Download Gene expression

Control of
Eukaryotic Genes
AP Biology
2007-2008
The BIG Questions…
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How are genes turned on & off
in eukaryotes?
How do cells with the same genes
differentiate to perform completely
different, specialized functions?
AP Biology
The BIG Review

Carrying information in DNA

DNA codes for one amino acid in sets of three
(codon)

Amino acids link to form polypeptides

Genes code for polypeptides that control:
 The expression of traits (how we look)
 The function of the cell
 Other genes
AP Biology
Epigenetics
What causes cells with the same DNA
to differentiate?
There are chemical reactions which
activate and deactivate parts of the genome.

Epigenetics is the study of
these chemical reactions and
the factors that influence them.
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AP Biology
Epigenome
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A genome is the complete set of DNA.
Epi means "above". The epigenome
consists of chemical compounds that mark
the genome.
The marks tell the DNA what to do, where
to do it and when to do it.
Can be passed on from cell to cell as cells
divide, and from one generation to the
next.
AP Biology
Changes to the Epigenome
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Development (during growth)
Environmental chemicals
Drugs and medicines
Aging
Diet
AP Biology
Gene Expression
• Gene – segment of DNA
that codes for a specific
gene product
• Gene product – functional
protein or RNA molecule
• Gene expression –
using the information
in a gene to produce a
gene product
Regulation in Gene Expression
• All cells within an organism contain the same DNA
sequence
• Only a small portion of genes are expressed in a given cell
– Expressed continuously
– Expressed only when needed
– Many genes are never expressed
Regulation in Gene Expression
• Cells have the ability to regulate:
– Timing of gene expression (turn genes on and off)
– Amount of gene product produced
Process of Gene Expression
• Four major stages:
–
–
–
–
Transcription
RNA processing
RNA transport
Protein translation
Gene
Primary transcript
mRNA
• Regulation occurs
at all four stages
Protein
Regulation of Transcription
• Transcription – synthesis
of an mRNA transcript
from a gene
Gene
Primary transcript
• Regulated by:
– Structural DNA changes
– Transcription factors
– Environmental factors
Transcription Factors
• Transcription factors – proteins that bind to specific DNA
sequences to promote or suppress gene expression
• Can bind to promoter, and start or stop RNA polymerase
from binding.
Environmental Factors
• Internal factors
– Cells release signaling proteins that change gene expression
• External factors
– Temperature
– Oxygen
Regulation of RNA Processing
• RNA processing –
modification of initial
mRNA transcript to
remove sections not
needed.
Primary transcript
mRNA
• Regulated by:
– Splicing – removing
sections
– Binding and degrading
mRNA
Regulation of RNA Transport
• RNA transport – export of
mature mRNA from
nucleus to cytoplasm in
eukaryotes
• Regulated by:
– Proteins that limit the amount
of mRNA exiting the nucleus
mRNA
Regulation of Protein Translation
• Protein translation –
synthesis of a protein
from mature mRNA
transcript
• Regulated by:
– mRNA structure and
proteins that affect
translation starting
– Environmental factors
• Example: temperature
Protein
Protein Modification
• Protein structure can be
changed by the
chemicals processing
them.
• Protein folding may be
changed and protein will
be inactive.
Regulation of Gene Expression
Learning Objectives
• Describe the
process of gene
expression
• Recognize factors
that regulate gene
expression
Gene
Primary transcript
mRNA
Protein
Cellular Differentiation
Stem Cells | Differentiation Process
Cellular Differentiation
Learning Objectives
• Describe cellular differentiation
• Identify the roles of DNA, RNA, and environmental
factors in the cellular differentiation process
Stem Cells
• Stem cell – a biological
cell that can divide and
differentiate into
specialized cell types
– Includes both embryonic
and adult stem cells
• Cellular differentiation –
the process of
converting a stem cell
into a specialized cell
Differentiation Process
• Differentiation occurs
during
– Development
– Growth
– Repair
Differentiation Process
• Proteins control cell differentiation
– Direct structural changes
– Direct the cell to begin specialized functions
• Differentiation of an individual cell depends on the
involvement of DNA, RNA, and the environment
Role of DNA
• DNA can only be used when it is uncoiled
• The segments of DNA that are uncoiled determine how
the cell will differentiate
Role of RNA
• RNA controls differentiation during and after transcription
– Removes pieces of mRNA during processing, altering the protein
produced
– Binds and destroy mRNA strands, stopping protein production
Role of Environmental Factors
• Environmental factors can trigger the cell to modify gene
expression
• Internal factors
– Specialized cells send out signaling proteins that bind receptors
on stem cells
• External factors
– Temperature
– Oxygen
Using Stem Cells for Tissue Regeneration
• Tissue regeneration research is attempting to alter the
differentiation of stem cells
– Embryonic stem cells
• Only in developing embryos
– Adult stem cells
• Remain undifferentiated in adults
Using Stem Cells for Tissue Regeneration
• Scientists attempt to initiate cell differentiation using
– Biochemical signaling
agents
– Varying environmental
conditions
– Embryonic genes in
adult stem cells
Cellular Differentiation
Learning Objectives
• Describe cellular differentiation
• Identify the roles of DNA, RNA, and environmental
factors in the cellular differentiation process