DNA and the Code of Life

1. DNA and the Code of Life

2. The Discovery of DNA • Many scientists have contributed to the discovery of DNA. • Miescher: found DNA in the nucleus of cells but didn’t know that it was the cause of heredity. • Hammerling: verified that genetic material was found in nucleus and that it directed the making of a new cell. • Hershey and Chase: used a bacterial virus DNA put into bacteria to produce more of the viruses. • Levene: figured out that DNA had 3 main components: a pentose sugar (5-carbon sugar), a phosphate group and a nitrogenous base. • Chargaff: discovered that the amount of adenine (A) equals the amount of thymine (T) and that the amount of guanine (G) equals cytosine (C). • Franklin and Wilkins: used X-ray crystallography and figured out that DNA is a helix (corkscrew shape). • Watson and Crick: built the model of DNA

3. A Model for DNA • Deoxyribonucleic acid. • Twisted ladder in a double helix. • Sides of the ladder made of repeating sugar (deoxyribose) and phosphate groups. • The rungs are made of the pairs of nitrogenous bases. • Adenine (A) binds with Thymine (T) and cytosine (C) binds with guanine (G). • These are called complementary base pairing. • The nitrogenous bases are held together in the middle by hydrogen bonds.

4. DNA Model

5. Mutations • Can be caused by environmental agents or as errors during cell division. • Point Mutation: is a failure by the replicating cell to copy the genetic information accurately. • 3 types of point mutations: • Base-pair substitution: a G is inserted instead of a C. • Insertion: An extra T is inserted • Deletion: a C was supposed to be there, but it is now missing.

6. Inheriting Mutations • Mutations that happen in the autosomal cells only affect that individual, but if a mutation happens in the sex cells, the baby will be completely affected. • Examples: Huntington’s disease (nerve cells in the brain degenerate) and Cystic Fibrosis (recessive disease that affects the mucous in the lungs)

7. Sickle-cell anemia: a single adenine base was substituted for a thymine base. The red blood cells are C-shaped and cannot move through the body as well. • Adults who have the tolerance to break down lactose, have a mutated gene because naturally adult humans cannot break down lactose.

8. What causes a mutation to occur? • Some occur naturally by accident and are called spontaneous mutations. They are caused by incorrect copying of DNA during the replication of chromosomes. • Induced mutations are a result of exposure to a physical or chemical agent. • Radiation • Cigarette smoke

9. Technology • Microarray: a small membrane or glass slide that has been coated in predictable and organized manner with a genomic sequence. • Each fragment corresponds with a different gene. • Samples can be tested against the control to see if there are any differences in genes. • Parkinson’s (tremors, loss of balance, slowness) was discovered in just 9 days using microarray technology.

10. Genomes • Human Genome Project: to determine the complete 3 billion nitrogenous base sequence of human DNA. • Parts of the DNA code for genes and they are called coding DNA • Parts do not code for any genes and are highly repetitive DNA sequences called non-coding DNA. • We can determine who you are based on DNA and have used this technology in criminology. • We can also use DNA banks for endangered species. Maybe some day we can bring back an endangered specie?

11. DNA Fingerprinting • Produces a pattern of bands on a gel that is characteristic of each individual but highly variable form person to person. • Can be used to settle paternity suits, determine ancestry, locate long-lost relatives, identify remains and prove guilt/innocence in a crime.