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DNA. The Molecule Of Life. DNA Structure. Nucleotides The Backbone Base Pairing The Double Helix Chromosomes Nucleosomes Genes. Nucleotide: the basic molecule of DNA. 3 parts: Nitrogenous base Sugar Phosphate. 5’. 3’. Nucleotides: 4 bases.

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The Molecule Of Life

Dna structure

DNA 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:

  • Nitrogenous base

  • Sugar

  • Phosphate



Nucleotides 4 bases

Nucleotides: 4 bases

The nucleotides in DNA use 4 different bases:

  • GuanineG

  • CytosineC

  • AdenineA

  • ThymineT

    * Just think G-CAT, you know that rapper

Nucleotide bases 2 classes

Nucleotide Bases: 2 classes


  • Adenine

  • Guanine


  • 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’



Base pairing

Base Pairing

Hydrogen Bonds for spontaneously between specific nitrogenous bases

Pairing Rule:

  • Cytosine bonds with GuanineC-G

  • Thymine bonds with AdenineT-A

Base pairing1

Base Pairing

A double strand of dna

A Double Strand of DNA





How a dna strand is written

How a DNA strand is written



Strands are anti-parallel

Try writing one yourself

Try writing one yourself


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’

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

Are the strands anti-parallel?

Where are covalent bonds between nucleotides?

Where are the hydrogen bonds?

The double helix

The Double Helix


High Resolution image of Actual DNA molecule

Dna within a cell

DNA 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 nucleosome

A Nucleosome

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



  • 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 dna

Junk 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

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