All cells have the same genome. What genes they have regulated on ＝ cell function.
Cell Differentiation | Cell Specialization
Gene Expression Regulation
Cells use gene regulation:
- to conserve energy.
- to allow cell specialization.
- to respond to environmental changes.
- Differential Gene Expression
- Allows cell specialization.
Chromatin Structure
Wrapped DNA is not accessible. Either open or closed.
- Heterochromatin
- Closed chromatin
- Not accessible DNA.
- Euchromatin
- Open chromatin.
- DNA is accessible.
Transcriptional Control
- Transcriptional Control
- Making RNA & Epigenetics
- Controls if and how much mRNA is made. Controls if chromatin is open or closed.
- Post-Transcriptional Control
- Processing mRNA
- Regulation Doesn't Stop at Transcription
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- Once mRNA is made, it can still be regulated.
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- Alternative splicing adds flexibility and speed to gene regulation.
- Efficient, so one gene can do 2 jobs quickly.
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Membrane bound antibodies detects germs - stays on the cell surface, can be secreted (released from the cell) to fight germs. It's the same gene, but differs in whether the last exon is included or not.
Transcriptional Regulation
- Epigenetics
- Epigenetics
- A process that produces huge differences in phenotypes from environmental factors that modifies genes w/o changing the genome sequence.
- Epigenetic Inheritance
- Epigenetic changes can be inherited.
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Dutch hunger winter
2 Ways Epigenetics Works
- Acetyl groups (tags) placed on histone proteins tell the chromatin to open.
- Methyl groups (tags) placed on DNA tells the chromatin to close.
Modifications (tags) influence chromatin structure:
- Tags are placed on DNA/histones
- Epigenetics influences chromatin structure
- DNA Methylation Methyl Groups (tags)
- Influences open vs closed DNA without changing DNA sequences (the A/G/C/Ts)
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- When DNA is supercoiled and not accessible for transcription, it exists as condensed heterochromatin
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- When the DNA is loosely packed and therefore accessible to the transcription machinery, it exists as euchromatin
- Histone Acetylation Acetyl Groups (tags)
- Acetyl groups are attached to an amino acid in a histone tail
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- Reduces the positive charge of the histone
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- This appears to open up the chromatin structure, thereby promoting the initiation of transcription
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When gene expression needs to be turned off, histone deacetylases (HDACs)remove acetyl groups and DNA becomes tightly wound and inaccessible again.
Post-Transcriptional Regulation
- Alternative Splicing
- One gene can make multiple proteins.
- Can't change order, can't duplicate exons.
- Different exon combinations in different cell types.
- Increases protein diversity without increasing genome size.
- One gene can produce many different proteins through the removing of exons.
- Gene Regulation
- Splicing can be regulated
- Controls which proteins are made
Translational Control
- Translational Control
- Making proteins
- Does the protein get made?
- Post-Translational Control
- Modifying proteins
- How does the protein get folded/processed?
Gene Transcription Factors
- Gene Transcription Factor Proteins Transcription Factors
- Proteins that influence whether expression starts or not.
- Combinatorial control - most genes require multiple transcription factors.
- Basal Transcription Factors
- Generic, genes are always transcribed at moderate rates.
- Activators Enhancers
- Speeds up transcription.
- Positive gene expression.
- Repressors Silencers
- Slows down transcription.
- Negative gene expression.