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98 Cards in this Set

  • Front
  • Back

Define mutation

change in the nucleotide sequence in the genome of an organism

Define genetic recombination

genetic rearrangements in the genome

Prokaryotes do not have ______ reproduction.

sexual

Prokaryotes exchange genetic information (T/F)

True

What is a point mutation?

Involves a single base mutation

What are the three different point mutations?

Missense


Nonsense


Silent mutations

What do frameshift mutations result in?

Frameshift mutations result in change in the reading frame. Insertion or deletions

Frameshift mutations (picture)

What are two examples of chemical mutagens?

Base analogs


Intercalative dyes

Define base analogs

substitutes for bases in DNA. Pair with the wrong base - induce a mutation

Define intercalative dyes

Ethidium bromide. Causes abnormal DNA conformation and results in inserations/deletions

What are two types of radiation?

Ionizing radiation


nonionizing radiation

Define ionizing radiation

X-rays, cosmic rays, gamma rays. Generate hydroxyl radicals that can mutate the DNA



Define nonionizing radiation

UV light. Bases of DNA absorb UV light and generate altered DNA structures

DNA repairs systems act to do what?

DNA repair systems act to repair damaged DNA prior

When is SOS repair system activated?

SOS repair - activated by DNA damage

What is SOS repair system usually repressed by?

LexA

When LexA is inactivated what happens?

LexA inactivated by RecA when DNA damage occurs

What does SOS repair induce?

Induces error-prone DNA, called mutases


Also induces error-free mechanism

What does RecA bind to?

RecA binds preferentially to single-stranded DNA to form a RecA-DNA filament

What does RecA form when it binds to single-stranded DNA?

RecA-DNA filament

What does the RecA-DNA filament act to do?

The filament acts to catalyze LexA cleavage. (single stranded DNA is increasingly formed following DNA damage...)

Non-SOS repair is basically error-_____, but SOS repair is error-_____.

free


prone

Why is UV a mutagen?

Because SOS repair is error prone

It is better to survive with genetic errors than to die. (T/F)

True

What is the Ames test used to determine?

Used to determine the mutagenicity of a compound - related to the carcinogenicity (high correlation)

What does a Ames test use?

Use a mutant strain and screen for mutations that repair the defect (revertants)

Important things to remember about Ames test

Important that the mutation is a point mutation


Also has a mutation in the error-proof DNA repair mechanism

How is the compound tested in the Ames Test?

The compound tested is first "activated" by incubation with liver enzymes

Example of Ames test using Salmonella

A histidine mutant of salmonella is grown on medium without histidine, cells do not grow


A filter containing water or a test compound was placed on the plates


Revertants are increased in the presence of the test compound, revealing it to be a mutagen

About what fraction of chemicals turn out positive to be rodent carcinogens?

About three-fourths of chemicals that are positive in the Ames test are found to be rodent carcinogens, but not all substances that cause cancer in laboratory animals are mutagenic in this assay.

All substances that cause cancer in laboratory animals are mutagenic in the Ames assay. (T/F)

False. Not all substance that cause cancer in laboratory animals are mutagenic in this assay

Why is the Ames test used even though it is not completely precise?

The ease, rapidity (results in 3-4 weeks) and low cost of the text make it an important tool for screening substances for potential carcinogenicity

How long does it take to get results from an Ames test?

about 3-4 weeks

Define genetic recombination

the physical exchange of genetic material between genetic elements

Define homologous recombination

Exchange between homologous DNA sequences from different sources

What does homologous recombination require?

Requires RecA protein


Homologs of RecA have been found in all species

Homologs of RecA have been found in all species. (T/F)

True

What does RecA bind to?

RecA binds to single-stranded DNA and catalyzes stand invasion of recipient DNA

What does RecA catalyze?

catalyzes strand invasion of recipient DNA

What does DNA strand exchange generate?

DNA strand exchange generates a crossover structure, called a Holliday junction

Define holliday junction

A mobile junction between four strands of DNA

What does the resolution of Holliday junction produce?

Produces recombinant products

Holliday Junction/Rec A (picture)

Who is Holliday junction named after?

The structure is named after Robin Holliday, who proposed it in 1964 to account for DNA exchange during meiosis in yeast

When did Robin Holliday propose Holliday junctions?

1964

Why did Robin Holliday propose Holliday junctions?

To account for DNA exchange during meiosis in yeast

What are the 4 methods to exchange genetic material?

Transformation


Transduction


Conjugation


Nanotubes

Define Transformation

a cell takes up DNA from the environment

Define Transduction

DNA is transferred from one cell to another by a virus

Define conjugation

DNA is transferred by cell to cell contact

Define competence

The ability to take up DNA from the environment

There are many ______ involved in transformation.

Genes

What genes are involved in transformation?

Membrane-associated DNA binding proteins, cell wall autolysins, nucleases

Natural competence occurs in only a few Bacteria. (T/F)

True

What is an example of a bacteria that has natural competence

Bacillus subtilis

What is Bacillus subtilis' competence controlled by?

Competence controlled by quorum sensing pathway

E. Coli is naturally competent. (T/F)

False. E. Coli is not naturally competent

How can you make E. Coli competent?

Treat with high concentrations of Ca2+ and then chill

How does a cell integrate transforming DNA

the DNA binds to a DNA binding protein on cell membrane


DNA is taken up - can be degraded by a nuclease as it enters the cell


Bound by competence specific ssDNA binding proteins in cytoplasm

What does RecA bind to when a cell is integrating transforming DNA?

RecA binds to the DNA and integrates it into the genome (by homologous recombination)

What are the two types of transduction?

Generalized transduction


Specialized transduction

Define generalized transduction

Transfers DNA from any region on chromosome

Define specialized transduction

transfers DNA from a specific region

Describe the process of generalized transduction

Virus infects a cell


Accidentally packages some of the host cell's DNA into a viral particle - transducing particle


Tranducing particle infects a new cell


The donor's DNA recombines with the recipients genome

Define transducing particle

A viral particle that a virus accidently packaged some of the host cell's DNA into

Generalized transduction (picture)

Describe the normal process of specialized transduction

Phage DNA inserts into host DNA. Always in same location


Becomes induced and excises out of chromosome


Make more phage particles

Specialized transduction - normal (picture)

Describe specialized transduction when it is not perfectly normal

Sometimes excises a piece of the host's DNA


Packed into the phage particle


The transducing particles can transfer the genes to a new cell

Specialized transduction - not normal (picture)

Conjugation is bacterial sex (T/F)

True

Conjugation is what type of mechanism

Plasmid encoded mechanism -conjugative plasmid

What do conjugative plasmids contain?

Conjugative plasmids contain an operon that codes for proteins involves in DNA transfer, replication, and mating pair formation

Other genetic elements can be transferred at the same time during conjugation. (T/F)

True

Cells that contain conjugative plasmids can not act as ______

recipients

What happens when a cell contains a conjugative plasmid?

transfer is blocked by proteins encoded by the plasmid

Who discovered that cells that contain conjugative plasmids cannot act as recipients

Discovery - 1953, Lederberg found that mixing of two auxotrophic bacteria could produce a prototrophic one

Define donor cell

contains a conjugative plasmid

What does the donor cell code for?

codes for a sex pilus

What does the Pilus bind to?

Pilus binds to receptor on recipient cell - pulls it closer

How is the Plasmid copied?

Plasmid is copied by rolling circle replication. The displaced strand is transferred

Where does second strand synthesis occur?

Second strand synthesis occurs in recipient

Rolling circle replication (picture)

What do some conjugative plasmids integrate?

Some conjugative plasmids can integrate into the chromosome - episome

Define episome

Some conjugative plasmids can integrate into the chromosome

What is an example of an episome?

F plasmid in E. Coli

When the plasmid is integrated into the chromosome called _____ - _____/______/______/_____

Hfr


high/frequency/of/recombination

What does Hfr lead to?

Leads to transfer of chromosomal genes

Archaea contain _____ circular chromosome

single

Genetic manipulation of Archaea lags behind Bacteria. (T/F)

True

Give two examples of how genetic manipulation of Archaea lags behind Bacteria.

Most antibiotics do not effect Archaea


No single species is a model organism for Archaea

Examples of transformation, transduction, and conjugation do not exist in Archaea. (T/F)

False. They do exist.

______ works reasonably well in Archaea.

Transformation

Define Nanotubes

Small tubes linking different species

Bacteria exchange cytoplasmic molecules (T/F)

True

Why should we care about genetic exchange in bacteria?

Plasmids often confer resistance to antibiotics


Virulence plasmids - can encode for toxins that promote disease


Horizontal gene transfer

Define virulence plasmids

Can encode for toxins that promote disease