Central dogma

central dogma of genetics
DNA replication
transcription and
protein translation

1. Welcome Topic:- CENTRAL DOGMA OF BIOLOGY.

2. introduction “The central dogma of molecular biology deals with the detailed residue-by-residue transfer of sequential information. It states that such information cannot be transferred back from protein to either protein or nucleic acid.” Francis Crick, 1958

3. Protein information cannot flow back to nucleic acids Fundamental framework to understanding the transfer of sequence information between biopolymers

4. The central dogma of biology is that information stored in DNA is transferred to RNA molecules during transcription and to proteins during translation . DNA RNA proteins Genotyping Phenotyping RNA DNA/RNA proteins virus

5. Four requirements for DNA to be genetic material Must carry information Cracking the genetic code Must replicate DNA replication Must allow for information to change Mutation Must govern the expression of the phenotype Gene function

6. DNA Replication Process of duplication of the entire genome prior to cell division Biological significance extreme accuracy of DNA replication is necessary in order to preserve the integrity of the genome in successive generations In eukaryotes , replication only occurs during the S phase of the cell cycle. Replication rate in eukaryotes is slower resulting in a higher fidelity/accuracy of replication in eukaryotes

7. Basic rules of replication Semi-conservative Starts at the ‘origin’ Synthesis always in the 5-3’ direction Can be uni or bidirectional Semi-discontinuous RNA primers required

8. DNA replication 3 possible models

9. Semi-conservative replication: One strand of duplex passed on unchanged to each of the daughter cells. This 'conserved' strand acts as a template for the synthesis of a new, complementary strand by the enzyme DNA polymerase

10. How do we know that DNA replication is semiconservative? Meselson-Stahl experiments

11. B) Starts at origin Initiator proteins identify specific base sequences on DNA called sites of origin Prokaryotes – single origin site E.g E.coli - oriC Eukaryotes – multiple sites of origin (replicator) E.g. yeast - ARS (autonomously replicating sequences) Prokaryotes Eukaryotes

12. In what direction does DNA replication occur? Where does energy for addition of nucleotide come from? What happens if a base mismatch occurs? C) Synthesis is ALWAYS in the 5’-3’ direction

13. Why does DNA replication only occur in the 5’ to 3’ direction? Should be PPP here

14. D) Uni or bidirectional Replication forks move in one or opposite directions

15. E) Semi-discontinuous replication Anti parallel strands replicated simultaneously Leading strand synthesis continuously in 5’– 3’ Lagging strand synthesis in fragments in 5’-3’

16. Semi-discontinuous replication New strand synthesis always in the 5’-3’ direction

17. F) RNA primers required

18. Core proteins at the replication fork Topoisomerases Helicases Primase Single strand binding proteins DNA polymerase Tethering protein DNA ligase - Prevents torsion by DNA breaks - separates 2 strands - RNA primer synthesis - prevent reannealing of single strands - synthesis of new strand - stabilises polymerase - seals nick via phosphodiester linkage

19. The mechanism of DNA replication Arthur Kornberg, a Nobel prize winner and other biochemists deduced steps of replication Initiation Proteins bind to DNA and open up double helix Prepare DNA for complementary base pairing Elongation Proteins connect the correct sequences of nucleotides into a continuous new strand of DNA Termination Proteins release the replication complex

20. Core proteins at the replication fork

21. 21 Proofreading New DNA DNA polymerase initially makes about 1 in 10,000 base pairing errors Enzymes proofread and correct these mistakes The new error rate for DNA that has been proofread is 1 in 1 billion base pairing errors

22. 22 DNA Damage & Repair Chemicals & ultraviolet radiation damage the DNA in our body cells Cells must continuously repair DAMAGED DNA Excision repair occurs when any of over 50 repair enzymes remove damaged parts of DNA DNA polymerase and DNA ligase replace and bond the new nucleotides together

23. Transcription Process of copying DNA to RNA Differs from DNA synthesis in that only one strand of DNA, the template strand , is used to make mRNA Does not need a primer to start Can involve multiple RNA polymerases Divided into 3 stages Initiation Elongation Termination

24. General Features of RNA Synthesis Similar to DNA Synthesis except The precursors are ribonucleoside triphosphates. Only one strand of DNA is used as a template. RNA chains can be initiated de novo (no primer required). The RNA molecule will be complementary to the DNA template (antisense) strand and identical (except that uridine replaces thymidine) to the DNA non-template (sense) strand. RNA synthesis is catalyzed by RNA polymerases and proceeds in the 5’3’ direction. © John Wiley & Sons, Inc.

25. Transcription: The final product

26. Types of RNA Molecules Messenger RNAs (mRNAs) —intermediates that carry genetic information from DNA to the ribosomes. Transfer RNAs ( tRNAs ) —adaptors between amino acids and the codons in mRNA. Ribosomal RNAs ( rRNAs ) —structural and catalytic components of ribosomes.

27. Translation Components required for translation: mRNA Ribosomes tRNA Aminoacyl tRNA synthetases Initiation, elongation and termination factors

28. Translation: initiation Ribosome small subunit binds to mRNA Charged tRNA anticodon forms base pairs with the mRNA codon Small subunit interacts with initiation factors and special initiator tRNA that is charged with methionine mRNA-small subunit- tRNA complex recruits the large subunit Eukaryotic and prokaryotic initiation differ slightly

29. Translation: initiation The large subunit of the ribosome contains three binding sites Amino acyl (A site) Peptidyl (P site) Exit (E site) At initiation, The tRNA fMet occupies the P site A second, charged tRNA complementary to the next codon binds the A site.

30. Translation: elongation Elongation Ribosome translocates by three bases after peptide bond formed New charged tRNA aligns in the A site Peptide bond between amino acids in A and P sites is formed Ribosome translocates by three more bases The uncharged tRNA in the A site is moved to the E site.

31. Translation: elongation EF-Tu recruits charged tRNA to A site. Requires hydrolysis of GTP Peptidyl transferase catalyzes peptide bond formation (bond between aa and tRNA in the P site converted to peptide bond between the two amino acids) Peptide bond formation requires RNA and may be a ribozyme-catalyzed reaction

32. Translation: termination Termination Elongation proceeds until STOP codon reached UAA, UAG, UGA No tRNA normally exists that can form base pairing with a STOP codon; recognized by a release factor tRNA charged with last amino acid will remain at P site Release factors cleave the amino acid from the tRNA Ribosome subunits dissociate from each other Review the animation of translation

33. Refrences :- Life sciences, fundamentals and practices-2,pranav kumar and usha mina,5 th edition,2016. Slideshare.com http://www.thelifewire.com

34. Thank you….