Gene regulation Flashcards
*Why is gene regulation important?
so that you don’t waste resources or energy synthesising proteins you don’t need at the moment
How does gene regulation help a bacterial cell quickly adapt?
gene regulation will switch genes on or off to adapt to the cond. of the surroundings (ie. reduce or increase synthesis of proteins in response to the cond.= survive)
How does gene regulation help cells in a human to specialise?
gene regulation controls which genes are to be switched on in a cell for it to function properly w/ other cells in the tissue (= so organ functions properly)
Explain why in some situations it may be more correct to talk about genes being “turned up” or “turned down” rather than “turned on or off”.
“turned up or down” is correct because it means expression of genes are up-/down-regulated. Genes aren’t really “turned off”, bc they can still be transcribed (& translated?) but inefficiently
What is chromatin remodeling?
- localised loosening of DNA around histone core
=> access DNA for transcription
What is an operon?
many genes in a section of DNA (in b/w a promoter & terminator) => transcribed to give polycystronic mRNA
Explain what is meant by “an inducible gene”.
Genes normally switched OFF but can be switched on by an INDUCER
Explain what is meant by “a repressible gene”
Genes normally switched ON but can be switched off by a REPRESSOR
Explain what is meant by “a constitutive gene”.
Genes that are ALWAYS ON (not regulated)
In gene regulation, explain what is meant by “positive control”.
Gene expression controlled by an ACTIVATOR
In gene regulation, explain what is meant by “negative control”.
Gene expression controlled by a REPRESSOR
What is a promoter? Is this cis acting or trans acting?
Region w/in DNA that is upstream of a gene. Types: Core & Regulatory promoter
- cis acting
What is an enhancer? Is this cis acting or trans acting?
(cis acting) DNA sequences w/in, up- / down-stream from gene & interact w/ multiple regulatory proteins & activator proteins (=> alter rate of transcription). It is specific for the PROMOTER
What are transcription factor? Are they cis acting or trans acting?
(trans-acting) bind to regulatory region = control transcription of genes
Explain how high levels of tryptophan (trp) in a cell can cause decreased expression of the operon. (through 2 lvls of control)
- Allosterically activated repressor: inducer (trp) binds to repressor => allosteric shift = can bind to operator = blocks pathway for transcription
- Attenuation: trp-charged tRNA available => ribosome moves @ quicker rate = prevent 2:3 stem-loop from forming, but 3:4 loop forms pulling mRNA out of RNA pol = transcription terminated
* =>both methods aim to stop synthesis of enzymes which make trp (bc Hi [trp])
Explain how low levels of tryptophan (trp) in a cell can cause increase expression of the operon. (through 2 lvls of control)
- Allosterically activated repressor: repressor protein can’t bind to operator = RNA pol binds to promoter => transcription
- Attenuation: trp-charged tRNA scarce => ribosome moves @ slower rate = 2:3 stem-loop forms = transcription continues
* =>both methods aim to synthesise enzymes which make trp (bc Lo [trp])
Explain the effect of Hi Lactose levels on the lac operon expression.
- repressor protein expressed
- lactose (inducer) binds to repressor => allosteric shift
- repressor can’t bins to operator => RNA pol binds => transcription => translation
- => Enzymes convert lactose into galactose & glucose
Explain the effect of Low Lactose levels on the lac operon expression.
- repressor protein expressed
- binds to operator
- RNA binds to promoter but can’t transcribe bc blocked by repressor
- ≠ no enzymes
Explain the effect of High Glucose levels on the lac operon expression.
- Glucose = decreases cAMP lvls
- cAMP - Catabolite-activitaing protein (CAP) complex can’t form
- CAP can’t bind to promoter
- Binding of RNA pol on promoter is unstable & weak ≠ transcription
Explain the effect of Low Glucose levels on the lac operon expression.
- No glucose = increase cAMP lvls
- cAMP - CAP complex forms
- complex binds to promoter
- Binding of RNA pol is stable = transcription
In lac operon control, where does the repressor protein come from?
from Lac I gene that is always expressed
In mRNA processing, what is meant by the term “alternative splicing”
- different versions of mRNA from the same pre-mRNA due to various ways it is spliced
- one gene can make many proteins
- important in development
List the genes of E.coli: Lac _ gene
i: repressor P: promoter O: operator Z: B-galactosidase > breakdown lactose Y: permease > transport lactose in the cell A: transacetylase
What are the 6 points that control gene regulation?
- DNA structure: heterochromatin/euchromatin
- (rate) Transcription
- (rate) mRNA processing
- RNA stability: half-life
- (rate) Translation
- (rate) Post-translation modification
