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Class notes Life science
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This is the first part covering the Life science topic of DNA. This document summarises some key concepts. This is the first part, however, the second document will cover the rest of the topic. I hope this will be of some help to you, all the best

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  • September 10, 2024
  • 2
  • 2024/2025
  • Class notes
  • Ms. randburg
  • 12

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GRADE 12 LIFE SCIENCES: DNA THE CODE OF LIFE SUMMARY-PART 1

-All living organisms have DNA and RNA
1.DNA

● DNA - Deoxyribonucleic acid -Is mainly found on chromosomes in the nucleus.
● Gene is a segment of DNA that carries genetic information of a particular
characteristics.(Also carries code for proteins).
● Three places in which DNA can be found:
- Nucleus: Known as nuclear DNA ;makes up genes on chromosomes.
- Mitochondria: Mitochondrial DNA ; used for tracing ancestry
- Chloroplasts: Chloroplast DNA ;only found in plants(humans cannot photosynthesise
therefore do not have chloroplasts.)
● Discovery of DNA
-In 1952 ,Rosalind Franklin and Maurice Wilkins researched the structure of DNA using X-ray
diffraction images.
-The diffraction images were used by Watson and Crick to create a 3-D double helix model for
DNA in 1953.
-Watson and Crick received the Nobel Prize for the discovery of the structure of DNA in 1962

The structure of DNA-Natural shape is a double helix
Each strand of the double helix is made up of a sequence of DNA nucleotides.The nucleotides
of the DNA molecules consist of:
1. Phosphate
2. Deoxyribose sugar(THE PENTOSE SUGAR FOR DNA)
3. Nitrogenous base:
a.Adenine(A)-Purine
b. Thymine(T)Pyrimidine
c.Cytosine(C)-Pyridine
d.Guanine(G)-Purine
4. Weak hydrogen bonds between the nitrogenous bases




● PURINES-DOUBLE RING STRUCTURE
● PYRIMIDINES-SINGLE RING STRUCTURE

● The nitrogenous bases are complementary to each other:

Adenine(A) is complementary to Thymine(T)
(Apple Tree)
Cytosine(C) is complementary to Guanine(G)

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