Mutations & DNA Damage

Question 1

What is a mutation?

Answer 1

A change in the DNA sequence

Question 2

What are the two main types of mutations by cause?

Answer 2

Spontaneous (natural) and induced (caused by mutagens)

Question 3

What is a mutagen?

Answer 3

Any physical or chemical agent that causes mutations

Question 4

How do X-rays damage DNA?

Answer 4

They break the sugar-phosphate backbone of DNA

Question 5

What type of DNA damage does UV light cause?

Answer 5

Thymine dimers (covalent bonding between adjacent thymine bases)

Question 6

Why are thymine dimers harmful?

Answer 6

They distort the DNA double helix, blocking replication

Question 7

What are the general steps of DNA repair?

Answer 7

Recognize damage → cut damaged strand → remove fragment → fill with correct bases → seal with ligase

Question 8

What enzyme cuts the damaged DNA during repair?

Answer 8

A nuclease

Question 9

Which enzyme fills in the missing DNA during repair?

Answer 9

DNA polymerase

Question 10

Which enzyme seals the repaired DNA backbone?

Answer 10

DNA ligase

Question 11

What are somatic mutations?

Answer 11

Mutations in body cells that are not inherited

Question 12

What are germline mutations?

Answer 12

Mutations in reproductive cells that can be passed to offspring

Question 13

Which type of mutation can lead to cancer but not be inherited?

Answer 13

Somatic mutations (e.g., in skin cells from UV damage)

Question 14

What is a point mutation (SNP)?

Answer 14

A change in a single nucleotide pair

Question 15

What is a silent mutation?

Answer 15

A base change that doesn’t alter the amino acid due to redundancy in the genetic code

Question 16

What is a missense mutation?

Answer 16

A base change that substitutes one amino acid for another

Question 17

What is a nonsense mutation?

Answer 17

A base change that turns an amino acid codon into a stop codon

Question 18

Which type of mutation usually produces a truncated, nonfunctional protein?

Answer 18

Nonsense mutation

Question 19

What is a frameshift mutation?

Answer 19

An insertion or deletion not in multiples of 3 that alters the reading frame

Question 20

Why are frameshift mutations usually severe?

Answer 20

They change every codon after the mutation and often introduce premature stop codons

Question 21

What is an in-frame insertion or deletion?

Answer 21

Adds or removes a multiple of 3 bases, preserving the reading frame

Question 22

Do in-frame indels always cause problems?

Answer 22

No — effects vary depending on which amino acids are affected

Question 23

How can mutations affect protein function?

Answer 23

By altering amino acid sequence, causing misfolding, truncation, or preventing transcription

Question 24

Can mutations in promoter regions affect protein production?

Answer 24

Yes, they can prevent transcription from occurring or they can increse gene expression

Question 25

What is a chromosomal deletion?

Answer 25

A segment of DNA is lost from a chromosome

Question 26

What is a duplication mutation?

Answer 26

A segment of the chromosome is copied and repeated

Question 27

What is an inversion mutation?

Answer 27

A chromosomal segment is reversed end to end

Question 28

Why are inversions often harmless?

Answer 28

No genetic material is lost or gained

Question 29

What is a translocation?

Answer 29

A segment of one chromosome breaks off and attaches to a non-homologous chromosome

Question 30

What is a common consequence of translocations during meiosis?

Answer 30

Reduced fertility due to improper chromosome segregation

Question 31

What are trinucleotide repeats?

Answer 31

Short DNA sequences (like CAG) repeated multiple times in a row

Question 32

What happens when trinucleotide repeats expand?

Answer 32

Too many repeats disrupt gene function and cause disease

Question 33

Which mutation types can be silent, missense, or nonsense?

Answer 33

Point mutations in coding regions

Question 34

Which mutations cause reading frame shifts?

Answer 34

Indels not in multiples of three

Question 35

Which mutation types usually have the most severe effects?

Answer 35

Nonsense, frameshift, and large deletions

Question 36

What are examples of large-scale chromosomal mutations?

Answer 36

Deletion, duplication, inversion, translocation

Question 37

What are two ways DNA can be damaged?

Answer 37

Physical (UV, X-rays) or chemical (vinyl chloride, nitrosamines)