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GTS 351 summary
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Summaries for chapters 1 and 2, some hand written notes from a Practical and some example MCQs
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Chromosomes and Gene Maps
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Study unit 1 'Sunday, 05 March 2017 11:54
Notes are note complete but do go into some detail for chapters 1 and 2. There are example
questions and hand written notes at the end from a prac. The Module might have changed slightly
but I hope these notes might help you. The notes will be free to access due to the incomplete nature
of the notes.
GTS 51 Page 1
,Intro lecture
Sunday, 12 February 2017 16:31
Levels of Gene Control:
There are 4 control points in gene expression :
1. transcription
2. Post transcription processing
3. Functional mRNA transported to cytosol
4. Translation
• Expression of genes are primarily regulated a the transcriptional level. The control mechanisms
dictate which genes will be switched on by initiating transcription in the nucleus. This will
dictate how much mRNA will be transcribed by the RNA polymerase using genomic DNA as a
template.
• Regulation can also occur at the post-transcriptional level. Control mechanisms that
determines how pre-mRNAs are processed (Via capping, splicing and polyadenylation) into
mature mRNAs and subsequently transported to the cytoplasm. mRNA splicing and stability
(degradation) may play a role
Genes may be regulated at the level of transcription initiation or mRNA stability
• Mrna abundance does not necessarily indicate control at initiation of gene transcription
• Steady-state abundance depends on the rate of mrna synthesis (control at transcription
initiation) as well as the rate if decay that takes place in the nucleus . Mrna stabilities vary
widely with half-lives ranging from 15 minutes to 10 hours. Intrinsic stability can have
profound influence on abundance of specific mrna. i.e. abundance of protein
• Assays are available to determine if the gene is regulated at transcription initiation, post
transcriptional level or mrna stability level
Techniques to study the rate of mrna synthesis
1. Pulse labelling : the synthesis of RNA from DNA by RNA polymerase involves the incorporation
of ribonucleotides into an RNA chain. The synthesis of RNA can be measured by adding
radioactive ribonucleotides (usually uridine labelled with tritium ) to the cells and measuring
how much radioactivity is incorporated into RNA specific for the gene of interest. The
incorporation of radioactivity into newly synthesised mrna for a short time called a pulse. RNA
is purified from the cells and analysed by hybridisation. The rate of transcription is measured
by exposing cells briefly to the labeled uridine in a process referred to as pulse labeling
a. This method provides the most direct method of measuring transcription. It shows the
induction of globin production that occurs in friend erythroleukemia cells in response to
treatment with dimethyl sulfoxide
b. This method provides a direct measure of transcription rates, the requirement to use
very short labeling times to minimize any effects of rna degradation limits its
applicability . With many rna species the rates of transcription are insufficient to provide
measurable incorporation of label in the short pulse time
2. Nuclear run-on transcription assay: similar to pulse labeling but the radioactive pulse is
performed within isolated nuclei of the cell. Isolated rna is also analysed by hybridisation.
a. Isolated nuclei from cells, add radioactively labelled nucleotide to the isolated nuclei.
After 1-2 hours isolated rna from nuclei (including labelled rna produced by transcribing
polymerase running on to the end of the gene) hybridized labelled RNA to dot blot
containing DNA from genes whose transcription is being measured
GTS 51 Page 2
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GTS 51 Page 3
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