Self replication of DNA, RNA SYNTHESIS AND THE GENETIC CODE

Question 1

Components required for DNA replication

Answer 1

1. Synthesised in the 5’-3’ direction
2. Elongation occurs by addition to the 3’ end
3. DNA polymerase
4. Substrate= deoxyribonucleoside triphosphate– nucleotide + pyrophosphate
5. Template strand read 3’-5’
6. Short double stranded NA supplied by RNA primer
7. Mg2+

Question 2

How does Mg2+ help replication

Answer 2

Incoming dNTP has two Mg2+ ions coordinated to phosphate groups which interact with Aspartate residues highly conserved in DNA (and RNA) Pol
One Mg2+ binds to the 3’-OH of the growing strand lowering its affinity for H, promoting Nu: attack on α-phosphate of incoming dNTP
Second Mg2+ assists in departure of Pyrophosphate product
Both Mg2+ stabilize pentacovalent transition state on the α-phosphorus atom

Question 3

How is DNA replicated? RNA synthesised

Answer 3

DNA is unwound
Both strands are copied in DNA replication (semiconservative)
1 strand is copied to make RNA (Transcription)

Each replication for has a leading strand and lagging strand
Complementary base pairing provides mechanism for copying the information encoded by DNA
DNA polymerase has high fidelity, very few errors
Exonuclease activity proof read

Question 4

Okazaki fragments

Answer 4

100-200 nts

DNA polymerase and ligase fill in gaps on lagging strand

Question 5

RNA synthesis

Answer 5

Substrate= ribonucleoside triphosphate
RNA polymerase
1 DNA strand is copied
mRNA encodes the polypeptide
tRNA bind appropriate amino acid and directs it to mRNA
rRNA together with various proteins forms the ribosome= workbench protein is made