Structure and Function of DNA

Structure and Function of DNA

Halil Gürhan KARABULUT, MD, Ph.D.

Department of Medical Genetics

Friedrich Miescher (1868)

– nuclein

(acidic -DNA- and basic -protein-)

Avery-McLeod-McCarty

Avery-McLeod-McCarty (1944) Hershey-Chase (1952)

• DNA is the genetic material

Chargaff rules

• the composition of DNA varies from one species to another but not in the same species

• the composition of DNA does not change according to sex, nutritional or environmental conditions

• in any sample of DNA, the amount of adenine is equal to the amount of thymine and the amount of guanine is equal to cytosine:

A=T, G=C

• Total amount of purine bases is equal to total amount of pyrimidine bases:

A+G=T+C

The Nobel Prize in Physiology or Medicine 1962

"for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material"

Francis Harry Compton Crick James Dewey Watson Maurice Hugh Frederick Wilkins

1/3 of the prize 1/3 of the prize 1/3 of the prize

United Kingdom USA United Kingdom and New

Zealand MRC Laboratory of Molecular

Biology

Cambridge, United Kingdom

Harvard University

Cambridge, MA, USA London University London, United Kingdom

b. 1916

d. 2004 b. 1928 b. 1916

(in Pongaroa, New Zealand) d. 2004

DNA: deoxyribonucleic acid

RNA: ribonucleic acid

building blocks of nucleic acids are nucleotides

DNAdeoxyribonucleotide

RNAribonucleotide

Nucleotides:

• Phosphate,

• Five-carbon sugar and,

• Nitrogenous bases

Nitrogenous bases:

– Purines:

• Adenine

• Guanine – Pyrimidines:

• Cytosine

• Thymine

• Uracil

• Phosphate group is linked to 5’ carbon atom by ester bond

• Bases are linked to 1’ carbon atom by N-glycosidic bond

Bases Nucleoside (base+sugar)

Nucleotide

(base+sugar+phosphate)

Symbol Nucleic acid Adenine Adenosine

Deoxyadenosine

Adenylate

Deoxyadenylate

AMP dAMP

RNA DNA Guanine Guanosine

Deoxyguanosine

Guanylate

Deoxyguanylate

GMP dGMP

RNA DNA Cytosine Cytidine

Deoxycytidine

Cytidylate

Deoxycytidylate

CMP dCMP

RNA DNA Thymine Deoxythymidine Deoxythymidylate dTMP DNA

Uracil Uridine Üridylate UMP RNA

Structure of DNA

• Double-stranded, right-handed helical structure

• Strands are antiparallel (run in opposite directions)

• Sugar phosphate on the outside and nitrogen bases on the inner side

• Nitrogen bases of the two strands form complementary pairs with purine of one and pyrimidine of the other, held together by hydrogen bonds

• Contains major and minor grooves

• Each turn of the helix contains 10.5 base pairs

• The model defined by Watson-Crick is B form DNA

• In high salt concentrations or in alternate purine and pyrimidine bases Z form may be seen

• Under conditions of low humidity A form may be seen

Functional importance of DNA structure

• replication

• recombination

• repair

• transcription

hybridization