8.2 Study Guide Flashcards
What does it mean to replicate DNA?
to create an exact copy of a DNA molecule
What does it mean for DNA replication to be semi-conservative?
Each new DNA molecule formed during replication contains one original (parent) strand and one newly formed strand.
How do we know that DNA replication is semi-conservative?
Due to the Meselson-Stahl experiment, which used density labeling to track the fate of DNA strands during replication.
Why is it important that DNA replication creates an exact copy?
It is crucial for cell division as it ensures each new cell receives a complete set of DNA instructions
When would DNA replication occur?
Before Cell Division in “Interphase”
Where would DNA replication occur in Eukaryotic Cells?
The Nucleus
Where does DNA replication begin?
Sites called Origins of Replication
What is the first step in DNA replication? What enzyme is involved?
Part of the DNA Double Helix is Unwound
Enzyme = Helicase
How is the DNA strand stabilized during the first step?
Single-Stranded binding proteins (SSB proteins)
What is the replication fork?
Y shaped region where the parental strands of DNA are being unwound
What is the second step in DNA replication? What enzyme is involved?
RNA primer is laid down providing a free 3’-hydroxyl group to attach new nucleotides to
Enzyme=Primase
Can DNA Polymerase I initiate synthesis on its own?
No, it can only add nucleotides to an existing chain and cannot initiate synthesis on its own
Can DNA Polymerase I build onto the 5’ end of an existing DNA strand?
No, only the 3’ end of an existing DNA strand
What is the third step in DNA replication? What enzyme is involved?
DNA Nucleotide bases are added to the growing (daughter) strand at the replication fork
Enzyme = DNA Polymerase III
Where does the energy for DNA replication come from?
The Phosphate (P-P-P) bonds in nucleosides (ATP, GTP,TTP and CTP)
What are nucleosides?
Nucleotides with P-P-P
Nucleotides are added to a growing DNA strand by their _______ to the _____ end.
Phosphate
3’
DNA stands only grow in this direction?
5’ to 3’
Nucleotides need a starter ________ to bond to during replication.
nucleotide
What is the fourth step in DNA replication? What Enzyme is involved?
The RNA Primer is replaced by DNA
(happens with replication is almost complete)
Enzyme=DNA Polymerase I
What is the fifth step in DNA replication? What Enzyme is invovled?
Okazaki Fragments are glued together to form a continuous strand.
Enzyme = DNA Ligase
What are Okazaki Fragments?
Small fragments of DNA in the lagging strand that are generated due to the discontinuous synthesis from the 5’ to 3’ direction
What are the five primary enzymes in DNA replication?
- DNA Helicase
- RNA Primase
- DNA Polymerase I
- DNA Polymerase III
- DNA Ligase
What does DNA Helicase do?
Unwinds and separates double stranded DNA by breaking the H bonds between base pairs
Happens at specific regions and creates a replication fork of two strands running in antiparallel directions
Nucleotides have to be added in opposite directions on the two parent strands during DNA replication because?
DNA strands are antiparallel
Which direction is DNA Polymerase moving on the leading strand?
Toward the replication fork
Is DNA continuous or discontinuous on the leading strand?
Continuous
Which direction is DNA Polymerase moving on the lagging strand?
Away from the replication fork
Is DNA continuous or discontinuous on the lagging strand?
Discontinuous
Why are Primes (3’, 5’) are used in numbering carbons on the sugar portion of the nucleotide?
to distinguish them from the nitrogenous base carbons
Why do you think multiple replication bubbles form during the process of DNA replication?
To significantly speed up the process by allowing for simultaneous replication at various points along the DNA molecule.
Why is the helicase able to break the H bonds between base pairs?
It acts as a molecular motor, using energy derived from ATP hydrolysis to physically disrupt the weak hydrogen bonds, allowing the DNA strands to separate and unwind.
Does Replication occurs on one side of the replication fork at a time?
No, replication occurs on both sides of the fork simultaneously
As a new nucleotide is added to the growing DNA strand, which part of the new nucleotide forms a bond with the 3’ OH group of the existing strand?
5’ phosphate group of the new nucleotide forms a bond with the 3’ OH group of the existing strand.
What does DNA Polymerase III do?
Main DNA Builder
1000 bases/ second
What does DNA Polymerase 1 do?
Proofreads and corrects typos
Repairs Mismatched Bases
Removes Abnormal Bases
Overall reduces error rates from 1 in 10,000 to 1 in 100 million bases
RNA Primer removal
In DNA Synthesis, the DNA template strand is read in the ______ direction, while the new strand is made in the direction.
3’ to 5’
5’ to 3
