DNADNA

The Molecule Of Life

DNA StructureDNA Structure

• Nucleotides• The Backbone• Base Pairing• The Double Helix• Chromosomes• Nucleosomes• Genes

Nucleotide: the basic molecule of DNA

Nucleotide: the basic molecule of DNA

3 parts:1. Nitrogenous

base

2. Sugar

3. Phosphate

5’

3’

Nucleotides: 4 basesNucleotides: 4 bases

The nucleotides in DNA use 4 different bases:

1. Guanine G

2. Cytosine C

3. Adenine A

4. Thymine T

* Just think G-CAT, you know that rapper

Nucleotide Bases: 2 classesNucleotide Bases: 2 classes

Purine:• Adenine• Guanine

Pyrimidine• Cytosine• Thymine

Purines Pyrimidines

The Backbone

The Backbone

• Nucleotides combine by covalent bond between phosphates and sugars

A single strand of

DNA

A single strand of

DNA

Written as: 5’-ACTGTCAAGGTCGAT-3’

5’

3’ 3’

Base PairingBase Pairing

Hydrogen Bonds for spontaneously between specific nitrogenous bases

Pairing Rule:• Cytosine bonds with Guanine C-G• Thymine bonds with Adenine T-A

Base PairingBase Pairing

A Double Strand of DNAA Double Strand of DNA5’

5’3’

3’

How a DNA strand is writtenHow a DNA strand is written

5’ - ATAGGGCCTAGAACCTGG - 3’

3’ - TATCCCGGATCTTGGACC - 5’

Strands are anti-parallel

Try writing one yourselfTry writing one yourself

3’ - TTAAGCTATGCT - 5’

What is the complementary DNA strand?

Now draw a double strand, including bases and backbones

Now draw a double strand, including bases and backbones

5’ - ATGC - 3’

1. Does your diagram have sugars, phosphates, and nitrogen bases?

2. Are the strands anti-parallel?3. Where are covalent bonds between

nucleotides?4. Where are the hydrogen bonds?

The Double HelixThe Double Helix

High Resolution image of Actual DNA molecule

DNA within a CellDNA within a Cell

• DNA combine with proteins called histones to create structures called chromosomes

• Each cell contains many chromosomes, each with a specific DNA sequence

A NucleosomeA Nucleosome

• DNA strands are tightly wrapped around histone proteins to create a complex known as a nucleosome

GenesGenes

• A gene is a specific sequence of DNA nucleotides

• The DNA sequence contains the information necessary to build a protein

• Each specific gene codes for a specific protein

How much DNA is there?How much DNA is there?

The human genome contains 3 billion base pairs of DNA, about the same amount as frogs and sharks. But other genomes are much larger. A newt genome has about 15 billion base pairs of DNA, and a lily genome has almost 100 billion.

Unravel all the DNA in your body…

Unravel all the DNA in your body…

…and it would stretch to the moon!

Junk DNAJunk DNA

• Only a very small percentage of your DNA (1.5%) is actually composed of coding genes, most of it is repetitive sequences or other non-coding sequences

• We still don’t know what the other 98.5% of DNA in our cells are for.

• We’ve still got a whole lot to learn