Lecture 9

Question 1

Mutation

Answer 1

heritable changes in DNA
the source of new genotypes

Question 2

Gene transfer

Answer 2

DNA exchange between cells
the spread of new genotypes

Question 3

genotype mutations

Answer 3

change in the genomes of organisms
wild-type and mutant

Question 4

phenotype mutations

Answer 4

change in observable properties of organisms
- some genotype mutations change phenotype
example: nonmotile flagella, pigment-less, and auxotroph

Question 5

Auxotroph

Answer 5

loss of enzyme in the biosynthetic pathway
phenotype mutation
leads to nutritional deficiency

Question 6

Point mutations

Answer 6

single nucleotide change
substitution

Question 7

Frameshift mutations

Answer 7

insertion or deletion of nucleotides
indel

Question 8

Types of point mutations

Answer 8

transition, transversion, silent, nonsense, missense, and reversions

Question 9

transition point mutation

Answer 9

purine to purine or pyrimidine to pyrimidine

Question 10

transversion point mutations

Answer 10

purine to pyrimidine or pyrimidine to purine

Question 11

Silent point mutation

Answer 11

same amino acid due to redundancy of genome

Question 12

nonsense point mutation

Answer 12

stop codon
leads to incomplete protein

Question 13

missense

Answer 13

different amino acid
leads to faulty protein

Question 14

reversions

Answer 14

back mutations– “mutation of a mutant”
occurs over multiple generation
changes from mutant to wild type

Question 15

types of frameshift mutations

Answer 15

insertions and deletions
both shift the reading frame

Question 16

insertions

Answer 16

adding nucleotides

Question 17

deletions

Answer 17

removing nucleotides

Question 18

Spontaneous mutations (natural)

Answer 18

due to errors in DNA replication
DNA polymerase is not 100% accurate
happens inside of the cell (occurrence: 1 in a billion base pairs)
- just enough for adaptive variability

Question 19

Induced mutations

Answer 19

come from outside the cell (much higher rate of occurrence)
due to external agents (e.g. chemicals)
“mutagens”

Question 20

mutation balance

Answer 20

lethal mutations vs. adaptive mutations

Question 21

Mutagens

Answer 21

agents that increase mutation rates
physical, chemical, and biological

Question 22

Physical mutagens

Answer 22

Ultraviolet radiation (pyrimidine dimers) and ionizing (x-rays) breaks DNA strands

Question 23

Chemical mutagens

Answer 23

nucleotide base analogs, chemical modifiers, and intercalating agents

Question 24

Nucleotide base analogs

Answer 24

resemble DNA bases
causes point mutations
incorporated

Question 25

chemical modifiers

Answer 25

change structure of nucleotides
cause point mutations
the chemical comes and cleaves part of the nucleotide

Question 26

intercalating agents

Answer 26

chemical inserted between DNA base pairs
causes frameshift mutations

Question 27

Biological mutagens

Answer 27

mobile DNA aka jumping genes
transposition causes mutation
- insertion into a gene will disrupt its function

Question 28

The Ames test

Answer 28

how we test for chemicals that are mutagenic
takes hours or a day using a bacterial model
- utilizes auxotrophic mutants
- grow mutants on low nutrient media
- add potential mutagen & observe growth

Question 29

Gene transfer

Answer 29

DNA exchange between cells
donor cell (source) and recipient cell (receiver)

Question 30

Horizontal transmission

Answer 30

have to be nearby ( in the vicinity)
- most of the time happens between closely related organisms
from cell to cell (not a parent to offspring)

Question 31

the fate of transferred DNA

Answer 31

1) rejected (degraded by recipient cell)
2) accepted (replicates independently)
3) accepted (inserted in recipient chromosome)

Question 32

Homologous recombination

Answer 32

DNA inserted into the chromosome
Cross over between different DNA strands

Question 33

Recombination mechanism

Answer 33

1. Donor DNA nicked (single strand break)
2. Single-stand binding proteins attach to donor DNA
3. RecA protein binds to single-stranded region
4. Heteroduplex formation (linked DNA molecules)
5. Resolution

Question 34

Types of gene transfer

Answer 34

transformation (“naked” DNA uptake)
transduction (virus-mediated)
conjugation (linked cells)

Question 35

Transformation

Answer 35

donor cells lyse -> DNA in environment
- DNA outside of cells = “naked” DNA
recipient cells take up naked DNA
Competent cells (cells able to take up naked DNA fragments)

Question 36

Transduction

Answer 36

Virus transfer of DNA between cells
- viruses that infect bacteria = bacteriophage
– inject their genome into host cells

Question 37

Conjugation

Answer 37

cell to cell contact and gene exchange
- direct gene transfer
- bacterial “mating”
genetic elements exchanged
- plasmids
- chromosomes

Question 38

F plasmids

Answer 38

genes for replication and transfer functions (tra)
-a single strand of plasmid enters the recipient cells
- synthesis of a complementary strand

Question 39

sex pilus

Answer 39

synthesized by tra genes
contacts recipient cell
retracts to bring cells together

Question 40

Hfr cell

Answer 40

F plasmid integrated into chromosome via recombination

Question 41

Mobile DNA

Answer 41

transposable elements and transposition

Question 42

transposable elements

Answer 42

genes that move within or between DNA molecules
“jumping” genes
cannot be replicated independently

Question 43

Transposition

Answer 43

the movement of transposable elements

Question 44

Insertion sequences (IS)

Answer 44

shorter DNA segments
inverted repeat sequences
single gene
- transposase

Question 45

Transposons

Answer 45

longer DNA segments
inverted repeat sequences
multiple genes
- ex. transposase + antibiotic resistance

Question 46

conservative transposition

Answer 46

transposon moved to a new DNA molecule
absent from donor DNA, present in recipient DNA

Question 47

replicative transposition

Answer 47

the transposon is replicated and moved
present in donor and recipient DNA