This document summarizes nucleic acid metabolism and genetic information transfer. It discusses the structure of DNA and RNA, DNA replication through the semi-conservative model, transcription, the genetic code, and translation. DNA replication in prokaryotes is described as semi-discontinuous and bidirectional, with continuous synthesis on the leading strand and discontinuous synthesis in fragments on the lagging strand. RNA primers are required for DNA synthesis, and DNA polymerase adds nucleotides to DNA in the 5' to 3' direction. Certain compounds that inhibit DNA and RNA processes are used as anticancer or antibacterial drugs.

1. UNIT IV :Nucleic acid metabolism and Genetic
information transfer
TOPIC TO BE DISCUSSED UNDER THIS ACC. TO
SYLLABUS:
Introduction to nucleotides and their functions.
Biosynthesis of Purine and Pyrimidine nucleotides
Catabolism of Purine nucleotides
 Hyperuricemia and Gout disease
Organization of mammalian genome
Structure of DNA and RNA and their functions
DNA replication (semi conservative model)
Transcription or RNA synthesis
Genetic code, Translation or Protein synthesis and inhibitors

7. IN PROKARYOTES

9. DNA SYNTHESIS IS SEMIDISCONTINUOUS
AND BIDIRECTIONAL
The replication of DNA occurs in 5' to 3‘ direction,simultaneously,
on both the strands of DNA. On one strand, the leading (continuous
or forward) strand-the DNA synthesis is continuous.
On the other strand, the lagging (discontinuous or retrograde)
strand-the synthesis of DNA is discontinuous. Short pieces of DNA
(15-250 nucleotides) are produced on the lagging strand.
ln the replication bubble, the DNA synthesis occurs in both the
directions( bidirectional) from the point of origin..

20. Initiation :-Occurs attheoriginofreplication.
Elongation:- Involves theadditionofnew nucleotides based
on complementarityofthetemplate strand.
Termination:- Occurs ata specifictermination site.
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23. ORI is theregion where process ofreplication starts..This region is rich inA &T base

29. RNA PRIMER
For the synthesis of new DNA, a short fragment of RNA
(about 5-50 nucleotides, variable with species) is required as a
primer.
The enzyme primase (a specific RNA polymerase)in
association with single-stranded binding proteins forms a
complex called primosome, and produces RNA primers.
A constant synthesis and supply of RNA primers should occur
on the lagging strand of DNA. This is in contrast to the leading
strand which has almost a single RNA primer.

31. Replication is continuous.
There are no fragments.
DNA polymerase III adds nucleotides inthedirectionof5’→3’.
◦ DNA polymerase only worksinthedirectionof5’→3’.
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32. The lagging strandruns from3’to5’oftemplatestrand.
1.AfterRNA primer is inplace DNA nucleotides are added by DNA
polymerase III.
2. Eventually, thesegment of DNA willrun intoanotherRNA primer.
The DNA segments are called Okazaki fragments(The small fragments of the
discontinuously synthesized DNA are called Okazaki pieces)
1. Once Okazaki fragmentsare formedDNA polymerase I replaces theRNA
primer withDNAnucleotides.
2. DNA Ligase linksthefragments together.
3. In thelagging strandDNA replicationisdiscontinuous.
4. DNA is replicatedinsegments thatbecome joined together.
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43. (human topoisomerase)

44. Certain compounds that inhibit human topoisomerases are used
as anticancer agents e.g. adriamycin, etoposide, doxorubicin.
The nucleotide analogs that inhibit DNA replication are also
used as anticancer drugs e.g. 6-mercaptopurnie , 5-fluorouracil.

45. INHIBITORS OF DNA REPLICATION (INHIBIT
BACTERIAL GYRASE)
This enzyme cuts and resealst he circular DNA (of bacteria),a
nd thus overcomes the problem of supercoils. Bacterial gyrase is
inhibited by the antibiotics ciprofloxacin, novobiocin and
nalidixic acid.
These are widely used as antibacterial agents since they can
effectively block the replication of DNA and multiplication of
cells