1. DNA: Structure
Biology 12

2. DNA Facts: Each cell has about 2 m of DNA.
The average human has 75 trillion cells.
The average human has enough DNA to go from the earth to the sun more than 400 times.
DNA has a diameter of only m.
The earth is 150 billion m
or 93 million miles from
the sun. 2

3. DNA: Deoxyribonucleic acid
DNA is often called the blueprint or building blocks of life.
In simple terms, DNA contains the instructions for making proteins within the cell
Our genes are on our chromosomes.
Chromosomes are made up of DNA and other proteins.
Why is DNA called the blueprint of life? 3

4. DNA Structure:
DNA consists of two polymers (chainlike molecules) that are arranged into a ladder-like structure called a Double Helix.
A molecule of DNA is made up of millions of tiny subunits called Nucleotides.
Each nucleotide consists of:
Phosphate group
Pentose sugar
Nitrogenous base

5. The Double Helix….
The double helix has two strands of DNA twisted together. 5

6. Structure cont’d:
The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rungs”.
Ladder or zipper analogy!

7. Nucleotides:
Phosphate
Nitrogenous
Base
Pentose
Sugar

8. DNA has four nitrogenous different bases:
Cytosine C
Thymine T
Adenine A
Guanine G
They are abbreviated by using their first letters.
These four bases are abbreviated by using their respective first letters.

9. Nucleotides cont’d: A
Adenine T
Thymine C
Cytosine G
Guanine

10. There are two kinds of bases in DNA:
Pyrimidines (1 ring)
Thymine (T)
Cytosine (C)
Purines (2 rings)
Adenine (A)
Guanine (G)

12. Back to the double helix….
Remember, DNA has two strands that fit together something like a zipper.
The teeth are the nitrogenous bases
But why do they stick together?
How do they pair up?
{Point to the 3-D model to show the parts as you discuss them.}

13. Nucleotides cont’d:
Each base will only bond with one other specific base.
Called Chargraff’s Rule:
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Form a base pair.
Form a base pair.

14. A C T G G A T C

15. The bases attract each other because of hydrogen bonds.
Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.
The bases attract each other because of hydrogen bonds.
Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA.

17. What does it all mean?
A gene is a section of DNA that codes for a protein.
Each unique gene has a unique sequence of bases.
This unique sequence of bases will code for the production of a unique protein.
It is these proteins and combination of proteins that give us a unique phenotype.

18. To do : Colour code, highlight or label your diagram
Complete worksheet
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