Unit 10 Flashcards
What are the 3 hypotheses of DNA replication test by Meselson and Stahl?
-Conservative replication
-Dispersive replication
-Semi-Conservative replication
What is semi-conservative replication?
The two nucleotide strand separate and each serves as a template for a new strand
What is a replication fork?
Point at which a double-stranded DNA molecule separates into two single strands that serve as templates for replication
What end of a DNA strand is used by Pol I or Pol III to add new nucleotides?
3’
What are the differences between leading and lagging strands of DNA? Why are they necessary?
-The leading strand goes through continuous replication while the lagging strand goes through discontinuous replication.
-This is necessary because the lagging strand runs out of room and has to start over at the origin of replication creating Okazaki fragments
What are Okazaki fragments?
-The short lengths of newly synthesized DNA produced by discontinuous replication on the lagging strand
-After Reiji Okazaki
Why is an RNA primer necessary to initiate DNA synthesis?
They provide a 3’ -OH group for the attachment of a DNA nucleotide at the initiation of replication.
What happens when DNA polymerase selects the wrong nucleotide to insert?
Polymerase III uses its 3’ - 5’ exonuclease activity to back up and remove the incorrect nucleotide
What prevents the ends of a linear chromosome from getting shorter each time the chromosome is copied?
The G-rich overhang can be extended by telomerase
How can eukaryotic cells generate a large amount of DNA in a small amount of time?
Thousands of origins of replication
Initiator proteins
Proteins that bind to the origin of replication and causes a short section of DNA to unwind
Helicase
Breaks the hydrogen bond that exist between the bases of the two nucleotide strands of a DNA molecule
Single-Strand binding proteins
Protein that attaches tightly to the exposed single-stranded DNA during replication and prevents the formation of secondary structures that would interfere with replication
Topoisomerase (DNA gyrase)
Enzyme in E. coli that relieves the torsional strain that builds up ahead of the replication fork
Primase
An enzyme that synthesizes a short stretch of RNA on a DNA template; functions in replication to provide a 3’ -OH group for the attachment of a DNA nucleotide
DNA Polymerase III
Bacterial DNA polymerase that synthesizes new nucleotide strand by adding new nucleotides to the 3’ -OH group provided by the primer
DNA Polymerase I
Bacterial DNA polymerase that removes RNA nucleotides and replaces them with DNA nucleotides
DNA ligase
Enzyme that catalyzes the formation of a phosphodiester bond between adjacent 3’ -OH and 5’ phosphate groups in a DNA molecule without adding another nucleotide to the strand
What gradient was used in the Meselson and Stahl 1958 experiment?
A cesium chloride gradient
Explain the Meselson and Stahl experiment:
- First, E. coli were grown on a 15N “heavy” medium as well as a lighter 14N medium.
- A centrifuge tube is filled with a heavy salt solution and DNA fragments containing both 14N and the 15N
- It is then spun in a centrifuge at high speeds for several days
- A density gradient develops within the tube. Heavy DNA ( with 15N) will move toward the bottom and the lighter 14N will be at the top
- They DNA is then goes through a single replication and is promptly measured to see the proportions of 15N and 14N
What technique did Meselson and Stahl use?
Equilibrium density gradient centrifugation
What is the function of the conserved DnaA Box within OriC, the origin of replication in bacterial DNA?
It is the binding site, conformation change of chromosome opens up the double helix and “brings in” DnaB and DnaC helicase proteins that break the hydrogen bonds to “unzip” DNA
What is the function of the AT-rich region of the conserved site within the OriC origin of replication?
Weaker interaction, open up DNA with conformation change
What structure is made during DNA replication of circular DNA?
Theta structure
