Microbial Genetics

 DNA replication is semi- conservative:  What does it mean? During cell division, each daughter cell inherits 2 DNA strands, One is old and one is new.

 Genetic information can be transferred either:  Within the cell itself (in this case the genetic information is used to produce proteins needed for the cell function).This is called “Gene expression”  Or from parent cell to daughter cells (during cell division). This is called “Replication”  Or from one cell to another cell of same generation, resulting in new combinations of genes ”Recombination”

 Gene (DNA) contains all the information needed by cell to make a particular protein. But, how the gene changes to a protein? DNA  mRNA  protein transcription translation Transcription and processing of the newly made mRNA occurs in the nucleus of the cell. Once a mature mRNA transcript is made it is transported to the cytoplasm for translation into protein. Transcription and processing of the newly made mRNA occurs in the nucleus of the cell. Once a mature mRNA transcript is made it is transported to the cytoplasm for translation into protein. Transcription and processing of the newly made mRNA occurs in the nucleus of the cell. Once a mature mRNA transcript is made it is transported to the cytoplasm for translation into protein Transcription and processing of the newly made mRNA occurs in the nucleus of the cell. Once a mature mRNA transcript is made it is transported to the cytoplasm for translation into protein. Central Dogma of Molecular Genetics

Transcription and processing of the newly made mRNA occurs in the nucleus of the cell. Once a mature mRNA transcript is made it is transported to the cytoplasm for translation into protein. Transcription and processing of the newly made mRNA occurs in the nucleus of the cell. Once a mature mRNA transcript is made it is transported to the cytoplasm for translation into protein. Transcription and processing of the newly made mRNA occurs in the nucleus of the cell. Once a mature mRNA transcript is made it is transported to the cytoplasm for translation into protein Transcription and processing of the newly made mRNA occurs in the nucleus of the cell. Once a mature mRNA transcript is made it is transported to the cytoplasm for translation into protein. Transcription and processing of the newly made mRNA occurs in the nucleus of the cell (eukaryotic cell) or nuclear area (prokaryotic cell) Once a mature mRNA transcript is made it is transported to the cytoplasm for translation into protein

 Double stranded DNA is transcribed into single stranded messenger RNA (mRNA) 5’ 3’ 5’ 3’ Promoter Terminator region Coding region of gene

In case of eukaryotic cell: Ist step in transcription process is the binding of Transcription Factors to promoter region of gene. This is followed by binding of RNA polymerase to Transcription Factors. In case of prokaryotic cell: There is no transcription factors and RNA polymerase binds directly to promoter region of gene. Transcription Factors

RNA polymerase begins to move downstream in 5’ to 3’ direction, unwinding and making RNA copy of DNA

RNA polymerase reaches Terminator region RNA polymerase detaches mRNA Transcript is released

Ways in which RNA & DNA differ:  mRNA is single stranded  Sugar is ribose  (U) instead of (T)  A-U base pairing Now the mRNA moves into cytoplasm to be translated into a protein.

How does the nucleotide sequence of mRNA specify the specific order of amino acids in a protein? The answer lies in what is known as the genetic code.  DNA: triplet code e.g. TAC CAC CCC GCC ATC  mRNA: codon AUG GUG GGG CGG UAG (complimentary to triplet code of DNA) Amino acid sequence Met- Val- Gly- Arg- Stop

 Codons: code for the production of a specific amino acid  20 amino acids  3 base code  Degenerative: more than 1 codon codes for an amino acid  Universal: in all living organisms

. 1 st step in translation is the attachment of the small ribosomal subunit (30S) to mRNA at the start codon (AUG).This is followed by the recruitment of large subunit (50S). On the assembled ribosome (70s), tRNA carries amino acid to the ribosome..Each tRNA matches and binds to a specific codon.. If codon does not match, tRNA rejected.

On assembled ribosome, a tRNA carrying the first amino acid is paired with the start codon on the mRNA. The place on ribosome where the 1st tRNA is located is called P site. tRNA carrying the 2 nd amino acid approaches. P site

A site next to P site, the second codon of the mRNA pairs with a tRNA carrying the second amino acid (A site).

The 1 st amino acid joins the second amino acid by a peptide bond The 1 st tRNA is released.

The ribosome moves along the mRNA until the 2 nd tRNA is in the Psite, and the process continues.

As ribosome continues to move along the mRNA, new amino acids are added to the polypeptide.

When the ribosome reaches a stop codon, the polypeptide is released. Stop codons are UGA, UAA, UAG.

Finally, the last tRNA is released, and the ribosomes comes apart.The released polypeptide forms a new protein.

 Three types:  mRNA: messenger RNA ▪ Contains 3 bases ( codon)  rRNA: ribosomal RNA ▪ Comprises the 70 S ribosome  tRNA: transfer RNA ▪ Transfers amino acids to ribosomes for protein synthesis ▪ Contains the anticodon (3 base sequence that is complimentary to codon on mRNA)