DNA
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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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DNA

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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

The nucleotides in DNA use 4 different bases:

  • GuanineG

  • CytosineC

  • AdenineA

  • ThymineT

    * Just think G-CAT, you know that rapper


Nucleotide Bases: 2 classes

Purine:

  • Adenine

  • Guanine

    Pyrimidine

  • Cytosine

  • Thymine

Purines Pyrimidines


The Backbone

  • Nucleotides combine by covalent bond between phosphates and sugars


5’

A single strand of DNA

Written as: 5’-ACTGTCAAGGTCGAT-3’

3’

3’


Base Pairing

Hydrogen Bonds for spontaneously between specific nitrogenous bases

Pairing Rule:

  • Cytosine bonds with GuanineC-G

  • Thymine bonds with AdenineT-A


Base Pairing


A Double Strand of DNA

5’

3’

3’

5’


How a DNA strand is written

5’ - ATAGGGCCTAGAACCTGG - 3’

3’ - TATCCCGGATCTTGGACC - 5’

Strands are anti-parallel


Try writing one yourself

3’ - TTAAGCTATGCT - 5’

What is the complementary DNA strand?


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


High Resolution image of Actual DNA molecule


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

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


Genes

  • 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?

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…

…and it would stretch to the moon!


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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