LEC 5: Regulation of Gene Expression II

Question 1

DNA Methylation

Answer 1

Transcriptionally active genes possess significantly lower levels of methylated DNA than inactive genes

• Genes that are methylated are less active
• DNA Methylation is related to the Heterochromatin formation

Question 2

Fragile X Syndrome

Answer 2

• FMR-1 gene encodes fragile X mental retardation protein (FMRP)
• Within this gene are CGG repeats, and when methylated the FMR-1 gene is silenced

Question 3

Histone Modification: Acetylation

Answer 3

Acetylation by HATs and co-activators leads to euchromatin formation (active chromatin)
- transcriptionally active

Question 4

Histone Modification: Methylation

Answer 4

Methylation by HDACs and co-repressors leads to heterochromatin formation (inactive chromatin)
- not transcriptionally active

Question 5

Gene Amplification

Answer 5

Repeated rounds of DNA replication yield multiple copies of a particular chromosomal region
- Extra copies of genes usually result in increased level of the resulting protein

Question 6

Control at Transcription Initiation

Answer 6

By using different sequences (promoter, enhancer or silencer sequences) and factors, the rate of transcription of a gene is controlled
- Temporal, Spatial, Time Controlled

Question 7

Control of mRNA Splicing

Answer 7

Splicing allows a cell to ‘swap’ exons during gene expression

• Changing the way mRNA is spliced changes the amino acid sequence in the protein made from it, thus altering protein and function
• Splicing can thus regulate gene expression in eukaryotic cells depending on health of the cell

Question 8

Calcitonin mRNA Splicing

Answer 8

Depending on how the Calcitonin gene is spliced, proteins of varying functions are produced:

• 32 AA’s: Reduces bone resorption
• 37 AA’s: Vasodilator

Question 9

Splicing and Regulating Cell Survival: Bcl-x Gene

Answer 9

Bcl-x gene responsible for the generation of 2 distinct proteins

• Anti-apoptotic or pro-apoptotic
• Extremely important gene/signalling pathway to target in cancer and neurological disorders

Question 10

Control of mRNA Stability

Answer 10

Different transcripts have different half-life which directly correlate to function and expression of gene
- The longer half-life of mRNA, more time for translation to occur and thus more proteins produced