MM 5-6 Flashcards
What is DNA replication and when does it occur in the cell cycle?
DNA replication occurs in during S phase of interphase. Editing of DNA happens during G2 phase. It is Semi-conservative, so each copied strand of DNA has one parent strand.
Topoisomerase
Topoisomerase unwinds the supercoil during DNA replication and transcription.
Topoisomerase bind to double-stranded DNA and cut the phosphate backbone of either one or both the DNA strands. This intermediate break allows the DNA to be untangled or unwound, and, at the end of these processes, the DNA backbone is resealed again.
Helicase
Helicases are motor proteins that move directionally along a nucleic acid backbone, separating two annealed nucleic acid strands using energy derived from ATP hydrolysis. Many cellular processes, such as DNA replication, transcription, recombination, and DNA repair involve the separation of nucleic acid strands that necessitates the use of helicases.
Single-Strand Binding Proteins
Single-Strand Binding Proteins attach to single strands to prevent strands from re-associating.
primase
Primase makes a small RNA primer that is 5 bases long and runs complimentary to the template. This occurs because DNA polymerase cannot extend a chain from scratch. After replication, the primer is removed and replaced by DNA Polymerase.
DNA Polymerase
DNA polymerase reads in a 3-5 direction and replicates in a 5-3 direction by adding nucleotides with Watson Crick base pairing and catalyzing the phosphodiester bonds.
Proliferating Cell nuclear antigen (PCNA)
Proliferating Cell nuclear antigen (PCNA) keeps DNA polymerase bound to the template like a sliding clamp.
DNA Polymerase alpha:
DNA Polymerase alpha: involved with initiation but lacks proofreading, later replaced by sigma or epsilon.
DNA Polymerase sigma:
DNA Polymerase sigma: Lagging strand synthesis and fills gaps
DNA Polymerase epsilon
DNA Polymerase epsilon: Leading strand synthesis and fills gaps
DNA Polymerase beta:
DNA Polymerase beta: involved in DNA repair. Performs base excision repair required for DNA maintenance, replication, recombination.
DNA Polymerase gamma:
DNA Polymerase gamma: Replicates mitochondrial DNA
Okazaki fragments
segments on the lagging strand, separated by primer.
Telomeres
Telomeres (TTAGGG): thousands of repeated sequences that are synthesized and maintained by Telomerase. Telomerase exists in rapidly dividing single cells and germ line cells. It is absent in most somatic cells, so they get shorter through time
Types of DNA editing
Mismatch repair, base excision repair, nucleotide excision repair, recombination repair.