DNA Structure

DNA - Deoxyribonucleic Acid

•Found in nucleoid of prokaryotic cells•Found in the nucleus of all eukaryotic cells

•In mitochondria (mtDNA)•In chloroplasts (ctDNA)

•Different segments along the DNA are genes• Genes - determine body function and

physical characteristics

• Genes are located on chromosomes.• Chromosomes are made of DNA & proteins

Simplified Nucleotide Model

S

P

B

Draw & Label

Nitrogenous Bases of DNA

Nitrogen Bases

•Adenine•Guanine•Thymine•Cytosine

Purines

Pyrimidines

STRUCTURE OF DNA

• Double stranded

– helix (twisted, curved)

– Right-handed twist

DNA - Double Helix Structure

1) Sides of the ladder are made up of sugar and phosphates

2) Nitrogen bases stick out from the sides of the ladder (rungs)

3) When the two sides (chains) of the ladder are connected, it’s a complete DNA molecule

DNA - Double Helix

4) Adenine bonds with Thymine*

5) Guanine bonds with Cytosine*

6) Hydrogen bonds connect the bases

*see next slide

Edwin Chargaff – 1947Studied DNA in various species

Nitrogen bases are proportionate within a speciesRatio of bases are various between species

•Adenine and Thymine were found in proportionate amounts•Cytosine and Guanine were found in proportionate amounts

Chargaff’s Rules

S

P

P

P

PP

P

S

S

S

S

S

T

T

C

Draw DNA

Bases

Side/backbone

Nucleotide

DNA Structure

DNA Structure

3.4

0.34

1

Base pair

deoxyribose

deoxyribose

phosphate

hydrogen

bonds

5’

5’

3’

3’