Nucleic acids, comprising DNA and RNA, are long polymers made of nucleotides that play crucial roles in genetic information storage and protein synthesis. DNA, discovered as a double helix by Watson and Crick in 1953, contains instructions for protein synthesis, while RNA exists in different forms and is synthesized in the nucleus before being exported to the cytoplasm. Notably, the structure of nucleotides includes a sugar, phosphate group, and nitrogenous base, with specific pairing rules governing DNA base pairings.

2. • Nucleic Acids are very long, thread-like
polymers, made up of a linear array of monomers
called nucleotides.
• Nucleic acids vary in size in nature
• tRNA molecules contain as few as 80 nucleotides
• Eukaryotic chromosomes contain as many as
100,000,000 nucleotides.

3. Two types of nucleic acids
• Deoxyribonucleic acid (DNA)
• Ribonucleic acid (RNA)

4. DNA
• DNA is often
called the
blueprint of life.
• In simple terms,
DNA contains the
instructions for
making proteins
within the cell.

5. A HISTORY OF DNA
• Discovery of the DNA double helix
A. Frederick Griffith – Discovers that a
factor in diseased bacteria can transform
harmless bacteria into deadly bacteria
(1928)
B. Rosalind Franklin - X-ray photo of
DNA.
(1952)
C. Watson and Crick - described the
DNA molecule from Franklin’s X-ray.
(1953)

6. Structure of DNA
• Discovered in 1953
by two scientists:
• James Watson
(USA)
• Francis Crick (GBR)
• Known as the
double-helix
model.

7. RNA
RNA
ribonucleic acid
3 types of RNA in a cell
•Ribosomal RNAs (rRNA) are components of
ribosomes
•Messenger RNAs (mRNA) carry genetic
information
•Transfer RNAs (tRNA) are adapter molecules in
translation
RNA

8. DNA has
deoxyribose, RNA
has ribose;
DNA has 2
strands, RNA has
one strand;
DNA has
thymine, RNA has
uracil.

9. The distribution of nucleic acids in
the eukaryotic cell
• DNA is found in the nucleus
with small amounts in mitochondria and
chloroplasts
• RNA is found throughout the cell

10. The nucleus contains the cell’s DNA (genome)
Nucleus

11. RNA is synthesized in the nucleus and
exported to the cytoplasm
Nucleus
Cytoplasm

12. NUCLEOTIDE STRUCTURE
PHOSPHATE
SUGAR
Ribose or
Deoxyribose
NUCLEOTIDE
BASE
PURINES PYRIMIDINES
Adenine (A)
Guanine(G)
Cytocine (C)
Thymine (T)
Uracil (U)

13. DNA Nucleotide
O
O=P-O
O
Phosphate
Group
N
Nitrogenous
base(A, G, C,
or T)
CH2
O
C1
C4
C3 C2
5
Sugar
(deoxyribose)

15. The double-helix
• A twisted ladder with two long chains
of alternating phosphates and sugars.
The nitrogenous bases act as the
“rungs” joining the two strands.

16. DNA Double Helix
P
P
P
O
O
O
1
2
3
4
5
5
3
3
5
P
P
P
O
O
O
1
2 3
4
5
5
3
5
3
G C
T A

17. 17
One Strand of DNA
• The backbone of
the molecule is
alternating
phosphates and
deoxyribose sugar
• The teeth are
nitrogenous bases.
phosphate
deoxyribose
bases

18. THE SUGAR-PHOSPHATE
BACKBONE
• The nucleotides are all
orientated in the same
direction
• The phosphate group joins
the 3rd Carbon of one
sugar to the 5th Carbon of
the next in line.
P
P
P
P
P
P

19. ADDING IN THE
BASES
• The bases are
attached to the 1st
Carbon
• Their order is
important
It determines the
genetic information
of the molecule
P
P
P
P
P
P
G
C
C
A
T
T

20. 20
Two Stranded DNA
• Remember, DNA
has two strands
that fit together
something like a
zipper.
• The teeth are the
nitrogenous bases
but why do they
stick together?

21. RIBOSE DEOXYRIBOSE
CH2OH
H
OH
C
C
OH OH
C
O
H HH
C
CH2OH
H
OH
C
C
OH H
C
O
H HH
C
Spot the difference

22. Nitrogenous Bases
• PURINES
1. Adenine (A)
2. Guanine (G)
• PYRIMIDINES
3. Thymine (T)
4. Cytosine (C) T or C
A or G

23. 23
Thymine and Cytosine are
pyrimidines
• Thymine and cytosine each have one
ring of carbon and nitrogen atoms.
C
N
N
O
N
cytosine
C
N
N
O
O
thymine
C
C
C
C
C
C
C

24. 24
Adenine and Guanine are
purines
• Adenine and guanine each have two
rings of carbon and nitrogen atoms.
C
C
C
C
N
N
N
Adenine
N
N
C
C
C
C
C
N
N
O
N
Guanine
N
N
C

25. Chargaff’s Rule
• Adenine must pair with
Thymine
• Guanine must pair with
Cytosine
• Their amounts in a given DNA
molecule will be about the
same.
G CT A

26. BASE-PAIRINGS
CG
H-bonds
T A

28. How long is the DNA molecule?

30. DNA IS MADE OF TWO STRANDS
OF POLYNUCLEOTIDE
 The sister strands of the DNA molecule run in
opposite directions (antiparallel)
 They are joined by the bases
 Each base is paired with a specific partner:
A is always paired with T
G is always paired with C
“Purine with Pyrimidine”
 The sister strands are complementary but not
identical
 The bases are joined by hydrogen bonds,
individually weak but collectively strong
 There are 10 base pairs per turn

31. Structure of Nucleotide Bases
Purines & Pyrimidines

32. Nucleotides are
linked by
phosphodiester
bonds

33. DNA Organization

34. 1. Try the problem from this link:
http://www.dnaftb.org/dnaftb/19/concept/index.html
Self-test
2. Use the questions on the following
slides

35. What sugar is used in a DNA?
A) ribose
B) fructose
C) deoxyribose
D) Glucose

36. What is the base found in
RNA but not DNA?
A) Cytosine
B) Uracil
C) Thymine
D) Adenine

37. What covalent bonds link
nucleic acid monomers?
A) Carbon-Carbon double bonds
B) Carbon-Nitrogen bonds
C) Hydrogen bonds
D) Phosphodiester bonds

38. Each deoxyribonucleotide is
composed of
A) 2'-deoxyribose sugar, Nitrogenous base, 5'-
hydroxyl
B) 3'-deoxyribose sugar, Nitrogenous base, 5'-
hydroxyl
C) 3'-deoxyribose sugar, Nitrogenous base, 5'-
Phosphate
D) Ribose sugar, Nitrogenous base, 5'-hydroxyl
E) 2'-deoxyribose sugar, Nitrogenous base, 5'-
phosphate