Gene regulation Flashcards
all cells in an organism have the same …
…DNA sequence
regardless of their different morphology all cell types in the human body have…
…the same complement of DNA (with a couple of exceptions)
different cell types make…
…different proteins – yet proteins are the product of genes
proteins can be visualised by …
…electrophoresis
proteins can be separated by…
…electrophoresis as with DNA
proteins have different…
…charges (think of the different amino acids they are made up of)
Proteins have different charges (think of the different amino acids they are made up of) – hence we bind…
…SDS molecules to protein extracts which give proteins a uniform negative charge – an electric current separates them
same protein in both tissues is a…
…housekeeping gene
some genes are turned on in …
…all cells.
some genes are turned on in all cells
these are known as …
…housekeeping genes.
Housekeeping genes are involved in…
…processes that are fundamental to all cells – e.g. glycolysis, DNA replication, cell division control, RNA polymerases, ribosomal proteins etc
other genes are specific to…
…the individual type of cell
other genes are specific to the individual type of cell – these include genes such as those that …
…encode insulin (only expressed in β-cells of the pancreas) or CD4 which is expressed only in certain cells of the immune system
if all cells produced the same complement of proteins then they …
…could not differentiate
multicellular organisms depend upon…
…different functions being allocated to different cell types
multicellular organisms depend upon different functions being allocated to different cell types – therefore if all had the same protein complement they …
…could not do this
- If all cells produced the same complement of proteins then they could not differentiate.
- Multicellular organisms depend upon different functions being allocated to different cell types – therefore if all had the same protein complement they could not do this
- So there is a need for…
… tissue specific gene expression (proteins are encoded by genes)
- If all cells produced the same complement of proteins then they could not differentiate.
- Multicellular organisms depend upon different functions being allocated to different cell types – therefore if all had the same protein complement they could not do this
- So there is a need for tissue specific gene expression (proteins are encoded by genes).
- So multicellular organisms have …
…spatial regulation of gene expression
expression of genes can be visualised in many ways – the following experiments use a …
…‘reporter gene’ (gives a colour change) fused to the promoter of the gene being studied – introduced using ‘genetic modification’ or transformation
the gene contains the sequence that will eventually be translated into …
… a protein
the gene contains the sequence that will eventually be translated into a protein
but adjacent to this lies a region of DNA called…
…the promoter
the promoter is involved in…
…deciding when and where a gene is expressed.
The promoter consists of a DNA sequence which…
…other proteins bind to and affect recruitment of RNA polymerase
the pictures of gene expression on the previous slide and following slides are obtained by …
…putting a reporter gene onto the promoter to see when and where the gene is expressed.
the reporter gene’s product gives …
…a colour when incubated with its substrate or glows.
the reporter gene’s product gives a colour when incubated with its substrate or glows
this is then transformed into an …
…animal or plant – genetic engineering
multicellular organisms go through a process of development from a single cell to the…
…complex multicellular adult organism
at different times certain genes may need to be switched on in order for organs to…
…develop correctly
if genes are not switched on in the right place and time then development will be …
… aberrant
multicellular organisms go through a process of development from a single cell to the complex multicellular adult organism
at different times certain genes may need to be switched on in order for organs to develop correctly – if genes are not switched on in the right place and time then development will be aberrant
so multicellular organisms have …
…temporal regulation of gene expression
cells are constantly bombarded by signals from the environment such as…
…light, temperature, pathogens, toxins, nutrients, signals from other cells
Causes changes in gene expression
genes are regulated at various points in …
…transcription/translation
the promoter of the tryptophan biosynthesis genes lies …
…upstream of the gene (i.e. before the transcription start point)
it is the binding of transcription factors to the…
…operator region of the promoter that determines whether a gene is on or off
proteins bind to the …
…minor groove or major groove of DNA
hydrogen bonds form between amino acids on the …
…protein and the bases in DNA like below
proteins binding to the promoter can either …
…repress transcription or activate transcription
in the above example the tryptophan synthesis genes are turned off when …
…a repressor protein that is bound to tryptophan binds to an ‘operator’ region within the promoter in this way when tryptophan is present.
binding of tryptophan to the repressor protein causes a …
…conformational change in the repressor protein.
binding of tryptophan to the repressor protein causes a conformational change in the repressor protein.
as the protein changes shape it is able to…
…bind to the promoter and repress transcription – without tryptophan the parts of the protein involved in binding were unable to bind DNA
the binding of a protein to the promoter helps to recruit …
…RNA polymerase to the promoter and so activates transcription
– an example of both activation and repression will be seen with the lac operon
bacteria control expression of …
… catabolic operons
not all useable carbon sources are …
… always available
the preferred sugar for metabolism is…
…glucose
only when glucose is used up are …
…other catabolic operons transcribed
the lac repressor protein …
… represses transcription of the lac operon in the absence of lactose
β-galactosidase …
…catalyses the hydrolysis of lactose to glucose and galactose
β-galactoside permease …
… is a transporter protein which allows lactose to enter cell
galactoside acetylase is not…
…essential
What is Lacl?
the lac repressor protein
What is LacZ?
β-galactosidase
What is LacY?
β-galactoside permease
What is LacA?
galactoside acetylase
in the absence of lactose the repressor (LacI) …
…binds to the operator
in the absence of lactose the repressor (LacI) binds to the operator
this blocks …
…transcription of the operon
in the absence of lactose the repressor (LacI) binds to the operator
this blocks transcription of the operon because …
…RNA polymerase is unable to move past the repressor
in the absence of lactose the repressor (LacI) binds to the operator
this blocks transcription of the operon because RNA polymerase is unable to move past the repressor
because RNA polymerase is blocked…
…no transcription of the lacZ, lacY and lacA occurs.
- therefore there are no catabolic enzymes formed to break down lactose
in the absence of lactose the repressor (LacI) binds to the operator
this blocks transcription of the operon because RNA polymerase is unable to move past the repressor
because RNA polymerase is blocked, no transcription of the lacZ, lacY and lacA occurs
therefore there are no catabolic enzymes formed to break down lactose
this is energy efficient as …
…they have no substrate to work on
when lactose is present it binds to LacI which …
…changes its conformation and LacI dissociates from the operator – RNA polymerase is then able to transcribe the lac operon
Whats allolactose?
an isomer of lactose which acts as the lac inducer
this is the DNA sequence to which the Lac repressor (LacI) binds and inhibits transcription of the lac operon
note that the sequence is nearly …
…palindromic – this is a feature of many operator sequences
binding of LacI to this operator region of the promoter depends on …
…those hydrogen bonds between the amino acids of the protein and the bases of the DNA
the interaction is …
sequence specific – so LacI only binds at this point – it doesn’t stop transcription of other genes or randomly bind to DNA
when glucose is present …
…transcription is repressed
when glucose is present transcription is repressed
this is controlled by a protein called …
…CRP (cAMP receptor protein)
in the presence of glucose CRP doesn’t bind to …
…the CRP binding site
in the presence of glucose CRP doesn’t bind to the CRP binding site – because CRP is not bound then RNA polymerase will not …
…bind to the promoter
CRP requires cAMP to be bound to it in order to …
…bind to the CRP binding site
cAMP is produced from …
…ATP by adenlylate cyclase – glucose inhibits this reaction
CRP requires cAMP to be bound to it in order to bind to the CRP binding site
cAMP is produced from ATP by adenlylate cyclase – glucose inhibits this reaction.
this means that when glucose is present in the cell the amount of cAMP is …
… low
however when glucose molecules are at a low concentration inhibition of cAMP synthesis is lifted and …
…cAMP levels start to rise
when CRP is bound – as long as lactose is present – then the lac operon is …
… transcribed
the lac operon has two levels of control:
1) repression by LacI in the absence of lactose
2) activation by CRP in the absence of glucose
the transcription initiation complex (TIC) itself is a combination of…
…many different component proteins that interact with each other
binding of the core promoter in eukaryotes is accomplished by …
…TATA-binding protein
the binding of the initiation complex is itself controlled by interactions with…
…transcription factors (activators or repressors) bound to other parts of the promoter
genes are regulated at…
… many steps
- transcription of mRNA is only one of these!
