DNA replication Flashcards
(30 cards)
Reminder: function of nucleic acids?
store and transmit genetic information
reminder: characteristics of DNA?
genetic material, passed on from generation to generation
Contains genes which code for protein synthesis
Double stranded
Reminder: characteristics of RNA?
functions in the synthesis of proteins, there is rRNA, tRNA, mRNA and it is single stranded
What does it mean for DNA to be antiparallel?
one strand runs from 5 to 3 and the other from 3 to 5
How is DNA formed?
from 2 DNA polymers held together by H bonds between nitrogenous bases
How are DNA polymers formed?
linking phosphate of one nucleotide to pentose of the next
When is DNA replication happening in the cell cycle?
S phase before mitotic phase
Key players of DNA replication
Helicase, DNA polymerase, primase, ligase
What does Helicase do?
Unwinds DNA strands, or breaking hydrogen bonds
What does DNA polymerase do?
Synthesizes DNA by catalyzing the formation of phosphodiester bonds between nucleotides, using parental strand as template, reading from 3 to 5, synthesizing from 5 to 3
What does Primase do?
RNA polymerase synthesizes a RNA primer on template strand
Why is Primase required
DNA polymerase can only add nucleotide free 3- OH group
What does Ligase do?
glues together nicks in DNA sugar phosphate backbone, needed after RNA rimers are replaced by DNA and for okazaki fragments
What do single stranded binding proteins do
Stabilizes single stranded DNA
In prokaryote chromosome, how many origins of replication are there
One
On eukaryotic chromosomes, how many origins of replication could there be
hundreds to thousands
What are the steps of dna replication
Initiation and elongation
What happens during initiation of dna replication?
Helicases bind to origins of replication and unwind DNA to form replication bubble
single stranded binding proteins bind to single stranded DNA
What happens during elongation of DNA replication
Primase makes complementary RNA primer, DNA polymerase synthesizes of a new strand of DNA using parental strand as template
What are the characteristics of the leading strand?
Continuous DNA synthesis, DNA polymerase synthesizing DNA in same direction as DNA unwinding, one RNA primer
Characteristics of lagging strand
Many RNA primers, okazaki fragments, DNA polymerase must synthesize in opposite direction of DNA unwinding
Explain how replication works for leading strand
- Helicase unwinds DNA, primase makes RNA primer, DNA pol extends from primer, DNA pol replaces primer with DNA, ligase repairs nick in backbone
Explain how replication works for lagging strand
Helicase unwinds DNA, Primase makes RNA primer 1, DNA pol extends from primer 1, primase makes primer 2, DNA pol extends, etc…
- THEN DNA pol replaces RNA primers with DNA, ligase repairs nicks between primers nd rest of strand
True or False? DNA polymerase can only synthesize DNA in the 5 -3 direction
True
