DNA Replication

What does DNA stand for?

D = deoxyribo + N = nucleic + A = acid

Put it all together and it spells-

deoxyribonucleic acid

• 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 by using Rosalind Franklin’s lab notes and pictures.

- 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.