chapter 10: molecular biology of gene expression jones and bartlett publishers © 2005
TRANSCRIPT
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Chapter 10:
Molecular Biology of
Gene Expression
Jones and Bartlett Publishers © 2005
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Chapter 10.1- 10.3
• Details of the central dogma will be discussed in Chapter 10.
• For Exam 3, we will cover up through p. 408.
• Our main topic for the rest of this lecture will be transcription, but first we will review amino acids and polypeptide chains.
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Structure of an amino acid
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Structure of all 20 amino acids commonly found in proteins
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Joining of amino acids by peptide bonds to create polypeptides
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Three-dimensional structure of a monomeric protein
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Location of a number of mutants in the trpA gene and the resulting amino acid replacements
Colinearity – the sequence of base pairs in DNA determines the amino acid sequence in a colinear manner.
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Transcription
• Transcription is the synthesis of RNA from the DNA coding for the gene.
• (Remember the differences between DNA and RNA).– RNA uses the four ribonucleosides ATP, GTP
CTP and UTP.– RNA polymerase is used instead of DNA
polymerase.– A promoter is used for initiation of
transcription (not a primer, as with DNA).
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A ribonucleoside differs from a deoxyribonucleoside in 2 ways
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RNA is synthesized by the addition of new nucleotides to the 3’-OH end of a growing chain
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Types of RNA polymerases
• Bacterial cells use only one RNA polymerase, with six polypeptides.
• The RNA polymerase holoenzyme contacts the promoter, then 35 nt of DNA.
• Processivity can be 10,000 nt for prokaryotes and 1,000,000 for eukaryotes.
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Mechanism of transcription
1. Promoter recognition
2. Chain initiation
3. Chain elongation
4. Chain termination
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RNA synthesis creates a bubble in the double-stranded DNA template
Note the 5` triphosphate group, and that only one strand is the template.
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Comparison of a number of E. coli promoter sequences reveals two conserved sequences (at -10 and -35 nt)
The position in DNA where the RNA chain starts is called +1 site. DNA 5’ to the start site is called “upstream” sequence and DNA to
the 3’-side is called “downstream” sequence.
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Rho-independent site for transcription termination generates RNA that can form a stable hairpin
followed by a number of U residues
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During transcription, RNA is copied from only one DNA strand for any one gene