NUCLEIC ACIDS
Below is one of the molecules that makes up DNA.
What functional groups do you see in the
molecule:
0%
12%
88%
0%
1.
2.
3.
4.
Hydroxyl
Carboxyl
Amino
Phosphate
Functions of DNA
• Control the processes of heredity by which
cells and organisms reproduce proteins
Types of Nucleic Acids
1. DNA
(deoxyribonucleic
acid): doublestranded
2. RNA (ribonucleic
acid): singlestranded
Nucleic Acid Structure
• The monomer units of DNA are known as
nucleotides
• All nucleotides have three “parts” in
common:
a. Phosphate “backbone”
b. Pentose sugar (ribose or deoxyribose)
c. Nitrogen base
Deoxyribose Sugar (DNA)
• Has 5 carbons and 3 oxygens
• Carbon atoms are numbered 1', 2', 3', 4',
and 5'
– Distinguishes from the numbering of the
atoms of the purine and pyrmidine rings
• 5'-carbons link to the phosphate groups
• 3'-carbons link to the hydroxyl groups
• Direction of the nucleotides in one strand
is opposite to their direction in the other
strand: the strands are antiparallel.
• Asymmetric ends of DNA strands are
called the 5′ (five prime) and 3′ (three
prime) ends
– 5' end having a
terminal phosphate group
– 3' end having a terminal
hydroxyl group
Nitrogen Bases
• Weak hydrogen bonds connect
complementary nitrogen bases
• Two types:
a. Pyrimidines: form hexagon shaped rings
1. Cytosine
2. Thymine (only DNA)
3. Uracil (only RNA)
b. Purines: combination of a pentagon
shaped ring and a hexagon shaped ring
1. Adenine
2. Guanine
Nitrogen Base Pairing
• Adenine and Thymine must form two
hydrogen bonds to be stable while
Guanine and Cytosine must form three
– Makes the base pairing system an extremely
simple: the A-T and C-G pairs are the only
ones physically possible
Let’s Practice How to Form
DNA!
We will use our hands to represent a
nucleotide.
PHOSPHATE
NITROGEN
BASE
SUGAR
The four different Nitrogen Bases for DNA
are abbreviated using the following letters….
A
Adenine
T
Thymine
G
Guanine
C
Cytosine
Using your two hands, please show how
you think two nucleotides will/should bond
together.
Did you put your hands like this???
Time to find out why this is
wrong!!!
Adenine and Guanine are larger
molecules known as…
PURINES
LOOK! TWO RINGS!!!
THYMINE and CYTOSINE are smaller
molecules known as…
PYRIMIDINES
LOOK! Only one ring!!
Now, when using our hands to represent the
nucleotides, we must modify the nitrogen
base in order to represent these PURINES
and PYRIMIDINES.
How would you
represent a large
PURINE?
How would you
represent a small
PYRIMIDINE?
Full Finger
Half Finger
In DNA, a PURINE always bonds with a
PYRIMIDINE when forming a “rung” of the DNA
ladder.
LOOK! A long finger pairs with a short finger! In
other words, a purine pairs with a pyrimidine.
In DNA, Adenine always pairs
with Thymine using two hydrogen
bonds.
A
T
In DNA GUANINE always pairs with
CYTOSINE using three hydrogen
bonds.
G
C
Time to use your brain and
hands in order to review
nucleotide structure and type.
USING YOUR HAND, SHOW ME THYMINE
USING YOUR HAND SHOW ME ADENINE
SHOW ME CYTOSINE
SHOW ME HOW CYTOSINE AND THYMINE BOND
TO FORM A RUNG ON THE LADDER
THEY DON’T
OK
Now that you recognize
nucleotide type and structure, it’s
time to start building the polymer
from these monomers.
The molecules marked “W” are
best described as:
100%
0%
0%
0%
1.
2.
3.
4.
Monomers
Polymers
Isomers
isotopes
Reactions A and B
are respectively
known as:
A
12%
0%
0%
88%
1.
2.
3.
4.
Dehydration, hydrolysis
Condensation, hydrolysis
Polymerization, decomposition
Hydrolysis, dehydration
B
Molecule(s) “X” are most likely:
0%
0%
0%
100%
0%
1.
2.
3.
4.
5.
Carbohydrates
Monomers
Polymers
Water
Starch
If molecule “W” is a nucleotide,
molecule marked “Y” is most likely:
12%
0%
88%
0%
0%
1.
2.
3.
4.
5.
Protein
Starch
DNA
Galactose
Fructose
In order to make a molecule of DNA,
you would need to create many rungs
to the DNA ladder.
Look. Many Rungs.
Etc…
What part of the nucleotide alternates
to form the sides of the DNA ladder?
Sugar, Phosphate.
Sugar, Phosphate.
Sugar, Phosphate.
Etc…
Etc…
What makes up the
“RUNGS” of the ladder?
The Nitrogen
Bases
Go Ahead!
Stack you hand on top of your partners
hands building two rungs of the DNA
ladder.
Why is this
WRONG????
The sides of the DNA ladder “run” in opposite
directions. One side is actually flipped and the
nucleotides are upside down!
TRY IT!!!
Because the sides of the DNA “run” in
opposite directions, DNA is said to be
ANTIPARALLEL.
In this DNA molecule, the THUMB part or
better known as the PHOSPHATE
GROUP, is said to be the 5 prime (5’) end.
5 prime
5 prime
The “hand” or sugar part of the DNA
molecule makes up the 3 prime (3’) end of
the DNA ladder.
3 Prime
3 Prime
If you link enough nucleotides together,
the DNA molecule begins to take on
the characteristic shape known as the
Double Helix