repair Mechanisms

What is the name for a mutation that occurs when one nucleic acid in the sequence is switched with another?

Possible Answers:

frame shift

deletion

Insertion

point mutation

Correct answer:

point mutation

Explanation:

Point mutations occur when one nucleic base is swapped for a different nucleic base.

Example Question #221 : Genetics

If a nucleic acid is added into the RNA sequence, what type of mutation is this?

Possible Answers:

point mutation

insertion

deletion

addition 

Correct answer:

insertion

Explanation:

It is an insertion because a nucleic acid was added to the sequence.

Example Question #221 : Genetics

Which of the following represents a transition mutation in the following strand?

ATGCTGCAAGTA

Possible Answers:

ATGCTGCCAGTA

ATGTCGCAAGTA

AGGCTGCAAGTA

ATGTCTGCAAGTA

ATGCTCCAAGTA

Correct answer:

ATGCTCCAAGTA

Explanation:

A transition mutation represents a purine-to-purine mutation or a pyrimidine-to-pyrimidine mutation. This could be a change of A to T, or vice versa. It could also be a change of C to G, or vice versa. Remember, a transition mutation does not insert or delete any bases. It simply changes a base.

Example Question #221 : Genetics

Which of the following mutation would be most deleterious?

Possible Answers:

A insertion of two bases in the splice site

An insertion of one base in an intron

Deletion of one base int he 3'UTR

A change of one base in the wobble position in a coding region of mRNA

Insertion of three bases in a coding region of mRNA

Correct answer:

A insertion of two bases in the splice site

Explanation:

The most deleterious mutation would be a frameshift mutation. This would attained by inserting or deleting multiples of 1 or 2 bases in any important coding regions (exons, splice site, translation start site). Inserting or deleting multiples of 3 bases would not cause a frameshift mutation. A mutation in 3' UTR or intron would essentially have minimal effects. A mutation in the wobble position would most likely not change the amino acid.

Example Question #14 : Dna Mutations, Damage, And Repair Mechanisms

A T G C C T G G A T A G C T A

T A C G G A C C T A T C G A T

The original strand of DNA is written above. Which of the following choices represents a possible frameshift mutation?

Possible Answers:

A T G C T G G A T A G C T

T A C G A C C T A T C G A

A T G C C T G G G T A G C T A

T A C G G A C C C A T C G A T

A T G C A T G G A T A G C T A

T A C G T A C C T A T C G A T

A T G G G A T A G C T A

T A C C C T A T C G A T

Correct answer:

A T G C T G G A T A G C T

T A C G A C C T A T C G A

Explanation:

Recall that a frameshift mutation occurs when part of one or more codons in lost in such a way that the entire sequence of codons "shifts," making the transcribed mRNA translate as a different pattern of amino acids during protein synthesis. This is a big problem, since it means that a sequence of DNA coding for a specific protein now likely codes for a completely, fundamentally different one.

The correct answer is:

A T G C T G G A T A G C T A

T A C G A C C T A T C G A T

Compare to the original DNA, and note where one base pair was removed:

A T G C C T G G A T A G C T A

T A C G G A C C T A T C G A T

The codons on a piece of mRNA transcribed from the top strand of the non-mutated form would read:

UAC GGA CCU AUC GAU

However, mRNA transcribed from the mutated DNA would read:

UAC GAC CUA UCG AT[ ] (we don't know the last codon, since the next base pair is not given)

This is a serious issue. The non-mutated form codes for these first four amino acids...

tyr  gly  pro  ile

...while the mutated form codes for these first four amino acids:

tyr  asp  leu  ser

Clearly, frameshift mutations can be very dangerous.

 

Example Question #11 : Dna Mutations, Damage, And Repair Mechanisms

If a cell cannot repair itself, how does it take action to destroy itself?

Possible Answers:

it cannot repair itself, leading to cancerous cells

translesion synthesis

senescence

 

apoptosis

Correct answer:

apoptosis

Explanation:

The correct answer here is apoptosis. All other options are things that can occur to a cell that has been damaged, however, the only option where a cell will abruptly commit suicide is apoptosis. The other options, such as cancerous cells or dormancy do occur. 

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