DNA Replication Flashcards
(20 cards)
Semi-conservative replication
Two parental strands separate and each serves as a template for a new progeny strand
Correct theory
Conservative replication
Two parental strands stay together and somehow produce another daughter helix and completely new strands
Incorrect theory
Dispersive replication
DNA becomes fragmented so that new and old DNA coexist in the same strand a after replication
Incorrect theory
DNA helicase
Enzyme that breaks hydrogen bonds between complimentary base pairs (strands unzipped)
Single stranded binding proteins (SSBS)
Bind to exposed strands, preventing them from rejoining (annealing?)
Why does DNA need to be replaced?
Growth
Repair
Reproduction
DNA gyrase
In bacteria, it relieves tension by cutting and re annealing the two strands
Topoisomerase
In eukaryotic cells relieves tension between two strands of the DNA
DNA polymerase lll
Adds complementary nucleotides in the 5’ to 3’ direction using RNA primers as starting points
RNA primers
Short segments of RNA that provides a starting point for DNA nucleotides to attach to
Primase
The enzyme required to add RNA primers
Okazaki fragments
Lagging strand is discontinuous in short fragments away from fork
DNA polymerase l
Removes RNA primers and replaces them with correct DNA nucleotides
DNA ligase
Joins Okazaki fragments together by making a phosphodiester bond
DNA polymerase l & lll
Are the proofreaders of new daughter DNA
Stage one of DNA replication
- DNA helicase
- SSBS
- Topoisonerase relieves tension
- Sections of DNA are replicated as soon as it unwinds
- Replication forks
- Two daughter DNA molecules formed
Replication forks
- Junction where DNA is still joined and enzymes are bound
- several forks found on one DNA molecule to increase speed of replication
- replicating bubbles form and meet creating daughter DNA molecules
Priming
- DNA polymerase cannot start incorporating nucleotides on its own
- needs help from RNA polymerase lll
Stage two of DNA replication
- Elongation
- Direction of replication occurs in the 5’ to 3’ direction
- bidirectional (occurs toward fork on one strand and away from fork on the other strand)
- leading strand (built continuously towards fork 5’ to 3’)
- lagging strand (discontinuously in shirk fragments)
Stage 3 of DNA replication
- quality control
- DNA polymerase l and lll are the proof readers of new daughter cells
- when they encounter a mistake in the sequence they act as an exonuclease and cut out the wrong nucleotide and replace with correct one
- the process happens immediately
