Structure of DNA

Function of DNA

• DNA is the genetic DNA is the genetic material of the cellmaterial of the cell

• The structure of DNA The structure of DNA must allow:must allow:– the storage and the storage and

transmission of genetic transmission of genetic informationinformation

– exact replication to exact replication to occur.occur.

Genes code for proteins

• Genetic information Genetic information must tell cells how to must tell cells how to make proteins.make proteins.– Sections of the DNA Sections of the DNA

called genes code for called genes code for one proteinone protein

– Proteins form Proteins form structures and structures and control chemistry of control chemistry of cell.cell.

Think: Proteins are made in the cytoplasm but DNA Think: Proteins are made in the cytoplasm but DNA remains in nucleus. How do you think that works?remains in nucleus. How do you think that works?

DNA StructureDNA Structure• DNA is a polymer.DNA is a polymer.• The monomer of DNA is The monomer of DNA is

called a called a nucleotidenucleotide..• Nucleotides linked Nucleotides linked

together to form the sides together to form the sides of the DNA molecule.of the DNA molecule.

• DNA molecule has shape DNA molecule has shape of a double helix.of a double helix.– The sides are anti-parallel.The sides are anti-parallel. deoxyribonucleic deoxyribonucleic

acidacid

WhatWhat’’s in a name?s in a name?

• One 5 carbon sugar One 5 carbon sugar called deoxyribose.called deoxyribose.– ““Deoxy” = one less Deoxy” = one less

oxygen.oxygen.– ““ribo” = than ribose.ribo” = than ribose.

• Deoxyribonucleic acidDeoxyribonucleic acid– ““nucleic” = found in nucleic” = found in

nucleus.nucleus.– ““acid” = acidicacid” = acidic

Deoxyribose, a pentose Deoxyribose, a pentose sugar, has each carbon sugar, has each carbon

numbered.numbered.

Nucleotide StructureNucleotide Structure

•Phosphate group attached to Phosphate group attached to the #5 carbon of the sugar. the #5 carbon of the sugar. •One nitrogenous base attached One nitrogenous base attached to the #1 carbon in the sugar.to the #1 carbon in the sugar.

•Purines -2 ringsPurines -2 ringsAdenine Adenine GuanineGuanine

–Pyrimidines -1 ringPyrimidines -1 ring CytosineCytosineThymine Thymine

Four bases of DNAFour bases of DNA

Think: how will you recognize the name of a base on a quiz?

Complementary base pairing rulesComplementary base pairing rules

• Nitrogenous bases form rungs of the helix.– Adenine (2 rings) is bonded with Thymine (1 ring) using 2

hydrogen bonds. (A-T)– Guanine (2 rings) is bonded with Cytosine (1 ring) using 3

hydrogen bonds. (G-C)

Think: how will you remember which bases pair with each other?

Summary questions1. Name 2 functions of DNA

2. Who discovered the structure of DNA?

3. What are the 4 base pairs.

4. What is the structure if DNA?