Central Dogma

1953: James Watson and Francis Crick presents the DNA structure Basis: Maurice Wilkins and Rosalind Franklin’s X-ray crystallography images of DNA

Watson, Crick and Wilkins – Nobel prize in Physiology or Medicine in 1962

Nucleic Acid Chemistry

purine pyrimidine

Nucleotide Chain

Base-pairing

RNA Structure

Classes of RNA

• rRNA• mRNA• tRNA

The Central Dogma

DNA REPLICATION 1. Origin of DNA Replication

2. Unwinding of the DNA

3. Stabilization of the Y-junction

4. Polymerization of the nucleotides

5. Formation of the Leading and Lagging Strand

6. Formation of the Replisome

7. Replication of the Leading and Lagging Strand

Replication of the Lagging Strand

1. Primer synthesis-enzyme primase provide the free 3’-OH group at the site of Okazaki fragment initiation in the lagging strand

2. Elongation 3. Primer Removal and Gap Filling – exonuclease– endonuclease

4. Ligation

8. Primer Removal and Gap Filling

9. Ligation

Ligation- the polymerase cannot attach together the fragments, the enzyme DNA ligase completes this task by making a phosphodiester bond

DNA TRANSCRIPTION (Prokaryotic)1. Initiation of Transcription– Promoter.– TATAAT known as Pribnow box

2. Polymerization – It begins 6 to 8 nucleotides down from the Pribnow box.– Uses the DNA coding strand. – RNA polymerase – First base to be transcribed is noted as +1.

3. Termination – terminator sequence or stop signal– stem-loop structure is formed which causes the RNA

polymerase to pause which may then allow termination to occur under two different circumstances.• Rho dependent termination• Rho independent termination

1. Initiation of Transcription

2. Polymerization

Pribnow box

Bacterial PromoterThe lactose operon promoter and its consensus sequences. The start point for RNA synthesis is labeled 1. The region around 35 is the site at which the RNA polymerase first attaches to the promoter. RNA polymerase binds and begins to unwind the DNA helix at the Pribnow box or RNA polymerase binding site, which is located in the 10 region.

3. Termination

RNA TRANSCRIPTION

PROTEIN TRANSLATION

Reading Frames and Their Importance The place at which DNA sequence reading begins determines the way nucleotides are grouped together in clusters of three (outlined with brackets), and this specifies the mRNA codons and the peptide product. In the example, a change in the reading frame by one nucleotide yields a quite different mRNA and final peptide.

Protein Translation

• takes place in the ribosomes • ribosome is composed of a small sub-unit and

large sub-unit• uses the genetic code – is a series of codons that contain the triplets of

bases in the DNA and mRNA. Several mRNA codons may code for a single amino acid (degeneracy of code).

Three Stages of Protein Biosynthesis

When does translation start?1. INITIATION • Components of translation

– Ribosome with its small sub-unit – mRNA– formyl methionine (fMEt-tRNAf

Met)

– initiation factors

• initiation codons– prokaryotes- GUG, AUG and UUG– eukaryotes-AUG and CUG

1. INITIATION

2. ELONGATION

3. TERMINATION

Stop Codons: UAG, UAA, UGA