Download The Code of Life: Topic 3

The Code of Life: Topic 4
Regulation of gene expression
What determines your phenotype?
• Gene expression!
• You have 23 pairs of
chromosomes.
• In each pair you get one from your
mother and one from your father.
• Each chromosome in a pair holds
all the same genes as the other.
• So what determines which gene is
expressed when you develop?
• ie how do you get your mother's
eyes or your father's nose?
Regulation of gene expression
starts with cell differentiation
during development.
• Selective gene
expression
– All your cells contain ALL
of your genes, they are
not split up.
– Depending on the function
of the cell, some genes
will be expressed and
some will be permanently
"turned off".
• Can you think of a gene
that is needed in red
blood cells, but not in the
pancreas?
Neuron
(nerve cell)
liver cells
muscle
cells
DNA Coiling Affects Gene Expression
Nucleosome
Chromosome
DNA
double
helix
Coils
Supercoils
Histones
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DNA is negatively charged (phosphate groups)
Histone proteins are positively charged
This makes the DNA wrap around groups (8-9) of histones
Each wrapped group is called a nucleosome
The string then coils due to further charged-region interactions
Levels of chromatin packing
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Chromatin modifications
Remember…
DNA is slightly negative
Histone proteins have positive regions
This results in coiling of the DNA, making it
difficult for enzymes to reach some portions
of the DNA for transcription and keeping
other portions exposed.
• This can be modified by two processes:
• Methylation: addition of methyl functional
groups to histone proteins.
• Acetylation: addition of acetyl functional
groups to histone proteins.
– Acetyl groups are negatively charged.
– They neutralize the histones they attach to,
so DNA will not wrap as tightly and will
uncoil.
– This exposes regions of DNA to
transcription enzymes.
Acetylation
Epigenetics
• The study of how environmental factors
can change gene expression without a
change in DNA.
• Examples:
– Diet (during development and beyond)
– Stress
– Hormones
– Chemicals
– Inheritance of methylation patterns
Extra slides
Regulation of gene expression
• Regulation occurs
at many stages:
– Chromatin coiling
and modification
– Transcription
– Processing
– Translation
Regulation of gene expression
Transcription
Alternative RNA Splicing
Gene
DNA
Exon 1 Intron Exon 2 Intron Exon 3
Transcription
RNA processing
Translation
Domain 3
Domain 2
Domain 1
Polypeptide