Summary DNA : CODE OF LIFE

DNA: The Code of Life (Grade 12 Life
Sciences)
1. What is DNA?
DNA (Deoxyribonucleic Acid) is the hereditary material in almost all living organisms. It
carries the genetic instructions used for development, functioning, and reproduction.


2. Structure of DNA
DNA has a double helix structure — imagine a twisted ladder.

Each nucleotide consists of:

 - A phosphate group
 - A deoxyribose sugar (5-carbon sugar)
 - A nitrogenous base

The 4 Nitrogenous Bases:

 - Adenine (A)
 - Thymine (T)
 - Cytosine (C)
 - Guanine (G)

Base Pairing Rules:

 - Adenine pairs with Thymine (A = T)
 - Cytosine pairs with Guanine (C = G)

These bases are held together by hydrogen bonds:

 - A–T: 2 hydrogen bonds
 - C–G: 3 hydrogen bonds

The sides of the ladder are made of alternating phosphate and deoxyribose sugar molecules.

The double helix structure was discovered by James Watson and Francis Crick in 1953, with
help from Rosalind Franklin.


3. Function of DNA
 - Carries genetic instructions in genes
 - Controls the production of proteins that determine traits