1. DNA replication and transcription

2. DNA structure review Where in the cell is DNA located?
Nucleus
DNA is comprised of what monomer?
nucleotides
A nucleotide is made of what 3 parts?
base, phosphate, & deoxyribose sugar
The 4 bases in DNA are?
Thymine, cytosine, guanine, & adenine

3. Will DNA ever work any other way?
Pair up the bases
Adenine pairs up with?
Thymine
Thymine pairs up with?
Adenine
Cytosine pairs up with?
Guanine
Guanine pairs up with?
Cytosine
Will DNA ever work any other way?

4. Two more things to remember :
Phosphates and sugars make up what part of the double helix?
The backbone
The bases are bound to each other by what?
Hydrogen bonds

5. Replication: is the process of copying DNA
Think:
Why must DNA replicate?
The end result of cell division is two identical cells. Both new cells must have the same DNA

6. So…how does DNA replicate?
Watson and Crick model suggested a mechanism for replication.
Think of a zipper, as you pull it apart you end up with half the zipper on each side of the jacket. The double helix unwinds and the hydrogen bonds break in the same manner, creating 2 single strands of nucleotides where the bases are exposed.

7. Once the double helix is spilt into two, free floating nucleotides will start pairing with the exposed bases, to form complementary base pairs.
The sugars and phosphates of the free floating nucleotides form the second backbone of the new strands of DNA.

8. A – adenine
T – thymine
G – guanine
C - cytosine

9. According to Watson and Crick’s model, each side of the double helix is complementary to the other. In other words the sequence of bases on one side of the helix will determine the sequence of bases on the other side of the helix.
If the sequence of the single strand is the following, what will the sequence be of the bases pairing up with the strand?
T G C A T G G T C A T C C T
A C G T A C C A G T A G G A

11. Replication does not happen by magic, it requires a bit of work
Replication requires the help of enzymes.
Do you remember?
An enzyme is a catalyst and speeds up chemical reactions.

12. Enzymes aid the process of replication in two major ways:
Enzymes break the hydrogen bonds between the bases, allowing the double helix to “unzip”
An enzyme called DNA polymerase moves along the separated parent DNA strands matching bases with the free floating nucleotides.

14. Think……
Why is the end result of mitosis two daughter cells that are identical?
Replication has occurred

15. What if something goes wrong
Mutation can happen if during replication a base is accidently left out or inserted.
Definition: mutagen
Environmental factor that can alter the DNA structure