DNA Replication Flashcards
Describe the basic structure of DNA
Double helix (2 strands of DNA), complementary strands pair up A and T, G and C, and strands are anti-parallel, 5 to 3 prime end
How is DNA replicated and when during the cell cycle is it replicated.
DNA creates a new strand by matching nucleotides to an existing strand. 3 steps: initiation, elongation and termination. DNA polymerase synthesizes new strand. DNA rep occurs in the S phase of the cell cycle, which is part of interphase (after gap 1, but before gap 2)
What are the 7 basic rules of DNA replication
a) semi-conservative b) starts at the origin c) bidirectional d) semi-discontinuous e) synthesis always in the 5 to 3 prime direction f) RNA primers required
How can large amount of DNA in eukaryotic cells replicate in such a short period of time.
B/c have multiple polymerases that can synthesize two new strands at the same time by using unwound strand from original DNA template
Identify the leading and lagging strand (although labeled)
leading= continuous
lagging- discontinuous- forms okazaki fragments. After separating from RNA primers ligase can connect fragments
structure of deoxyribonucleoside triphosphatase
Explain what proofreading is and what enzyme is involved in the process
DNA polymerase proofreads using 3 to 5 prime exonuclease. When DNA polym. reads an incorrect base pair, DNA polymerase moves backwards one base pair of DNA. 3-5 exonuclease excises the incorret base pair and then DNA polym. re-inserts adds correct base pair.
Explain why DNA synthesis only occurs in the 5 to 3 prime direction
the 5 to 3 prime method removes 2 phosphate groups (hydrolysis) from deoxyribonucleoside triphosphate to create energy for the reaction. DNA synthesis adds nucleotide to 3 prime end of DNA TEMPLATE. If synthesize in opposite direction, NO high energy bond would be cleaved thus resulting in insufficient energy for continuing the process.
CANNOt proofread–dont have enough energy
Explain the functions of all core proteins at the replication fork
Topoisomerase 1/2- prevents torsion by DNA breaking (1-cuts 1 strand of DNA, 2-cuts 2 strands of DNA)
Helicase (MCM 2-8)- separates 2 DNA strands
Primase (DNA pd alpha)- RNA primer synthesis
Single Strand Binding Protein (RPA)- prevents reannealing (coming back together) of single strand
DNA polymerase- synthesizes new DNA. EPSILON= leading strand and DELTA- lagging strand
DNA B-sliding clamp- keeps polymerase on DNA (aka PCNA= proliferating cell nuclear antigen)
DNA ligase= seals nick via PHOSPHODIESTER bond linkage. Especially important for lagging strand synthesis
How is the lagging strand replication problem dealt with?
The lagging strand of telomeres cannot be replicated by the usual mechanism.
Solution: special telomere sequence: tandem repeats TTAGGG
Telomerase: a specific enzyme with integrated RNA template–a RNA-dependant DNA polymerase–reverse transcriptase enzyme.
Insertion of telomere nucleotides by telomerase. Adds nucleotides to 3 prime end of template.
