1. Sickle cell anemia is a genetic disease affecting hemoglobin in which blood cells carrying the defect assume a sickle shape under conditions of low oxygen. The disease appears to confer an advantage, as explained below.
2. The mutated gene in sickle cell anemia acts recessively, meaning that it takes two copies to show the disease. People who are heterozygous (one copy of the gene and one normal copy) appear to have a better survival rate against malari, particularly as children.
3. Proper folding is critical for proper protein function. Mad cow disease arises from improper folding of a protein that, when misfolded, induces properly folded proteins to misfold, as well. The misfolded proteins tend to aggregate and lead to death of nerve cells in the brain. Mad cow disease and its human homolog lead to dementia.
4. Chaperonins are proteins synthesized in cells that help proteins to fold properly. The are particularly important in cells that have been exposed to heat shock.
Protein Structure & Purification
1. To study a protein, one must purify it away from all the other proteins in a cell. Steps in the purification typically include 1) busting cells open; 2) centrifuging cellular components apart from the cytoplasm; and 3) using techniques that separate molecules by several different processes.
2. Most proteins require more than one method to be purified.
3. Gel exclusion chromatography is a technique for isolating proteins on the basis of their different sizes. The method uses 'beads' with uniform holes in them. The holes are openings to tunnels through the bead. Small molecules that fit into the holes travel throught the tunnels and take longer to pass through the column than large molecules that do not fit into the holes.
4. Ion exchange chromatography uses beads that don't have holes, but instead have charged molecules linked to them. Anion exchange chromatography has positive ions linked to the beads and a chloride counterion. When a solution of charged molecules pass through the column, the negative chloride ions are replaced by the negatively charged molecules, which 'stick' to the positive ions linked to the column. Cation chromatography uses negative ions linked to the beads with sodium or potassium counterions.
5. Affinity chromatography uses the structure of a molecule that a protein binds (such as ATP) as a means of purifying the protein. For example, proteins that bind ATP would be retained by a column full of beads with ATP on their surface. The non-ATP-binding proteins will pass through first. ATP-binding-proteins can be removed from the column by adding ATP.