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1 2 DNA DNA.DNA is often called the blueprint of life. In simple terms, DNA contains the instructions for making proteins within the cell.

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Presentation on theme: "1 2 DNA DNA.DNA is often called the blueprint of life. In simple terms, DNA contains the instructions for making proteins within the cell."— Presentation transcript:

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3 2 DNA DNA.DNA is often called the blueprint of life. In simple terms, DNA contains the instructions for making proteins within the cell.

4 3 Watson & Crick’s Model Watson and Crick were the first scientists to model DNA in 1953.

5 4 DNA 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.

6 What is DNA? DNA (deoxyribonucleic acid) carries the genetic code for all organisms In Eukaryotes DNA is found in the nucleus of the cell. All organisms contain DNA or RNA DNA is a Nucleic Acid made up of nucelotides. 5

7 6 DNA Structure Nucleotides include:Nucleotides include: 1. phosphate group 2. pentose sugar (5-carbon) 3. nitrogenous bases: adenine (A) thymine (T) DNA only cytosine (C) guanine (G)

8 7 Nucleotide O O=P-O OPhosphate Group Group N Nitrogenous base (A, G, C, or T) (A, G, C, or T) CH2 O C1C1 C4C4 C3C3 C2C2 5 Sugar Sugar(deoxyribose)

9 8 Chromosomes and DNA Our genes are on our chromosomes. Chromosomes are made up of a chemical called DNA.

10 9 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.

11 10 The Double Helix Molecule The DNA double helix has two strands twisted together.

12 11 DNA - double helix P P P O O O P P P O O O G C TA

13 12 One Strand of DNA The backbone of the molecule is alternating phosphates and deoxyribose sugar The teeth are nitrogenous bases. phosphate deoxyribose bases

14 13 Nucleotides CC C O Phosphate O C C O -P O O O O O O O One deoxyribose together with its phosphate and base make a nucleotide. Nitrogenous base Deoxyribose

15 14 One Strand of DNA One strand of DNA is a polymer of nucleotides. One strand of DNA has many millions of nucleotides. nucleotide

16 15 Four nitrogenous bases Cytosine C Thymine T Adenine A Guanine G DNA has four different bases:

17 16 Two Kinds of Bases in DNA Pyrimidines are single ring bases.Pyrimidines are single ring bases. Purines are double 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

18 17 Thymine and Cytosine are pyrimidines Thymine and cytosine each have one ring of carbon and nitrogen atoms.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

19 18 Adenine and Guanine are purines Adenine and guanine each have two rings of carbon and nitrogen atoms.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

20 19 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?

21 20 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

22 21 Hydrogen Bonds, 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

23 22 Chargraff’s Rule: Adenine and Thymine always join together A T Cytosine and Guanine always join together C G

24 23 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 m. The earth is 150 billion m or 93 million miles from the sun.

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