Topic J. Mutation, Information Transfer

Question 1

What is conjugation (bacterial sex) in bacteria?

Answer 1

• conjugation is the process where a living bacterium transfers a single strand of DNA to another bacterium through a pore/channel
• f factor is necessary for pilus assembly and DNA transfer

Question 2

What is the F Factor?

Answer 2

• fertility plasmid
• necessary for pilus assembly and DNA transfer

Question 3

What is transformation (funeral pass) in bacteria?

Answer 3

transformation is when a bacterium takes up naked DNA from its environment (from dead cells), which can either remain as a circular plasmid or be integrated into the recipient’s genome

Question 4

What is transduction (viral pass) in bacteria?

Answer 4

transduction is when a bacteriophage (virus) transfers bacterial DNA from one cell to another during viral infection –> facilitates gene exchange between bacteria

Question 5

What types of mutagens cause DNA mutations?

Answer 5

1. radiation (UV and ionizing radiation)
2. chemicals (base analogs)
3. biological

Question 6

How do UV and ionizing radiation affect DNA?

Answer 6

• UV –> causes thymine dimers in DNA
• ionizing radiation –> may lead to double-stranded DNA breaks

Question 7

How do chemical mutagens like base analogs (5-BrU) induce mutations?

Answer 7

5-BrU, a base analog of thymine, can mispair during replication –> leads to T:C transitions

Question 8

What are the different type of point mutations?

Answer 8

1. silent
2. missense
3. nonsense
4. frameshift

Question 9

What is a silent mutation?

Answer 9

a mutation that results in a change in the DNA sequence that does not alter the amino acid sequence of the resulting protein

Question 10

What is a missense mutation?

Answer 10

a mutation that results in a change in the DNA sequence that results in a different amino acid being incorporated into the protein

Question 11

What is a nonsense mutation?

Answer 11

a mutation that introduces a premature stop codon –> results in a shortened and usually nonfunctional protein

Question 12

What is a frameshift mutation?

Answer 12

a mutation that results in nucleotides being inserted or deleted from the DNA sequence in numbers not divisible by three –> shifts the reading frame of the codons

Question 13

What factors influence whether a mutation will impact phenotype?

Answer 13

1. the type of mutation (silent, missense, nonsense, or frameshift)
2. where in the gene it occurs
3. the redundancy of the genetic code

Question 14

Which type of mutations are most likely to have a large effect on the phenotype?

Answer 14

1. nonsense (introduces early STOP codon)
2. frameshift (alters reading frame)

Question 15

What are the steps of conjugation in gram-negative bacteria?

Answer 15

1. donor bacterium forms a pilus to attach to the recipient
2. transfers a single strand of DNA (plasmid)
3. plasmid is replicated in both donor and recipient cells

Question 16

What are the steps of transduction in bacteria?

Answer 16

1. bacteriophage infects a bacterium
2. picks up bacterial DNA during assembly of new viral particles
3. transfers DNA to new bacterial host during subsequent infections

Question 17

What are two methods to make bacteria artificially competent?

Answer 17

1. electroporation (uses electric field to make transient pores in the cell membrane –> allows DNA to enter)
2. chemical competence (uses high concentration of cations followed by a heat shock to facilitate DNA uptake)

Question 18

What is the most costly stage for a mutation to occur during gene expression:

a. DNA replication
b. transcription
c. translation?

Answer 18

a. DNA replication because errors in DNA will affect RNA and protein