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)

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.

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.