DNA & RNA Replication Flashcards
What is the structure difference between DNA and RNA?
RNA (ribonucleic acid) has -OH groups at both the C2 and C3 position in the sugar residue. DNA (deoxyribonucleic acid) has an -OH group at C3 only. Both DNA and RNA form a phosphodiester bond with C3 of one sugar residue and C5 of the subsequent sugar residue.
Describe base pairing and hydrogen bonds in DNA.
In DNA, adenine (A) binds to thymine (T) with two hydrogen bonds. Cytosine (C) binds to guanine (G) with three hydrogen bonds. GC rich DNA is more stable than AT rich DNA due to van der Waals forces and hydrogen bonding.
What are the major proteins and enzymes involved in eukaryotic DNA replication and what are their functions?
The major proteins and enzymes involved in eukaryotic DNA replication are the following:
-Helicase - An enzyme that catalyzes the unwinding of parental DNA ahead of the replication fork (catalysis is coupled to the hydrolysis of ATP)
-Replication protein A (RPA) - A protein that stabilizes the unwound template DNA to keep it in an extended single-stranded state so that it can be copied by polymerase (analogous to single-stranded binding proteins in prokaryotes)
-Replication factor C (RFC) - A clamp-loading protein that specifically recognizes and binds the DNA at the junction between the primer and the template
-Proliferating cell nuclear antigen (PCNA) - A sliding-clamp protein that binds adjacently to the the clamp-loading proteins, forming a ring around the template DNA
-DNA polymerase - An enzyme that catalyzes the joining of deoxyribonucleoside 5’triphosphate (dNTPs) to form the growing DNA chain
-Fen 1 - An endonuclease that functions in removal of the RNA primers by cutting between the RNA primer and DNA
-RNase H - An enzyme that functions in removal of the RNA primers by removing the RNA through the destruction of the RNA in RNA:DNA hybrid
-DNA ligase - An enzyme that joins the small pieces of newly synthesized DNA on the lagging strand (the Okazaki fragments)
-Topoisomerase - An enzyme that catalyzes the reversible breakage and joining of DNA strands to prevent rotation of the DNA ahead of the replication fork.
What is deamination of 5’-methylcytosine and what is the significance of it?
Deamination of 5’-methylcytosine (mC) is the removal of an amine (NH2) from C4 of the 5’-methylcytosine. The result of deamination is that 5’methylcytosine is converted to thymine. Deamination of 5-methyl cytosine is an example of a point mutation (a change in a single base pair of DNA). After the mutated parental strand of DNA is replicated one set of semi-conserved DNA now has thymine bonded to adenine (A-T) while the other set of semi-conserved DNA has the normal methylated cytosine bonded to guanine (G-C). Thus, deamination of 5’-methylcytosine causes a GC to AT transition mutation.
What are the three major polymerases involved in eukaryotic DNA replication, and what are their functions?
The three major polymerases involved in eukaryotic DNA replication are the following: DNA polymerase α, DNA polymerase δ, and DNA polymerase ε.
DNA polymerase α is associated with primase.
DNA polymerase δ functions in replication of the lagging strand and has high processivity with PCNA.
DNA polymerase ε functions in replication of the leading strand.
What are NRTIs and how are they used in the treatment of viral infections?
NRTIs are nucleoside reverse transcriptase inhibitors, and they comprise a subclass of reverse transcriptase inhibitors used in the management and treatment of HIV. The structure of NRTIs (lack of a 3’ OH group) prevents the formation of a 3’-5’ phosphodiester bond in growing DNA chains and can prevent the replication of the virus.
What are NNRTIs and how are they used in the treatment of viral infections?
NNRTIs are non-nucleoside reverse transcriptase inhibitors, and they comprise a subclass of reverse transcriptase inhibitors used in the management and treatment of HIV. The primary mechanism of action is through the binding of NNRTI to reverse transcriptase which results in a reduction in the overall polymerase activity of the virus.
