DNA(Deoxyribonucleic Acid)

Mr. ColemanBiology

DNADNA

• DNADNA is often called the blueprint of life..

• In simple terms, DNA contains the instructions for making proteins within the cell.

Genetic material of cells…Genetic material of cells…

• GENES – units of genetic material that GENES – units of genetic material that CODES FOR A SPECIFIC TRAITCODES FOR A SPECIFIC TRAIT

• Called Called NUCLEIC ACIDSNUCLEIC ACIDS

• DNA is made up of repeating molecules DNA is made up of repeating molecules called called NUCLEOTIDESNUCLEOTIDES

A HISTORY OF DNAA HISTORY OF DNA

• Discovery of the DNA double helixDNA double helix

A. Frederick Griffith – Discovers that a factor in diseased bacteria can transform harmless bacteria into deadly bacteria (1928)

B. Rosalind Franklin - X-ray photo of DNA.(1952)

C. Watson and Crick - described the DNA molecule from Franklin’s X-ray.(1953)

Why do we study DNADNA?

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 DNAChromosomes and DNA

• Our genes are on our chromosomes.

• Chromosomes are made up of a chemical called DNA.

The Shape of the MoleculeThe 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 MoleculeThe Double Helix Molecule

• The DNA double helix has two strands twisted together.

• (In the rest of this unit we will look at the structure of one strand.)

NucleotidesNucleotides

C C

C

OPhosphate

O

CC

O -P OO

O

One deoxyribose together with its phosphate and base make

a nucleotide.

Nitrogenous base

Deoxyribose

One Strand of DNAOne Strand of DNA

• One strand of DNA is a polymer of nucleotides.

• One strand of DNA has many millions of nucleotides.

nucleotide

One Strand of DNAOne Strand of DNA• The backbone

of the molecule is alternating phosphate and deoxyribose.

• The teeth are nitrogenous bases.

phosphate

deoxyribose

bases

Nitrogenous BasesNitrogenous Bases

• PURINESPURINES

1. Adenine (A)Adenine (A)

2. Guanine (G)Guanine (G)

• PYRIMIDINESPYRIMIDINES

3. Thymine (T)Thymine (T)

4. Cytosine (C)Cytosine (C) T or C

A or G

Two Kinds of Bases in DNA

• Pyrimidines are Pyrimidines are single ring bases.single ring bases.

• Purines are double Purines are double ring bases.ring bases.

C

C

C

C

N

N

OO

N

CC

CC

N

N

N

N

N

C

Thymine and Cytosine are Thymine and Cytosine are pyrimidinespyrimidines

• Thymine and cytosine each have one ring Thymine and cytosine each have one ring of carbon and nitrogen atoms.of carbon and nitrogen atoms.

C

C

C

C

N

N

OO

N

cytosinecytosine

C

C

C

C

N

N

OO

OO

thyminethymine

C

Adenine and Guanine are Adenine and Guanine are purinespurines

• AdenineAdenine and and guanineguanine each have two each have two rings of carbon and nitrogen atoms.rings of carbon and nitrogen atoms.

C

C

C

C

N

N

N

AdenineAdenine N

N

C

C

C

C

C

N

N

OO

N

GuanineGuanine N

N

C

Two Stranded DNATwo 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?

C

C

C

C

N

N

OO

N

C

C

C

C

N N

OO

N

N

N C

Hydrogen BondsHydrogen 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.

Hydrogen Bonds, Hydrogen Bonds, cont.

• When making hydrogen bonds, cytosine always pairs up with guanine,

• And adenine always pairs up with thymine.

C

C

CC

N

N

N

N

N

C

C

C

C

C

N

N

OO

OO

C

BASE-PAIRINGSBASE-PAIRINGS

CG

H-bonds

T A

ChargaffChargaff’’s Rules Rule

• AdenineAdenine must pair with ThymineThymine

• GuanineGuanine must pair with CytosineCytosine

• Their amounts in a given DNA molecule will be about the sameabout the same.

G CT A

Important:Important:

• Adenine and Thymine always join together

A T

• Cytosine and Guanine always join together

C G

Watson & Crick proposed…Watson & Crick proposed…

•DNA had specific pairing between the DNA had specific pairing between the nitrogen bases:nitrogen bases:

ADENINEADENINE – – THYMINETHYMINE

CYTOSINECYTOSINE - - GUANINEGUANINE

•DNA was made of DNA was made of 22 long stands of long stands of nucleotides arranged in a specific way nucleotides arranged in a specific way

called the called the ““Complementary RuleComplementary Rule””

DNA Double HelixDNA Double Helix

P

P

P

O

O

O

1

23

4

5

5

3

3

5

P

P

PO

O

O

1

2 3

4

5

5

3

5

3

G C

T A

DNA by the numbersDNA 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 mor 93 million miles from the sun.

Genetic Diversity…Genetic Diversity…• Different Different

arrangements of arrangements of NUCLEOTIDESNUCLEOTIDES in a in a nucleic acid (DNA) nucleic acid (DNA) provides the key to provides the key to DIVERSITYDIVERSITY among among living organisms.living organisms.

The Code of Life…The Code of Life…

• The The ““codecode”” of the chromosome is the of the chromosome is the SPECIFIC ORDERSPECIFIC ORDER that bases occur. that bases occur.

A T C G T A T G C G G…A T C G T A T G C G G…