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Regulation of Gene Expression - Prokayotes
Chapter 17
12
Biology
Undergraduate 3
11/16/2013

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Term
Describe the levels at which gene expressions is regulated in prokaryotes
Definition
1. Transcription - DNA
2. RNA processing - RNA
3. RNA stability - mRNA
4. Translation - protein
5. Post-translational- function performed by protein
Term
Describe the following genes

1. Housekeeping
2. Regulated
3. Induced
4. Repressed
5. Regulator
Definition
1. always turned on (rRNAs, tRNAs, structural proteins)
2. usually have specific function (growth, defense)
3. normally off but can turn on when needed
-catabolism
-turns on when food is present (lac operon)
4. normally high but can be turned off
-anabolism
-maintaining growth (tryptophan)
5. control expression of inducers and repressors
Term
Describe Positive Control of Gene Regulation
Definition
-regulator gene product is called an activator
-bind to regulator protein binding sites and INCREASE transcriptional output
-influenced by effector molecules ->from environment
ex. inducers- inactive->activated trxn
ex. corepressors- active -> inactive (decreases trxn)

Changes can be
1. induced fit
2. translocation- place protein into nucleus so it can bind to DNA
3. sequestration- release inhibitory protein so activator can bind to DNA
Term
Describe Negative Control of Gene Regulation
Definition
-regular gene product called repressor
-bind to regulator protein binding sites and DECREASE transcriptional output
-influenced by effector molecules-> from environment

inducer- de-repressed
corepressor- repressed
Term
Describe Operons
Definition
promoter+operator+gene

-genes with related functions that are grouped in a unit
-regulated by repressor gene that binds to operator and prevents polymerase from binding and transcribing
Term
Describe the Lac Operon

1. Classification
2. Repressor
3. Inducer
4. Glucose
5. cAMP
Definition
1. Negatively controlled induced operon-derepressed
2. LacI gene (binds to OPERATOR and allows polymerase to bind)
3. Allolactose- bind to LacI protein repressor
-changes shape of protein and it falls off
-polymerase can come in and transcribe
4. Glucose effect- when glucose is present, lac operon stays off
-inhibits adenylcyclases->> makes cAMP
5. inducer of lac operon- binds to catabolite activator protein (CAP-binds to PROMOTER and activates gene)
Glucose high- low cAMP > no trxn
Glucose low- high cAMP > trxn
Term
Describe the Tryp Operon- Negative Control

1. Classification
2. Repressor
3. Corepressor
Definition
1. negative control of repressed system
2. TrypR
3. Tryptophan
-binds to TrypR and stops polymerase from binding, stopping transcription
Term
Describe the Tryp Operon- Attenuation

1. Discovery
2. Binding Regions
3. Summary
Definition
1. deleted TrypR and there was still repression
2. Region 3 and 4 can bind leading to hairpin - ending transcription of gene
-Region 2 and 3 can bind, preventing hairpin
3. Without tryp, polymerase will stall at trpL peptide
-2 can then bind to 3, preventing hairpin
-polymerase can bind and continue to trxn
-with excess tryp, polymerase will finish trypL
-3 and 4 will bind, creating hairpin, ending trxn and preventing more tryp from being produced
Term
Describe Temporal Control of Gene Expression
Definition
SP01 Bacteriophage -> B. subtilis
-early genes transcribed by host
-middle genes turn off early
-other genes turn off middle and turn on late
Term
Describe Translation Control of Gene Expression
Definition
-stop mRNA from being turned into protein
-mRNA can be degraded or wait around until ready to be translated
*allows for more specific stopping point and more control
Term
Describe Translation Control in E. coli
Definition
-ribosomal proteins need to be equal to amount of rRNA

1. S10 transcript- ribosomal protein that can build up in excess
2. L4 is protein that can build up and stop translation
-binds to 5' end of mRNA and inhibits translation
-as it builds up, ribosomal proteins will stop being produced
-when it slows down, it will bind to rRNA and continue
Term
Describe Post Translational Control- Feedback Inhibition
Definition
-occurs when product of pathway binds inhibits activity of first enzyme in the pathway
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