19.2 controlling gene expression Flashcards
in what ways are genes regulated?
being turned on or off
increasing or decreasing the rate of production
why is gene regulation important?
allows for an organism to respond to different changes to the external and internal environments
what are the 4 ways of gene regulation?
transcriptional
post-transcriptional
translational
post-translational
what is transcriptional regulation?
when a gene is turned on or off
what is post-transcriptional regulation?
when the mRNA is modified to regulate translation
what is translational regulation?
when translation is tuned on or off
what is post-translational regulation?
when proteins are modified after synthesis to change their function
what is heterochromatin?
tightly wound DNA which allows DNA to be visible
what is euchromatin?
loosely wound DNA which prevents DNA from being visible
why cant DNA transcription occur in heterochromatin?
Heterochromatin is too tightly wound for RNA polymerase to operate
therefore transcription of DNA cannot occur
can euchromatin be transcribed?
as it is loosely wound, RNA polymerase can operate
therefore transcription occurs
how does euchromatin and heterochromatin regulate DNA transcription?
DNA is kept as euchromatin in interphase which allows for transcription
when in cell division, DNA is kept as heterochromatin which prevents transcription
why is the regulation of DNA transcription important?
prevents the waste of energy during protein synthesis as transcription is not happening all the time
how can histones become more negatively charged?
acetylation (adding acetyl groups)
phosphorylation (adding phosphate)
what is the effect of reducing the positive charge of a histone?
causes the DNA to coil less tightly which only allows for certain genes to be transcribed
histone (less positive with addition of acetyl/phosphate) has a weaker attraction to the negative DNA
how can histones become more hydrophobic?
methylation (adding a methyl group)
what is the effect of making the histones hydrophobic?
causes DNA to coil more tightly which prevents the transcription of genes
what is epigenetics?
the control of gene expression by modifying the DNA
what is an operon?
group of genes under the control of a regulatory mechanism
which organisms mainly have operons?
prokaryotes
why are operons useful?
by regulating protein synthesis, operons can save resources when a protein is not needed
what is the lac operon composed of?
lacZ
lacY
lacA
what is a structural gene?
section of DNA which codes for a protein/enzyme
what is a regulatory gene?
section of DNA which codes for a transcription factor
what is a transcription factor?
a protein which either switches genes on or off
on = activator
off = repressor
what is the operator?
section of DNA where the transcription factor binds to
what is the promoter?
section of DNA where the RNA polymerase binds to
what are introns?
non-coding sections of DNA
what are exons?
coding sections of DNA
which are EXPRESSED
how does a transcription factor turn on a gene?
binds to the operator in an operon to cause RNA polymerase to bind to the DNA and activate
ACTIVATOR
what role do inhibitors play with transcription factors?
they bind to transcription factors and cause a conformational change preventing it from binding to the operator
how is the lac operon turned off?
a repressor gene produces a repressor which, when bound to the operator, prevents the binding of RNA polymerase to the DNA at the promoter and thus prevents transcription
how is the lac operon turned on?
in the presence of lactose, lactose molecules bind to the repressor causing it to deactivate (by changing it’s shape) which stops it binding to the operator and allows RNA polymerase to bind to DNA at the promoter
what can increase the rate of transcription of structural genes?
cAMP
what does cAMP bind to to increase the rate of transcription?
CRP
if glucose and lactose are both present what is metabolised and why?
glucose
increase in glucose conc, decreases the cAMP conc which means less transcriptions of genes needed for lactose metabolism
what are the two methods of post-transcriptional control?
RNA processing
RNA editing
what is produced at the end of transcription?
pre-mRNA
what is RNA processing?
conversion of pre-mRNA to mature mRNA by splicing
what is splicing?
the removal of introns and the joining of exons to produce mature mRNA
what is RNA editing?
when the codons are mixed up
means that a range of proteins are produced from a single strand of mRNA
in what ways is translation controlled?
degradation of mRNA
inhibitory proteins
initiation factors
degradation of mRNA
damaged mRNA molecules cannot bind to the ribosome so translation cannot occur
inhibitory proteins
bind to mRNA to prevent it from binding to ribosomes
initiation factors
aid mRNA in binding to ribosomes
what are protein kinases?
enzymes which catalyse phosphorylation to proteins
causes a change in the protein’s structure and function
what ways is post-translational control carried out?
addition of non-protein groups
modifying amino acids
folding of proteins
modification by cAMP
how does cAMP carry out post-transcriptional control?
binds to proteins to change the tertiary structure causing it to activate or deactivate
