DNADNA ReplicationReplication

Before We Begin – Let’s Review

• Take out your DNA Structure Worksheet– Let’s grade it!!!

1. What is the full name of DNA?

2. What is a gene?

3. Where in the cell are chromosomes located?

4. What two scientists established the structure of DNA?

5. What is the shape of DNA?

6. What are the sides of the DNA ladder made of?

7. What are the “rungs” of the ladder made of?

8. Adenine always binds with _______________________ and _____________________ always binds with Cytosine.

9. Using what you know about nitrogenous base pairing fill in the missing nucleotides:

10.Why is DNA called the “Blueprint of Life?”

A Perfect Copy

• When a cell divides, each daughter cell receives a complete set of chromosomes. This means that each new cell has a complete set of the DNA code. Before a cell can divide, the DNA must be copied so that there are two sets ready to be distributed to the new cells.

A Perfect Copy Cont.

1. On a sheet of scrap paper, draw a curving or zig-zagging line that divides the paper into two halves. Vary the bends in the line as you draw it. Without tracing, copy the line on a second sheet of paper.

2. Hold the papers side by side, and compare the lines. Do they look the same?

3. Now, stack the papers, one on top of the other, and hold the papers up to the light. Are the lines the same?

4. How could you use the original paper to draw exact copies of the line without tracing it?

5. Why is it important that the copies of DNA that are given to new daughter cells be exact copies of the original?

Duplicating DNADuplicating DNA

• During DNA replication:1. The DNA molecule separates into two

strands– Each strand of the double helix of DNA

serves as a template, or model for the new strand

2. Two new complementary strands are produced following the rules of base pairing

The Semi-ConservativeReplication Model

Both Both strands of strands of

original original DNA DNA

serve as serve as templatestemplates

Daughter Daughter chromosomeschromosomes

halfhalf oldold, , half half newnew

DNA Replication

Replication Fork

How Replication Occurs

1.An enzyme

called

helicase unzips

the DNA

2. An enzyme

called

polymerase adds

loose nucleotides

to the growing

strands

Picture It!!!

How Replication Occurs Cont.

3. An enzymecalled ligaseconnects the short strands

together

Replication fork

DNA polymerase

New strand

Original strand

How fast does in happen?

• In each of our cells, the DNA is being

replicated at 50 – 500 nucleotides per second!!!

Let’s put you to the test!

1. The main enzyme involved in linking individual nucleotides into DNA molecules is

a. Transfer RNA

b. Ribose

c. Helicase

d. Polymerase

Let’s put you to the test!

2. The enzyme responsible for “gluing” the new strand of DNA together is:

a. Polymerase

b. Ligase

c. Helicase

d. Dunnocase

Let’s put you to the test!

3. During DNA replication, the DNA molecule separates into ____ strands.

a. Four

b. Three

c. Two

d. One

Let’s put you to the test!

4. The sister chromosomes formed at the end of DNA replication consist of:

a. Half old, half new DNA

b. All new DNA

c. All old DNA

Let’s put you to the test!

5. DNA is replicated at a rate of 50 -500 nucleotides per:

a. Day

b. Hour

c. Minute

d. Second