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bio 113 Lecture 9
Bacterial genetics
49
Biology
Undergraduate 1
02/01/2013

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Term
what are the advantages of using bacteria for genetics?
Definition

cheap and easy to grow

short generation time

haploid - easy to see effect of mutations 

Term
which bacteria is commonly used?
Definition
Escherichia coli but not the 0157 strain. this is associated with food poisoining.
Term
if you innoculate a few bacteria on a agar plate what would you get?
Definition
a colony where each bacteria lands
Term
if you innoculate a million bacteria in an agar plate what would you get?
Definition
a bacterial lawn due to confluent growth.
Term
what would you see if you put a few bacteria in a media?
Definition
the media would become increasingly cloudy as the bacteria multiply
Term
what type of DNA has E. coli got?
Definition
 a single double stranded circular chromsome compacted in the nucleoid.
Term
how many base pairs and how many genes in the E.coli?
Definition

base pairs 4.6 million

genes 4500

Term

the nucleiod containing bacterial DNA occupies

 

a. a small fraction of the cell volume

b. a large fraction of the cell volume?

Definition
b. a large fraction of the cell volume.
Term
what are bacteriphages?
Definition
viruses that can infect bacteria. they are structurally and functionally diverse.
Term
name the 2 bacteriophage life cycles
Definition

lytic (virulent) results in host cell lysis

lysogenic (temperate) viral DNA integrated with host. remains dormant and replicates with host dna.

Term
in the lytic cycle how many sets of proteins are needed to assemble the phage?
Definition

3 sets.

head

tail

tail fibres

Term
in the lytic cycle how does the phage escape the host cell?
Definition
directs lysozyme that digests the bacterial cell wall. damaged cell wall results in osmosis causing cell to swell and burst and phage escapes releasing 100-200 phage particles.
Term
give an example of a temperate phage
Definition
lamba phage
Term
what is a bacteria with viral DNA intergrated in its chromsome known as?
Definition
a lysogen
Term
what can induce the lambda phage to go from lysonic to lytic cycle?
Definition
stress such as UV.
Term
gene transfer and recombination occurs through 3 processes in bacteria. what are they?
Definition

Transformation

Transduction

Conjugation

Term
what is transformation?
Definition
taking up naked DNA from environment can be in the form of a plasmid.
Term
what is transduction?
Definition
transfer of bacterial genes form one bacteria to another by a bacteriophage.
Term
how many types of transduction are there?
Definition

2

generalised - lytic/virulent phage

specialised - temperate/lysogenic phage

Term
explain generalised transduction.
Definition

only in lytic/ virulent phage.

after infecting host, DNA is hydrolised into pieces and phage DNA/proteins are made.

occasionally bacterial dna is packaged in phage capsid.

transducing phages infect new hosts, crossing over takes place and recombinant bacteria result

Term
explain speacialised transduction
Definition

only in Lysogenic/temperate phage.

prophage intergrates dna between 2 genes. occasionaly prophage exits incorrectly taking with it part of the bacterial dna. phage particle carry bacterial dna. crossing over takes place when phage infects new bacteria resulting in recombinant bacteria.

Term
what is conjugation involving the F factor known as?
Definition
rolling circle replication
Term
what must a bacteria have in order to be able to form sex pili?
Definition
the F factor (fertility factor -a plasmid)
Term
how does conjugation promote variation?
Definition
whilst the the F factor is being transferred the dna comes through in a linear fashion and then rolls up. sometime the mating bridge is broken before the whole f factor is transfered resulting in not all of the dna transferred thus a different set.
Term
what is the mating bridge in conjugation also known as?
Definition
the cytoplasmic bridge
Term
in conjugation what is the recipient bacterial cell known as?
Definition
an exconjugant
Term
does the donor keep a copy of the F factor? 
Definition
yes it does.
Term
how is a F+ male converted into a Hfr male? what is a Hfr male?
Definition
the F+ is a plasmid. Intergration of it into the chromsome makes it into a Hfr cell. Hfr is High Frequency recombination.
Term
when a Hfr is transferring it dna to a F- bacterium what can happen?
Definition
not all of the DNA is transferred thus the bits that are transfered can cross over with host dna to make recombinant F- bacterium
Term

the cell that has the f factor is aka?

The cell that doesnt have it is aka?

Definition

F+ if they have plasmid

F- if they dont

Term
genes which code for proteins required all the time by the bacteria are?
Definition
constitutively expressed
Term
genes that are only active when required are called?
Definition
regulated genes.
Term
in bacterial cells when does transcription begin?
Definition
when RNA Polymerase binds to a promoter
Term
in negative regulation the binding of a repressor does what to transcription?
Definition
blocks transcription
Term
explain the control of tryptophan biosynthesis
Definition
when tryptophan is present, it is bound to the repressor as a corepressor, the operon is off because there is no need to make any unessecary protein if it is already available. but when tryptophan is absent it is not bound to the repressor, the repressor is not blocking the operator binding site and mRNA is made to synthesise proteins for tryptophan.
Term
what is polycistronic messaging?
Definition

mRNA that carry several open reading frames each of which is tanslated into a polypeptide. These polypeptides usually have a related function (they often are the subunits composing a final complex protein) 

monocistronic mRNA is when it contains the genetic information to translate only a single protein chain (polypeptide)

Term
what 3 enzymes are produced when the lac operon is on?
Definition

B-galactosidase

Permease

transacetylase

Term
what is the name of the inducer that inactivates the repressor in lac operon?
Definition
allolactose.
Term
why is the repressor active when lactose is absent?
Definition
it doenst have to make enzymes to break down lactose if lactose isnt present. it prefers to use glucose anyways.
Term
binding to promoter to prevent transcription is an example of?
Definition
negative regulation
Term
what happens when tyrphonin binds to repressor?
Definition
it binds to operator and transcripted is prevented
Term
in the absence of lactose lac operon is?
Definition
OFF
Term
binding of a molecule to the operator to turn on gene expression is an example of ?
Definition
positive regulation
Term
what does permease do in lac operon?
Definition
creates lactose permeable pore in bacteria which make it quicker for lactose to come into the cell
Term
what does B -galactosidase do?
Definition
break down lactose into galactose and glucose
Term
what are the 3 genes in the lac operon?
Definition
lacZ lacY lacA
Term
how many genes in try operon?
Definition

5

trpE trpD trpC trpB trpA

Term
what role does cAMP play in lac operon?
Definition
when lactose is present and glucose is scarce there are high levels of cAMP. this binds to its receptor protein called CRP and this binds to the promoter region. result:Abundant lac mRNA synthesis
Term
when glucose is abundant what happens to levels of cAMP?
Definition
they are low. and this results in little lac mRNA synthesis because prefers using glucose
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