DNA replication and transcription Chapter 8, sections 8-1 p. 140 & 8-2 pp

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

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?

Two more things to remember : 1.Phosphates and sugars make up what part of the double helix? The backbone 2.The bases are bound to each other by what? Hydrogen bonds

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

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.

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.

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

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

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.

Enzymes aid the process of replication in two major ways: 1.Enzymes break the hydrogen bonds between the bases, allowing the double helix to “unzip” 2.An enzyme called DNA polymerase moves along the separated parent DNA strands matching bases with the free floating nucleotides.

Think…… Why is the end result of mitosis two daughter cells that are identical?

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