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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.
RNA
DNA
Protein
Transcription(RNA Polymerase)
Translation
Reverse Transcription(Reverse Transcriptase)
Post-translational Modifications (PTMs)
Cellular Functions
Genomics
Proteomics
Replication
Replication: Semi-conservative
Preserving and propagating the cellular message
Replication begins at a predetermined site, the origin of replicationin a bidirectional mode.
re
(Replication in vitro)
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 atterminator sequence.
DNA as the Template for RNA Synthesis
DNA as the Template for RNA Synthesis
RNA polymerase always reads in the 3’ to 5’-direction.One strand of DNA serves as the template or sense strand.
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
• 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 -galactosidase is somehow abolished in the presence of glucose.
Question: What is the mechanism that suppresses synthesis of lactose enzymes?
Inada et al, Genes to Cells, 1, 293, 1996
OD
-galactosidase
Model of Lac Operon (animation)