Control of gene expression

Different levels at which gene control can be exerted
(click on pic for full size image)

We started considering the mechanisms through which cell "knows" what subset of the genetic information must express in order to become the cell that it's supposed to be (a neuron, a lymphocite, a pancreatic cell, etc...). We considered the different levels at which a cell can control what proteins and RNAs are produced.

We also introduced the concept of gene regulatory proteins (a.k.a. transcription factors) and their relation to regulatory DNA sequences., and how they can read the information coded in the DNA without openeing the double helix, based solely on unambiguous chemical properties of the phosphate backbone of each base pair in the major grooves of the helix.

Material covered: pages 411-418

Reading for next class: pages 418-454

Quiz 12 Qs&As:

1. What is DNA repair?
The mechanism to correct changes in DNA sequence after transcription (after proofreading), before the information is passed to daughter cells. It is performed by a battery of enzymes, and not by a single one.

2. Mention or explain (briefly!) a way in which DNA damage can be removed
Base excision repair, nucleotide excision repair

3. What happens to DNA sequence when it is repaired by non-homologous end joining compared to when it is repaired by homologous recombination?
In non-homologous end joining one or more nucleotides of each strand are deleted.
In homologous recombination the information of the missing piece of strand can be copied from the sister chromatid and restored.

4. Which protein detects DNA damage during the transcription process?
RNA polymerase

5. What is control of gene expression?
Biochemical mechanisms to express selected genes and repress those that are not necesary