CHAPTER 9 & 10 CHAPTER 9 & 10 NOTESNOTES

DNA DNA STRUCTURESTRUCTURE&& FUNCTIONFUNCTION

What is DNA?What is DNA?

NucleicNucleic acidacid – a compound – a compound composed of a 5-carbon sugar, a composed of a 5-carbon sugar, a nitrogen base, and a phosphate.nitrogen base, and a phosphate.

DeoxyribonucleicDeoxyribonucleic acidacid – DNA – controls – DNA – controls the cells activities, carries genetic the cells activities, carries genetic information. It is found in the nucleus of information. It is found in the nucleus of the cell.the cell.

Who discovered DNA?Who discovered DNA?

DNA was discovered DNA was discovered in the late 1940’s, in the late 1940’s, but the structure but the structure was not discovered was not discovered until until 19531953. Two . Two scientists named scientists named JamesJames WatsonWatson and and FrancisFrancis CrickCrick came came up with a model of up with a model of the structure of the structure of DNA.DNA.

What does Watson and What does Watson and Crick’s DNA model look Crick’s DNA model look

like?like?1.1. The shape looks like a twisted ladder The shape looks like a twisted ladder

– – doubledouble helixhelix..2.2. Each side is made up of alternating Each side is made up of alternating

sugarsugar and and phosphatephosphate molecules. The molecules. The sugar in DNA is called sugar in DNA is called deoxyribose.deoxyribose.

3.3. Attached to each sugar is a Attached to each sugar is a nitrogennitrogen basebase..

4.4. To make the ladder complete, each To make the ladder complete, each base is joined by a weak base is joined by a weak hydrogenhydrogen bond to a base on the other side.bond to a base on the other side.

DNA double helixDNA double helix

What are the nitrogen What are the nitrogen bases?bases?

There are 4 different nitrogen bases There are 4 different nitrogen bases in DNA:in DNA:

1. guanine - G1. guanine - G

2. thymine - T2. thymine - T

3. adenine - A3. adenine - A

4. cytosine - C4. cytosine - C

How do the bases bond?How do the bases bond?

The nitrogen bases always bond in the The nitrogen bases always bond in the same way:same way:

adenineadenine to to thyminethymine A - TA - T

guanineguanine to to cytosinecytosine G - CG - C

Base PairingBase Pairing

How are these parts put How are these parts put together?together?

DNA is built up in small units. Each unit is DNA is built up in small units. Each unit is made up of a made up of a sugarsugar, a , a phosphatephosphate, and a , and a nitrogen basenitrogen base. This small unit is called a . This small unit is called a nucleotidenucleotide..