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high-energy bond:
Covalent bond whose hydrolysis releases an unusually large amount
of free energy under the conditions existing in a cell. A group
linked to a molecule by such a bond is readily transferred from
one molecule to another. Examples include the phosphodiester
bonds in ATP and the thioester linkage in acetyl CoA.
histamine:
Small molecule derived from the amino acid histidine, released
from mast cells and basophils in allergic reactions. Causes
irritation, dilation of blood vessels, and contraction of smooth
muscle.
histone:
One of a group of small abundant proteins, rich in arginine
and lysine, that are associated with DNA in eucaryotic chromosomes.
homeobox:
Short (180 base pairs long) conserved DNA sequence that encodes
a DNA-binding motif famous for its presence in genes that are
involved in orchestrating the development of a wide range of
organisms.
homeodomain:
DNA-binding motif of 60 amino acids encoded by a homeobox.
homeotic mutation:
Mutation that causes cells in one region of the body to behave
as though they were located in another, causing bizarre disturbance
of the body plan.
homologous chromosome (homologue):
One of two copies of a particular chromosome in a diploid cell,
each copy being derived from a different parent.
homology:
Similarity in structure of an organ or a molecule, reflecting
a common evolutionary origin. Specifically, such a similarity
in protein or nucleic acid sequence. Contrasted with analogy
- a similarity that does not reflect a common evolutionary origin.
homozygote:
Diploid cell or organism having two identical alleles of a specified
gene.
housekeeping gene:
Gene serving a function required in all the cell types of an
organism, regardless of their specialized role.
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