2.6 STRUCTURE OF DNA
AND RNA
UNDERSTANDING
• The nucleic acids DNA and RNA are polymers of
nucleotides
• DNA differs from RNA in the number of strands
normally present, the base composition and the
type of pentose
• DNA is a double helix made of two antiparallel
strands of nucleotides linded by hydrogen bonding
between complimentary base pairs
SKILLS
• Drawing simple diagrams of the structure of single
nucleotides and of DNA and RNA using circles,
pentagons and rectangles to represent
phosphates. pentoses and bases.
BASIC STRUCTURE OF A NUCLEOTIDE
• Like polysaccharides and proteins, nucleic acids
are polymers. That is, large molecules made up of
many repeating subunits.
• For nucleic acids, the subunit is called a nucleotide
• They have three components
1. A phosphate (PO4-)
2. A 5 carbon sugar
3. A nitrogen containing base
HOW DNA AND RNA DIFFER - 1
DNA
1.The sugar is deoxyribose
RNA
1. The sugar is ribose
HOW DNA AND RNA DIFFER - 2
DNA
2. DNA is usually double
stranded
RNA
2. RNA is usually single
stranded
HOW DNA AND RNA DIFFER - 3
DNA
• Contains the bases
Cytosine, Guanine,
Adenine and Thymine
RNA
• Contains the bases
Cytosine, Guanine,
Adenine and Uracil
A SIMPLE MODEL
• You should know how to draw a
simple representation of DNA
(and RNA) using a cirlce as a
phosphate, a pentagon as
the sugar and a rectangle
as the base
(see pages 107-8 in text)