Download DNA - Southington Public Schools

DNA: the molecule of heredity
What is DNA?
A very large molecule that controls the production of proteins.
Almost all functions of living things including growing,
reproducing, digesting food, moving, fighting disease, even
thinking rely on the production of various proteins. Without DNA,
living things would not exist very long.
Parts of DNA
DNA is very complex and long (almost 1m in each human cell!),
but actually is made up of simple subunits called nucleotides.
Nucleotides have three parts: 1. simple sugar
2. phosphate group
3. nitrogen base
 The simple sugar in DNA is deoxyribose
 There are 4 possible nitrogen bases:
Adenine (A), Guanine (G), Thymine (T), Cytosine (C)
3D Structure of DNA
DNA molecules look like a twisted ladder. This structure is known
as a “double helix”. The sides of the ladder are the sugar and
phosphate groups. The rungs of the ladder are the nitrogen
bases.
Certain nitrogen bases always pair up together.
A always pairs with T
G always pairs with C
How is it possible to make thousands of different proteins using
only 4 different bases? Proteins are combinations of amino acids.
Amino acids are associated with 3-base groups called codons.
One base difference in a codon usually makes different amino
acid.
Example: T-T-T is read differently than A-T-T or C-T-T
DNA replication
DNA strands are copied following precise steps that insure exact copies
are made.
1. The helix uncoils and the two sides of the ladder “unzip”
(separate).
2. Complementary bases pair with the exposed pairs (A-T and GC).
3. New sugar and phosphate groups form the sides of the ladder.
4. Each new DNA formed has one old and one new strand.