1. Regulation of Gene Expression by Eukaryotes

2. Gene expression in eukaryotic cells
Typical human cell: only 20% of genes expressed at any given time
Different cell types (with identical genomes) turn on different genes to carry out different functions
Differences between cell types is due to differential gene expression

3. Eukaryotic gene expression regulated at different stages

4. First stage: At the DNA level
Chromatin Structure:
Tightly bound DNA  less accessible for transcription

5. First stage: At the DNA level
DNA methylation:
Methyl groups are added to the DNA molecule
Changes the activity of a DNA segment without changing the sequence
When located in a gene promoter, it typically acts to repress gene transcription

6. First stage: At the DNA level
Histone acetylation:
acetyl groups added to histones;
Chromatin loosened;  transcription

7. Epigenetic Inheritance
Epigenome:
All of the chemical compounds that have been added to the entirety of one’s DNA
Not part of the DNA sequence
Can be inherited through the generations

8. Video: The Epigenome at a Glance
Genetic Science Learning Center
Video: The Epigenome at a Glance

9. Video: The Epigenetics of Identical Twins
Genetic Science Learning Center

10. Second stage: At the transcription level
Transcription Initiation:
Specific transcription factors (activators or repressors) bind to control elements (enhancer region)
Activators: increase transcription
Repressors: decrease transcription

11. Transcription Initiation Complex
TATA box: attracts transcription factors
Transcription factors: attracts RNA Polymerase
Enhancer: A DNA region that can be bound by activators/repressor to increase/decrease transcription

12. Cell type-specific transcription
A particular combination of control elements can activate transcription only when the appropriate activator proteins are present

13. Third stage: At the post transcriptional level
Alternate splicing of RNA
Makes it possible for a single gene to encode several polypeptide
Initiation of translation
Can be blocked by regulatory proteins that binds to sequences or structures of the mRNA
After translation
- Various types of protein processing, including cleavage and chemical modification

14. Alternate Splicing A prominent mechanism to generate protein diversity
Takes place within the nucleus either during or immediately after transcription
Particular exons of a gene may be included within or excluded from the final mRNA

15. Third stage: At the post transcriptional level
Regulation of mRNA:
Micro RNA (miRNA): Inhibit translation of mRNA
Small interfering RNA (siRNA): Cleave mRNA

16. Prokaryotic Vs. Eukaryotic
Transcription in cytoplasm
Uses operon as functional units
Regulatory gene makes repressor
DNA mRNA Protein
One mRNA codes for several proteins (Polycistronic)
Eukaryotic
Transcription in nucleus
Uses transcription factors
Regulatory gene are bound by various transcription factors
DNA PremRNA mRNA Protein
One mRNA codes for one protein