DNA ReplicationDNA Replication

Before We Begin – Let’s ReviewBefore We Begin – Let’s Review Take out your DNA Structure WorksheetTake out your DNA Structure Worksheet

Let’s grade it!!!Let’s grade it!!!

1.1. What is the full name of DNA?What is the full name of DNA?2.2. What is a gene?What is a gene?3.3. Where in the cell are chromosomes located?Where in the cell are chromosomes located?4.4. What two scientists established the structure of What two scientists established the structure of

DNA?DNA?5.5. What is the shape of DNA?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 CopyA Perfect Copy

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

A Perfect Copy Cont.A Perfect Copy Cont.1.1. On a sheet of scrap paper, draw a curving or zig-zagging On a sheet of scrap paper, draw a curving or zig-zagging

line that divides the paper into two halves. Vary the line that divides the paper into two halves. Vary the bends in the line as you draw it. Without tracing, copy bends in the line as you draw it. Without tracing, copy the line on a second sheet of paper.the line on a second sheet of paper.

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

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

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

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

Duplicating DNADuplicating DNA

During DNA replication:During DNA replication:1.1. The DNA molecule separates into two The DNA molecule separates into two

strandsstrands– Each strand of the double helix of DNA Each strand of the double helix of DNA

serves as a template, or model for the serves as a template, or model for the new strandnew strand

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

The Semi-ConservativeThe Semi-ConservativeReplication ModelReplication 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 OccursHow Replication Occurs

1.An enzyme called

helicase unzips the DNA

2. An enzyme called

DNA polymerase addsloose nucleotides

to the growing strands

Picture It!!!Picture It!!!

How Replication Occurs Cont.How Replication Occurs Cont.

3. An enzyme3. An enzymecalled called ligaseligaseconnects the connects the

Okasaki Okasaki fragmentsfragments togethertogether

Replication fork

DNA polymerase

New strand

Original strand

How fast does in happen?How fast does in happen?

In In eacheach of our cells, the DNA is being of our cells, the DNA is being replicated at replicated at 50 – 500 nucleotides 50 – 500 nucleotides per second!!!per second!!!

Let’s put you to the test!Let’s put you to the test!

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

a.a. Transfer RNATransfer RNAb.b. RiboseRibosec.c. HelicaseHelicased.d. PolymerasePolymerase

Let’s put you to the test!Let’s put you to the test!

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

a.a. PolymerasePolymeraseb.b. LigaseLigasec.c. HelicaseHelicased.d. DunnocaseDunnocase

Let’s put you to the test!Let’s put you to the test!

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

a.a. FourFourb.b. ThreeThreec.c. TwoTwod.d. OneOne

Let’s put you to the test!Let’s put you to the test!

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

a.a. Half old, half new DNAHalf old, half new DNAb.b. All new DNAAll new DNAc.c. All old DNAAll old DNA

Let’s put you to the test!Let’s put you to the test!

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

a.a. DayDayb.b. HourHourc.c. MinuteMinuted.d. SecondSecond