DNA REPLICATION

Chapter 11, Section 1

DNA Review• What is the building block of DNA?• Nucleotides (Sugar, Phosphate, Base)• What is the shape of DNA?• Double Helix• What 2 bonds hold nucleotides together?• Hydrogen bonds(bases) Covalent (Sugar Phosphate)• During what part of the Cell Cycle does DNA replicate? • Interphase (S-phase)• What pairs with G? A? Number of Hydrogen Bonds?• Guanine & Cytosine (3), Adenine & Thymine (2)• Which are the Purines? Pyrimidines? Rungs for each?• Purines A&G (2 rungs) Pyrimidines T&C (1 rung)• What are the complimentary bases for the following

sequence? AATCCGC• TTAGGCG

How DNA Replicates

• DNA has to be replicated before a cell divides

• New cells at the end of Mitosis need identical strands of DNA

• One strand of DNA gets used as a template (pattern) to make a new strand that matches up with it

• Special enzymes are required for DNA replication

Steps of DNA Replication

• 1. Replication begins with the unwinding & separation of the DNA double helix by enzymes called helicases– The process is

like unzipping a zipper

• 2. New strands are formed by enzymes called DNA polymerase which adds complimentary nucleotides to the original strands

• 3. Leading Strand (continuous) vs. Lagging Strand (discontinuous)

Semi-conservativeReplication

• Each new strand compliments one of the original strands

• 2 identical DNA double helix strands are the result of DNA replication

• http://www.wiley.com/college/pratt/0471393878/student/animations/dna_replication/index.html

Uneven formation of DNA

• When DNA is replicating one strand forms continuously and the other strand forms in chunks with spaces that need to be filled in

DNA 5’ to 3’

• Anti-parallel • In the double helix one

strand is “right-side up,” the other strand is “up-side down”

• If not, the nitrogen bases wouldn’t be able to bond together

• 5’ and 3’ come from how the carbons in the 5-carbon sugar get numbered

5’ end 5’ end

3’ end3’ end

• DNA polymerase can only add nucleotides to the 3’ end of a strand of DNA

• That means that the newly forming strand is forming from 5’ to 3’

That means…• One strand gets to form

continuously• The other strand gets

formed in chunks called Okazaki fragments that need to be connected by the enzyme DNA Ligase

• http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120076/micro04.swf::DNA%20Replication%20Fork

• Important Terms- semiconservative replication, anti-parallel, 5’ to 3’

• 3 enzymes you must know the function of are Helicase, DNA Polymerase, and Ligase