Unit 3 Chapter 17: Gene Expression in Bacteria/Viruses + Gene Regulation

Question 1

What were viruses first known as

Answer 1

disease agents that are smaller than bacteria

Question 2

How are viruses classified

Answer 2

• host specificity/pathology
• genetic material
• size and shape

Question 3

What genetic material do viruses use

Answer 3

• single and double stranded RNA and DNA

- linear or circular

Question 4

What are virions

Answer 4

-virus particles that consist of a simple protein coat or capsid and a nucleic acid

Question 5

What are the bacteriophages 2 strategies for survival?

Answer 5

1. virulent (lytic cycle)

2. temperate (lysogenic)

Question 6

What is the lytic cycle

Answer 6

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

Question 7

What is the lysogenic cycle

Answer 7

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

Question 8

What do viral phenotypes do

Answer 8

change the way the viruses are able to infect and lyse bacteria

Question 9

What makes eukaryotic viruses different from bacterial (phage) viruses

Answer 9

-shape

Question 10

What do eukaryotic viruses do

Answer 10

• many are like lytic phages

- lysogenic version are called retroviruses

Question 11

What do retroviruses do

Answer 11

• 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

Question 12

What is bacterial sex

Answer 12

how bacterium exchange genetic info

Question 13

What is specialized transduction

Answer 13

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

Question 14

What is generalized transduction

Answer 14

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

Question 15

What is transformation

Answer 15

• bacteria can take up DNA floating in their environment
• which can be integrated by recombination
• plasmids

Question 16

What are plasmids

Answer 16

• small DNA circles used to transform bacteria
• do not integrate
• can be duplicated
• carry and express a few genes

Question 17

What are R factors

Answer 17

plasmids that carry antibiotic resistance genes

Question 18

What is conjugation

Answer 18

• 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+

Question 19

What are integrated F strains referred to as

Answer 19

Hfr- high frequency recombination

Question 20

What is transcriptional control

Answer 20

• regulatory proteins affect RNA polymerase’s ability to bind to promoter and start transcription
• efficiency
• gene amplification

Question 21

What is translational control

Answer 21

• 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

Question 22

What is posttranslational control

Answer 22

proteins are manufactured in an inactive form and must be activated by chemical modification
-most rapid response

Question 23

What is an inducer

Answer 23

a substrate in a reaction that stimulates the expression of a specific gene or genes
ie. lactose

Question 24

What is lac-z

Answer 24

gene that encodes for beta galactosidase

Question 25

What is lac-y

Answer 25

cells can’t accumulate lactose

-no lactose permease to import lactose

Question 26

What is lac-I

Answer 26

gene that shuts down expression of lac Z and Y is broken so theres constant expression of them

Question 27

What happens when lactose is absent

Answer 27

lac-I shuts down expression of z and y

-lac repressor binds to operator which is between promoter and where transcription starts, blocking transcription

Question 28

What happens when lactose is present

Answer 28

transcription of lac z and y is induced

• lactose binds to repressor which unbinds from operator
• genes can be transcribed

Question 29

What is the operon

Answer 29

the whole section where this transcription is regulated

Question 30

What is lac A

Answer 30

codes for transacetylase which is a protective enzyme

that exports sugars when too abundant

Question 31

How does the trp operon work

Answer 31

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

Question 32

How does CRP act

Answer 32

as an enhancer, binds near promoter and facilitates transcription

Question 33

What is the CAP binding site in the lac operon

Answer 33

one of 2 binding sites

• one is for rna polymerase
• this one is for cap which is a regulatory protein