HYS CH7.4 Control of Expression in Prokaryotes

Question 1

prokaryotes ____ have specialized organelles or a ____

Answer 1

prokaryotes __dont__ have specialized organelles or a __nucleus__

Question 2

where is DNA in the prokaryotic cell?

Answer 2

in the cytoplasm

Question 3

where does mRNA and protein synthesis take place in the prokaryotic cell?

Answer 3

in cytosplasm almost same time

Question 4

how is gene expression regulated in prokaryotes? and what is the name of the model used?

Answer 4

Jacob-Monod model
operons

Question 5

What did Francois Jakob and Jaques Monod discover?

Answer 5

system by which prokaryotes can regulate mutliple genes at one time

operon - cluster of genes
- structural genes - regulation targets
- promoter site is upstream (play)
- operator site where repressors can bind and prevent RNA polymerase (on/off switch)
- regulatory gene codes for the repressor protein which can be far away from rest of operon

Question 6

How do operons regulate gene expression?

Answer 6

with repressible or inducible operons
repressible (default: always on)
- trp operon
inducible (default: always off)
- lac operon

Question 7

how does a repressible operon work?

Answer 7

repressible—-reversible— default: always on
- trp operon makes amino acid tryptophan
- operon is usually on bc repressor is inactive and the cell wants the operon active to make constant supply
- when too much tryptophan, 2 molecules bind to repressor and act as a co-repressor wihch allows the repressor to attach and turns off production
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Question 8

How does a inducible operon work?

Answer 8

—inducible— default: always off
- a smoke detector need turn on the system
- lac operon which codes for lactase enzyme
– lactose: 1 glucose, 1 galactose
–bacteria get glucose by digesting lactose but it requires extra enzymes so it would only need to do this when glucose is low since it would otherwise digest glucose

lactose high and glucose low, then isomer of lactose (alllacotose) induces the lac operon and cell makes lactase enzyme

Question 9

How are operons under positive and negative control mechanisms in lac operon?

Answer 9

lac operon is regulated by 2 proteins

neg control - binding decreases transcription
- when no lactose a repressor binds to operator site and blocks RNA polymerase
– to remove the block, an inducer binds to the repressor protein so RNA polymerase can move
— as concentration of inducer increases, it pulls more copies of repressor off the operator region and frees up genes for transcription

pos control - binding increases transcription
- when glucose low it makes cAMP and binds to catabolite activator protein (CAP protein) which binds to promoter side ( CAP site ) lac operon and recruits RNA polymerase

CAP is a transcriptional activator used by E coli that is created when glucose is low to signal alternate mechanism

Question 10

what are the differences in operon the cell when lactose is present and absent?

Answer 10