Lecture 9 Bacterial Genetics Flashcards Preview

BIO 425: Microbiology > Lecture 9 Bacterial Genetics > Flashcards

Flashcards in Lecture 9 Bacterial Genetics Deck (28)
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1

How do new Genotypes occur in microbes?

Through

Mutation

-heritable change in DNA

-SOURCE of new genotypes

Gene Transfer

-DNA exchange between cells

-SPREAD of new genotypes

2

What is wildtype and mutant?

Wild type = normal

Mutant=changed

3

What is a phenotype mutation?

Change in observable properties of the organism

4

What are the different types of mutations?

Point Mutations

-single nucleotide change

-substituion

-same length

 

Frame Shift Mutations

-Insertion OR Deletion of nucleotides

-Also known as Indel

-Most Dangerous

-lengthened or shortened

5

What are the types of point mutations?

Transition

-Purine to Purine A⇔G

-Pyrimidine to Pyrimidine C⇔T

 

Transversion

-Purine to Pyrimidine A/G⇔C/T

-Pyrimidine to Purine C/T⇔AG

 

Reversion

-change from mutant to wild type

6

What are the types of effects of mutations?

Silent

-mutation results in same amino acid

Nonsense

-mutation inserts premature stop codon

Missense

-Mutation causes different amino acid

7

What are the types of Frame Shift Mutations?

Insertions

-Adding nucleotides

Deletions

-Removing nucleotides

Both shift the reading frame by adding/removing nucleotides

8

What are the sources of mutations?

Spontaneous Mutations

-due to errors in DNA replication

-DNA Polymerase not 100% accurate

Induced Mutations

-Due to external agents, ie mutagens

9

How often do spontaneous mutations occur?

10-9 /bp

 

Lethal mutations balanced by adaptive mutations

 

Vriruses have a higher frequency of mutations

10

What are the types of mutagens?

Physical, Chemical, and Biological

11

What are the types of physical mutagens?

UV

-pyrmidine dimers

Ionizing

-breaks DNA strand

12

What are the types of chemical mutagens?

Nucleotide base analogs

-resemble nucleotide but not, used by DNA polymerase by mistake

-causes point mutation

Chemical modifiers

-change structure of nucleotides

-cause point mutation

Intercalating agents

-chemical inserted between DNA base pairs

-cause frameshift mutation

13

Sometimes mutagenisis causes carcinogenesis.  How do we test for chemicals that mutagenic?

The Ames Test

-start with bacteria we've mutated with single substitution

-place in low nutrient media

-add mutagen

-if mutagenic then we will see growth b/c some of the mutations caused by mutagen will be reversions and the mutated bacteria will go back to wild type

14

When using the Ames test, how can you tell if you have spontaneous or induced mutations from the potential mutagen?

Spontaneous Mutations

-Few colonies b/c non-mutagen

 

Induced Mutations

-Many colonies b/c mutagen

15

How does gene transfer occur and what are the possible outcomes?

Horizontal Gene transfer between source and receiver

 

1.  Rejected - degraded by recipient cell

2. Accepted - replicates independently, eg plasmid

3. Accepted - inserted in recipient chromosome

16

How is DNA inserted into the chromosome?

Homologous recombination between Donor DNA and Recipient DNA 

-Homologous = similar DNA sequences

-crossing over like in meiosis

17

What are the different types of gene transfer?

Transformation

-naked DNA uptake from the environment

Transduction

-virus-mediated, virus injects bacterial DNA into host cell

Conjugation

-direct passage of DNA from one cell to antoher

18

How does transformation occur?

Donor cells lyse → DNA in environment

-DNA outside of cell = ''naked'' DNA

 

Recipient cells take up nake DNA

19

What kinds of cells can undergo transformation gene transfer?

Competent cells able to take up naked DNA fragments

-not all bacterial cells are competent

20

How does bacteria choose the right naked DNA to uptake from environment for transformation gene transfer?

Induced competency

-quorum sensing causes bacteria to take up DNA

Binding sequence

-must be present to uptake DNA

-recognition sequence in DNA must be present to be taken up

21

What is transduction?

Form of gene transfer where virus transfers DNA between cells

-viruses that infect bacteria=bacteriophage

-bacteriophages inject their genome into host cells

-normal phage destroys host cells

-in transduction the bacteriophage injects it's genome that contains some of last bacterial host into new host

-New host cell intact w/ new DNA

22

What is conjugation?

Form of gene transfer that involves cell-to-cell contact

-direct gene transfer

-bacterial sex

-plasmids and chromosomes are exchanged

23

What is machinery is involved in conjugation?

F Plasmid

-genes for replication and transfer functions

 

Sex Pilus

-contacts recipient cell

-retracts to bring cells together

24

What does the F plasmid do?

single strand of plasmid enters recipient cell and synthesizes complementary stran

-gives recipient cell ability to conduct horizontal gene transfer

-F plasmid integrates into chromosome via recombination

25

What is mobile DNA?

Type of mutagenesis

-has transposable elements

-genes that move within or between DNA molecules

-can't replicate independently

 

Transposition

-the movement of transposable elements

26

What are the types of transposable elements?

1.  Insertion sequences (IS)

-shorter DNA segments

-single gene, transposase, an enzyme that cuts out segment of DNA and puts somewhere else

 

2. Transposons

-longer DNA segments

-multiple genes

-eg. transposase+antibiotic resistance

27

What are the types of transposition?

Conservative

-transposon moved to new DNA molecule

-absent from donor DNA, present in recipient DNA

 

Replicative

-transposon is replicated AND moved

-present in donor and recipient DNA

28

What is a biological mutagen?

When transposition causes mutation

-insertion into a gene which disrupts its function

 

Lab application

-transposition used to create bacterial mutants

-disrupting the gene to study its function

 

Correlation

-# of transposons related to how fast you involve