Wednesday, February 2, 2011

DNA and RNA Structure

Candidates should be able to:
Describe two pieces of experimental evidence to support the conclusion that DNA is the genetic material.
Outline the important events that led to the present knowledge of the nature of the DNA molecule.
Describe the structure of RNA and DNA and explain the importance of base pairing and hydrogen bonding.

1. Deoxyribonucleic acid (DNA)

DNA carries the genetic information of a cell!

Consist of thousands of genes!

A. Pentose

A sugar containing 5 carbon atoms

In DNA, sugar deoxyribose is present
In RNA, sugar ribose is present

B. Phosphoric acid

The formula for phosphoric acid is H3PO4

Its structural formula is as follows:

There are 2 categories of bases


2-ringed structure


1-ringed structure

1-ringed structure

Adenine, A
Guanine, G

Cytosine, C
Thymine, T

How is a polynucleotide formed?

Sugar-phosphate backbone

All units are identical
along the chain


Base sequence changes
along the length of chain

Sequence of bases carry
genetic information of
the organism

What makes up a DNA molecule?

1. Consists of 2
Polynucleotide chains

2. The 2 chains run in
opposite directions

3. Hydrogen bonds hold
the chains together

3. Complementary base
pairs are formed by
the hydrogen bonds

More details about the DNA molecules

1. A double helix of 2 polynucleotide chains

2. The width between the backbones
are constant and equal to the width
of a purine and a pyrimidine

3. The ratio of A to T is 1
the ratio of C to G is 1

What makes up an RNA molecule?

Its a single stranded molecule (except for some viruses).
The pentose sugar is ribose.
The nitrogenous base, instead of thymine, is uracil.
There are 3 types of RNA
Messenger RNA (mRNA)
Ribosomal RNA (rRNA)
Transfer RNA (tRNA)


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