DNA Replication Flashcards
What examples are there of polymers
DNA
RNA
Which of the nitrogenous bases are purines
Adenine
Guanine
Which of the nitrogenous bases are pyrimidine
Cytosine
Uracil
Thymine
What makes up a nucleoside
Sugar and base
What makes up a nucleoside phosphate
Nucleoside (sugar and base) and phosphate
Where does a covalent bond form
Between phosphate group of one nucleotide and 3’ carbon of sugar of another nucleotide
Which bond is 5’-3’ and what are the characteristics
Phosphodiester
Very strong
Make backbone stable
What causes the width to be the same between backbones
Purine always paired with a pyrimidine
What must happen before DNA replication
Initiator protein binds to origin of replication (initiator protein recognises specific DNA sequence)
What does DNA helicase do
Cause DNA to untwist, form Y shape
Break hydrogen bonds between bases
Forms two single-stranded template strands
What is single-stranded DNA-binding (SSB)
Proteins bind to each single stranded DNA molecule, hold them in place, stop the strands rejoining
How many nucleotides does single-stranded DNA-binding (SSB) bind to
32 nucleotides
What is a tetramer
Four molecules joined together
What does DNA topoisomerases do
Aid unwinding process - cuts DNA backbone
What does DNA primase do
Synthesis short RNA primer (5-10 bases)
Attaches to 3’ end of template strand
What does DNA polymerase do
Causes nucleotide addition to primer
Must be complementary to base on template
Catalyses phosphodiester bond formation between 3’ carbon of last nucleotide and 5’ phosphate of incoming nucleotide
Where does the DNA polymerase read from
3’ to 5’
So new strand grows 5’ to 3’
How is 5’ to 3’ polarity maintained
DNA synthesised in opposite directions on two template strands
What is the leading strand
New strand made in same direction as movement of replication fork
What is the lagging strand
The stand synthesised in opposite direction
Where does DNA polymerase remove nucleotide
From end of DNA chain - exonuclease activity
Which strand does DNA polymerase synthesise
New strand toward replication fork
Leading strand only needs single RNA primer for synthesis
How is the DNA on the lagging strand synthesised
Discontinuously
Needs a series of primers
New primer attaches at replication fork - short second segment synthesised
What is the name of short segments on lagging strand
Okazaki fragments
How is the second new DNA strand made (from lagging)
Okazaki fragments have to be joined
Used DNA polymerase and DNA ligase
How does DNA polymerase remove nucleotides - exonuclease activity
DNA polymerase reads RNA primer in DNA recognises not meant to be there - chops out nucleotides of RNA primer
Left with gap where DNA polymerase removed RNA primer, DNA ligase closes gap, form phosphodiester bond
What is ‘proof reading site’
DNA polymerase reads what’s just been added to molecule, cuts out wrong nucleotides adds right base instead
What is needed before DNA synthesis starts
RNA primer
