Within the body, many molecules are able to pass across the membranes that surround cells. These molecules can accomplish this feat due to specific transport systems. These systems include special receptors on the membrane of the cell and special carrier proteins. The receptor recognizes the molecule and receives it on the cell membrane. Then the molecule hitches a ride through the cell membrane on the back of a carrier protein.
With such remarkable specificity, it is little wonder that sometimes there are defects in transport systems. Several dozen different diseases are now known to be due to transport defects.
Am example of a transport disease is cystinuria, the most common defect known in the transport of an amino acid (namely, cystine) and a significant cause of kidney stones. Like cystinuria, all transport defects are genetic (inherited).
- Transport disease, cystine
Commonly known as cystinuria, this is an inherited (genetic) disorder of the transport of an amino acid (a building block of protein) called cystine. The result is an excess of cystine in the urine (cystinuria) and the formation of cystine stones.
- Transposition, genetics
The ability of genes to change position on chromosomes, a process in which a transposable element is removed from one site and inserted into a second site in the DNA. Genetic transposition was the first type of genetic instability to be discovered. This remarkable phenomenon was discovered by the great American geneticist Barbara McClintock (1902-1992) […]
A short mobile DNA sequence that can replicate and of which copies can be inserted at random sites within chromosomes. A transposon has almost identical sequences at each end and inverted repeat sequences (that run in the opposite direction). It codes for the enzyme, transposase, that catalyses its insert in the chromosome.
A person who desires or has achieved transsexualism.
Consistently strong desire to change one’s anatomical gender. Some transsexuals were misassigned gender at birth (for example, being anatomically male but raised as female), either on purpose or due to indistinct anatomy. Most, however, are perfectly normal physically. Transsexuals may dress and behave as individuals of the opposite sex, and they may choose to use […]