Similarities between mammalian and E. Coli replication
Similar replication fork geometry
Multiprotein replication machine
Differences between E. Coli and mammalian DNA replication
E. Coli: Single origin of replication and same polymerase for leading and lagging strand synthesis
Mammalian: Multiple origins of replication and same or different polymerases for leading and lagging strand synthesis
Function of DNA polymerase alpha
Primase
Function of DNA polymerase beta
Repair
Function of DNA polymerase gamma
Mitochondrial replication
Function of DNA polymerase delta
Nuclear replication
Function of DNA polymerase epsilon
Nuclear replication
Function of RNaseH
Enzyme that degrades RNA part of an RNA/DNA hybrid
There is no polymerase that performs ___ activity
3’ to 5’ activity
What end of DNA shortens after each replicaition cycle?
5’ end
What are the consequences of the shortening of DNA after each cycle?
Coding sequences may be eventually lost
Senescence or death signal may be triggered
Chromosome Replication and Stable propagation require
Origins of replication (Ori or ARS)
Centromere
Telomere
What is the function of telmoeres
Seal the ends of chromosomes
Prevents undesirable fusion
Prevents aberrant recombination
Attach chromosomes to nuclear envelope
Facilitate replication
Telomeres have
Hexameric repeats
What are the hexameric repeats of telomeres?
TTAGGG/TTGGGG
What is telomerase?
Ribonucleoprotein (RNP) = Protein + RNA
What is the function of the protein part of telomerase: RNP
Reverse transcriptase (RNA dependent DNA polymerase)
What is the structure and function of the RNA part of telomerase: RNP
150 nucleotides long
Functions as a template
How is the G-tail of telomeres created
By limited digestion of CA strand
How do telomeres protect chromosome ends?
The four G bases on the same strand stack up by base pairing
What cells have no detectable activity of telomerase?
Somatic cells (differentiated cells)
What cells show detectable activity of telomerase?
Germ cells/stem cells
Tumors
Length of telomeres serves as a
Mitotic clock
Shortened telomeres induce
Replicative senescense
Apoptosis
Therapeutic applications of telomeres- targets for intervention
Telomerase activity
Telomere structure
What is a telomerase inhibitor and how does it work?
GRN163L
Is a competitive inhibitor binding to active site of enzyme
What is RHPS4
G-quadruplex ligand- stabilizes the G-quadruplex and prevents attachement of telomerase
What is the function of GRN163L and RHPS4
Block the replicative potential of cancer cells
What is a virion?
An inert virus particle outside of the cell host
Replication of viruses involves
Synthesis of genome
Transcription of genome
Translation
Viral genomes are variable in
Size, organization, and replication patterns
Some common viral processes include
Replication
Packaging
Host cell alternations for efficient propagation of viruses
Genome of HIV
Two identical copies of 9749 nucleotide RNA
Replication of RNA requires __ which is done by __
Viral RNA –> DNA
Done by priming by tRNA-lys and cDNA formation by reverse transcriptase
What is reverse transcriptase?
RNA dependent DNA polymerase
Integration of cDNA copy of viral RNA into the host genome is done by
Integrase
Which is more prone to error, reverse transcriptase or DNA polymerase?
Reverse transcriptase
What are the targets of inhibition of HIV?
Fusion
Reverse transcriptase
Protease
Integrase
What is zidovudine
ZDV/AZT
An analogue of deoxythymidine
Antimetabolite drug used to treat AIDS
How does Zidovudine/AZT work?
Prevents DNA chain elongation by reverse transcriptase because it lacks a 3’ OH group
Replication of HIV can be inhibited by?
Impairment of or interference with the activity of various enzymes involved in DNA replication
Limiting the supply of substrates by inhibiting the synthesis of dATP, dCTP, dGTP, dTTP
HIV: inhibitors of bacterial gyrase are used as ___
Antibiotics
HIV: inhibitors of human topoisomerase are used for
Chemotherapy
HIV: inhibitors of synthesis of dATP, dCTP, dGTP, and dTTP are used for
Chemotherapy
What is 5-Florouracil
Inhibitor of DNA replication
Used for cancer chemotherapy
How does 5-Florouracil inhibit DNA synthesis
By inhibiting thymidyalte synthase (an enzyme for TMP synthesis)
How is 5-Florouracil created?
Capecitabine (Xeloda) = orally administered chemotherapeutic agent that is convered to fluorouracil in the body
5-Florouracil is an analogue of
Uracil or Thymine