DNA: The Molecule of Heredity

DNA Structure

• Deoxyribonucleic acid.• A macromolecule

composed of two strands of monomers called nucleotides.

• These strands are joined in the middle by hydrogen bonds.

• The strands twist around one another forming a double helix.

• Monomer=Nucleotide

Nucleotide Structure• 5-C sugar –

deoxyribose• Phosphate

group• Nitrogen

containing base -4 of two types– Adenine (A)– Guanine (G)– Cytosine (C)– Thymine (T)

http://www.msu.edu/course/isb/202/ebertmay/drivers/nucleotide.jpg

Types of Nitrogen Bases

• Pyrimidines – have one ring in their structure– Thymine – Cytosine

• Purines – have two rings in their structure– Adenine – Guanine– PUAG2

Nitrogen Base Pairing

• Bases pair in a specific pattern.

• A purine always bonds to a pyrimidine

• Adenine bonds to thymine.

• Guanine bonds to cytosine.

Nitrogen Base Pairing• The bases are

held together by weak hydrogen bonds.

• The sides of the DNA ladder are composed of alternating sugar and phosphate and are called “backbones”.

Discovery of DNA Structure

• The credit for the discovery of this structure is given to James Watson and Francis Crick.

• These two scientists viewed x-ray images of DNA crystals that were created by Rosalind Franklin and Maurice Wilkins.

http://www.peace-files.com/ICELANDIC_FILES/QF-R-08/02_A-DNA-Sagan.gif

Functions of DNA

• DNA must be able to copy itself exactly. • This process is called replication. Occurs during S

phase of Cell Cycle in the nucleus.• Then DNA splits during Mitosis/Meiosis

Depending on the type of cell.• Enzymes control the process. • DNA is the molecule of heredity.

- It provides instructions for cell functioning and is a blueprint for the production of proteins that do the work of the cell.

Replication – Overview

· DNA “unzips” down its H-bonds

· One strand then acts as a template for the production of a new strand

· Each new DNA molecule has one old strand of nucleotides and one new strand.

Control Of Cell Activities

• DNA is copied into RNA. (transcription)

• RNA in turn controls the production of proteins. (translation)

• Proteins then do the work of the cell.