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(Греч.: βίος = βϊοτή = βϊοτος = βίωσις - жизнь, 1819).
Схема. Трёхступенчатое управление секрецией гормонов с участием передней доли гипофиза = Model for regulation of anterior pituitary hormone secretion by three tiers of control.
Схема. Синтез пептидных гормонов клеткой = Cellular synthesis of polypeptide hormones.
Примечание: с. 44 (32)= Figure 3-2 Cellular synthesis of polypeptide hormones. Steps that take place within the nucleus include transcription of genetic information into a messenger
ribonucleic acid precursor (pre-mRNA) followed by post-transcriptional processing, which includes RNA cleavage, excision of introns, and rejoining of exons,
resulting in formation of mRNA. Ends of mRNA are modified by addition of methylguanosine caps at the 5ЃЊ end and poly(A) tracts at the 3ЃЊ ends. The cytoplasmic
mRNA is assembled with ribosomes. Amino acids, carried by amino-acylated transfer RNAs (tRNAs), are then polymerized into a polypeptide chain.
The final procesess in protein synthesis take place during growth of the nascent polypeptide chain (cotranslational) and after release of the completed chain
(post-translational). They include proteolytic cleavages of the polypeptide chain (conversion of pre-prohormones or prohormones to hormones), derivatizations
of amino acids (e.g., glycosylation, phosphorylation), and cross-linking and assembly of the polypeptide chain into its conformed structure. Posttranslational
synthesis and processing of a typical secreted polypeptide require vectorial or unidirectional transport of the polypeptide chain across the
membrane bilayer of the endoplasmic reticulum, resulting in sequestration of the polypeptide in the cisterna of the endoplasmic reticulum, a first step in the
export of proteins destined for secretion from the cell (see Fig. 3-6). Most translational processing occurs within the cell (presecretory); in some instances,
it occurs outside the cell, when further proteolytic cleavages or modifications of the protein take place (postsecretory). CHO, carbohydrate.
Схема. Гипотеза о начальных стадиях синтеза полипептидных гормонов в клетке. = Cellular events in the initial stages of synthesis of a polypeptide hormone according to the signal hypothesis.
Примечание: с. 47 (35)= Figure 3-6 Cellular events in the initial stages of synthesis of a polypeptide hormone according to the signal hypothesis. In this schema, a signal recognition
particle, consisting of a complex of six proteins and an RNA (7S RNA), interacts with the amino-terminal signal peptide of the nascent polypeptide chain
after approximately 70 amino acids are polymerized, arresting further growth of the polypeptide chain. The complex of the signal recognition particle and
the polyribosome nascent chain remains in a state of translational arrest until it recognizes and binds to a docking protein, which is a receptor protein located
on the cytoplasmic face of the endoplasmic reticular membrane. This interaction of the signal recognition particle complex with the docking protein releases
the translational block, and protein synthesis resumes. The nascent polypeptide chain is discharged across the membrane bilayer into the cisterna of the
endoplasmic reticulum and is released from the signal peptide by cleavage with a signal peptidase located in the cisternal face of the membrane. In this model,
the signal peptide is cleaved from the polypeptide chain by signal peptidase before the chain is completed (i.e., cotranslational cleavage). The configuration of
the polypeptide during transport across the membrane and the forces and mechanisms responsible for its translocation are unknown. The loop, or hairpin,
configuration of the chain shown here is an arbitrary model; other models are equally possible.
Схема. Ген глюкагона поджелудочной железы и его мРНК (матричная, информационная РНК, кодированный посредник): комплементарная ДНК = The pancreatic glucagon gene and its encoded messenger RNA (mRNA): complementary DNA.
Примечание: с. 51 (39)= Figure 3-9 The pancreatic glucagon gene and its encoded messenger RNA (mRNA): complementary DNA. In the glucagon gene, exons precisely encode
separate functional domains. The gene consists of six exons (E1 through E6) and five introns (1A through 1E). The mRNA encoding pre-proglucagon, the
protein precursor of glucagon, consists of 10 specific regions: from left to right, a 5ЃЊ untranslated sequence (UN-TX, open), a signal sequence (S, stippled), an
amino-terminal extension sequence (N, hatched), glucagon (Gluc, shaded), a first intervening peptide (IP-I, hatched), a first glucagon-like peptide (GLP-I, shaded),
a second intervening peptide (IP-II, hatched), a second glucagon-like peptide (GLP-II, shaded), a dilysyl dipeptide (hatched) after the GLP-II sequence, and an
untranslated region (UN-TX, open). Exons from left to right encode the 5ЃЊ untranslated region, signal sequence, glucagon, GLP-I, GLP-II, and 3ЃЊ untranslated
sequence. Letters shown above the mRNA denote amino acids located at positions in the pre-proglucagon molecule that are cleaved during cellular processing
of the precursor. The amino acid methionine (M) marks the initiation of translation of mRNA into pre-proglucagon. H, histidine; K, lysine; Q, glutamine;
R, arginine.
Схема. Наиболее вероятные точки воздействия для управления экспрессией генов при выработке гормонов = Potential control points in an endocrine
cell for regulation of gene expression during hormone production.
Примечание: с. 51 (39)= Figure 3-10 Potential control points in an endocrine
cell for regulation of gene expression during hormone
production. Specific effector substances bind to plasma
membrane receptors (peptide effectors) or to cytosolic
or nuclear receptors (steroids), which leads to
initiation of a series of events that couple the effector
signal with gene expression. Peptide effector–receptor
complex interactions act initially through activation of
adenylate cyclase (AC) coupled with a guanosine
triphosphate–binding protein (G). Coupling factors and
substances such as glucose, cyclic adenosine monophosphate,
and cations activate protein kinases, resulting
in a series of phosphorylations of macromolecules.
Specific effectors for various endocrine cells appear to
act at one or more of the indicated five levels of gene
expression (see text for details), with the possible
exception of post-translational processing of prohormones,
for which no definite examples of metabolic
regulation have yet been found.
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Санкт-Петербург, Россия, 1996-2015
Разрешается некоммерческое цитирование материалов данной энциклопедии при условии
полного указания источника заимствования: имени автора, названия и WEB-адреcа данной энциклопедии
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