Transcript Ch 15 - .Gene Regulation

Ch 15 - .Gene Regulation
 Prokaryote



Regulation
Operon * not found in eukaryotes
Regulator gene = codes for repressor. Active
repressor binds to operon
Promoter – where RNA polymerase attaches
2 types of regulators
 Repressible

operon
1 – always “on” = repressor cannot bind,
therefore RNA polymerase can attach and
protein is made.
• Ex. Trp operon
-To turn off the protein product binds to repressor =
repressor can bind & transcription ceases
Inducible Operon
2
– always “off” = repressor can always
bind therefore RNA polymerase cannot
attach = no protein produced

Ex. Lac operon
Presence of molecule (inducer)
turns on transcription by binding
to lac repressor to disable
binding.
Eukaryotic Regulation
–
allows differential protein expression
dependent on specialized function of cell.
5
ways [3** within the nucleus &
2## in the cytoplasm]
 1**
– chromatin structure – packaging
makes RNA [epigenetic] polymerase
binding impossible * cancer results when
mutations occur in transcriptional factor
genes.
2** – Transcriptional control –
[transcription factors- proteins
that initiate RNA pol. binding]
once a gene is unpackaged it
will be transcribed. (transposons
shut down genes by interrupting
code, gene jumping, also
encourages mutations)
3** – posttranscriptional
control-mRNA processing
excising introns
4## - translational control –
poly a tail protects mRNA from
being degraded & allows for
translation
5## - Posttranslational control
– modification of a protein after
synthesis determines biological
activity.
Chromatin Structure
 DNA
wrapped around 8 histones
 DNA = histone = nucleosomes
 Highly condensed = heterochromatin –
inactive, methyl groups
 Loosely condensed = euchromatin – active
* have attached acetyl group. DNA can be
methylated = not expressed can be
inherited that way
KINASES
 Proteins
that dephosphorylate to signal
protein expressions in membrane to
nucleus regulatory pathway
TRANSPOSONS
 Jumping
genes of repetitive sequence that
interrupt gene expression
GENETIC MUTATIONS- good,
bad, non effective
1-germline → passed on
2- somatic → not passed on → cancer
MUTATIONS
[causes- spontaneous, environ.
mutagens, inherited0
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Point Mutations- Change a single base→
change codon
Frame shift mutations- deletion or addition
result in a completely new amino acid
sequence.
Mutations in proto-oncogenes or tumor
suppressor →cancer
Study Questions
 What
part of mRNA sections are spliced
together into the finished mRNA
molecules?
 What are 4 potential control mechanisms
for regulation of gene expression in
eukaryotic organisms?
 What is the correct order of protein
synthesis?
Study Questions
 What
is the role of DNA in controlling
cellular activity?
 What word describes the attachment of
groups of particular amino acids of specific
proteins to nucleosomes as thought to be
an important control mechanism for gene
expression?
 Define the term gene
Study Questions
 The
expression of genes can be controlled
at what 4 stages of protein synthesis?