DNA REVIEW

Objective: To review the structure and function of DNA.

IntroductionIntroduction• You are made up of billions of cells and each cell has its own unique set of 46 chromosomes.• A chromosome is just one big long chain of DNA! • DNA (Deoxyribonucleic Acid) contains all the information that determines who you are!

DNADNA• DNA DNA is often called the

blueprint of life..

• DNADNA contains the instructions for making proteins within the cell.

Chromosomes and DNAChromosomes and DNA

• Our genes are on our chromosomes.

• Chromosomes are made up of DNA.

The Shape of the MoleculeThe Shape of the Molecule

• DNA is a very long polymer. (chain of nucleic acids)

• Its basic shape is like a twisted ladder or zipper.

• It is called a double helix.

The Double Helix MoleculeThe Double Helix Molecule

• The DNA double helix has two strands twisted together.

One Strand of DNAOne Strand of DNA• The backbone of

the molecule is alternating phosphates and deoxyribose sugar.

• Nitrogenous bases are attached to the backbone.

phosphate

deoxyribose

nitrogenous bases

Four nitrogenous basesFour nitrogenous bases

• Cytosine C• Thymine T

• Adenine A

• Guanine G

DNA has four different bases:

TThymine and hymine and CCytosine are ytosine are pyrimidinespyrimidines..

• Thymine and cytosine each have Thymine and cytosine each have one one ringring 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

AAdenine and denine and GGuanine are uanine are purinespurines..

• Adenine and guanine each have Adenine and guanine each have two two ringsrings of carbon and nitrogen atoms. of carbon and nitrogen atoms.

C

C

C

C

N

N

N

AdenineAdenine N

N

C

C

C

C

C

N

NOO

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 NOO

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.

To the right: Cytosine and Guanine hydrogen bonded

Hydrogen Bonds, Hydrogen Bonds, cont.

• When making hydrogen bonds:– Cytosine always

pairs up with Guanine.

– Adenine always pairs up with Thymine.

To the right: Adenine and Thymine hydrogen

bonded

C

C

CC

N

N

N

N

N

C

C

C

C

C

N

N

OO

OO

C

Important:Important:

• Adenine and Thymine always join together

A T

• Cytosine and Guanine always join together

C G

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