1. (CHAPTER 15- Brooker Text) October 23 & 25, 2007 Bio 184 Dr. Tom Peavy
Eukaryotic
Gene Regulation
(CHAPTER 15- Brooker Text) October 23 & 25, 2007 Bio Dr. Tom Peavy

2. Eukaryotic Gene Regulation
Transcriptional Regulation:
Regulatory transcription factors may activate or inhibit
Compaction level of chromatin influences transcription
DNA methylation (usually) inhibits transcription
(note: prokaryotes use DNA methylation but rather for
protection from invasive organisms and replication)
RNA processing to mRNA (e.g. alternative splicing)

3. REGULATORY TRANSCRIPTION FACTORS
There are two main types
General transcription factors
Required for the binding of the RNA pol to the core promoter and its progression to the elongation stage
Are necessary for basal transcription
Regulatory transcription factors
Serve to regulate the rate of transcription of nearby genes
They influence the ability of RNA pol to begin transcription of a particular gene

4. Regulatory transcription factors recognize cis regulatory elements located near the core promoter
The binding of these proteins to these elements, affects the transcription of an associated gene
activators bind enhancers
repressors bind silencers

5. Regulation of Regulatory Transcription Factors
There are three common ways that the function of regulatory transcription factors can be affected
1. Binding of an effector molecule
2. Protein-protein interactions
3. Covalent modification

6. Figure 15.5 The transcription factor can now bind to DNA
Formation of homodimers and heterodimers
Figure 15.5

7. CHANGES IN CHROMATIN STRUCTURE
Changes in chromatin structure can involve changes in the structure of DNA and/or changes in chromosomal compaction
These changes include
1. Gene amplification
2. Gene rearrangement
3. DNA methylation
4. Chromatin compaction
Uncommon ways to regulate gene expression
Common ways to regulate gene expression

8. Chromatin Structure
The three-dimensional packing of chromatin is an important parameter affecting gene expression
Chromatin is a very dynamic structure that can alternate between two conformations
Closed conformation
Chromatin is very tightly packed
Transcription may be difficult or impossible
Open conformation
Chromatin is highly extended
Transcription can take place
Variations in the degree of chromatin packing occur in eukaryotic chromosomes during interphase
During gene activation, tightly packed chromatin must be converted to an open conformation in order for transcription to occur

9. Only one strand is methylated Both strands are methylated
DNA Methylation
CH3
(or DNA methylase)
Only one strand is methylated
CH3
Both strands are methylated
Figure 15.15

10. DNA methylation usually inhibits the transcription of eukaryotic genes
Especially when it occurs in the vicinity of the promoter
In vertebrates and plants, many genes contain CpG islands near their promoters (not common
in yeast and Drosophila)
These CpG islands are 1,000 to 2,000 nucleotides long
In housekeeping genes
The CpG islands are unmethylated
Genes tend to be expressed in most cell types
In tissue-specific genes
The expression of these genes may be silenced by the methylation of CpG islands

11. Figure 15.16 Transcriptional silencing via methylation
Transcriptional activator binds to unmethylated DNA
This would inhibit the initiation of transcription
Can also cause conformational changes of chromatin

12. Stability of mRNA The stability of eukaryotic mRNA varies considerably
Several minutes to several days
The stability of mRNA can be regulated so that its half-life is shortened or lengthened
This will greatly influence the mRNA concentration
And consequently gene expression
Factors that can affect mRNA stability include
1. Length of the polyA tail
2. Destabilizing elements (e.g. AU-rich elements)

13. Initiation Factors and the Rate of Translation
Modulation of translation initiation factors is widely used to control fundamental cellular processes
Under certain conditions, it is advantageous for a cell to stop synthesizing proteins
Viral infection
So that the virus cannot manufacture viral proteins
Starvation
So that the cell conserves resources

14. (CHAPTER 3- Brooker Text)
Transmission of DNA
By Mitosis
(CHAPTER 3- Brooker Text)
BIO 184
Dr. Tom Peavy

15. Mitosis Synthesis Gap 1 Gap 2 Eukaryotic cells that are
destined to divide progress
through a series of stages
known as the cell cycle
Synthesis
Gap 1
Gap 2

16. Figure 3.6 (b)

17. Mitosis is subdivided into five phases
Prophase
Prometaphase
Metaphase
Anaphase
Telophase

18. Chromosomes are decondensed
By the end of this phase, the chromosomes have already replicated
But the six pairs of sister chromatids are not seen until prophase
The centrosome divides

19. Nuclear envelope dissociates into smaller vesicles
Centrosomes separate to opposite poles
The mitotic spindle apparatus is formed
Composed of mircotubules (MTs)

20. Spindle fibers interact with the sister chromatids
Kinetochore microtubules grow from the two poles
If they make contact with a kinetochore, the sister chromatid is “captured”
If not, the microtubule depolymerizes and retracts to the centrosome
The two kinetochores on a pair of sister chromatids are attached to kinetochore MTs on opposite poles

21. Pairs of sister chromatids align themselves along a plane called the metaphase plate
Each pair of chromatids is attached to both poles by kinetochore microtubules

22. The connection holding the sister chromatids together is broken
Each chromatid, now an individual chromosome, is linked to only one pole
As anaphase proceeds
Kinetochore MTs shorten
Chromosomes move to opposite poles

23. Chromosomes reach their respective poles and decondense
Nuclear membrane reforms to form two separate nuclei
In most cases, mitosis is quickly followed by cytokinesis

24. (CHAPTER 3- Brooker Text)
Meiosis &
Chromosomal Theory
(CHAPTER 3- Brooker Text)

25. MEIOSIS
Like mitosis, meiosis begins after a cell has progressed through interphase of the cell cycle
Unlike mitosis, meiosis involves two successive divisions
These are termed Meiosis I and II
Each of these is subdivided into
Prophase
Prometaphase
Metaphase
Anaphase
Telophase

26. Figure 3.12 Spindle apparatus complete
Chromatids attached via kinetochore microtubules
Figure 3.12

28. Bivalents are organized along the metaphase plate
Pairs of sister chromatids are aligned in a double row, rather than a single row (as in mitosis)
The arrangement is random with regards to the (blue and red) homologues
Furthermore
A pair of sister chromatids is linked to one of the poles
And the homologous pair is linked to the opposite pole
Figure 3.13

29. The two pairs of sister chromatids separate from each other
However, the connection that holds sister chromatids together does not break
Sister chromatids reach their respective poles and decondense
Nuclear envelope reforms to produce two separate nuclei