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Lecture23 (Brandl1).docx

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Biochemistry 2280A
Eric Ball

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Lecture 1 – Brandl Gene Expression DNA – the blueprint of life:  Information is stored in DNA in the form of genes  The human genome encodes ~25,000 different protein encoding genes  In any one cell type ~5000 to 10,000 are expressed at various levels  The expression of the correct genes is essential for growth and differentiation of all cells Significance of Gene Expression:  Most disease states result from alterations in gene expression of one or more genes  Too much or too little can lead to a disease state o In cancers, many tumor suppressors (proteins required for the prevention of cancer) and oncogenes (a gene that makes a cell cancerous) are transcription factors  By manipulating gene expression, we have the potential to prevent or reverse disease The Central Dogma:  DNA  RNA  protein  Why have this RNA step? Why can’t we go from DNA to protein? 1. The RNA step allows genes to be expressed at different levels - Get a lot of RNA from this one gene - Allows an amplification  unlike DNA where unit copies exist, the RNAs for different messages can be produced at different levels 2. RNA allows expression of a gene to be stopped quickly because it can be rapidly degraded – is unstable in the cellular environment, unlike DNA - Rapid degradation provides a mechanism to turn genes off – quick and efficient 3. RNA provides additional opportunities to regulate the expression of genes - Provides many other steps for amplification There are 2 steps at which genes can be regulated?  False there are many more than two steps in gene expression Points at which gene expression can be regulated in a eukaryotic cell: 1. Transcription – initiation - Principle site of regulation 2. Transcription – elongation 3. Transcription – termination 4. RNA editing (Type of RNA processing) a. Some RNAs can be modified to change genetic code b. Breaks central dogma 5. 5’ capping (RNA processing) 6. Splicing (RNA processing) 7. 3’ polyadenylation (RNA processing) 8. mRNA export - Numerous proteins involved - Highly regulated, active process - Key cite of regulation for a number of genes - Does not happen in prokaryotes because no nucleus so does not need to be exported out 9. Translation - Initiation, elongation, termination - Is a key point for gene regulation 10. mRNA degradation - How quickly it is degraded has an important effect - Key in the amount of gene expression 11. Protein modification - In many cases, the protein has to be modified to be functional - E.g. proteolytic cleavage to activate a protein (insulin), phosphorylation (addition of a covalent phosphate group from ATP), glycosylation (addition of one or more sugar moieties), acetylation (addition of an acetyl group) 12. Protein degradation - Loss of the protein or turnover - The amount of protein present is determined by the balance of its rate of synthesis and its rate of loss *The first step in a biological process is often highly regulated as it saves the energy required in the subsequent steps* - if you regulate the D  E step instead of A  B, the cell would consume 2ATP unnecessarily Transcription – significance:  Because transcription is the first step in gene expression, it is often highly regulated  Many genes are regulated at the level of transcription  Many diseases result from defects in transcription factors (cancer)  The specificity of many transcription factors makes them logical drug targets  Mess up transcription, cell programming goes off, and that results in cancer  If we can affect transcription factors and modify their activity, maybe we can cure disease Prokaryotic Transcription:  Mechanistically, it is very similar to eukaryotic transcription Terminology:  Promoter: the DNA sequence required to specifically initiate transcription of a gene (or operon) o The promoter includes the sequences that recognize RNA polymerase
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