U
Uracil (or the corresponding
nucleoside or nucleotide) in a nucleic acid.
U-RNA
see snrna.
U1–U6 snRNAs
See SNRNA.
UACUAAC box
see split gene (a).
UAS
Upstream activation site: a
sequence in the DNA of Saccharomyces cerevisiae which is involved in the
regulation of transcription; it apparently resembles an enhancer except that it
cannot function when located downstream of a promoter.
ubiquinones
See quinones
.
ubiquitin
A polypeptide (containing 76 amino
acids) present – either free or covalently bound to protein – in the cells of
higher eukaryotes and in various microorganisms. Energy-dependent binding of
ubiquitin to a protein is apparently an essential signal for the selective
proteolysis of that protein in the cell. The ubiquitin–PROTEASOME pathway has
been reported to be essential for proteolysis during morphological changes in Trypanosoma
cruzi
ultimate causation
The
hypothetical evolutionary explanation for the existence of a certain pattern of
animal behavior.
unsaturated
fatty acid
A fatty
acid possessing one or more double bonds between the carbons in the hydrocarbon
tail. Such bonding reduces the number of hydrogen atoms attached to the carbon
skeleton.
urea
[Gk. ouron, urine]
A soluble form of nitrogenous waste excreted by mammals and most adult amphibians.
A soluble form of nitrogenous waste excreted by mammals and most adult amphibians.
ureter
[Gk.
from ourein, to urinate]
A duct leading from the kidney to the urinary bladder.
A duct leading from the kidney to the urinary bladder.
urethra
[Gk.
from ourein, to urinate]
A tube that releases urine from the body near the vagina in females or through the penis in males; also serves in males as the exit tube for the reproductive system.
A tube that releases urine from the body near the vagina in females or through the penis in males; also serves in males as the exit tube for the reproductive system.
uric acid
[Gk. ouron, urine]
An insoluble precipitate of nitrogenous waste excreted by land snails, insects, birds, and some reptiles.
An insoluble precipitate of nitrogenous waste excreted by land snails, insects, birds, and some reptiles.
urine
[Gk. ouron, urine]
The liquid waste filtered from the blood by the kidney and stored in the bladder pending elimination through the urethra.
The liquid waste filtered from the blood by the kidney and stored in the bladder pending elimination through the urethra.
urochordate
A
chordate without a backbone, commonly called a tunicate, a sessile marine
animal.
uterus
[L. womb]
A female reproductive organ where eggs are fertilized and/or development of the young occurs.
A female reproductive organ where eggs are fertilized and/or development of the young occurs.
