You Need:
1. Your folders
2. Your binders
3. A piece of paper with three holes punched
(See paper drawer if you need it)
Bellwork (in your head first, then share)
 If you recall, we spent the last unit discussing how
cells are made. If you remember, somatic cells are
created through the process of Mitosis. Prior to
mitosis, DNA must replicate.
1. In which step of the cell cycle are the
chromosomes copied?
2. Why must this process happen?
DNA
Deoxyribonucleic Acid
Sounds complicated, but to put it in a
nutshell…
The blueprint for you!
And now for a trip down memory lane…
 DNA is a macromolecule (Remember that word?
Carbohydrates, Lipids, and Proteins ring a bell?)
 Type of macromolecule= nucleic acid
 Nucleic acid is a polymer built from monomers called
nucleotides
 4 types of nucleotides make up DNA. Oh, but here’s
the catch, there are 3 parts to each nucleotide.
Part 1
Part 2
Part 3
The Four Types of Nucleotides
 Nucleotides differ in their bases (fancy name=
nitrogenous bases)
 The bases are:
 Thymine (T)
 Cytosine (C)
 Adenine (A)
 Guanine (G)
 The nucleotides pair together in something called
complementary base pairs… More to come on this
later.
DNA Strands
Sugar
Phosphate
Base
Sugar-phosphate
backbone
 Strands held together by
covalent bonds
 Sugar of one nucleotide
to the phosphate group
of another
 The bases are lined up
along this backbone
Now you give it a whirl.
•Make one strand of DNA using any of the 4
puzzle pieces on the table.
•We will use the other pieces in a minute.
Complementary Base Pairs
 The bases of one strand
pair up with bases of
another strand.
 The pairing is caused by
hydrogen bonds
 There are specific “rules”
for the pairing
 A pairs with T
 G pairs with C
Now you give it a whirl.
•Use the remaining puzzle pieces to match
four more sets of base pairs together
•Check with your neighbor to make sure you
have matched correctly.
The Double Helix
Watson (left) and Crick
 Due to DNA’s unique
chemical properties the
two stands look like a
ladder.
 The ladder twists though
giving it the double helix
shape.
Let’s Recap
Turn to your partner and discuss the answers to
these questions.
•What type of macromolecule is DNA?
•What are the monomers that make up this polymer?
•What are the three parts to this monomer?
•What are the names of the nitrogenous bases?
•How do the bases pair up?
DNA Replication
Original strand
 Prior to cell division DNA has to make a
copy of itself= DNA Replication
 Follows a template mechanism for this
process much like a photograph is made
from a photo negative.
 More than a dozen enzymes are involved
in the process.
 It is fast and amazingly accurate- errors
occurring in only about one of a billion
nucleotides.
Replicated strand 1
Replicated strand 2
Steps Involved in DNA Replication
Two strands of the double helix separate with the help of
Helicase
1.
a.
b.
This takes place at sites called origins of replication
The copying proceeds outward in both directions creating
replication bubbles.
Each single strand acts as a “negative” for producing a new
complementary strand.
3. Nucleotides line up one at a time across from the existing
strand as predicted by the base pairing rules.
4. Enzymes (DNA polymerases) link the nucleotides
covalently to form new DNA strands.
2.
More on DNA replication
• Eventually these replication bubble merge, yielding two
double-stranded
DNA molecules.
• In eukaryotes there are many origins of replication allowing the time to
copy all of the DNA to be much shorter.
Lets Watch this Happen
http://www.johnkyrk.com/DNAreplication.html
Now you give it a whirl.
•Refer to the DNA model you made earlier
•Make a replication bubble in the middle
•These would be consider the original strands.
•Now discuss with your shoulder partner what the new
strands will look like? How many new DNA molecules
will you have and what are they composed of?
•Tape/glue the original DNA model that you made
into your spiral notebook.
•Hot Dog! You have a model DNA!
Final Recap
Turn to your partner and discuss the answers to
these questions.
•Why does DNA replicate?
•When does DNA replicate?
•How does DNA replicate?
Time to Write
Write down the answer to these questions next to your DNA
model.
• Why does DNA replicate?
• When does DNA replicate?
• How does DNA replicate?