Bellwork 10/7/15

• Why does the order of bases matter in DNA?

Most missed quiz

• When you’re done, raise your hand and I’ll collect your work

• Then, begin reading and highlighting key terms in your DNA replication hand out

Replication:making an

identical copy

Before a cell divides, it must copy its DNA.

Why make a copy?• cells copy their DNA so that every new

cell will have the exact same DNA in its nucleus

*DNA never, ever, ever, ever, EVER leaves the nucleus!*

DNA replication begins at a single point in the sequence and proceeds, in two directions, until the entire strand (chromosome) is replicated. This takes

place in the nucleus.

Why does DNA replication always happen in the nucleus of eukaryotic

cells?

• enzymes are used to add new base pairs to both strands

•replication happens in a 5’ 3’ direction

•end result = two identical DNA molecules

•enzymes used include:−helicase = unzips the double helix−DNA polymerase = creates the new DNA

polymer

How does the structure of DNA make it easy to replicate?

Why is the unzipping enzyme called “helicase”?

(remember, enzymes are named after their job!)

•each half of the DNA double helix has everything it needs to recreate the other half•the two strands are complementary• complementary = something that completes or

enhances something else

If you only have half of a DNA double helix, how can you fill in the

other half?

•Semi-conservative: each replicated DNA molecule is made of one original strand and one new (complementary) strand

The complementary strand for AGGCTAAGTCGGTA is

TCCGATTCAGCCAT…

Your turn…

Write the complementary strand for the following sequence:

CGGAATTCG

GCCTTAAGC

DNA Replication Foldable1. Fold the edges of your paper toward the BACK along

the dotted lines.2. Now fold the two sides in to meet in the middle (also

marked with a dotted line).3. Using the given ORIGINAL strand, complete the

complementary strand.4. Open your edges. Now “replicate” the DNA by filling in

the two new strands.5. Put your name on your paper and turn it in! I will keep

them until next week, when we will add another step.

Exit ticket:

• Explain why DNA replication is considered to be semi-conservative.