Unit 3 Chapter 17: Gene Expression in Bacteria/Viruses + Gene Regulation Flashcards
What were viruses first known as
disease agents that are smaller than bacteria
How are viruses classified
- host specificity/pathology
- genetic material
- size and shape
What genetic material do viruses use
- single and double stranded RNA and DNA
- linear or circular
What are virions
-virus particles that consist of a simple protein coat or capsid and a nucleic acid
What are the bacteriophages 2 strategies for survival?
- virulent (lytic cycle)
2. temperate (lysogenic)
What is the lytic cycle
the phage binds to the bacteria, injects its DNA, causes the bacteria to immediately produce more phage proteins and more phage DNA (instead of its own proteins and DNA) and when the cell is used up, the cell lyses and the newly assembled viruses are released
What is the lysogenic cycle
the virus takes a wait-and-see approach. It inserts its DNA (now called a prophage) into the bacterial chromosome and waits while the bacteria divide (replicating the prophage along with their own DNA). When the moment is right, the prophage pops out of the chromosome and resumes (temporarily) the lytic reproductive cycle
What do viral phenotypes do
change the way the viruses are able to infect and lyse bacteria
What makes eukaryotic viruses different from bacterial (phage) viruses
-shape
What do eukaryotic viruses do
- many are like lytic phages
- lysogenic version are called retroviruses
What do retroviruses do
- lysogenic eukaryotic viruses
- bend rules of central dogma by making DNA copy from RNA genome
- DNA copy is integrated into chromosome and just hangs out until time is right
What is bacterial sex
how bacterium exchange genetic info
What is specialized transduction
When a prophage excises itself from the chromosome, it can be sloppy and pick up a gene from the bacterial chromosome. The bacterial gene becomes part of the virus genome and will be inserted into the chromosome of another bacteria when infected by that phage
What is generalized transduction
Sometimes the phage do a poor job of chopping up the bacterial DNA and instead of packaging phage DNA into the virions they package chunks of bacterial chromosome. When those virions infect another bacterium, the chunk of bacterial DNA gets
injected into the infected bacterium and can be incorporated into the chromosome. Since adjacent genes are more likely to be transferred together, generalized transduction can be used to map genes
What is transformation
- bacteria can take up DNA floating in their environment
- which can be integrated by recombination
- plasmids
What are plasmids
- small DNA circles used to transform bacteria
- do not integrate
- can be duplicated
- carry and express a few genes
What are R factors
plasmids that carry antibiotic resistance genes
What is conjugation
- most sex like way bacteria exchange DNA
- 2 strains of bacteria F- and F+
- F+ have an F- plasmid
- F+ can conjugate with F- donating one strand of their F plasmid to F- making it F+
What are integrated F strains referred to as
Hfr- high frequency recombination
What is transcriptional control
- regulatory proteins affect RNA polymerase’s ability to bind to promoter and start transcription
- efficiency
- gene amplification
What is translational control
- regulatory molecules alter the length of time mRNA survives before it is degraded or affect translation initiation or affect elongation factors/other proteins
- allows rapid changes
What is posttranslational control
proteins are manufactured in an inactive form and must be activated by chemical modification
-most rapid response
What is an inducer
a substrate in a reaction that stimulates the expression of a specific gene or genes
ie. lactose
What is lac-z
gene that encodes for beta galactosidase
What is lac-y
cells can’t accumulate lactose
-no lactose permease to import lactose
What is lac-I
gene that shuts down expression of lac Z and Y is broken so theres constant expression of them
What happens when lactose is absent
lac-I shuts down expression of z and y
-lac repressor binds to operator which is between promoter and where transcription starts, blocking transcription
What happens when lactose is present
transcription of lac z and y is induced
- lactose binds to repressor which unbinds from operator
- genes can be transcribed
What is the operon
the whole section where this transcription is regulated
What is lac A
codes for transacetylase which is a protective enzyme
that exports sugars when too abundant
How does the trp operon work
when trp is low, RNA polymerase can bind to promoter and transcribe genes
when trp is high, trp binds to repressor which binds to operator and blocks RNA polymerase from binding
trp is a co repressor
How does CRP act
as an enhancer, binds near promoter and facilitates transcription
What is the CAP binding site in the lac operon
one of 2 binding sites
- one is for rna polymerase
- this one is for cap which is a regulatory protein
