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DNA REPLICATION AND REPAIR - Coggle Diagram
DNA REPLICATION AND REPAIR
DNA CHARACTERISTICS
Antiparallel strands are templates for each other.
specific base pair hydrogen bonding allows for accurate copying
tightly wound helical structure is stable and needs to break hydrogen bonds for strands to unwind.
torsional stress in winding the extremely long molecule needs to be overcome.
DNA REPLICATION IS SEMI-CONSERVATIVE TWO DNA ARE PRODUCED EACH WITH ONE ORIGINAL AND ONE NEW STRAND
THERE ARE ALSO DISPERSIVE AND CONSERVATIVE REPLICATION WITH DISPERSIVE HAVING ORIGINAL AND NEW STRAND EMBEDED THROUGHOUT DNA AND CONSERVATIVE PROUDICING ONE WHOLE NEW STRAND FROM ORIGINAL STRAND
Messelon Stahl experiment
bacteria grown with source of Nitrogen15 instead of N14 cells collected after division, DNA extracted centrifuged and the density measured only semiconservative replication made sense.
PHASES OF DNA REPLICATION
INITIATION
DNA REPLICATION IN BACTERIA STARTS FROM ONE POINT OF ORIGIN HOWEVER IN EUKARYOTES THERE ARE MULTIPLE POINT OF ORIIGIN
SPECIFIC PROTEINS RECOGNISE DNA sequence AT ORIGIN SNF BINF TO DNA TO BEGIN TO OPEN AND UNWIND IT. THIS FORMS A REPLICATINO BUBBLE WHICH ALLOWS ACCESS TO THE PROTEIN THAT SYNTHESISE THE NEW STRAND , THEY MOVE AWAY FRO THE ORIGIN A STHEY MAKE NEW DNA A DNA FORK ID PRODUCTE. BIDIRECTIONAL REPLICATION IS MORE COMMON THAN UNIDIRECTIONAL)
ELONGATION
DNA ELONGATES IN A 5' TO 3' DIRECTION
DNA polymerase AN ONLY ADD DNA AT THE 3' END OF DEOXYRIBOSE BUT DNA HAS ANTIPPARALLEL STRANDS
DNA polymerase IS THE KEY ENZYME RESPONSIBLE FOR ELONGATION OF DNA STRANDS.
THE TWO STRANDS MUST BE COPIED IN DIFFERENT WAYS ONE STRAND CAN BE COPIED CONTINUOUSLY BY ADDING TO THE 3' END (LEADING STRAND) AND THE OTHER STRAND NEEDS TO BE REPLICATED IN SMALLER SECTIONS AS A DISCONTINOUS PRCOESS(LAGGING STRAND)
OKAZAKI FRAGMENTS ARE PRODUCED BY CONTINUOS RE-INITIATION ON THE LAGGING STRAND THIS
RESULTS
IN FRAGMENTS, OKAZAKI FRAGMENTS ARE SHORT DNA NUCLEOTIDE SQUENCES , FORMED DISCONTINUOUSLY ON THE LAGGING STRAND AT TIME OF REPLICATION.
DNA POLYMERASE
ENZYME RESPONSIBLE FOR ELONGATION.
CANNOT DO de nover synthesis, require primer, require nucleotide triphosphate and magnesium ions, can only extend on the 3' end. Several types of DNA polymerase with different roles.
DNA PRIMASE- enzyme that synthesises short RNA sequences called primers. These primers serve as a starting point for DNA synthesis. Primase function. by synthesising short RNA sequences that are complimentary to a single strand piece of DNA which serve as a template.
THEY ARE INTIATED BY THE CREATION OF ANEW RNA PRIMER BY THE PRIMASR , THESE FRAGMENTS THEN NEED TO BE PROCESSED.
DNA LIGASE JOIN OKAZAKI FRAGMENTS TOGETHER
OTHER ENZYMES AND PROTEINS REQUIRED
DNA HELICASE, SINGLE STRANDED DNA BINDING PROTEIN, TOPOISOMERASE
INCORPORATION OF NEW NUCLEOTIDES
AS BASE PAIRING OCCURS BETWEEN THE TEMPLATE STRAND BASE AND THE BASE OF FREE FLOATING NUCLEOTIDE, THE TRIPHOSPHATE ON FREE FLOATING NUCLEOTIDE IS ATTACKED BY OH GROUO ON THE RIBOSE SUGAR OF PRIMER STRAND(NON TEMPLATE STRAND). TO FORM A PHOSPHODIESTER BOND.
DNA HELICASE CONVERTS DOUBLE STRANDED DNA INTO SINGLE STRANDED SO IT CAN BE ACTED ON BY THE POLYMERASE AND PRIMASE
SINGLE STRANDED BINDING PROTEINS PROTECT STRANDS FROM TANGLING AND BEING ATTACKED FROM NUCLEASE
DNA polymerase PROCESSETIVITY
A PROCESSETIVITY FACTOR OR A CLAMP PROTEIN VASTLY IMPROVES THE PROCESSETIVITY OF DNA polymerase. USUALLY multimeriz with a ring shape.
Most DNA polymerases are low-processivity enzymes - defined as the.ability of DNA polymerase to carry out continuous DNA synthesis on a template DNA without frequent dissociation.
THE FIDELITY- refers to DNA polymerase ability to accurately replicate a protein.
DNA polymerase ALSO HAS PROOFREADING ACTIVITIES- CHECKS BASE PAIRING INCORRECT bp TRIGGERS CATALYTIC SITE WHICH REMOVES INCORRECT BP.
DNA REPLICATION DRUG INHIBITORS- antibacterials, antimalarials(folate antagonists), antivirals(HIV)
HOW DOES DNA GET DAMAGED
ENDOGENOUS SOURCES
REPLICATION ERRORS- INCORRECT BASE INSERTED, INSERTION DELETIONS
SPONTANEOUS ALTERATIONS IN DNA
OXIDATIVE ALTERING BY FREE RADICALS
ALKYLATION AGENTS
EXOGENOUS AGENTS
UV
POLLUTION
RADIOTHERAPY
CHEMOTHERAPY
BOTH EXOGENOUS AND ENDOGENOUS ALTERATIONS CAN LEAD TO DNA BACKBONE BREAKING, STRANDS BECOME CROSSSLINKED, BASES CAN BECOME COVALENTLY BONDED, BASES CAN BE OXIDISED, DAMAGED, ALKYLATED, DEAMINATED
HOW CAN THESE BE REVERSED?
RECOMBINATION REPAIR, DIRECT REVERSALS, MISMATCH REPAIR, NON HOMOLOGOUS END JOINING. NER
