How Cell Work
-Introduction of Molecular Biology
Molecular biology: study the information flow and control of cells.
Central dogma is universal from the simplest to most complex
organisms.
Replication
DNA
Reverse Transcription
(Reverse Transcriptase)
Transcription
(RNA Polymerase)
RNA
Genomics
Translation
Proteomics
Protein
Post-translational
Modifications (PTMs)
Cellular Functions
Replication: Semi-conservative
Preserving and propagating the cellular message
Replication begins at a predetermined site, the origin of replication
in a bidirectional mode.
(Replication in vitro)
r
e
Transcription:
Sending the message
Sigma factor recognizes a specific
sequence of nucleotide sequence
(promoter) on a DNA strand. It is
involved only in initiation.
Transcription stop at
terminator sequence.
DDNA as the Template for RNA Synthesis
N
A
a
s
t
h
e
T
e
m
p
RNA polymerase always reads in the 3’ to 5’-direction.
l
One strand of DNA serves as the template or sense strand.
a
t
e
Conserved sequences in promoters recognized by
E. coli RNA polymerase
Prokayrotic Promoter Sequences
Model of Lac Operon (animation)
In procaryotes related proteins are often encoded without interspacing terminators. Transcription
from a single promoter may result in a polygenic message.
The lac operon mRNA.
The genetic code (as
written in RNA).
Universal Message
Translation of an RNA
message into a protein
The diauxie
OD
bgalactosidase
Inada et al, Genes to Cells, 1, 293, 1996
• When exposed to glucose + lactose, E. coli does not consume lactose until glucose is
exhausted, resulting in two exponential growth phases separated by a lag. This is called the
diauxie or “double growth.”
• Diauxie occurs because synthesis of lactose permease and
b-galactosidase is somehow abolished in the presence of glucose.
Question: What is the mechanism that suppresses synthesis of lactose enzymes?
Model of Lac Operon (animation)