13.2 DNA Structure13.2 DNA Structure

What does DNA stand for?Deoxyribonucleic acid

What does DNA stand for?Deoxyribonucleic acid

DNAs Functions:DNAs Functions:

• Controls the production of proteins

• Can copy itself for new cells• Carries genetic information from one generation to the next

• Controls the production of proteins

• Can copy itself for new cells• Carries genetic information from one generation to the next

replication

transcription processing translation

II. Structure of DNAII. Structure of DNA

• Monomer of DNA= nucleotide• DNA is made of 2 chains of nucleotides.

• 3 parts of a nucleotide:– Pentose (5C) sugar= deoxyribose– Phosphate group– Nitrogen base

• Monomer of DNA= nucleotide• DNA is made of 2 chains of nucleotides.

• 3 parts of a nucleotide:– Pentose (5C) sugar= deoxyribose– Phosphate group– Nitrogen base

Bases in DNA

purines

pyrimidines

adenine

guanine

cytosine

thymine

N9

N1

• The nucleotides are joined in a chain; each nucleotide joined to the next by a covalent bond between the sugar and phosphate.

• Therefore the DNA molecule has a direction to it.

• The nucleotides are joined in a chain; each nucleotide joined to the next by a covalent bond between the sugar and phosphate.

• Therefore the DNA molecule has a direction to it.

• Due to Rosalind Franklin’s x-ray diffraction work, Watson and Crick knew that DNA was a helix.

• Due to Rosalind Franklin’s x-ray diffraction work, Watson and Crick knew that DNA was a helix.

• Watson and Crick realized in 1953 that the DNA molecule is composed of two strands running in opposite directions= antiparallel

• Watson and Crick realized in 1953 that the DNA molecule is composed of two strands running in opposite directions= antiparallel

Double helixDouble helix

• The two strands are linked in the center by hydrogen bonds.

• The two strands are linked in the center by hydrogen bonds.

“Chargaff’s rules”“Chargaff’s rules”

• 1950• Determined that the amount of:– Adenine=Thymine– Cytosine=Guaninein DNA.

• 1950• Determined that the amount of:– Adenine=Thymine– Cytosine=Guaninein DNA.

• Watson and Crick deduced that A must pair with T and G with C

=complimentary pairs

• Watson and Crick deduced that A must pair with T and G with C

=complimentary pairs

What about the structure of DNA varies from one

individual to the next?

What about the structure of DNA varies from one

individual to the next?

The sequence of nitrogen bases

The sequence of nitrogen bases