UNIT ___: DNA Replication Name: _____________________

Essential Idea(s):

The structure of DNA is ideally suited to its function.

IB Assessment Statements

7.1.U1	DNA structure suggested a mechanism for DNA replication. Outline the features of DNA structure that suggested a mechanism for DNA replication.
2.7.U1	The replication of DNA is semiconservative and depends on complementary base pairing. Describe the meaning of “semiconservative” in relation to DNA replication. Explain the role of complementary base pairing in DNA replication.
2.7.S2	Analysis of Meselson and Stahl’s results to obtain support for the theory of semi-conservative replication of DNA. Compare dispersive, conservative and semi-conservative replication. Predict experimental results in the Meselson and Stahl experiment if DNA replication was dispersive, conservative or semi-conservative.
2.7.NOS	Obtaining of evidence for scientific theories- Meselson and Stahl obtained evidence for the semi-conservative replication of DNA. Describe the procedure of the Meselson and Stahl experiment. Explain how the Meselson and Stahl experiment demonstrated semi-conservative DNA replication.
2.7.U2	Helicase unwinds the double helix and separates the two strands by breaking hydrogen bonds. State why DNA strands must be separated prior to replication. Outline the function of helicase. State the role of the origin of replication in DNA replication. Contrast the number of origins in prokaryotic cells to the number in eukaryotic cells.
7.1.U4	DNA replication is carried out by a complex system of enzymes. Outline the role of the following proteins in DNA replications: helicase, topoisomerase (AKA gyrase), single stranded binding proteins, primase, DNA polymerase III, DNA polymerase I, and DNA ligase.
2.7.U3	DNA polymerase links nucleotides together to form a new strand, using a pre-existing strand as a template. Describe the movement of DNA polymerase along the DNA template strand. Describe the action of DNA polymerase III in pairing nucleotides during DNA replication.
7.1.U5	DNA polymerases can only add nucleotides to the 3’ end of a primer. Explain the need for RNA primers in DNA replication. Explain what is meant by DNA replication occurring in a 5' to 3' direction.
7.1.U3	DNA replication is continuous on the leading strand and discontinuous on the lagging strand. Compare replication on the the leading strand and the lagging strand of DNA. Explain why replication is different on the leading and lagging strands of DNA. Outline the formation of Okazaki fragments on the lagging strand.
3.5.U2	PCR can be used to amplify small amounts of DNA. State the function of the PCR. Describe the selectivity of the PCR.
2.7.A1	Use of Taq DNA polymerase to produce multiple copies of DNA rapidly by the polymerase chain reaction (PCR). Outline the process of the PCR. Explain the use of Taq DNA polymerase in the PCR.

DNA Structure 🡪 DNA Replication

"It hasn't escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for genetic material." Watson and Crick

DNA’s structure allows it to perform its function of storing information in a way that can be copied and passed down to future generations.

Structure	Importance in DNA Replication

Semi-Conservative Replication

Meselson and Stahl Experiment: DNA Replication is Semiconservative

RESULT	Expect if Semiconservative	Expect if Conservative	Expect if Dispersive
Start
After 1 Cycle
After 2 Cycles		❌
After 3 Cycles			❌

HELICASE

Breaks ______________ bonds between bases unzipping the double helix

Begins to unwind the DNA at the _______________________________________ (a specific nucleotide sequence).

Prokaryotes:

Eukaryotes:

Helicase enzymes move in both directions from the origin, forming a:

At either end of the replication bubble is a _______________________________, a Y-shaped region where the new strands of DNA are elongating

Single Stranded Binding Proteins

Hold the DNA strands apart (keeps the separated strands apart and stabilize the unwound DNA).

GYRASE

Ahead of the replication fork, gyrase unwinds the super coil of DNA. Also known as topoisomerase.

Primase and Primers

The enzyme ______________ adds _________ nucleotides to complementary base sequences. These RNA nucleotides act as a _______________ for DNA nucleotides.

_____________ are short segments of RNA, about _________ nucleotides long

Must have a primer because DNA polymerase can only add nucleotides to another nucleotide

DNA Polymerase III

Adds DNA nucleoside ______phosphates to an existing nucleotide in a _________________ direction. DNA polymerase III can only add nucleotides to ___________________ of a growing DNA strand