K
Lysine
See amino acids
K antigens
Capsular antigens – usually capsular polysaccharides. Examples
include the capsular antigens of Streptococcus pneumoniae, colominic
acid, and VI antigens. In Gram-negative bacteria, K antigens can mask O antigens;
in some bacteria the K antigens can be removed by heating , but in others (e.g.
Klebsiella spp) they are heat-stable. In Escherichia coli,
several surface antigens originally designated K – e.g. K88, K99 – are actually
(proteinaceous) fimbrial antigens, and it has been proposed that they be
renamed F antigens (K88 = F4, K99 = F5); polysaccharide K antigens may occur
together with fimbrial antigens in certain strains of E. coli.
K+-ATPase
see ion transport.
K cells
Killer cells: lymphoid cells which have cytotoxic/cytolytic activity
against target cells; syn. NK CELLS.
K+ pump
see ion transport.
K-selection
The
concept that in certain (K-selected) populations, life history is centered
around producing relatively few offspring that have a good chance of survival.
K+ transport
see ion transport.
K virus
see polyomavirus.
K vitamins
see quinones.
K1 killer strain (of Saccharomyces cerevisiae)
see killer factor.
K1 RNA, K2 RNA
see rnase p.
K88, K99
In Escherichia coli : fimbrial
antigens of certain strains pathogenic in animals – see Etec, Fimbriae and K antigens.
Kabackosome
A type of vesicle formed by the hypotonic
lysis of a sphaeroplast. A Kabackosome (which contains little or no cytoplasm)
is composed of cytoplasmic membrane; the inner and outer faces of the membrane
correspond to those in the original cell. (cf. ETP.)
KAF
syn. factor i.
Kaffir pox
see smallpox.
Kagami fever
see ehrlichia.
Kahn test
A standard test for syphilis.
kala-azar
see visceral leishmaniasis.
Kanagawa phenomenon
The phenomenon in which those strains of Vibrio
parahaemolyticus isolated from human patients exhibit clear (b) haemolysis
when grown on WAGATSUMA AGAR containing human RBCs but not on that containing
horse RBCs (a Kanagawa +ve reaction), while almost all strains isolated from
other sources, including food suspected of causing V. parahaemolyticus food
poisoning, do not (i.e. are Kanagawa −ve). (Discoloration (a-haemolysis)
and clear haemolysis on both human and horse RBC-containing media are
both regarded as Kanagawa −ve results.) The Kanagawa haemolysin is heatstable, extracellular,
cytotoxic and cardiotoxic, and is haemolytic for human, dog and rat RBCs, weakly
so for rabbit and sheep RBCs, and inactive against horse RBCs. In feeding
experiments (in man), only Kanagawa +ve strains were capable of causing gastroenteritis,
but the role of the haemolysin in pathogenesis is unknown; Kanagawa +ve strains
appear to be better able to
multiply in the intestine than are
Kanagawa −ve strains.
kanamycin
Any of several related aminoglycoside
antibiotics (kanamycins A, B, C) produced by Streptomyces kanamyceticus;
the drug used clinically is composed mainly of kanamycin A.
kanchanomycin (albofungin)
A complex polycyclic antibiotic, produced
by Streptomyces sp, which has both antibacterial and antitumour
activity. In the presence of divalent cations, kanchanomycin binds to DNA and
inhibits DNA and RNA synthesis.
Kaposi’s sarcoma (KS)
A rare multifocal neoplastic
disease which occurs in two forms: (i) slow and indolent (limited mainly to the
skin), and (ii) rapid and fulminant (involving skin and gastrointestinal
tract). The milder form occurs in certain ethnic groups (e.g. Ashkenazi Jews).
The aggressive form occurs in children in tropical Africa and is also a common
feature in HIV infected patients. Kaposi’s
sarcoma appears to be associated with human (gamma) herpesvirus 8 (HHV8) in
conjunction with the immunosuppressive effects of HIV. Activation of latent
HHV8 in vitro has been achieved by demethylation of the promoter of a
transactivator region by means of the reagent tetradecanoylphorbol acetate
(TPA), and studies on the level of methylation of the transactivator region in
biopsies have suggested a relationship between methylation status and the
development of HHV8- associated disease
Kaposi’s varicelliform eruption
May refer either to eczema herpeticum or eczema vaccinatum
kappa chain
see light chain.
kappa particles
see caedibacter.
Karatomorpha
see proteromonadida.
K¨arber method
see end-point dilution assay.
Karelian fever
see sindbis virus.
Karnal bunt (partial bunt; new bunt)
A wheat disease caused by Neovossia
indica (formerly e.g. Tilletia indica); originally
a minor disease confined to NW India, it
has recently spread through northern India and has become established in Afghanistan,
Iraq, Pakistan, and Mexico, apparently transmitted on and in wheat seed.
Usually only some of the grains in an ear are attacked; infected parts of the
grain are initially grey but gradually turn black and emit a foul odour
(trimethylamine).
karyogamy
The
fusion of nuclei of two cells, as part of syngamy.
karyokinesis
Division
of the nucleus during the cell cycle.
karyotype
(kar-ee-oh-type)
[Gk. kara, the head + typos, stamp or print]
A method of organizing the chromosomes of a cell in relation to number, size, and type.
A method of organizing the chromosomes of a cell in relation to number, size, and type.
keratin
[Gk. karas, horn]
One of a group of tough, fibrous proteins formed by certain epidermal tissues and especially abundant in skin, claws, hair, feathers, and hooves.
One of a group of tough, fibrous proteins formed by certain epidermal tissues and especially abundant in skin, claws, hair, feathers, and hooves.
keystone
predator
A
predatory species that helps maintain species richness in a community by
reducing the density of populations of the best competitors so that populations
of less competitive species are maintained.
keystone
species
A species
that is of exceptional importance in maintaining the species diversity of a
community; when a keystone species is lost, the diversity of the community
decreases and its structure is significantly altered.
kidney
In
vertebrates, the organ that regulates the balance of water and solutes in the
blood and the excretion of nitrogenous wastes in the form of urine.
kilocalorie
(kcal)
A
thousand calories; the amount of heat energy required to raise the temperature
of 1 kg of water 1°C.
kin
selection
A
phenomenon of inclusive fitness, used to explain altruistic behavior between
related individuals.
kinesis
(kih-nee-sis)
A change in activity rate in response to a stimulus.
A change in activity rate in response to a stimulus.
kinetic
energy
(kih-net-ik)
[Gk. kinetikos, putting in motion]
The energy of motion, which is directly related to the speed of that motion. Moving matter does work by transferring some of its kinetic energy to other matter.
The energy of motion, which is directly related to the speed of that motion. Moving matter does work by transferring some of its kinetic energy to other matter.
kinetochore
(kih-net-oh-kor)
[Gk. kinetikos, putting in motion + choros, chorus]
A specialized region on the centromere that links each sister chromatid to the mitotic spindle.
A specialized region on the centromere that links each sister chromatid to the mitotic spindle.
kingdom
A
taxonomic category, the second broadest after domain.
Koch's
postulates
A set of
four criteria for determining whether a specific pathogen is the cause of a
disease.
Krebs
cycle
A
chemical cycle involving eight steps that completes the metabolic breakdown of
glucose molecules to carbon dioxide; occurs within the mitochondrion; the
second major stage in cellular respiration.