This presentation features DNA. It's structure and how cells replicate it.

1. Sounds complicated, but to put it
in a nutshell…
The blueprint for you!
DNA
Deoxyribonucleic Acid

2. 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

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.

4. DNA Strands
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
Sugar
Phosphate
Base

5. 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.

6. 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

7. 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.

8. 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.

9. •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?
Let’s Recap
Turn to your partner and discuss the answers to
these questions.

10. DNA Replication
 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.
Original
strand
Replicated
strand 1
Replicated strand 2

11. Steps Involved in DNA Replication
1. Two strands of the double helix separate
a. This takes place at sites called origins of
replication
b. The copying proceeds outward in both directions
creating replication bubbles.
2. 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.

12. 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.

13. Lets Watch this Happen
http://www.johnkyrk.com/DNAreplication.html

14. 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

15. •Why does DNA replicate?
•When does DNA replicate?
•How does DNA replicate?
Final Recap
Turn to your partner and discuss the answers to
these questions.

16. 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?