BI279fs Study Guide - Midterm Guide: Catabolite Repression, Lactose Permease, Adenylyl Cyclase

28 views14 pages
6 Nov 2019
Department
Course
Professor
Regulation of Gene Expression in E. coli
Gene regulation= control of the amount of product that is made from a specific gene in a
cell
Monod & Jacob found that bacteria can change gene expression based on the
environment
- Operon= a cluster of structural genes involved in a common pathway controlled
by a single regulatory region
LAC Operon: NEGATIVE INDUCIBLE
Lactose → Glucose
Lactose= inducer, when lactose binds to Lac1 expression turns ON
Default state is ON
Lac1 produces an allosteric repressor protein= negative control
-Lac Z encodes B-galactosidase
-Lac Y encodes lactose permease
-Lac A encodes transacetylase
Genetic Proof of the Operon Model:
Constitutive mutants= structural genes that are always transcribed (→enzymes)
LacI-mutant→ repressor protein can’t bind to operator (trans acting)
LacO(c)→ operator sequence is altered and repressor molecule can’t bind (cis)
Catabolite Repression: Catabolite-activating protein (CAP)- facilitates RNA pol binding
in promoter region = positive control
CAP site is before the Operator
a) No Glucose: CAP binds → transcription ON (more glucose)
b) Glucose: adenyl cyclase is blocked so no cAMP receptor, so CAP can’t bind→ no
extra glucose
TRP Operon: NEGATIVE REPRESSIBLE
five structural genes coding for enzymes involved in tryptophan synthesis
- Repressor gene upstream of operon and independently transcribed
b) No Tryptophan: denatured repressor protein → Transcription ON
c) Tryptophan: repressor binds to tryptophan operator→ Transcription OFF
ARA Operon:
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 14 pages and 3 million more documents.

Already have an account? Log in
b) AraC binds to arabinose → araB, araA, araD espression ON
c) No arabinose: AraC binds I and O site → no CAP binding Transcription OFF
Induciblue (LAC, ARA)
•Gene expression is dependent on
environmental conditions
•Inducers allow and repressors block
transcription
Repressible (TRP)
•Expression of a gene is blocked when its
product is already present
•Repressor is typically a substrate of the
enzyme encoded by the gene
•Common form of regulation in
biosynthetic (anabolic) pathways
Negative Control
-default is ON
-must be turned off with a repressor
protein (LacI, TrpR)
Positive Control
-default is OFF
-must be turned on with an activator
protein (araC, CAP)
Regulation of Gene Expression in Eukaryotes
-multiple cell types, complex life cycle, more genetic info, DNA w/ histones, 3 RNA pols,
mRNA processing, transcription in nucleus and translation in cytoplasm, mRNA decay
rates can be altered, translational and posttranslational regulation
Chromatin and Histones: transcription only when decondensed (extra regulation)
Specific DNA Sequence (cis-acting)
Binding Protein (trans-acting factor)
Promoter
General transcription factor (GTF)
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 14 pages and 3 million more documents.

Already have an account? Log in
Enhancer
Transcriptional activator (specific)
Silencer
Transcriptional repressor (specific)
Gal4/UAS System= a gene cluster that codes for proteins/enzymes in the metabolism of
galactose→ glucose
GAL4= tissue specific regulatory sequence UAS= coding sequence for an
isolated protein of interest
****Inducible transcription, positive control*******
- No Galactose:
Gal80p binds to and represses Gal4p OFF
Mig1p gets phosphorylated & sent to the nucleus, then it blocks Gal1 to
suppress expression → catabolite repression OFF
-- Glucose:
Gal3p binds galactose while also binding to and represses Gal80p this
exposes the Gal4p transcription activation domain ON
RNA INTERFERENCE (RNAi)
-discovered in plants by Fire and Mello
TWO types of short RNA molecules:
1) Small interfering RNAs (siRNA)
2) microRNAs
Dicer- cleaves long dsRNA molecules
-short ds RNA associate with RNA-induced silencing complex (RISC) 5’→3’
-RISC targets mRNAs with complementary sequences
Silenced Via:
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 14 pages and 3 million more documents.

Already have an account? Log in

Get OneClass Grade+

Unlimited access to all notes and study guides.

Grade+All Inclusive
$10 USD/m
You will be charged $120 USD upfront and auto renewed at the end of each cycle. You may cancel anytime under Payment Settings. For more information, see our Terms and Privacy.
Payments are encrypted using 256-bit SSL. Powered by Stripe.