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1. What are the three parts of a nucleotide?- Sugar (deoxyribose), phosphate, nitrogen base

2. Adenine (A) bonds with ____________

- Thymine (T)

3. Guanine (G) bonds with ____________- Cytosine (C)

Objective: Describe DNA replication. Explain the importance of DNA replication. Model DNA replication.

DNA ReplicationMaking New DNA Molecules

Objective: Describe DNA replication. Explain the importance of DNA replication. Model DNA replication.

Overview of DNA Replication

• DNA replication is the process by which the cell copies its DNA.– Happens in the S phase (synthesis) of cell cycle.

• The double helix separates, and each strand serves as a template on which a new strand is built.

• Each new piece of DNA has one old strand and one new strand.

Step 1: Separation of the Strands• In order for the DNA to replicate, the

two strands need to be separated.– This happens easily because the hydrogen

bonds holding them together are weak.

• An enzyme called helicase breaks the hydrogen bonds and separates the strands.

Step 2: Building New DNA

• A second enzyme called DNA polymerase attaches to the DNA strands to attach complementary nucleotides.

• The DNA polymerase joins the nucleotides by covalent bonds in the backbone and hydrogen bonds between the 2 strands.

Animation animation 2

Objective: Describe DNA replication. Explain the importance of DNA replication. Model DNA replication.

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Objective: Describe DNA replication. Explain the importance of DNA replication. Model DNA replication.

Step 3: Proofreading• DNA replication is very accurate, with only

about one error in 10,000 paired nucleotides.

• Mutations are mistakes or changes to the DNA.– Some of them can be fixed, and some cannot.– Some can have serious effects, and some do not

affect the cell at all.

• Enzymes proofread and repair many of the mutations that can occur.– This reduces the error rate to about 1 in every 1

billion base pairs.

End Result of Replication

• Replication results in the creation of two identical molecules of DNA.

• The process is described as being semi-conservative.– “semi” = half– “conserve” = to save– Replication is semi-

conservative, because each new molecule is made of one old strand of DNA and one newly created strand.

Activity time!

• Now you are going to take your DNA model from yesterday and simulate replication.

• You need your model, scissors, glue and colored pencils, using same colors as yesterday!

Sugars – Red Adenine - Purple

Phosphates – Black Thymine - Pink

Guanine – Green Cytosine – Blue

• Listen to the instructions as they are given!!