Digestion The organs of the gastrointestinal system directly involved with digestion are the mouth, stomach, small intestine and large intestine. Each organ produces different enzymes which are activated or deactivated by changes in the acidity level of the food-fluid mixture as it moves through through the tract. Salivary glands in the mouth secrete pytalin. This enzyme breaks down starches and complex sugars. Several other enzymes are released in the stomach. Pepsin and gelatinase break down proteins. Amylase continues conversion of complex carbohydrates to simple sugars, and lipase begins breakdown of fats. Lactase breaks down lactose, a disaccharide found in milk products. After leaving the stomach, the mixture enters the small intestine. The pancreas releases many enzymes into the small intestine. These include lipase, amylase, chymotrypsin, and trypsin. The actions of lipase and amylase were described above. Chymotrypsin and trypsin break down proteins. Nutrients are absorbed in the small intestine.

Chromosomes
Changes in chromosomal structure are mutations. Mutations occur when the total amount of information on the chromosome changes or the amount of genetic information stays the same but is rearranged. Two ways in which the total amount of genetic information available can be altered are deletion or duplication. In a deletion, a gene or segment of genes is lost during replication. This can be caused by radiation, viruses and chemicals. In duplication, a gene or segment of genes is repeated during replication. Genetic material can be rearranged in two ways, inversion or translocation. Inversion occurs when the genes on a single chromosome are reversed. Translocation occurs when the gene(s) of one chromosome attach to another chromosome. It can be a reciprocal exchange between chromosomes, or a one-way transfer.

Transcription occurs in the nucleus. A gene sequence for a specific protein is copied into mRNA. During translation, the ribosome reads the mRNA, translates the amino acid sequence, and creates the protein. Each amino acid are defined by a specific nucleotide sequence called a codon. If the three nucleotides of the codon are not in the correct order, the wrong amino acid will be created. This results in a protein being produced that was not expected. The error in nucleotide sequencing could occur during transcription or translation.

Sickle Cell Anemia
Sickle cell anemia is a disease of red blood cells. It is caused by an inversion mutation of the hemoglobin gene called Hb S. This causes the GLU protein to be changed to the VAL protein. The VAL protein causes the changes to the red blood cells.

If an individual inherits the Hb S allele from both parents, then the person will have the disease. If only one Hb S allele is present, then the person has the trait, but does not have the disease. The mutation causes red blood cells to shrink and become sickle shaped instead of the normal disc shape. They cannot carry oxygen normally. People with sickle cell anemia are anemic because they do not have enough red blood cells. They often have pain, fatigue and shortness of breath. It cannot be cured.

If the mother is heterozygous for Hb S, she has inherited one allele for the disease. If the father is homozygous, he has two alleles for the disease. Any children of the two would have a 50% chance of having the disease or just being a carrier. Either way, the child will have the trait and can pass it on to his children.

Fossil Fuels
The term “fossil fuels” derives from the way in which the fuel is formed. With the exception of coal, these fuels were formed from the compression of marine microorganisms on the sea bed over millions of years. Coal was formed on land from the compression of layers of vegetation. There are several types: crude oil, coal, and natural gas. Because it took so long for them to be created, supplies are limited. Once they are depleted, we will have to develop alternative sources of energy.

The burning of fossil fuels for energy creates pollution in the air and water. These pollutants consist of carbon dioxide, sulphur and nitrogen. Some environmental problems linked to these gasses are the greenhouse effect and acid rain.

Fossil fuel energy has two major disadvantages. The first is that supplies are finite. The second is that their use creates health hazards, not only for humans but for all life. Before this becomes a crisis, countries have begun researching clean, renewable energy sources. Several of these are solar energy panels, windmills, and hydroelectric turbines. We can extract energy from sunlight, wind and water movement without depleting the supply. As a bonus, their use does not create pollution. The main disadvantage at this point is the high cost to generate energy and relatively low output.