Lecture 7 The 3R Flashcards
DNA needs be kept … and needs to be …
conserved, in order to keep the information that makes up the organism
flexible, in order to allow changes to accommodate in the environment of the cell
DNA replication
interphase: chromosome duplication
m-phase: mitosis and cell division
mitotic spindle
the Meselson-Stahl experiment
semi-conservative vs conservative vs dispersive
n15 and n14, replication, percentage
DNA synthesis
template strand, primer strand
5’ -> 3’ direction (free OH-group in the 3’ end)
DNA polymerase
two phosphates released
replication fork
structure formed when the helix is opened up for replication leading strand vs lagging strand RNA primers by DNA primase okizaki fragments by DNA polymerase RNA primers erased DNA ligase seal
how to open the helix
DNA helicase, ring structure
ATP -> ADP + P
how to stabilize the helix
single-strand DNA binding proteins (SSB)
hinder secondary structures to occur, bind the backbone of the DNA, bases still exposed to the enzymes
loading of the machinery
sliding camp
clamp loader
active replication fork
p
the winding problem
a lot of torsional stress will build if the DNA cannot rapidly rotate
solution: topoisomerase I makes a cut (nick) permitting the helix to spin. When relaxed the enzyme reconnects the broken strands
separating two replicated circles
topoisomerase II cleave and reconstruct
fidelity of DNA replication
quite high fidelity, active mechanisms to correct mistakes
DNA polymerase does the first check
spontaneous DNA damage/mutations
hydrolysis
oxidation
methylation
depurination and deamination
depurination: loss of purine base (G, A)
deamintation: loss of amino group
C -> U and therefore G -> A
thymine dimers
dangerous mutation caused by UV-light, chemical bonds between thymines formed -> not able to properly base pair with the bases introduced during the replication
