Download last of Chapter 9, beginning Chapter 10

Chapter 10:
Molecular
Biology of
Gene
Expression
Jones and Bartlett Publishers © 2005
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.
Structure of an amino acid
Structure of all 20 amino acids
commonly found in proteins
Joining of amino acids by peptide bonds
to create polypeptides
Three-dimensional structure of a
monomeric protein
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.
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).
A ribonucleoside differs from a
deoxyribonucleoside in 2 ways
RNA is synthesized by the addition of new
nucleotides to the 3’-OH end of a growing chain
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.
Mechanism of transcription
1. Promoter recognition
2. Chain initiation
3. Chain elongation
4. Chain termination
RNA synthesis creates a bubble in the
double-stranded DNA template
Note the 5` triphosphate group, and that only one strand is
the template.
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.
Rho-independent site for transcription termination
generates RNA that can form a stable hairpin
followed by a number of U residues
During transcription, RNA is copied from
only one DNA strand for any one gene