7- Chapter 11

Question 1

What is a mutation?
Mutant?
Wild type strain?

Answer 1

Mutation is a heritable change in DNA sequence that can lead to a change in phenotype
Mutant is a strain of any cell or virus differing from parental strain in genotype (nucleotide sequence of genome)
Wild-type strain- typically refers to strain isolated from nature

Question 2

What are selectable and non selectable mutations?

Answer 2

Selectable- give mutant growth advantage under certain conditions
(Useful for genetic research)
Non selectable- have neither an advantage nor a disadvantage over the parent
Detecting this mutation requires examining a large number of colonies and look for differences (screening)
Screening is always more tedious than selection

Question 3

What are induced mutants and spontaneous mutants?

Answer 3

Induced- those made environmentally or deliberately
Can result from exposure or natural radiation or oxygen radicals (Chernobyl)
Spontaneous- those that occur without external intervention
Happens in normal environment where you’d find that organism

Question 4

What are point mutations?

What are it’s types

Answer 4

Mutations that only change one base pair
Can lead to amino acid change in protein, incomplete protein, or no change at all
Silent mutation (does t affect amino acid sequence)
Missense mutation (amino acid changed; polypeptide altered) can sometimes be silent
Nonsense mutation (codon becomes stop codon; polypeptide is incomplete)
Examples on slide 9

Question 5

What are frameshift mutations?

Answer 5

Deletions and insertions that cause more dramatic changes in DNA
Result in a shift in the reading frame and result in a complete loss of gene function
Example on slide 11

Question 6

What is reversion and revertant?

Answer 6

Reversion- alteration in DNA that reversed the effects of a prior mutation (point mutations are often reversible)
Revertant- strain in which original phenotype is restored
Same site revertant is where mutation is same site as original
Second site revertant is where mutation is at different site
Suppressor is a mutation that compensated for the effect of the original mutation
Slide 13 example

Question 7

What is the Ames test?

Answer 7

Makes practical use of bacterial mutations to detect for potentially hazardous chemicals
Looks for an increase in mutation of bacteria in the presence of suspected mutagen
Slide 16 picture

Question 8

What are mutagens?

Answer 8

Mutagens- Chemical, physical, or biological agents that increase mutation rates
Several classes exists
Mutagenesis- several forms of radiation
Two main categories of mutagenic electromagnetic radiation (nonionizing- purines and pyrimidines absorb UV and ionizing- ionize water/produce free radicals)

Question 9

What are the three types of DNA repair systems in mutagenesis?

Answer 9

Direct reversal- damaged base is still recognizable and can be repaired without referring to other strand
Repair of single strand damage- damaged DNA is removed and repaired using opposite strand as template
Repair of double strand damage- a break in the DNA

Question 10

What is the SOS regulatory system?

Answer 10

Error prone repair system for DNA damaged at a large scale

Allows replication to proceed and cell to replicate (errors are more likely)

Question 11

What is genetic recombination and homologous recombination?

Answer 11

Recombination- physicals exchange of DNA between genetic elements
Homologous recombination- process that results in genetic exchange between homologous DNA from the two different sources

Question 12

What is transformation in DNA?

What is competence?

Answer 12

Genetic transfer by which DNA is incorporated into a recipient cell and brings about genetic change
Natural transformation is where integration of DNA is a highly regulated, multistep process
Competent- cells are capable of taking up DNA and being transformed

Question 13

What is transfection?

What is transduction and it’s two modes?

Answer 13

Transfection- transformation of bacteria with DNA extracted from a bacterial virus
Transduction- transfer of DNA from one cell to another by a bacteriophage
Has two modes:
generalized transduction- DNA from any portion of host is packed inside virion
specialized transduction- DNA from a specific region of host chromosome is integrated into virus genome
Slide 14-16 example

Question 14

What is phage conversion?

Answer 14

Alteration of the phenotype of a host cell by a lysogenization
Nondefective temperature phage lysogenizes a cell and becomes a prophage

Question 15

What is bacterial conjugation (mating)?

What is the F plasmid

Answer 15

Mechanism of genetic transfer that involves cell to cell contact
Donor cell contains conjugation plasmid
Recipient cell does not contain plasmid
F plasmid is a circular DNA molecule that contain genes that regulate DNA replication
Sex pious is essential for conjugation produced only by donor cell
Slide 20 and 21 and 23

Question 16

What is an episome?

Answer 16

Something that can integrate into host chromosome or independently replicate
F plasmid is a episome
Cells possessing a nonintegrated F plasmid are called F+
And integrated F plasmid are called Hfr

Question 17

What does the presence of f Plasmid result in?

Answer 17

Alterations of cell properties like:
Ability to synthesize F pilus
Mobilization of DNA for transfer to another cell
Alteration of surface receptors so that cell can no longer act as a recipient in conjugation

Question 18

What are F’ plasmids?

Answer 18

They transfer the captured genes from previously integrated F plasmids to recipient cells