DNA
DEOXYRIBONUCLEIC
ACID
O.L Lesson Objectives
At the end of this lesson you should be able to
1. Outline the simple structure of DNA – 2 strands and
A,T,C, G complement
2. Distinguish between coding and non coding
structures
3. Describe the triplet base code
4. Outline the structure of RNA – refer to Uracil and
complement to DNA
5. Know the function of mRNA
6. Discuss the replication of DNA
What is DNA
 Hereditary material
 Carries and passes on genetic information
 It is a nucleic acid
 Made up of nucleotides
The DNA Double Helix
 Two parallel strands
 Each with a series of bases to the inside
 The bases are directly opposite each other
 The bases link each other in pairs
 These links form the steps of the ladder
The DNA Double Helix
Hydrogen bond- link
Parallel Strand
Base
Parallel Strand
Base
The Bases
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
The Base Pair Rule
 The bases can occur in any sequence along a strand
of DNA
 But the sequence must be complimentary to the
sequence on the other strand
The Base Pair Rule
 Adenine can only join to Thymine
A
T
 Guanine can only join to Cytosine
G
C
Building DNA
http://www.zerobio.com/drag_gr9/DNA/dna.htm
Building DNA
http://learn.genetics.utah.edu/units/basics/builddna/
Learning Check
 What does DNA stand for?
 Name the four bases in DNA
 Which base complements Adenine?
 Which base compliments Guanine?
Non Coding DNA
 Only about 3% of DNA is composed of genes
 97% of DNA is non coding DNA or junk DNA
Coding DNA
 The parts of DNA that contain information to make
RNA or protein
 Coding DNA in genes are called exons
Non Coding DNA
 Do not contain critical information for the
production of protein
 They are now thought to play a role in gene
expression
 Non coding DNA within genes is called introns
Learning Check
Label a gene and a piece of non coding DNA in the
following picture
RNA
Ribonucleic Acid
Operates with DNA to make proteins
Has Uracil instead of Thymine
Differences between DNA and RNA
DNA
RNA
Double strand
Single strand
Sugar is deoxyribose
Sugar is ribose
Has Thymine
Has Uracil
Very long
Short molecule
Self replicating
Not self replicating
Found only in the
Found in nucleus and
nucleus
cytoplasm
Similarities between DNA and RNA
 Both are nucleic acids
 Both contain
adenine, guanine and cytosine nucleotides
 Operate together to produce specific proteins
Learning Check
1.
What does RNA stand for?
2. What three bases do DNA and RNA have in common?
3. What base does RNA have instead of Thymine?
4. Where do you find both DNA and RNA?
5. Where else will you find RNA?
H.L Objectives
 At the end of this section you should know …..
 DNA structure – deoxyribose sugar, sugar,




phosphate and 4 named nitrogenous bases
Nucleotide structure
Specific Purine and Pyramidine couples –
complementarybase pairs
Hydrogen bonding
Double helix
Higher Level
NUCLEIC ACID
STRUCTURE
Nucleotides
 Nucleotides are carbon ring structures containing
nitrogen linked to a 5-carbon sugar (a ribose)
 5-carbon sugar is either a ribose or a deoxyribose
 In eukaryotic cells nucleic acids are either:
Deoxyribose nucleic acids (DNA)
Ribose nucleic acids (RNA)
A Nucleotide
OH
HO
H+
Phosphate
P
NH2 Base
O
N
H
O
5’CH2
H
N
O
N
N
1’
4’
3’
OH
2’
H
OH
Sugar
Coding and Non Coding Parts
 Non coding Structures
Sugar – Phosphate
 Coding Structures
Base Sequences
Purine Bases
 Adenine and Guanine
Double ringed molecular structures
Known as Purine Bases
Pyrimidine Bases
 Thymine and Cytosine
single ringed structures
Known as Pyrimidine bases
Purines
NH2
Adenine
N
N
N
CH3
(DNA)
N
Guanine
NH
N
O
O
Thymine Uracil
(RNA)
NH
N
O
N
N
Pyrimidines
NH2
NH
O
N
O
NH2
Cytosine
N
N
O
Base Numbers
Number of Purine Bases
=
Number of Pyrimidine Bases
This led to the discovery of Base Pairing
Base Pairing
Guanine And Cytosine
-
+
+
+
-
Three Hydrogen Bonds
Base Pairing
Adenine And Thymine
+ -
Adenine
-
Thymine
+
Two Hydrogen Bonds
Base Pairing
Guanine And Thymine
+
+
-
-
-
-G C
- T CA
-
-
-
G
T A
G
A T
-
-
Major
groove
A T
C G
C
-
3.4 nm
1 nm
-
-
-
-
-
-
-
The Watson - Crick
Model Of DNA
-
-
Minor
groove
G
T A
A T
C G
C
-
-
-
-
0.34 nm
What have you learned
Can you ………………
1. Outline the simple structure of DNA
2. Name the four bases and the base pairs in DNA
3. Distinguish between coding and non coding
structures
4. Define triplet base code
5. Outline the structure of RNA
6. Name the bases in RNA and know the function of
mRNA
7. Discuss the replication of DNA
End