Chapter 16.2 - DNA Replication Flashcards
Important points about DNA replication (4)
- DNA replication occurs in the same way in all organisms
- DNA must be copied accurately
- Genetic info (DNA) must be transmitted to daughter cells
- DNA directs its own replication
Actual Process of DNA Replication (5)
- DNA strands separate
- Enzymes bind and use each strand as a template to make a new strand
- Semiconservative replication
- Each new double helix consists of one old and one new strand
- DIAGRAM
Semiconservative model
The two strands of the parental molecule separate, and each functions as a template for synthesis for a new, complimentary strand
Origin of Replication (4)
- Replication of each DNA molecule begins at sites with a specific sequence of nucleotides
- A-T rich sequence at origin of replication
- Specific proteins attach and separate strands
- Check diagrams!
Replication Fork
At the end of each replication bubble. This is a Y shaped region where the parental strands of DNA are being unwound by several types of proteins.
Origins of replication in a Eukaryote
DNA helix must unwind to expose template strand. See page 338!
3 Proteins involved in unwinding DNA
- Helicase
- Single-stranded bonding protein
- Topoisomerase
Helicase
- unwinds strands
- breaks hydrogen bonds between nitrogenous bases
Single-stranded binding protein
-binds to the unpaired DNA strands, keeping them from re-pairing after the parental strands separate
Topoisomerase
-an enzyme that helps relieve the strain by breaking, swivelling and rejoining DNA strands
Enzymes involved in DNA synthesis (2)
- DNA Polymerase
2. Primase
DNA polymerase
-catalyzes the synthesis of new DNA by adding nucleotides to the 3’ end of a preexisting chain
Primase
-makes the RNA primer and provides initial 3’ OH
Directional Polymerization of Nucleotides (4)
- DNA polymerase catalyzes addition of nucleotide triphosphate to 3’ end of growing strand
- Synthesis of Nucleic Acid is always 5’3’ and antiparallel to template
- Nucleotide added is determined by base on template strand
- Replication proceeds in both directions and occurs simultaneously in both strands
Lagging Strand
Discontinues synthesis
Leading strand
Continuous synthesis
Okazaki fragments
Fragments of the lagging strand (separately primed)
Proofreading (4)
- DNA polymerase can detect and remove non-complementary nucleotides during replication
- If incorrectly paired nucleotides are missed, other enzymes will later remove and replace the mismatched nucleotide
- These DNA repair systems also repair damaged DNA
- Result in mutation if not corrected. Mutations are perpetual
DNA ligase
An enzyme that joins all the sugar-phosphate backbones of the Okazaki fragments into a continuous strand
A summary of bacterial DNA Replication
Diagram on 341
Mismatch Repair
Other enzymes remove and replace incorrectly paired nucleotides that have resulted from replication errors
Termination of Replication in prokaryotes
- chromosomes are circular
- replication proceeds in both directions to end around 180 degrees
Termination of Replication in eukaryotes
- chromosomes are linear
- replication terminates at nucleotide sequences known as telomeres
- no genes present
Telomeres (3)
Telomeres do not contain genes and instead consists typically of repetitions of one short nucleotide sequence