Transcript Document

GENE EXPRESSION
AND
UNNATURAL MANIPULATION
What would be the
outcome of not regulating
of gene expression?
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AP Ch 18
Regulation of Gene Expression
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Why don’t all cells in your body look/work the
same if all are products of mitosis from the
zygote?
How can bacterial cells differentiate/evolve
without sex or meiosis?
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How can bacterial cells differentiate/evolve
without sex or meiosis?
• mutations occur every 107 cells, E.coli make
2x1010 a day, ∴ 2000 mutants a day = a lot of
variation
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Related bacteria terms (skip
for now)
• Transformation – alter a bacteria’s genotype by
the uptake of (plasmid) DNA
• Plasmid – small, circular, self-replicating piece of
DNA
– R plasmids – special
– genes inserted
• Transduction – transfer of bacterial genes via
phages
• Conjugation – direct transfer of genetic info.
between 2 joined bacteria (pilus), like sex
• Transposons – “jumping genes” genes that move
or get duplicated into other parts of the genome
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Gene control (in bacteria)
• Operons- group of genes that controls expression,
Starts with the promoter, RNA polymerase binds
• operator turns transcription on, mRNA gets made
– repressor – protein that can stop transcription by binding
to the operator, there are also corepressors that help
– inducer – activates by inactivating the repressor (binds)
• ex. lac operon → turns on when lactose is present because
allolactose binds to the repressor, makes genes that digest
lactose
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OPERONS
•Repressible (trp) vs
inducible (lac) enzymes
• Negative vs positive
gene regulation
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Figure 18.3
trp operon
Promoter
Promoter
Genes of operon
DNA
trpE
trpR
trpD
trpC
trpB
trpA
C
B
A
Operator
Regulatory
gene
3
RNA
polymerase
Start codon
Stop codon
mRNA 5
mRNA
5
E
Protein
Inactive
repressor
D
Polypeptide subunits that make up
enzymes for tryptophan synthesis
(a) Tryptophan absent, repressor inactive, operon on
DNA
No RNA
made
mRNA
Protein
Active
repressor
Tryptophan
(corepressor)
(b) Tryptophan present, repressor active, operon off
Eukaryotic Genomes
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Signal
NUCLEUS
Chromatin
DNA
Stages in
eukaryotic
genome
expression
Chromatin modification:
DNA unpacking involving
histone acetylation and
DNA demethylation
Gene available
for transcription
Gene
Transcription
RNA
Exon
Primary transcript
Intron
RNA processing
Cap
Tail
mRNA in nucleus
Transport to cytoplasm
CYTOPLASM
mRNA in cytoplasm
Degradation
of mRNA
Translation
Polypeptide
Protein processing, such
as cleavage and
chemical modification
Degradation
of protein
Active protein
Transport to cellular
destination
Cellular function (such
as enzymatic activity,
structural support)
Gene Expression Control
• 20% of genes in humans expressed at a
given time
• control occurs at any stage from
replication to post translation
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Major Methods of Gene Regulation
How are color groups related?
1. Histone Acetylation: promotes transcription b/c it
opens tightly packed nucleosomes, giving
transcription proteins easier access (–COCH3 )
2. DNA methylation: add –CH3 groups to DNA, often
shuts genes off
3. Control elements before the coded DNA that
regulate transcription = transcription factors
4. Splicing of RNA by spliceosomes
5. Non-coding RNAs: siRNAs (small interfering RNA),
miRNAs (micro RNA) degrade transcripts or block
translation
6. Protein degradation
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Figure 18.7
Histone
tails
Amino acids
available
for chemical
modification
DNA
double
helix
Nucleosome
(end view)
(a) Histone tails protrude outward from a nucleosome
Acetylated histones
Unacetylated histones
(b) Acetylation of histone tails promotes loose chromatin
structure that permits transcription
Transcription activators
Activators
Promoter
DNA
Enhancer
Distal control
element
TATA box
Gene
Transcription activators
Promoter
Activators
DNA
Enhancer
Distal control
element
Gene
TATA box
General
transcription
factors
DNAbending
protein
Group of mediator proteins
Figure 18.10-3
Promoter
Activators
DNA
Enhancer
Distal control
element
Gene
TATA box
General
transcription
factors
DNAbending
protein
Group of mediator proteins
RNA
polymerase II
RNA
polymerase II
Transcription
initiation complex
RNA synthesis
Enhancer
Expression of different genes
in different cell types
Control
elements
Promoter
Albumin gene
Crystallin
gene
LENS CELL
NUCLEUS
LIVER CELL
NUCLEUS
Available
activators
Available
activators
Albumin gene
not expressed
Albumin gene
expressed
Crystallin gene
not expressed
(a) Liver cell
Crystallin gene
expressed
(b) Lens cell
Splicing: Regulation Method # 4
Enhancer
(distal control
elements)
DNA
Upstream
Proximal
control
elements
Transcription
start site
Exon
Intron
Exon
Intron
Downstream
Poly-A
signal
Intron Exon
Exon
Cleaved
3 end of
primary
RNA processing
transcript
Promoter
Transcription
Exon
Primary RNA
transcript
5
(pre-mRNA)
Poly-A
Transcription
signal
sequence termination
region
Intron Exon
Intron RNA
Coding segment
mRNA
G
P
AAA AAA
P P
5 Cap
5 UTR
Start
Stop
codon codon
3 UTR Poly-A
tail
3
RNA degradation: Regulation Method # 5
Regulation and gene expression
by miRNAs (micro RNA)
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RNAi–
A form of siRNA (small interfering RNA)
• Used to treat various genetically-based disorders
– Recall bio 1 Nova: Science Now video
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Cell Differentiation –
How does a cell know what job it will do?
• 250 different cell types, all from one “stem” cell,
HOW?
• Differentiation = cell becomes specialized in structure
or function
• Morphogenesis =organisms shape is established
• mice, C. elegans & fruit flies etc.. used to study
development: goal is to find a “cells lineage”
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3 Factors that influence early
development
1) Influence of the egg’s cytoplasm
• cytosol is distributed unevenly, causes
differences in the new cells
• axis of the developing egg cell
• the egg’s RNA
2) embryonic induction - chemical signals
from neighboring cells signal change
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Sources of developmental info for
the embryo
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• 3) Homeotic Genes
• hox genes, turn genes on & off
• 180 base segment, called a homeobox that is
consistent across species, evolution… p.370 and
p.445
• Apoptosis - programmed cell death, all cells are
destined to die
– -why? Essential for proper development, ex. webbed
feet, when cells go "bad"
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Why did this occur?
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Cancer:
from expression of cell cycle genes
• Oncogene- cancer causing, 1 copy is bad = cancer
• Tumor suppressor – prevent uncontrolled cell
growth, both copies must be faulty
p53- fix DNA or shut bad DNA off, 5-7
things must happen for cancer to occur
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Figure 18.24
Two different transcription pathways can result in cancerous formations
MUTATION
1 Growth
factor
Ras
3 G protein
GTP
Ras
P
P
P
P
P
P
2 Protein kinases
Hyperactive Ras protein
(product of oncogene)
issues signals on its
own.
GTP
MUTATION
3 Active
form
of p53
UV
light
2 Receptor 4 Protein kinases
(phosphorylation
cascade)
1 DNA damage
in genome
Defective or missing
transcription factor,
such as
p53, cannot
activate
transcription.
DNA
NUCLEUS
5 Transcription
factor (activator)
Protein that
inhibits
the cell cycle
DNA
Gene expression
(b) Cell cycle–inhibiting pathway
Protein that
stimulates
the cell cycle
EFFECTS OF MUTATIONS
Protein
overexpressed
Protein absent
(a) Cell cycle–stimulating pathway
Cell cycle
overstimulated
(c) Effects of mutations
Increased cell
division
Cell cycle not
inhibited
Explain one of the following
Turning proto-oncogenes into oncogenes
Proto-oncogene
DNA
Translocation or
transposition: gene
moved to new locus,
under new controls
Gene amplification:
multiple copies of
the gene
New
promoter
Normal growthstimulating
protein in excess
Point mutation:
within a control
within
element
the gene
Oncogene
Normal growth-stimulating
protein in excess
Normal growthstimulating
protein in
excess
Oncogene
Hyperactive or
degradationresistant
protein
Transcription
Chromatin modification
• Genes in highly compacted
chromatin are generally not
transcribed.
• Histone acetylation seems
to loosen chromatin structure,
enhancing transcription.
• DNA methylation generally
reduces transcription.
• Regulation of transcription initiation:
DNA control elements in enhancers bind
specific transcription factors.
Bending of the DNA enables activators to
contact proteins at the promoter, initiating
transcription.
• Coordinate regulation:
Enhancer for
Enhancer for
liver-specific genes
lens-specific genes
Chromatin modification
Transcription
RNA processing
RNA processing
• Alternative RNA splicing:
Primary RNA
transcript
mRNA
degradation
Translation
Protein processing
and degradation
mRNA
or
Translation
• Initiation of translation can be controlled
via regulation of initiation factors.
mRNA degradation
• Each mRNA has a
characteristic life span,
determined in part by
sequences in the 5 and
3 UTRs.
SUMMARY
Protein processing and degradation
• Protein processing and
degradation by proteasomes
are subject to regulation.
Quick Quiz
Quick Quiz
1. Name four ways in which genes can be
regulated.
Quick Quiz
1. Name four ways in which genes can be
regulated.
2. What chemical group would bind up a strand
of DNA inhibiting transcription?
Quick Quiz
1. Name four ways in which genes can be
regulated.
2. What chemical group would bind up a strand
of DNA inhibiting transcription?
3. What would be the effect of reordering hox
genes?
Quick Quiz
1. Name four ways in which genes can be
regulated.
2. What chemical group would bind up a strand
of DNA inhibiting transcription?
3. What would be the effect of reordering hox
genes?
4. Name four structures that participate in
transcription regulation in eukaryotes.
Quick Quiz
1. Name four ways in which genes can be
regulated.
2. What chemical group would bind up a strand
of DNA inhibiting transcription?
3. What would be the effect of reordering hox
genes?
4. Name four structures that participate in
transcription regulation in eukaryotes.
5. What does the operon include?
6. How can RNAi be used to fight disease?
Quick Quiz
1. Name four ways in which genes can be
regulated. Slide 14
2. What chemical group would bind up a strand of
DNA inhibiting transcription? 14-15
3. What would be the effect of reordering hox
genes? 28
4. Name four structures that participate in
transcription regulation in eukaryotes. 18
5. What does the operon include? 9
6. How can RNAi be used to fight disease? vid