Our Guiding Question

• WHAT DETERMINES THE ORDER OF AMINO ACIDS IN A PROTEIN???

Warm-up

1. Which parts of the nucleotides are connected to make one strand (half) of DNA?

2. Which parts of the nucleotides connect the two strands (halves) of DNA?

3. What type of bond connects the two strands together?

4. If a DNA molecule is 30%Adenine how much Cytosine is there?

What does DNA look like?

• We can describe its molecular structure• We can say what DNA looks like after

isolation.

DNA replication

How is DNA made?

DNA Replication

Whenever a cell divides into two new cells, it needs to make an exact copy of the DNA.

What would happen if a cell divided without DNA making a copy of itself?

The process of copying DNA is called DNA replication.

Enzymes in DNA replication• Enzymes are proteins that act as machines

in the cell to do work.

• 2 enzymes do the work of DNA replication:– Helicase is responsible for separating the

2 strands of DNA– DNA Polymerase is responsible for

adding on new Nucleotides.

We will replicate (copy) our DNA molecule in class to produce 2 new identical DNA molecules

Helicase• Helicase unwinds and separates the 2 strands of DNA so

that each strand may be copied.• Helicase breaks the hydrogen bonds between the bases

of each strand.

Hydrogen Bonds

DNA Polymerase• DNA Polymerase

adds on the complimentary bases to the new strands of DNA

• DNA Polymerase makes bonds between the phosphate and the deoxyribose sugar of the nucleotides.

DNA Polymerase

Complementary base pairing

• If one strand of DNA has the following sequence, CTAATGT

What is the base sequence (order of nucleotides) for the complimentary strand?

GATTACA

Complicated picture of replication…

Replication in Action

• Replication occurs simultaneously at multiple places along a DNA strand.– 1 chromosome is about 80 million base pairs

long.– Replication is as fast as 50 base pairs a

second!

Flash Animation:

http://www.mcb.harvard.edu/Losick/images/TromboneFINALd.swf