D = deoxyribo + N = nucleic + A = acid
Put it all together and it spells-

What is DNA Replication?
• Process by whicha cell makes a copy of the DNA in its nucleus.

When does DNA Replication occur?
Before Mitosis beginsInterphase
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
DNA (genetic information)
Forming daughter cell
DNA (genetic information)

* 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.

• Looks like spiral staircase or twisted ladder
•Often called “ double helix ” helix shape that twists like threads of a screw

Sides (DNA Ladder)
• Alternating molecules of
• Deoxyribose sugar
• Phosphate
Rungs (DNA Ladder)
• Made up of pairs of nitrogen bases
• adenine
• thymine
• cytosine
• guanine
Nitrogen base
Phosphate
Deoxyribose sugar

• 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.

Step 1:
• Two sides of the DNA molecule unwind and separate between paired nitrogen bases on each rung.
• Like a zipper unzipping

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

Step 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.