Vivacious VirusesVivacious Viruses

Chapter 19Chapter 19

I. VirusI. Virus

A.A. CharacteristicsCharacteristics1.1. Smaller than a ribosomeSmaller than a ribosome2.2. Can form into regular crystals (cells won’t Can form into regular crystals (cells won’t

do this)do this)3.3. Made of Nucleic Acid - Genome is made of Made of Nucleic Acid - Genome is made of

one of the following:one of the following: DNA - double strandedDNA - double stranded DNA - single strandedDNA - single stranded RNA - double strandedRNA - double stranded RNA - single strandedRNA - single stranded

A. Characteristics (cont)A. Characteristics (cont)

4.4. Range from 4 genes to several hundredRange from 4 genes to several hundred

5.5. Protein coat surrounds nucleic acidProtein coat surrounds nucleic acid Capsid - protein coatCapsid - protein coat

can be rod shaped (helical), polyhedral or more can be rod shaped (helical), polyhedral or more complex complex

capsids are made from large numbers of protein capsids are made from large numbers of protein subunits called capsomeres subunits called capsomeres

A. Characteristics (cont)A. Characteristics (cont)

6.6. Accessory Structures (found in some Accessory Structures (found in some viruses)viruses)

Viral Envelopes - membranes surrounding Viral Envelopes - membranes surrounding capsidcapsid come from membrane of their host cell and come from membrane of their host cell and

contain the same proteins, glycoproteins and contain the same proteins, glycoproteins and phospholipids used by hostphospholipids used by host

These envelopes help viruses to infect host These envelopes help viruses to infect host without being detectedwithout being detected

Bacteriophages - have most complex Bacteriophages - have most complex capsidscapsids

B. Reproduction of Viruses B. Reproduction of Viruses

Happens only in a host Happens only in a host

cell because they have nocell because they have no

ribosomes or enzymes toribosomes or enzymes to

reproduce on their ownreproduce on their own

B. Reproduction of VirusesB. Reproduction of Viruses

1.1. Host Range - limited amount of host cells Host Range - limited amount of host cells that a virus can infect (can be one host that a virus can infect (can be one host or a few related species)or a few related species)

Host identified by “lock and key” fit between Host identified by “lock and key” fit between proteins on capsid and receptors on outside proteins on capsid and receptors on outside of host cellof host cell

Can be Tissue Specific - eukaryotic viruses Can be Tissue Specific - eukaryotic viruses may infect only certain tissues of their hostmay infect only certain tissues of their host ex. cold - respiratory tissue, HIV - white blood ex. cold - respiratory tissue, HIV - white blood

cells onlycells only

B. Reproduction of VirusesB. Reproduction of Viruses

2.2. Methods of Reproduction - virus infects host Methods of Reproduction - virus infects host first and overtakes host cell to make viral first and overtakes host cell to make viral nucleic acids and proteinsnucleic acids and proteins

Host provides the following:Host provides the following: Nucleotides for synthesizing viruses nucleic acidNucleotides for synthesizing viruses nucleic acid EnzymesEnzymes RibosomesRibosomes tRNA, amino acids, ATP and other parts needed by virus tRNA, amino acids, ATP and other parts needed by virus

to go through transciption and translation (to make viral to go through transciption and translation (to make viral proteins)proteins)

Reproduction of Viruses- Reproduction of Viruses-

3.3. Lytic Cycle - viral reproductive cycle that Lytic Cycle - viral reproductive cycle that ends in the death of the host cell (also ends in the death of the host cell (also called virulent virus) called virulent virus)

ex. T4 bacteriophageex. T4 bacteriophage

Lytic Cycle (cont)Lytic Cycle (cont)

a.a. Phage attaches to cell - uses tail fiber to Phage attaches to cell - uses tail fiber to stick to receptor site on host (e. coli)stick to receptor site on host (e. coli)

b.b. DNA is injected through cell wall and DNA is injected through cell wall and membrane into the host cellmembrane into the host cell

c.c. Empty capsid remains outside the cell and DNA of the Empty capsid remains outside the cell and DNA of the host is hydrolyzed (broken up)host is hydrolyzed (broken up)

d.d. Phage overtakes cell using its parts to manufacture Phage overtakes cell using its parts to manufacture viral nucleic acids and proteins. New phages are viral nucleic acids and proteins. New phages are reassembled inside host cellreassembled inside host cell

e.e. Phage makes host cell produce lysozyme - an Phage makes host cell produce lysozyme - an enzyme that digests the host’s cell wall. enzyme that digests the host’s cell wall.

Osmosis causes the cell to swell and burst Osmosis causes the cell to swell and burst releasing the new phages (may be 100-200 releasing the new phages (may be 100-200 new ones) Phages go find new host cell to new ones) Phages go find new host cell to infectinfect

Reproduction of VirusesReproduction of Viruses

4.4. Lysogenic Cycle - replicates viral Lysogenic Cycle - replicates viral genome without killing host cell genome without killing host cell

If they use both lytic and lysogenic - also If they use both lytic and lysogenic - also called temperate virusescalled temperate viruses

B. Lysogenic Cycle (cont)B. Lysogenic Cycle (cont)

a.a. Phage binds to host cell and injects DNAPhage binds to host cell and injects DNAb.b. Phage DNA forms a circle inside host - it can now go Phage DNA forms a circle inside host - it can now go

through either lytic or lysogenic cycle. (If lytic - see through either lytic or lysogenic cycle. (If lytic - see previous process)previous process)

c.c. Viral DNA lines up with host DNA and gets Viral DNA lines up with host DNA and gets incorporated into the host DNA by crossing over - it is incorporated into the host DNA by crossing over - it is now called a now called a prophageprophage - one of its genes represses - one of its genes represses the other genes so it’s basically not affecting the host the other genes so it’s basically not affecting the host at all at this pointat all at this point

d.d. When the host cell replicates and divides, it also When the host cell replicates and divides, it also replicates the virus and passes it on to its daughter replicates the virus and passes it on to its daughter cells cells

B. Lysogenic Cycle (cont)/B. Lysogenic Cycle (cont)/

e.e. At some point, phages will leave the host DNA At some point, phages will leave the host DNA and return to a lytic cycle. At this point they and return to a lytic cycle. At this point they will destroy their host cell - trigger can be will destroy their host cell - trigger can be chemicals, radiation or otherchemicals, radiation or other

f.f. Some other viral genes may be expressed Some other viral genes may be expressed when DNA is part of host cell and produce when DNA is part of host cell and produce toxins (like botulism, diptheria, scarlet fever)toxins (like botulism, diptheria, scarlet fever)

C. Animal Viruses C. Animal Viruses

Vary in type of nucleic acid and Vary in type of nucleic acid and presence/absence of viral envelopepresence/absence of viral envelope

1.1. Viral Envelopes Viral Envelopes

Outer membrane (outside capsid) that helps parasite Outer membrane (outside capsid) that helps parasite enter host cellenter host cell

Bind to animal cellBind to animal cell Envelope fuses with plasma membrane and injects Envelope fuses with plasma membrane and injects

virus + capsid into cellvirus + capsid into cell Enzymes of host cell remove capsid, virus overtakes Enzymes of host cell remove capsid, virus overtakes

cell (similar to bacteria)cell (similar to bacteria)

C. Animal VirusesC. Animal Viruses

Cycle does not always kill the host cellCycle does not always kill the host cell Some virus envelopes come from nuclear Some virus envelopes come from nuclear

membrane and virus is replicated inside the membrane and virus is replicated inside the nucleus of the host (like herpes)nucleus of the host (like herpes)

DNA of virus becomes integrated into host DNA of virus becomes integrated into host DNA and becomes a provirusDNA and becomes a provirus

Trigger will cause provirus to become active Trigger will cause provirus to become active and destroy host celland destroy host cell

C. Animal VirusesC. Animal Viruses

2.2. RNA virusRNA virusa.a. Classification - by # of strands and how they Classification - by # of strands and how they

function in hostfunction in host

Class IV - serve directly as mRNA - can be Class IV - serve directly as mRNA - can be translated into viral protein as soon as they translated into viral protein as soon as they infectinfect

Class V - RNA of virus serves as template to Class V - RNA of virus serves as template to make mRNA - must be transcribed into make mRNA - must be transcribed into mRNA before translationmRNA before translation

B. RNA viruses in animals B. RNA viruses in animals

Class VI - Retroviruses - reverse flow of Class VI - Retroviruses - reverse flow of genetic informationgenetic information Contain enzyme - Contain enzyme - reverse transcriptasereverse transcriptase - that - that

transcribes DNA from an RNA template (goes transcribes DNA from an RNA template (goes backward)backward)

DNA becomes a provirus in nucleus of hostDNA becomes a provirus in nucleus of host Viral DNA is now transcribed to RNA (can be Viral DNA is now transcribed to RNA (can be

mRNA for translation, or can be packaged and mRNA for translation, or can be packaged and sent to new host cells)sent to new host cells)

HIV is a retrovirus that causes AIDSHIV is a retrovirus that causes AIDS

E. Viral Diseases in AnimalsE. Viral Diseases in Animals

1.1. Causes Causes Virus could damage or kill cells Virus could damage or kill cells Virus may produce toxins that cause Virus may produce toxins that cause

symptomssymptoms

C. Viral Diseases in AnimalsC. Viral Diseases in Animals

2.2. Effects depend on ability of affected Effects depend on ability of affected tissue to make new cellstissue to make new cells

a.a. If virus affects rapidly dividing cells – can If virus affects rapidly dividing cells – can have complete recovery (throat)have complete recovery (throat)

b.b. If virus affects areas where cells have If virus affects areas where cells have stopped dividing, damage is permanent (like stopped dividing, damage is permanent (like nerve cells - polio virus)nerve cells - polio virus)

3. Vaccines3. Vaccines

Harmless variants of pathogenic microbes Harmless variants of pathogenic microbes that stimulate the immune system to that stimulate the immune system to mount defense against virusmount defense against virus

sensitizes immune system to the virus so sensitizes immune system to the virus so that it reacts vigorously if ever truly that it reacts vigorously if ever truly exposed to the virusexposed to the virus

4. New Viruses4. New Viruses Result from a variety of causesResult from a variety of causes

a.a. Mutation of existing virus - seen often in RNA Mutation of existing virus - seen often in RNA viruses because they have no proofreading viruses because they have no proofreading mechanismmechanism May lead to new varieties that individuals were already May lead to new varieties that individuals were already

immune to (flu)immune to (flu)

b.b. Spread of existing viruses from one species to Spread of existing viruses from one species to another another

c.c. Dissemination from small population to large Dissemination from small population to large population - due to increasedpopulation - due to increased travel, blood transfusions, travel, blood transfusions,

IV drug useIV drug use

5. Cancer causing viruses 5. Cancer causing viruses

Oncogenes - genes that trigger Oncogenes - genes that trigger cancerous characteristics in cells cancerous characteristics in cells

a.a. Proto-oncogenes - versions of oncogenes Proto-oncogenes - versions of oncogenes found in normal cells - code for proteins that found in normal cells - code for proteins that control growth factors and cell divisioncontrol growth factors and cell division

b.b. Virus may trigger proto-oncogenes to turn Virus may trigger proto-oncogenes to turn on causing uncontrolled cell division - on causing uncontrolled cell division - Usually only cause cancer in combo with a Usually only cause cancer in combo with a mutagenmutagen

F. Plant Viruses F. Plant Viruses

stunt growth in plants and diminish crop stunt growth in plants and diminish crop yieldsyields

1.1. Horizontal transmission of virus - insects, Horizontal transmission of virus - insects, high winds, injury, freezes - cause plants high winds, injury, freezes - cause plants outer layer of epidermis to become outer layer of epidermis to become damageddamaged

increases chance of virus to penetrate epidermis increases chance of virus to penetrate epidermis and infect plantand infect plant

farmers transmit from plant to plant using same farmers transmit from plant to plant using same pruning toolspruning tools

D. Plant VirusesD. Plant Viruses

2.2. Vertical transmission - plant inherits viral Vertical transmission - plant inherits viral infection from a parentinfection from a parent

Occurs during asexual reproduction or in Occurs during asexual reproduction or in seeds of sexual reproductionseeds of sexual reproduction

3.3. Virus spreads through plant via Virus spreads through plant via plasmodesmata plasmodesmata

G. ViroidsG. Viroids

Tiny molecules of naked RNA that infect Tiny molecules of naked RNA that infect plants onlyplants only

Make no proteins but replicate in plant Make no proteins but replicate in plant cells and stunt their growthcells and stunt their growth

H. Prions H. Prions

infectious proteins - usually affect brain infectious proteins - usually affect brain tissue (mad cow)tissue (mad cow)

Breathtaking BacteriaBreathtaking BacteriaChapter 27Chapter 27

Chapter 18Chapter 18

I. Major Characteristics I. Major Characteristics

A.A. DNA DNA One, double stranded, circular moleculeOne, double stranded, circular molecule Tightly packed into “nucleoid” regionTightly packed into “nucleoid” region No membrane surrounding itNo membrane surrounding it Plasmids - smaller circular pieces of DNA Plasmids - smaller circular pieces of DNA

outside nucleoid regionoutside nucleoid region

B. Reproduction B. Reproduction

Divide by binary fission from single origin of Divide by binary fission from single origin of replicationreplication

Asexual- no mating involved - Most offspring are Asexual- no mating involved - Most offspring are genetically identical to parentgenetically identical to parent

Fast process - many can divide every 20 Fast process - many can divide every 20 minutesminutes

Relatively high rate of mutation due to speed of Relatively high rate of mutation due to speed of reproductionreproduction

Mutation rate helps bacterial colonies to survive Mutation rate helps bacterial colonies to survive better better

C. Genetic Recombination C. Genetic Recombination

While bacteria do not reproduce sexually, While bacteria do not reproduce sexually, they are able to have some recombination they are able to have some recombination of genes with other bacteria of genes with other bacteria through one through one of the following methods: of the following methods:

1. Transformation 1. Transformation Uptake of “naked” foreign DNA from the surrounding Uptake of “naked” foreign DNA from the surrounding

environment (like the S-strain/R-strain killing mice)environment (like the S-strain/R-strain killing mice)Live, nonpathogenic cell takes up a piece of DNA that Live, nonpathogenic cell takes up a piece of DNA that

includes the allele to make it pathogenicincludes the allele to make it pathogenicForeign allele is incorporated into the bacterial Foreign allele is incorporated into the bacterial

chromosome and replaces the original allele by chromosome and replaces the original allele by crossing crossing overover

Many bacteria have receptors on their surface proteins Many bacteria have receptors on their surface proteins that aid in uptake of naked DNA only from closely related that aid in uptake of naked DNA only from closely related speciesspecies

CalciumCalcium - can be added to bacteria without - can be added to bacteria without these these receptors (like e.coli) and will artificially stimulate the receptors (like e.coli) and will artificially stimulate the bacteria to take up naked DNAbacteria to take up naked DNA

2. Transduction 2. Transduction

Phages carry bacterial genes from one Phages carry bacterial genes from one host to another host to another

Transduction (cont.) Transduction (cont.)

When a virus is reassembling in it’s host a When a virus is reassembling in it’s host a small piece of bacterial DNA from host is small piece of bacterial DNA from host is accidentally packaged into capsid of virusaccidentally packaged into capsid of virus

Phage can attach to another host and Phage can attach to another host and inject the bacterial DNA into itinject the bacterial DNA into it

Crossing over incorporates this DNA into Crossing over incorporates this DNA into the host cellthe host cell

RANDOM RANDOM

3. Conjugation 3. Conjugation

Direct transfer of genetic material between two Direct transfer of genetic material between two bacterial cells that are temporarily joined.bacterial cells that are temporarily joined.

bacterial version of “sex”bacterial version of “sex”One way transferOne way transferdonor = male - uses sex donor = male - uses sex pilipili to attach to to attach torecipient = femalerecipient = femalebridge forms between two bacteria and DNA can bridge forms between two bacteria and DNA can

be transferredbe transferred

D. Plasmids D. Plasmids

Small, circular, self-replicating DNA molecule Small, circular, self-replicating DNA molecule separate from bacterial chromosomeseparate from bacterial chromosome

Can remain separate from chromosomeCan remain separate from chromosomeEpisome:Episome: Can become part of bacterial Can become part of bacterial

chromosome and replicate with it chromosome and replicate with it No protein coats and can’t exist outside the cellNo protein coats and can’t exist outside the cellGenerally beneficial to bacteriaGenerally beneficial to bacteriaSmall number of genes that may help bacteria Small number of genes that may help bacteria

survive in stressful environmentssurvive in stressful environments

1. F Plasmid 1. F Plasmid

Contains 25 genes required for production of Contains 25 genes required for production of sex pilisex pili

F+ = cell that contains F plasmid - donatersF+ = cell that contains F plasmid - donaters F- = cell without F plasmid - recipientsF- = cell without F plasmid - recipients Heritable Heritable F+ bacteria give rise to F+ offspringF+ bacteria give rise to F+ offspring F+ x F- F+ x F- F+ (male) replicates it’s DNA, F+ (male) replicates it’s DNA,

transfers copy to F- (female) converting it to F+ transfers copy to F- (female) converting it to F+ (male). Now the newly converted F+ bacteria (male). Now the newly converted F+ bacteria can make sex pili and transfer its plasmid to new can make sex pili and transfer its plasmid to new bacterial cellsbacterial cells

2. Hfr cell 2. Hfr cell

F factor becomes part of bacterial chromosome. F factor becomes part of bacterial chromosome. During conjugation - F factor replicates and gets During conjugation - F factor replicates and gets

transferred to F-, but some of the bacterial transferred to F-, but some of the bacterial chromosome can be taken with it.chromosome can be taken with it.

Recipient cell is temporarily “diploid” for some Recipient cell is temporarily “diploid” for some genes and crossing over can occurgenes and crossing over can occur

When bacteria divides, it has the new genesWhen bacteria divides, it has the new genesAny pieces of Hfr DNA left will be degraded Any pieces of Hfr DNA left will be degraded

3. R-plasmids 3. R-plasmids

““Resistance” plasmids - contain genes that code for Resistance” plasmids - contain genes that code for resistance to antibioticsresistance to antibiotics

When a bacterial population is exposed to antibiotics, When a bacterial population is exposed to antibiotics, any “sensitive” bacteria are killed by the antibioticsany “sensitive” bacteria are killed by the antibiotics

Bacteria that contain the R plasmid with resistance to the Bacteria that contain the R plasmid with resistance to the antibiotic surviveantibiotic survive

These bacteria then reproduce, increasing the number of These bacteria then reproduce, increasing the number of antibiotic resistant bacteria (natural selection)antibiotic resistant bacteria (natural selection)

R-plasmids can also be transferred during conjugation R-plasmids can also be transferred during conjugation and may carry as many as 10 genes for resistance to and may carry as many as 10 genes for resistance to different antibioticsdifferent antibiotics

II. Control of Gene Expression in II. Control of Gene Expression in BacteriaBacteria

A.A. Purpose Purpose helps individual bacteria cope with helps individual bacteria cope with

changes in their surroundingschanges in their surroundings ex. E. coli in human intestine - rely on what ex. E. coli in human intestine - rely on what

the host eats for it’s nutrition. Bacteria must the host eats for it’s nutrition. Bacteria must be able to turn genes on and off depending be able to turn genes on and off depending on its nutritional needson its nutritional needs

B. Metabolic controlB. Metabolic control

Regulates which metabolic pathways are Regulates which metabolic pathways are turned on and off. Done by one of the turned on and off. Done by one of the following 2 methods.following 2 methods.

1.1. Adjust activity of enzymes already Adjust activity of enzymes already present in cell. Depends on sensitivity of present in cell. Depends on sensitivity of enzymes to chemical cues enzymes to chemical cues

ex. Feedback inhibition - when the end-ex. Feedback inhibition - when the end-product starts to accumulate, it will inhibit product starts to accumulate, it will inhibit one or more of the enzymes in the pathway one or more of the enzymes in the pathway turning it offturning it off

B. Metabolic controlB. Metabolic control

2.2. Regulation of gene expression - Regulation of gene expression - Control of enzyme/protein production by Control of enzyme/protein production by

controlling transcription and translation controlling transcription and translation (turning genes on and off). (turning genes on and off).

In bacteria - this regulation occurs with In bacteria - this regulation occurs with OperonsOperons

C. Operon C. Operon

contains all the necessary components for contains all the necessary components for controlling a metabolic pathway including:controlling a metabolic pathway including:

1.1. OperatorOperator - on/off switch located in the - on/off switch located in the promoter region of the DNA (before the genes)promoter region of the DNA (before the genes)

2.2. Promoter Promoter - binding site for RNA polymerase- binding site for RNA polymerase

3.3. Transcription unitTranscription unit - all of the genes necessary - all of the genes necessary for a certain metabolic pathwayfor a certain metabolic pathway

C. OperonC. Operon

4.4. Regulatory geneRegulatory gene - occurs somewhere - occurs somewhere else in the DNA and codes for a else in the DNA and codes for a repressor (off switch)repressor (off switch)

5.5. RepressorRepressor – a protein that switches an – a protein that switches an operon off. Specific to one operonoperon off. Specific to one operon

6.6. CorepressorCorepressor - binds to repressor and - binds to repressor and activates it, changes it’s shape so it can activates it, changes it’s shape so it can bind to the operator and turn the pathway bind to the operator and turn the pathway offoff

Negative Control.. The Repressible Negative Control.. The Repressible OperonOperon

This pathway is called repressible because the This pathway is called repressible because the system is normally system is normally onon but can be turned but can be turned offoff when there is enough when there is enough resourcesresources available for available for the bacteriathe bacteria

1.1. Normally the operon is in the on position, one Normally the operon is in the on position, one long mRNA is made for the 5 enzymes long mRNA is made for the 5 enzymes required in the pathway. The mRNA will attach required in the pathway. The mRNA will attach to a ribosome, produces the enzymes and the to a ribosome, produces the enzymes and the enzymes will make tryptophanenzymes will make tryptophan

2. Host eats Thanksgiving dinner2. Host eats Thanksgiving dinner

Turkey contains lots of tryptophanTurkey contains lots of tryptophan Why would the bacteria use its Why would the bacteria use its

resources/energy to make tryptophan resources/energy to make tryptophan when it can get it from its host? - it doesn’twhen it can get it from its host? - it doesn’t

Trp operon (cont)Trp operon (cont)

3.3. Tryptophan is a Tryptophan is a corepressorcorepressor in this pathway. It in this pathway. It will bind to the repressor molecules (floating in will bind to the repressor molecules (floating in cytoplasm but inactive)cytoplasm but inactive)

When trp binds to repressor, shape of When trp binds to repressor, shape of repressor changes and it becomes activerepressor changes and it becomes active

Active repressor then binds to operator region Active repressor then binds to operator region of DNA and turns the operon OFFof DNA and turns the operon OFF

No mRNA is made and the enzymes to make No mRNA is made and the enzymes to make trp are no longer producestrp are no longer produces

4.4. After that great turkey dinner is digested After that great turkey dinner is digested by the host and the tryptophan levels by the host and the tryptophan levels decrease again, the repressor becomes decrease again, the repressor becomes inactive again, releases from the inactive again, releases from the operator, and the operon is turned back operator, and the operon is turned back onon

E. Negative Control.. The E. Negative Control.. The Inducible Operon Inducible Operon

In this pathway, the repressor is made in In this pathway, the repressor is made in its active form and automatically binds to its active form and automatically binds to the operator. The system is normally OFF the operator. The system is normally OFF but can be turned on (induced) when it is but can be turned on (induced) when it is needed. (Why make the enzymes to needed. (Why make the enzymes to break down lactose if there’s no lactose break down lactose if there’s no lactose around) around) EX. The lac operon produces EX. The lac operon produces 33 enzymes to enzymes to

break down lactose break down lactose (milk sugar)(milk sugar) for energy. for energy.

Lac operon (cont)Lac operon (cont)

1.1. Host drinks a big glass of milk (contains Host drinks a big glass of milk (contains lots of lactose plus some allolactose)lots of lactose plus some allolactose)

2.2. Allolactose binds to the repressor and Allolactose binds to the repressor and releases it from the operator regionreleases it from the operator region

3.3. RNA polymerase can then go on and RNA polymerase can then go on and transcribe the mRNA needed to make transcribe the mRNA needed to make the enzymes for breaking down lactosethe enzymes for breaking down lactose

Positive Control of Gene Positive Control of Gene Expression Expression

There is another factor controlling the lac There is another factor controlling the lac operonoperon

Glucose is the best energy source for the Glucose is the best energy source for the bacteria. Lactose doesn’t provide as bacteria. Lactose doesn’t provide as much ATP as glucose does. much ATP as glucose does.

Enzymes to break down lactose will only Enzymes to break down lactose will only be made if lactose is present AND glucose be made if lactose is present AND glucose levels are LOW!levels are LOW!

Positive Control of Gene Positive Control of Gene ExpressionExpression

1.1. cAMP accumulates (when glucose is low)cAMP accumulates (when glucose is low)2.2. cAMP binds to a regulatory protein called cAMP binds to a regulatory protein called

cAMP receptor protein (CRP)cAMP receptor protein (CRP)3.3. This complex (cAMP+CRP) is an activator of This complex (cAMP+CRP) is an activator of

transcription and binds near the promoter of the transcription and binds near the promoter of the operon and makes transcription faster by operon and makes transcription faster by making it easier for RNA polymerase to bind to making it easier for RNA polymerase to bind to promoterpromoter

4.4. If glucose levels build up, cAMP/CRP will If glucose levels build up, cAMP/CRP will release and transcription will slow downrelease and transcription will slow down