Cell Biology: Chapter 7

DNA

every cell in your body has the exact same

3-5%

how many geenes are expressed at a time?

differentiation

long-term control of gene expression in tissue

regulation at transcription; regulation after transcription

ho to prevent expression?

turned off and on just like a light switch

based on needs, proteins being produced can be

regulatory genes

required to initiate (turn on or off) the expression

regulatory genes

regulatory proteins that bind to DNA to either block or stimulate transcription, depending on how they interact with RNA polymerase

constitutive expression

genes that are continuously expressed

housekeeping genes

genes that have constitutive expression i.e. Actin, GAPDH

induction and repression

genes that fluctuate in response to the external signals

gene

small scale chromatin regulation

chromosome

large scale chromatin regulation

heterochromatin

condensed; non-ecpressed

euchromatin

relaxed; expressed

Barr bodies

example of whole-chromosome regulation (X in females)

Eurkaryotic method of regulating transcription

• Activator proteins

  • promoters

prokaryotic method of regulating transcription

• operators

• promoters

• repressor protein

Eukaryotic method of regulation

splicing of mRNA

negatibe control

an active regulatory protein turns transcription OFF

induction

signal molecule turns the operon on

repression

signal molecule turns the operon offposi

positive control

an active regulatory protein enhances the rate of transcription

induction

signal molecule makes the regulatory protein active

repression

signal molecule makes the regulatory protein inactive

regulated

control the speed/amount

gene expression

using the information from a gene to express a protein

regulated gene expression

how a cell controls the speed or amount of a gene being expressed as a protein

prokaryotic transcription regulation

• several related genes can be transcribed together

• need RNA Polymerase to recognize a promoter region

eukaryotic transcription regulation

• genes are nearly always transcribed individually

• 3 RNA polymerases occur, requiring multiple proteins to initiate transcription

activivator protein

molecule that turns ON transcription

transcription factors

molecules that allows RNA Polymerase to bind to DNA and begin transcription

promoter

sequence on DNA before the gene where the activator proteins and transcription factors to bind to

enhancer

control element far from a gene or intron

activator

bind to enhancers to turn on transcription of a gene

transcription initiation complex

transcription factors + enhancer + activator + RNA Polymerase II

Repressors

inhibit gene expression

• turn off transcription

• block activators from binding to enhancers

control elements

DNA sequences that react with proteins to facilitate the binding of RNA polymerase

promoter; regulator sequences; enhancer sequences

RNA polymerase interacts with ___, ___ ___, and ___ ___ to begin transcription

regulatory proteins

bind to regulator sequences to activate transcription

• found prior to promoter

activator proteins

enhancer sequences bind

• typically far from the gene

silencer sequences

stop transcription if they bind with repressor proteins

alternative splicing

shuffling exons

Post-Transcription Regulation

• have mRNA variation

• change the lifespan of mRNA

• edit RNA and change the polypeptide produced

mRNA variation

• alternative splicing

• allows various proteins to be produced in different tissues from the same gene

change the lifespan of mRNA

produce micro RNA that will damage mRNA, preventing translation

edit RNA and change the polypeptide produced

insert or alter the genetic code

after transcription

portions of transcribed mRNA is spliced (cut out)

exons

the portions of the gene on mRNA that are cut, translated, and EXPRESS proteins

intron

the portions of the gene on mRNA that do not code for proteins and are NOT expressed

protein

spliced exons code for

alternative RNA Splicing

different regions of the pre-mRNA serve as introns or exons creating different mRNA strands depending on what is removed and spliced together

increases the number of different proteins

different exons are recombined in different ways for certain mRNAs

domains

proteins often have a modular architecture consisting of discrete regions

different domains

different exons code for

exon shuffling

may result in the evolution of new proteins

mutation

long term gene regulation

mRNA Degradation in prokaryotes

• short life span

• degraded in seconds

• allows rapid response to environmental changes

mRNA Degradation in eukaryotes

• survive from hours to weeks

• internal conditions constant, no need for rapid response

ubiquitin

target for breakdown via proteasome

proteasome

woodchipper

translation regulation

modify lifespan of proteins

modify the lifespan of proteins

attach ubiquitin

operon

grouped gened that are transcribed together—code for functionally similar proteins

prokaryotic gene expression key players

• promoter

• operator

• repressor protein

• regulatory gene

  • structural genes

negative gene regulation

repressible; inducible

lac operon

inducible; only turned on if lactose “eaten” lactose is not mecessary for the cell to function

Trp operon

repressible; always making tryptophan repressed iftryptophan is “eaten” tryptophan is necessary for the cell function

feedback inhibition

enough product is made the system shuts down