DNA Replication

What does DNA stand for?

D = deoxyribo + N = nucleic + A = acid

Put it all together and it spells-

deoxyribonucleicacid

• Process by which-

a cell makes a copy of the DNA in its nucleus.

What is DNA Replication?

When does DNA Replication occur?

Before Mitosis begins- Interphase

Cell Division: Stage1- Interphase

Why is DNA Replication an important cell process?• Ensures that each daughter cell will

have all of the genetic information it needs to carry out its activities.

Forming daughter cell

Forming daughter cell

DNA (genetic information)

DNA (genetic information)

History of DNA’s Discovery* 1950’s scientists showed DNA carries all cell’s instructions.

* Learned DNA passed from parent cell to its daughter cells.

* 1953 James Watson and Francis Crick discovered structure of DNA.

- Revealed important information about how DNA copies (replicates) itself.

Appearance of DNA

• Looks like spiral staircase or twisted ladder

•Often called “double helix”

helix-

shape that twists like threads of a screw

Structure of DNASides (DNA Ladder)

• Alternating molecules of• Deoxyribose sugar• Phosphate

Rungs (DNA Ladder)• Made up of pairs of nitrogen bases

• adenine• thymine• cytosine• guanine

Phosphate

Deoxyribose sugar

Nitrogen base

Ladder Rungs•Letters A, T, G, C

•Used to represent the four bases that make up ladder’s rungs

•Nitrogen bases on one side of ladder “match up” in specific way with bases on the other side.

•Adenine always pairs with Thymine (A-T)•Guanine always pairs with Cytosine (G-C)

Nitrogen Base

Nitrogen base

Pairing pattern of the nitrogen bases• key to understanding how DNA

replication occurs.

Replication ProcessStep 1: •Two sides of the DNA molecule unwind and separate between paired nitrogen bases on each rung.

•Like a zipper unzipping

Replication Process

Step 2:•Nitrogen bases floating in nucleus pair up with bases on each half of the DNA molecule.

•A always pairs with T•G always pairs with C

Replication ProcessStep 3: •Once new bases are attached, two new DNA molecules formed.

•Order of bases in each new DNA molecule exactly matches the order in the original molecule.

http://www.cfkeep.org/uploads/dna_replication.mov

http://video.search.yahoo.com/search/video?p=dna+structure&ei=UTF-8&fr=sbc-web&x=wrt

Chromatin• DNA takes the form of chromatin, it

looks like loos coils or spaghetti, very long. In the nucleus.

ChromosomeX- shaped structures composed of tightly coiled DNAOne comes from the mother and one comes from the father. This happens during cell division. They will attach in the middle, which forms a Gene.

Gene

Lab• Marshmallow DNA Replication

• Write down a code of 5 base pairsEx: A-T, T-A, G-C, G-C, T-A

• Using colored marshmallow make your base pairs and place them in the order of your code

• Green = Adenine Yellow= Thymine• Pink = Guanine White = Cytosine

• Use a broken demonstrated shown• Make sides of ladder, as demonstrated

• Deoxyribose = • Phosphate =

Applying What You Have Learned:

• Base-Pairing Mini-Lab• Materials• Small Marshmallows of 4 different colors• Large White marshmallows• Small White marshmallows• Toothpicks• Directions

• Use your knowledge of how the base pairs of DNA bond to create an accurate model of a DNA code that is handed to you at the start of the lab

• Use the colored marshmallows to represent the different base pairs, the large white marshmallows to represent the sugar, and the small white marshmallows for the phosphate groups. Keep in mind that purines bases are larger than pyrimidine bases!

• Record your random 7-digit code here ___________________________________• Use the space below to create a key that will identify the parts of the model, and

their corresponding parts in DNA• Follow-up Questions• 1. What is the sugar that makes up DNA?• 2. How does the number of adenines compare to the number of thymines?

How about cytosines to guanines? Provide sample numbers.• 3. How do the number of purines compare to the number of pyrimidines?

Provide sample numbers.

• DNA Extraction Lab