Management of GeneticInformation
Learning objectives   Understand the mechanism of DNA    replication, RNA synthesis and protein    synthesis
Flow of genetic information
Two possible models of the DNAreplication
Expt by Meselson-Stahl proved thesemiconservative model of replication
Which direction does replication go?   Major enzyme: DNA polymerase III       DNA double helix unwinds at a specific poi...
Replication inprokaryotes
Replication ineukaryotes
DNA synthesis based on two template strands: leading strand andlagging strand templates; mechanism in prokaryotes is prese...
Replication fork
Enzymes and proteins in DNA replication
The action of DNA polymerase                  Why 53’ direction?
Start of DNA replication
Unwinding   DNA gyrase introduces a swivel point in    advance of the replication fork   a helicase binds at the replica...
   Primase catalyzes the synthesis of RNA primer   Synthesis     catalyzed by Pol III     primer removed by Pol I    ...
Summary of DNA replication inprokaryotes   DNA synthesis is bidirectional   DNA synthesis is in the 5’ -> 3’ direction  ...
DNA polymerases   Five DNA polymerases have been found to exist in    E. coli       Pol I is involved in synthesis and r...
Eukaryotic DNA replication   Not as understood as prokaryotic. Due in no    small part to higher level of complexity.   ...
RNA synthesis   Transcription   Template is DNA   Major enzyme: DNA directed RNA polymerase   No need for primers   5...
RNA synthesis   Requires a promoter region in the template DNA    to which the RNA polymerse will bind   Promoter 40 bas...
Promoter 40 base pairs upstream (-40)away from the start site (+1)
INITIATION STEP
ELONGATION STEP
TERMINATION STEP
ρ-FACTOR INDEPENDENT- FORMATION OF HAIRPIN LOOP
Eukarotic transcription have 3 classes ofRNA polymerases   RNA pol I transcribes large ribosomal RNA    genes   RNA pol ...
Post transcriptional modification of theeukaryotic mRNA   Capping – methyl guanosine attachment at the    5’ end to prote...
Protein synthesis   Translation   Based on the m-RNA sequence, genetic    code   Starts from 5’ end of the transcript ...
Genetic code   Triplet nucleotide – one amino acid   Nonoverlapping   No punctuation   Degenerate   Almost universal
Initiation   Initiation factors   Shine-Dalgarno sequence in mRNA   30S ribosome   N-formylmet
Inhibitors of protein synthesis
Postranslational modification   Protein folding –chaperones   Proteolytic cleavage (zymogens) – hydrolytic    enzymes in...
Regulation of protein synthesis and geneexpression   20K to 25K genes in the human genome   Only a fraction of the genes...
Mv management of genetic information
Mv management of genetic information
Mv management of genetic information
Mv management of genetic information
Mv management of genetic information
Mv management of genetic information
Mv management of genetic information
Mv management of genetic information
Mv management of genetic information
Mv management of genetic information
Mv management of genetic information
Mv management of genetic information
Mv management of genetic information
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Mv management of genetic information

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Mv management of genetic information

  1. 1. Management of GeneticInformation
  2. 2. Learning objectives Understand the mechanism of DNA replication, RNA synthesis and protein synthesis
  3. 3. Flow of genetic information
  4. 4. Two possible models of the DNAreplication
  5. 5. Expt by Meselson-Stahl proved thesemiconservative model of replication
  6. 6. Which direction does replication go? Major enzyme: DNA polymerase III  DNA double helix unwinds at a specific point called an origin of replication  Polynucleotide chains are synthesized in both directions from the origin of replication; DNA replication is bidirectional in most organisms  At each origin of replication, there are two replication forks, points at which new polynucleotide chains are formed  There is one origin of replication and two replication forks in the circular DNA of prokaryotes  In replication of a eukaryotic chromosome, there are several origins of replication and two replication forks at each origin
  7. 7. Replication inprokaryotes
  8. 8. Replication ineukaryotes
  9. 9. DNA synthesis based on two template strands: leading strand andlagging strand templates; mechanism in prokaryotes is presented DNA is synthesized from its 5’ -> 3’ end (from the 3’ -> 5’ direction of the template)  the leading strand is synthesized continuously in the 5’ -> 3’ direction toward the replication fork  the lagging strand is synthesized semidiscontinuously (Okazaki fragments) also in the 5’ -> 3’ direction, but away from the replication fork  lagging strand fragments are joined by the enzyme DNA ligase
  10. 10. Replication fork
  11. 11. Enzymes and proteins in DNA replication
  12. 12. The action of DNA polymerase Why 53’ direction?
  13. 13. Start of DNA replication
  14. 14. Unwinding DNA gyrase introduces a swivel point in advance of the replication fork a helicase binds at the replication fork and promotes unwinding single-stranded binding (SSB) protein protects exposed regions of single-stranded DNA
  15. 15.  Primase catalyzes the synthesis of RNA primer Synthesis  catalyzed by Pol III  primer removed by Pol I  DNA ligase seals remaining nicks
  16. 16. Summary of DNA replication inprokaryotes DNA synthesis is bidirectional DNA synthesis is in the 5’ -> 3’ direction  the leading strand is formed continuously  the lagging strand is formed as a series of Okazaki fragments which are later joined
  17. 17. DNA polymerases Five DNA polymerases have been found to exist in E. coli  Pol I is involved in synthesis and repair  Pol II, IV, and V are for repair under unique conditions  Pol III is primarily responsible for new synthesis
  18. 18. Eukaryotic DNA replication Not as understood as prokaryotic. Due in no small part to higher level of complexity. Cell growth and division divided into phases: M, G1, S, and G2 DNA replication occurs during the S phase
  19. 19. RNA synthesis Transcription Template is DNA Major enzyme: DNA directed RNA polymerase No need for primers 5’ to 3’ direction
  20. 20. RNA synthesis Requires a promoter region in the template DNA to which the RNA polymerse will bind Promoter 40 base pairs upstream (-40) away from the start site (+1) Three stages:initiation, elongation, termination Termination may be  rho factor dependent – rho factor terminates synthesis  or rho factor independent – formation of a stable hairpin loop
  21. 21. Promoter 40 base pairs upstream (-40)away from the start site (+1)
  22. 22. INITIATION STEP
  23. 23. ELONGATION STEP
  24. 24. TERMINATION STEP
  25. 25. ρ-FACTOR INDEPENDENT- FORMATION OF HAIRPIN LOOP
  26. 26. Eukarotic transcription have 3 classes ofRNA polymerases RNA pol I transcribes large ribosomal RNA genes RNA pol II transcribes protein encoding gene RNA pol III transcribes small RNAs (including tRNA and 5SRNA)
  27. 27. Post transcriptional modification of theeukaryotic mRNA Capping – methyl guanosine attachment at the 5’ end to protect the cleavage of the RNA by exonucleases as RNA moves out of the nucleus Addition of poly A at the 3’ end (200-250 long) helps to stabilize the mRNA structure; increases resistance to cellular nucleases Splicing – removal of non coding sequences (introns)
  28. 28. Protein synthesis Translation Based on the m-RNA sequence, genetic code Starts from 5’ end of the transcript Occurs in the ribosomes Activation of amino acids – attachment to the tRNA Initiation, elongation, termination
  29. 29. Genetic code Triplet nucleotide – one amino acid Nonoverlapping No punctuation Degenerate Almost universal
  30. 30. Initiation Initiation factors Shine-Dalgarno sequence in mRNA 30S ribosome N-formylmet
  31. 31. Inhibitors of protein synthesis
  32. 32. Postranslational modification Protein folding –chaperones Proteolytic cleavage (zymogens) – hydrolytic enzymes in the gut Amino acid modifications Attachment of carbohydrates Addition of prosthetic groups
  33. 33. Regulation of protein synthesis and geneexpression 20K to 25K genes in the human genome Only a fraction of the genes are expressed at any given time Two types of gene expression: constitutive and inducible Inducible genes are highly regulated – regulatory proteins, hormones and metabolites
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