DNA NOTESDNA NOTES

DNA’s ShapeDNA’s Shape

• DNA’s shape was DNA’s shape was discovered by discovered by 22 scientists in the scientists in the 1950’s1950’s..

• WatsonWatson and and CrickCrick named the shape of named the shape of DNA the DNA the Double Helix.Double Helix.

• DNA looks like a DNA looks like a twisted ladder.twisted ladder.

Building Blocks of DNABuilding Blocks of DNA• DNA is made of DNA is made of nucleotidesnucleotides..• Nucleotides have 3 parts:Nucleotides have 3 parts:

a.a. 5-carbon 5-carbon sugarsugar called called deoxyribosedeoxyriboseb.b. A A phosphatephosphate group groupc.c. 1 of 4 1 of 4 nitrogenousnitrogenous bases bases

AdenineAdenine (A), (A), GuanineGuanine (G), (G), CytosineCytosine (C), (C), ThymineThymine (T) (T)

Purines vs. PyrimidinesPurines vs. Pyrimidines• Two of the nitrogenous bases belong to a group Two of the nitrogenous bases belong to a group

of compounds known as of compounds known as PurinesPurines – these are – these are Adenine & GuanineAdenine & Guanine

• The other 2 nitrogenous bases belong to a The other 2 nitrogenous bases belong to a group of compounds known as group of compounds known as PyrimidinesPyrimidines – – these are these are Cytosine & ThymineCytosine & Thymine

• Purines have Purines have 2 rings 2 rings in their structures and in their structures and pyrmidines only have pyrmidines only have 1 ring1 ring

• PurinesPurines can’t bond to other purines and can’t bond to other purines and pyrimidinespyrimidines can’t bond to other pyrimidines can’t bond to other pyrimidines

Base PairingBase Pairing

• The nitrogenous bases The nitrogenous bases only make only make complementarycomplementary bonds. bonds.

• Complementary means Complementary means two things that fit or go two things that fit or go togethertogether– Example: Example: salt & salt &

pepperpepper, PB & J, PB & J• The bases pair up The bases pair up

complementary also: complementary also: A-A-TT & & G-CG-C

Makeup of DNAMakeup of DNA

• Sides of DNA ladder are made up of: Sides of DNA ladder are made up of: SugarSugar & & phosphate phosphate groupgroup– The sides are held together by The sides are held together by

strong covalentstrong covalent bonds bonds• Middle (rungs) of DNA ladder are Middle (rungs) of DNA ladder are

made up of: made up of: Nitrogenous basesNitrogenous bases– The middle is held together by The middle is held together by

weakweak bonds called bonds called Hydrogen Hydrogen bondsbonds

Sample DNA StrandSample DNA Strand

Sides Made of:Sugar & Phosphate

Bonds:Strong, COVALENT

Rungs (Middle) Made of:Nitrogenous bases

Bonds:Weak, HYDROGEN

DNA StrandDNA Strand

• Note that the sides of the DNA Note that the sides of the DNA strand run in strand run in oppositeopposite directions of directions of each other (one side is each other (one side is rightright side side up and the other is up and the other is upsideupside down) down)

• Draw:Draw:

5’

5’3’

3’

Complementary StrandsComplementary Strands

DNA SimulationMake sure Biological Simulations CD Make sure Biological Simulations CD is in the drive or use the website is in the drive or use the website below to review DNAbelow to review DNA

http://learn.genetics.utah.edu/content/begin/dna/Click on “What is DNA”