Chapter 18 (Genetic Regulation) Flashcards by Neelam Chaud

Why do cells need gene regulation?

all genes can’t be expressed at the same time

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When are genes expressed in a cell?

When a cell needs it for the work that has to be done at any given moment

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Gene expression is altered in response to what?

any change in the environment

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Which are more responsive to their environment, single-celled organisms or multi-celled organisms and why?

single-celled organisms (prokaryotes) because they have to focus on internal and external environments

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What does gene regulation affect in multi-celled organisms in many steps?

development, cell differentiation, internal environments

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What can genes do to enzymes?

stop their formation so that there is potential for an enzymatic pathway to be shut down

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What are operons?

a genetic regulatory system in PROKARYOTES

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Where can operons be found?

in bacterial/prokaryotic cells ONLY

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Why did the operon system get developed in the first place?

structure of the genome in a prokaryotic cell, the genes are located in a given area (packed together)

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What are the components of operons?

operators and repressors

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What are operators?

highly conserved series of nucleotides (DNA-based) where the repressor protein binds in order to block RNA polymerase from working

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Where are operators found?

after the promoter region of the gene in question

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What are promotors regions?

portions on transcription starting sites that regulate the initiation transcription of the gene by controlling where RNA polymerase binds

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What does the repressor protein do?

represses gene transcription (turns off operon)

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What is the repressor protein?

the gene product of a separate regulatory gene (transcribed first at 5, upstream)

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Where is the repressor protein gene located?

5’ end, upstream

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How does the repressor protein inhibit the operon?

binds to the operator and inhibits RNA polymerase

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By what process is the repressor protein regulated?

allosterically (active or inactive)

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How is the repressor protein regulated?

a corepressor activates the repressor protein and an inducer inhibits the repressor protein

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What are the types of operons?

inducible and repressible

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What kind of gene regulation are the two operons?

negative gene regulation

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What is gene regulation?

ability to stop gene transcription (flipping switch off)

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Is the inducible operon active or inactive?

inactive

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What does the activity of the inducible operon rely on?

the activity level of the repressor protein

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What happens in an inducible operon?

binding of inducer inactivates the repressor and turns on transcription

Is the repressor protein naturally active or inactive?

inactive

What is the inducible operon used for?

catabolic needs

Are repressible operons on or off?

on most of the time

What happens in the repressible operons?

binding of a repressor to the operator shuts off transcription

What do cells utilize repressible operon for?

anabolic needs (stuff that is made all the time but is made a little too much at a certain time)

What is an example of a repressible operon?

trp operon

What is tryptophan?

amino acid for growth

Are tryp genes on or off most of the time?

on because the cell needs the tryptophan amino acid

Is the repressor for trp operon off or on?

can be in the inactive or active form

What is the corepressor for tryptophan production?

tryptophan itself (like feedback inhibition)

When is the trp operon turned off?

when there is too much tryptophan in the cell

What is an example of inducible operons?

lactose operon

What is lactose?

sugar source that is not always available to the cell

What do lac operon genes code for?

enzymes that hydrolyze lactose

Is the lac operon usually off or on?

repressed and no enzymes made until the presence of allolactose

Is the lac repressor protein active or inactive most of the time?

active

What activates the repressor protein in the lac operon?

allolactose

What kind of regulation can the lac operon do?

positive and negative regulation

How can the lac operon have positive regulation?

making more of operons so more enzymes are made to break down lactose

What is RNA polymerase?

needed to start transcription

What is a promotor?

the sequence of DNA that RNA polymerase binds (acts like a primer)

What is the trp operon essential for?

production of tryptophan

Where is trp operon located?

on e. coli bacteria in the intestines

Where does the RNA polymerase bind?

promotor region

What does the e.coli bacteria need?

tryptophan

What happens in the trp operon if there is low tryptophan?

the repressor protein isn't bound to the operator and allows RNA polymerase to transcribe the mRNA for tryptophan (inactive)

What happens in the trp operon if there is too high of tryptophan?

tryptophan acts as a corepressor and binds to detached repressor protein, the complex then binds to operon to block RNA polymerase (active), feedback inhibition-like

What kind of operon is the lac operon?

inducible operon

What does the lac operon code for?

enzymes involved in breaking down lactose (sugar)

What does the lac operon do if there is no lactose?

repressor protein bound to lac operator to prevent any breakdown of lactose by blocking RNA polymerase

What does the lac operon do if there is too much lactose?

allolactose (isomer of lactose) acts as inducer and binds to repressor protein and detatches the complex from operator for RNA polymerase to start

What happens to the lac operon if there is little glucose and lactose?

allolactose binds to repressor protein to induce lac operon and cap protein binds to cap site to further enhance activation/transcription to break down lactose

What happens to lac operon if there is more glucose and more lactose?

allolactose binds to repressor protein to induce RNA polymerase to transcribe, but cap protein doesn't bind to cap site so LESS transcription

What are transcription factors?

proteins found at operon that bind to a site on DNA to activate transcription

What do transcription factors rely on?

RNA polymerase

What are activators?

found at promotor region that increases transcription (ex: CAP)

All cells have what type of genome?

the same type of genome, but depends on what gene is activated or not

What is gene silencing?

genes switched off where only small fraction of DNA codes for proteins

What does microRNA do?

single-stranded RNA molecules that can bind to mRNA to turn off genes

How is miRNA made?

dicer protein chops up the primary transcript of double-stranded RNA and splits into 1 strand

How is RISC complex made?

RISC complex picks up miRNA pieces

What does the RISC complex do?

slices single-stranded RNA to make it stop producing amino acids