Cell Structure The major structures, called organelles, of the cell are shown in Figure 8-1. These structures are as follows: Figure 8-1 The structures of the cell. Homeostasis is the tendency of a cell or the whole organism to maintain a state of balance. Molecules pass into and out of the cell to maintain this balance. The cells of the body constantly adjust to preserve a balance of fluids, temperature, oxygen, electrolytes, and nutrients. Electrolytes are compounds made of charged particles called ions. These ions can conduct electrical current in water or in the cytoplasm of the cell. A positive charge, or cation, creates an acid. A negative charge, or anion, creates a base. The pH of a fluid is a measurement of how much acid or base is present. Each body tissue has a normal pH. The cells do not function properly if the normal pH is not maintained for the area of the body (Figure 8-2). Different electrolytes also have specific functions, as shown in Table 8-1. Figure 8-2 pH of the body. The body must maintain normal pH levels to function properly.
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Each single chromosome contains 3 billion phosphate base pairs that make up the 100,000 genes (Figure 34-2). A single gene, such as that for cystic fibrosis, is made up of 6100 base pairs. Some genes are expressed at one stage of development and no other. Ninety percent of the genome does not express itself at all.
The Human Genome Project, begun in 1988, is a multi-billion dollar international effort to identify and sequence all of the human chromosomes. This process is called gene mapping (Table 34-1). Computerization of the sequencing techniques has allowed biotechnologists to identify gene sequences at a much more rapid rate than in the past. Researchers involved in this project report the identification of at least 18 genes involved in insulin-dependent diabetes. Scientists have also identified the location of a gene called BRCA1 that causes 5% of all breast cancers. At least one gene that makes people susceptible to allergies and asthma also has been identified. In all, more than 50 genetic diseases can now be identified using DNA testing (Table 34-2).
Cell Genetics Deoxyribonucleic acid (DNA) is a molecule that, by the sequencing of its components, determines all of the characteristics of living things. A nucleic acid is made of a nitrogen base that is attached to a sugar and phosphate. Each strand of DNA is formed in a double helix of chains of these nucleotides. The DNA conveys its message by unfolding and breaking into two strands. Special units of three nucleotides replicate or form a messenger to leave the strand. The new messenger makes a protein that directs a body function. The genetic information of humans is found in the nucleus of the cell in 23 pairs of chromosomes (Figure 34-1). Each chromosome is made up of a chain of DNA. The protein messages expressed by the sequencing of the DNA determines characteristics and directs the body processes. There are more than 100,000 genes on the human chromosome. |
| Chromosome Number | Genetic Information Influenced |
|---|---|
| 1 | Rh blood type—blood protein |
| Thyroid-stimulating hormone—metabolism | |
| Amylase—starch digestion | |
| 2 | Myosin—coats neurons |
| Antibodies—fight infection | |
| Glucagon—sugar storage | |
| 3 | Rhodopsin—light-sensitive pigment |
| 4 | Huntingtons disease—neurotransmission defects |
| Alcohol dehydrogenase—breaks down alcohol in body | |
| Red hair color | |
| 6 | Major histocompatibility complex—antibodies |
| Several reproductive hormones | |
| 7 | Collage production |
| Trypsin—digestive enzyme | |
| Cystic fibrosis | |
| 9 | ABO blood grouping |
| 10 | Hexokinase enzyme—hemolytic anemia |
| 11 | Hemoglobin—sickle-cell anemia or thalassemia |
| Insulin | |
| Parathyroid hormone | |
| Albinism | |
| 12 | Phenylketonuria (PKU) |
| 14 | Antibody production |
| 15 | Tay-Sachs disease—neurological disorder |
| 16 | Chymotrypsinogen—protein digestion |
| 17 | Neurofibromatosis—nerve tissue tumors |
| Growth hormone | |
| 18 | Tourette syndrome—neurological disorder |
| 19 | Familial hypercholesterolemia |
| Brown hair color | |
| Green-blue eye color | |
| 20 | Adenosine deaminase—immunodeficiency disease |
| X | Duchenne muscular dystrophy |
| Red-green color blindness | |
| Hemophilia |
| Disease | Description |
|---|---|
| Adult polycystic disease | Multiple kidney growths |
| Alpha-1-antitrypsin deficiency | Can cause hepatitis, cirrhosis of the liver, emphysema |
| Charcot-Marie-Tooth disease | Progressive degeneration of muscles |
| Familial adenomatous polyposis | Colon polyp by age 35 years, often leading to cancer |
| Cystic fibrosis | Lungs clog with mucus; usually fatal by 40 years of age |
| Duchenne/Becker muscular dystrophy | Progressive degeneration of muscles |
| Hemophilia | Blood fails to clot properly |
| Fragile X syndrome | Most common cause of inherited mental retardation |
| Gauchers disease | Mild to deadly enzyme deficiency |
| Huntingtons disease | Lethal neurological deterioration |
| Amyotropic lateral sclerosis (ALS; “Lou Gehrigs” disease) | Fatal degeneration of the nervous system |
| Myotonic dystrophy | Progressive degeneration of muscles |
| Multiple endocrine neoplasia | Endocrine gland tumors |
| Neurofibromatosis | Café-au-lait spots to large tumors |
| Retinoblastoma | Blindness; potentially fatal eye tumors |
| Spinal muscular atrophy | Progressive degeneration of muscles |
| Tay-Sachs disease | Lethal childhood neurological disorder |
| Thalassemia | Mild to fatal anemia |
| Future Tests | |
| Alzheimer's disease | Most likely multiple genes involved |
| Breast cancer | 5%-10% of cases are thought to be hereditary |
| Diabetes | Most likely multiple genes involved |
| Nonpolyposis colon cancer | Several genes cause up to 20% of all cases |
| Manic depression | Most likely multiple genes involved |
Products that may serve as pharmaceuticals are being developed with biotechnology techniques in the emerging discipline called pharmacogenomics. Some genetically modified (GM) foods in development include edible vaccines, therapeutic proteins, and antibodies produced by plants. For example, the ProdiGene company (College Station, Tx) is developing vaccines and insulin to be produced by corn plants. CropTech is trying to grow plants that produce enzymes and anticancer proteins. Other researchers are developing bananas grown to contain the hepatitis B vaccine. However, a market for genetically modified plants has not been established. Although it may help prevent cancer, a GM tomato rich in the anti-oxidant nutrient (beta-carotene) has not been accepted by the American public.
Copyright © 2026 Elsevier Inc., its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies.
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