11. DNA

Lesson objectives
To establish a connection between the structure of DNA and its function.

How organisms differ if their DNA include same components?

Let’s recall !!!
Organic compounds in living things:
1) Carbohydrates
2) Lipids
3) Proteins
4) Nucleic acids

Nucleic acids
Nucleic acids are master molecules mainly found in nucleus.
They are polymers

Types of nucleic acids
Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)

DNA
DNA is a type of nucleic acid that stores genetic information and transmits it to the next generation.

DNA structure
Polymer.
Monomers are nucleotides.
Nucleotide structure:
5 C-sugar called deoxyribose
phosphate group (H3PO4)
nitrogenous base

Nitrogenous base
There are four types of nitrogenous base:
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
Purines (double ring)
Pyrimidines (single ring)

Pentose sugar is attached with its 5’ end to phosphate group.
Pentose sugar is attached with its 1’ end to nitrogenous base.

With it’s 3’ C sugar links to phosphate group of next nucleotide via posphodiester bond.
So posphodiester bond forms polynucleotide chain.

The sequence of nucleotides in polynucleotide chain determines genetic information of the organism.
It is the primary structure of DNA
5’ A-G-T-A-C-G 3’

Two chains of nucleotides make double helix structure.
These two chains are antiparallel to each other. One strand is 5’-3’ , second strand is 3’-5’

Double helix structure is revealed in 1953 by James Watson and Francis Crick.

Phosphate group with sugar make up the DNA’s backbone
Nitrogenous bases of antiparallel chains join via hydrogen bonds.
A pairs with T by two hydrogen bonds.
C pairs with G by three hydrogen bonds.
So hydrogen bonds join antiparallel chains.
Nucleotides in parallel chains are complementary paired to each other A is complementary to T, G is complementary to C.
So if we know one strand sequence we know sequence of the second one

For example:
5’ AAGCCCTTAT 3’
3’ TTCGGGAATA 5’
C in DNA is equal to 140. Total number of nucleotides is equal to 1000 Find:
G=?
A=?
T=?
Solution: number of C=G so G=140
A+T+C+G=1000
(C+G)=140+140=280
A+T=1000-280=720 since A=T
A=720:2=360
T=360

Problems
1)Find the sequence of the second strand:
5’ CGGTCATTT 3’
2)Amount of A is equal to 220 in DNA. C= 125 . Find:
T=?
G=?
Total nucleotides in DNA=?
How many hydrogen bonds are in DNA?