SCIE1106 Lecture Notes - Lecture 20: Rna Splicing, Cistron, Operon
L20 Gene regulation
•
Diff between gene regulation, in Pro vs Eu
•
Effect, Reasons for gene regulations
•
4 ways the cell can control the proteins it makes
•
Basic principles of coordinate regulation,
catabolic vs anabolic pathways, +ve vs –ve
regulation
•
Describe tryptophan operon of E.Ccoli and its –ve
regulation using diagrams
•
Operon, promoter, operator, repressor &
polycistronic mRNA
Promoter – a DNA sequence, that RNA polymerase binds
to, to open the DNA double helix and start transcription
(make mRNA)
Operator – short region of DNA within the promoter
sequence, in which the repressor protein binds to.
Operator controls expression of genes adjacent to it, in the
operon
Repressor – a protein, that binds to an operator sequence,
to prevent transcription of adjacent genes in the operon
Genes can be
1. Constitutive genes
• Are genes expressed as essential for the
basics of life
o DNA synthesis
o DNA replication
o DNA repair
o RNA synthesis
o Protein synthesis
2. Contigency genes
• Genes that are products that confer/give an
advantage under special conditions ( genes
that are needed in special conditions )
o Heat stress
o pH stress
o starvation
o Carbon source availability
Gene regulation differences
Prokaryotes(bacteria)
Eukaryotes (fungi,
animals, Protista,
plantae)
Purpose of gene
control
Provide maximum
growth
Regulate
development, and
differentiation into
different
tissues/organs
Challenges
encountered
Continual changes in
environment (hot,
cold, pH)
Constant
environment
Range of gene
expression
Total switch-off is rare,
off= refers to low
basal level
Complete turn off
of gene
Production of
mRNA
Coupled transcription
+ translation in
cytoplasm.
Mono/ Polycistronic
mRNA
Transcription in
nucleosome
RNA splicing in
nucleus
mRNA translated
in cytoplasm
Regulation of Gene activity
in Prokaryotes
Effect, Reason, Mechanisms (how it regulates)
Effect
# proteins produced / unit time, by active genes,
varies from gene to gene, and varies in response to
the environment.
Reason
To satisfy needs (to grow and survive) of the cell, but
to avoid waste
Don’t produce E when cells don’t need E as it’ll waste
E
1. Molecules that are only needed occasionally,
are synthesized only when needed
2. For e.g cell chooses 1 E prod pathway out of
2 that yields the most E
3. An enzyme that consumes the substrate of a
2nd enzyme, is inhibited if end product of 2nd
enzyme is required
Mechanisms (how)
Transcription and Translation, can be regulated
Common principle → on/off regulation , on when
needed off when not needed
Types of control mechanisms
1. Transcriptional control- Control when/how
often, a given gene is transcribed (going to be
transcribed? Not transcribed? To what
level?)
2. RNA processing control – control how RNA
transcript is spliced / processed
3. Translational control – select which mRNAs
in the cytoplasm are translated by ribosomes
(how efficiently/rapidly)
4. Post translational control – protein activity :
active/inactive proteins after they’ve been
made
For prokaryotes, Transcription initiation is the most
important of control
find more resources at oneclass.com
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Document Summary
Promoter a dna sequence, that rna polymerase binds. Operator short region of dna within the promoter. Repressor a protein, that binds to an operator sequence, sequence, in which the repressor protein binds to. Operator controls expression of genes adjacent to it, in the operon to, to open the dna double helix and start transcription (make mrna) to prevent transcription of adjacent genes in the operon. Total switch-off is rare, off= refers to low basal level. Rna splicing in nucleus mrna translated in cytoplasm. # proteins produced / unit time, by active genes, varies from gene to gene, and varies in response to the environment. To satisfy needs (to grow and survive) of the cell, but to avoid waste don"t produce e when cells don"t need e as it"ll waste. E: molecules that are only needed occasionally, are synthesized only when needed, for e. g cell chooses 1 e prod pathway out of.
