12-1 Chargaff Rule

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Slide1:

1 The Structure of DNA

DNA:

2 DNA DNA is often called the blueprint of life . In simple terms, DNA contains the instructions for making proteins within the cell.

Watson & Crick’s Model:

3 Watson & Crick’s Model

Why do we study DNA?:

4 Why do we study DNA ? We study DNA for many reasons, e.g., its central importance to all life on Earth, medical benefits such as cures for diseases, better food crops .

Chromosomes and DNA:

5 Chromosomes and DNA Our genes are on our chromosomes. Chromosomes are made up of a chemical called DNA.

The Shape of the Molecule:

6 The Shape of the Molecule DNA is a very long polymer. The basic shape is like a twisted ladder or zipper. This is called a double helix.

The Double Helix Molecule:

7 The Double Helix Molecule The DNA double helix has two strands twisted together.

One Strand of DNA:

8 One Strand of DNA The backbone of the molecule is alternating phosphates and deoxyribose sugar The teeth are nitrogenous bases . phosphate deoxyribose bases

Nucleotides:

9 Nucleotides C C C O Phosphate O C C O -P O O O O -P O O O O -P O O O One deoxyribose together with its phosphate and base make a nucleotide . Nitrogenous base Deoxyribose ribose ATP

One Strand of DNA:

10 One Strand of DNA One strand of DNA is a polymer of nucleotides. One strand of DNA has many millions of nucleotides. nucleotide

Four nitrogenous bases:

11 Four nitrogenous bases Cytosine C Thymine T Adenine A Guanine G DNA has four different bases:

Two Kinds of Bases in DNA:

12 Two Kinds of Bases in DNA Pyrimidines are single ring bases . Purines are double ring bases. C C C C N N O N C C C C N N N N N C

Thymine and Cytosine are pyrimidines:

13 Thymine and Cytosine are pyrimidines Thymine and cytosine each have one ring of carbon and nitrogen atoms. C C C C N N O N cytosine C C C C N N O O thymine C

Adenine and Guanine are purines:

14 Adenine and Guanine are purines Adenine and guanine each have two rings of carbon and nitrogen atoms. C C C C N N N Adenine N N C C C C C N N O N Guanine N N C

Two Stranded DNA:

15 Two Stranded DNA Remember, DNA has two strands that fit together something like a zipper. The teeth are the nitrogenous bases but why do they stick together?

Hydrogen Bonds:

16 C C C C N N O N C C C C N N O N N N C Hydrogen Bonds 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. The bonds between cytosine and guanine are shown here with dotted lines

Hydrogen Bonds, cont.:

17 Hydrogen Bonds, cont. When making hydrogen bonds, cytosine always pairs up with guanine Adenine always pairs up with thymine Adenine is bonded to thymine here C C C C N N N N N C C C C C N N O O C

Chargraff’s Rule::

18 Chargraff’s Rule: Adenine and Thymine always join together A T Cytosine and Guanine always join together C G

DNA by the Numbers:

19 DNA by the Numbers 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 0.000000002 m . The earth is 150 billion m or 93 million miles from the sun.

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