Download The structure of DNA

The structure of DNA
DNA molecules look like a twisted
ladder, or spiral staircase.
The two sides of the DNA ladder are made up of
molecules of sugar called deoxyribose and alternate
with molecules known as phosphates
• The sides of the ladder are often referred to as
the “backbone” of the DNA molecule
Each rung of the ladder is made up of a pair of
molecules called nitrogen bases.
•
•
•
•
•
•
•
•
There are four bases.
They are adenine (A),
thymine (T),
guanine (G), and
cytosine (C). They are
represented with the
capital letters A, T, G,
and C.
These nitrogenous bases will only pair
with a certain other base.
• With DNA the bases always pair like this:
• A with T (adenine with thymine)
• G with C (guanine with cytosine)
This pairing will help you understand
how DNA replication occurs.
• What is replication? It is the process by
which a cell makes a copy of the DNA in its
nucleus.
• How does this replication happen?????
• It begins when the two sides of the DNA
molecule unwind…………… HUH?!?!
Here is how it looks when the DNA
molecule unwinds- - - -
It then unzips like a zipper….
Why is it important that the DNA
molecule unzips?
• Because the base pairs separate and are left
open for the floating nitrogen bases to come
in, match up and build the duplicate DNA—
which is replication!!
• What do you mean floating nitrogen bases?
• Inside the nucleus are the other parts that are
needed to make a copy or duplicate of the
existing DNA.
Once “unzipped” you have two halves of the original
DNA molecule. The bases build up the missing sides = 2
molecules now----
• The duplicate DNA ---- so what?
• Because of the way in which the nitrogen bases pair
with one another, the order of the bases in each
new DNA molecule exactly matches the order in the
original DNA molecule.
This is vital when a cell duplicates—
why?
• So that there is DNA for each of the daughter
cells!!!
• OH!! Now I get it. Duplicate cells mean two of
the same.
Remember…..
• Adenine (A) always pairs with Thymine (T)
• Guanine (G) always pairs with Cytosine (C)
You will be building an edible DNA
molecule!!! 
• Remember your base pairings-work quickly
but carefully---then after you check it ---you
can eat it. The keys will be up front.
• WOW it even twists up
like a real DNA molecule.
Lets practice. . . . .
•
•
•
•
•
•
•
•
•
•
•
•
•
Write down this pattern:
A
C
G
T
G
G
T
C
C
Now write the matching pair
A
A
T
Here is the answer:
•
•
•
•
•
•
•
•
•
•
•
•
•
T
G
C
A
C
C
A
G
G
T
T
A
How did you do?
Let’s try another one…
•
•
•
•
•
•
•
•
•
Remember—apple tree and chewing gum
A
C
C
C
G
G
T
Now –write your matching base pairs. . . .
The answer is-----•
•
•
•
•
•
•
T
G
G
G
C
C
A
Ok—THAT’S GOOD
Tomorrow you will build one ---check it for
accuracy---clean up your mess and then you
can eat it. YUMMY!!