Biochemistry 2280A Lecture 17: Biochem 2280 Topics 17 and 18
28 Feb 2017
School
Department
Course
Professor
Topics 17-18
3 major topics
1) Gene expression (about 5 lectures)
2) Recombinant DNA technology (about 7 lectures)
3) Molecular basis of cancer (about 2 lectures)
Read tb and course notes – ALL are testable
Look at learning modules
Garland science ECB resources – vids, flashcards, and quizzes
Gene Expression
- The human genome encodes about 21,000 protein encoding genes
- In any cell type less than 10000 are expressed
- Genes are expressed at diff levels
- The expression of the correct genes is essential or growth and differentiation
Diff cell types express diff genes
- In the brain there is a protein that is highly expressed and in the liver the protein isn’t highly
expressed or not any at all
Significance of gene expression
- Most diseases are due to altered expression of one or more genes
- By therapeutically manipulating gene expression we have the potentially to prevent or
reverse the disease
The central dogma – DNA → RNA → protein
Q: at how many steps can gene expression be regulated in a eukaryotic cell?
A:
a) 2
b) 3-8
c) >8
14 steps
1) Transcription
- Initiation
- Elongation
- Termination
2) RNA processing (pre mRNA becomes mRNA)
- RNa editing
- 5’ capping
- splicing
- 3’ Polyadenylation
3) RNa export from the nucleus to the cytoplasm
- Highly _________ and can be regulated
find more resources at oneclass.com
find more resources at oneclass.com
4) mRNA degradation
- The amount of mRNA found in a cell depends on both its rate of synthesis and its rate of decay
- translation (RNa → protein )
o initiation
o elongation
o termination
- proteon modification
o phosphorylation
o acetylation
o cleavage (insulin)
- protein degration
o the amount of protein in a cell depends on both its rate of synthesis and its rate of
decay
why is there an RNA step in Gene expression?
- why cant we go from DNA to protein?
- 1) The RNA steps provides an amplification which contributes to differential gene
expression
- Why cant we amplify DNA? – it means lots of genome space wich is selected against
- 2) since RNA can be degraded, expression of a gene can be stopped quickly – stop signal
o cant eliminate DNA but you can eliminate RNA
- 3) rna provides additional opportunities to regulate gene expression e.eg,
o RNa processing
o RNa export from the nucleus
TRANSCRIPTION - is the first step in the expression of any gene and is often the most frequently
regulated step in the gene expression
• we are going to focus on prokaryotic transcription
• Gene and promoter structure, RNA polymerase, mechanism of trans, regulation of trans (trp
and lac operon
• Promoter: the DNA sequence required to initiate transcription of a gene or operon
• Terminator: the DNA sequence requires to stop transcription
• Operon: a set of genes transcribed from a single promoter and thus expressed from a
common RNA
• Consensus sequence: the most frequent base at each position in a group of functionally
related DNA elements – something you generate
Clicker Q: What is the consensus sequence for the DNA
element on the left?
(Add pic)
c) TGACTCA – most frequent base at the first position is
T, etc
In this example none of the elements are the same as the
consensus sequence
find more resources at oneclass.com
find more resources at oneclass.com
Bacterial operon structure
What are the key features of bacterial promoter?
+1 – start sight of transcription
-10
-35
There are no 0 in numbering genes
-10 and -35 are consensus sequences – they are centered at -35 and -10
The -10 and -35 sequences were found by comparing the sequences of many e coli promoters
• Common elements would suggest functional importance
A group of e coli promoter sequences were aligned maximising the similarly
- The numbers under the bases are percentages (e.g., 77% of the time was T)
You test if the -35 sequences is important by making mutations
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
3 major topics: gene expression (about 5 lectures, recombinant dna technology (about 7 lectures, molecular basis of cancer (about 2 lectures) Read tb and course notes all are testable. Garland science ecb resources vids, flashcards, and quizzes. The human genome encodes about 21,000 protein encoding genes. In any cell type less than 10000 are expressed. The expression of the correct genes is essential or growth and differentiation. In the brain there is a protein that is highly expressed and in the liver the protein isn"t highly expressed or not any at all. Most diseases are due to altered expression of one or more genes. By therapeutically manipulating gene expression we have the potentially to prevent or reverse the disease. The central dogma dna rna protein. Termination: rna processing (pre mrna becomes mrna) 3" polyadenylation splicing: rna export from the nucleus to the cytoplasm. Highly _________ and can be regulated: mrna degradation.
