Chapter 8: Microbial Genetics - Mutations

Question 1

What are two methods of genetic change in bacteria?

Answer 1

• mutation
• horizontal gene transfer

Question 2

What is a mutation?

Answer 2

• a change in the nucleotide sequence of DNA

Question 3

What can mutations cause?

Answer 3

• may cause a change in a protein encoded by a gene

Question 4

What is horizontal gene transfer?

Answer 4

• genetic info is passed from one living cell to another cell of the same generation
  ex. plasmids

Question 5

In either cases of mutations and horizontal gene transfer, is change stable?

Answer 5

yes, change is stable and is passed onto progeny

Question 6

What are two types of mutations?

Answer 6

• base substitution (point mutation)
• frameshift mutation

Question 7

What is a base (point) substitution?

Answer 7

• a single nucleotide is replaced by another nucleotide

Question 8

Why does a point mutation occur?

Answer 8

• when DNA replicates, it results in a substituted base pair
• so when DNA gets transcribed and translated, it results in an incorrect AA in the protein

Question 9

What is an example of a point mutation?

Answer 9

• missense mutation

Question 10

What is a frameshift mutation?

Answer 10

insertion or deletion of nucleotides to the gene

Question 11

What is an insertion?

Answer 11

• one or two nucleotides added to the gene

Question 12

What is a deletion?

Answer 12

• one or two nucleotides removed from the gene

Question 13

What does a frameshift mutation cause? (2)

Answer 13

• changes the reading frame of the mRNA
• then the sequence of AA is changed downstream of the mutation site

Question 14

What do frameshift mutations result in?

Answer 14

• almost always a non-functional protein

Question 15

What are two ways that mutations occur?

Answer 15

• spontaneous mutation
• induced mutation

Question 16

What is spontaneous mutation?

Answer 16

• occurs in the absence of mutagens, due to occasional mistakes during DNA replication

Question 17

What is induced mutation?

Answer 17

• occurs when DNA damaging agents cause changes in DNA sequence (mutagens)

Question 18

What are mutagens?

Answer 18

• DNA damaging agents

Question 19

What are some examples of induced mutations?

Answer 19

• radiation, some chemicals

Question 20

REGARDLESS of origin, mutations can result in what three things?

Answer 20

1. silent mutation
2. missense mutation
3. nonsense mutation

Question 21

What is a silent mutation?

Answer 21

• No effect on the protein (remains functional)
  thus no change in AA sequence

Question 22

What is a missense mutation?

Answer 22

• A protein with a different amino acid sequence that may have an altered function

Question 23

What is a nonsense mutation? (2)

Answer 23

• premature stop codon
• results in an incomplete (truncated) protein that is usually non-functional