Deoxyribonucleic Acid (DNA) Chapter 12 Section 12-2 Deoxyribonucleic Acid (DNA)

I. DNA – Deoxyribonucleic Acid DNA – is the genetic material of living organisms and is located in the chromosomes of each cell. Gene - is a sequence of DNA that codes for a protein thus determining a specific trait. Nucleotides: the subunits of DNA and are made up of 3 parts. Deoxyribose: a sugar molecule. A phosphate group: made of P surrounded by oxygen. Nitrogenous base: basic molecule that contains nitrogen.

II. Four Bases Adenine = A Guanine = G Cytosine = C Thymine = T Purine (2 carbon rings) Adenine = A Guanine = G Pyrimidine (1 carbon ring) Cytosine = C Thymine = T

Pyrimidines and Purines

III. The Double Helix The double helix: made of two nucleotide chains that wrap around each other to form a spiral staircase Backbone: Alternating sugar and phosphate groups, held together by covalent bonds. Rungs: Hydrogen bonds hold opposing bases to each other, perpendicular to backbone

IV. Complementary Base Pairing Base-pairing rules: Cytosine always bonds with guanine Three hydrogen bonds Between each. Adenine always bonds with thymine Two hydrogen bonds between each, One purine and one pyrimidine

V. The DNA Replication Process Replication: the process of DNA copying itself in the nucleus before division. Step 1: separation of the two nucleotide chains Replication fork: the point where the two chains separate during replication. Helicases: enzymes that separate the chains by breaking hydrogen bonds in replication.

Step 2: DNA polymerase - an enzyme that binds to the hydrogen bonds adding new free floating nucleotides to the opposing base, forming a new chain attached to the old chain. So you end up with 2 new chains one old and one new.

VI. Replication Replication occurs simultaneously in two directions at many points along the strand. There is no set beginning area or set end area. Eventually all DNA is replicated. After replication, the cell is ready to undergo cell division.

VII. Accuracy and Repair Only 1 error in 10,000 paired nucleotides Mutations may have serious effects in new cells Enzymes proofread and repair errors, keeping the error rate down to 1 in a billion.