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)