BIOL 301 Chapter Notes - Chapter 23: Hepatocyte, Hydroxylation, Membrane Potential
Chapter 23- 23.1 and 23.2
23.1 Hormones: Diverse Structures for Diverse Functions
• Hormones
• = small molecules or proteins that are produced in one tissue, released into the
circulation and carried to other tissues where they act thru receptors to bring
about changes in cellular activities
• Serve to coordinate the metabolic activities of several tissues/ organs
• Ex of things regulated by 1+ hormones:
• Maintenance of BP, blood volume, electrolyte balance
• Embryogenesis
• Sexual differentiation
• Development and reproduction
• Hunger, eating behavior, digestion, fuel allocation
• Etc
• Coordination of metabolism - achieved by neuroendocrine system
• Individual cells in one tissue sense a change in organisms circumstances
→ secrete a chemical messenger that passes to another cell in the same
or diff tissue→ messenger binds to a receptor molecule at tissue →
triggers change in second cell
• Hormonal signaling can be over short or long distances
• Neuronal signaling- chemical messenger is neurotransmitter and
can only travel v short distance to next neuron across synapse
• Hormonal signaling- messengers are carried in bloodstream to
neighboring cells OR distant organs and tissues
• Other than distance difference- mechanisms are similar
• Same molecule can sometimes act as both neural and
hormonal signal (like epinephrine and norepinephrine)
• The detection and purification of hormones requires a bioassay
• Hormones being detected and isolated
• Find physiological process in one tissue that depends on signal that
originates in another
• Like insulin - produced in pancreas and affects the concentration
of glucose in blood and urine
• Quantitative bioassay for hormone can be developed
• Insulin- assay consisting of injecting extracts of pancreas into
experimental animals deficient in insulin, then quantifying resulting
changes in glucose concentrations in blood and urine
• To isolate hormone: must fractionate extracts containing the putative
hormone (with same techniques used to purify other biomolecules- like
solvent fractionation, chromatography, electrophoresis) then assay each
fraction for hormone activity
• Hormone categorization
• Obtaining sufficient hormone to allow its chemical characterization
involves large scale isolations
• Radioimmulo-assay (RIA)
• Hormone specific antibodies are the key to the radioimmunoassay
and modern equivalent (enzyme-linked immunosorbent assay-
ELISA)
• Purified hormone → elicits antibodies that bind to hormone
with high affinity and specificity
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• Tagged antibodies allowed to interact with extracts
containing hormone
• Fraction of antibody bound by hormone in the extract is
quantified by radiation detection or photometry
• Hormones act thru specific high-affinity cellular receptors
• Each cell type has own combination of hormone receptors
• 2 cell types with same type of receptor may have diff intracellular targets
of hormone action and may respond diff to same hormone
• Specificity - from structural complementarity between hormone and
receptor
• Interaction very selective
• High affinity of interaction allows cells to respond to VERY low
concentrations of hormone
• hormone -receptor interactions can be quantified by Scatchard analysis
• Yields quantitative measure of affinity and number of hormone-binding
sites in a preparation of receptor
• Intracellular consequences of ligand-receptor interaction are of 5(+) general
types
• 1) second messenger
• Like cAMP, cGMP, or inositol triphosphate
• Generated inside cell actis as allosteric regulator of one or more
enzymes
• 2) receptor tyrosine kinase
• Activated by extracellular hormone
• 3) change in membrane potential
• From opening/closing of hormone-gated ion channel
• 4) adhesion receptor on cell surface
• Conveys info abt extracellular matrix to cytoskeleton
• 5) steroid or steroid-like molecule
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