Function of hormones Flashcards
what are hormones
cell to cell communication models made in glands or cells secreted into the bloodstream by endocrine galnds or cells only target cells with receptors for the hormone will respond to the signal
what is the function of hormones
control of enzymatic reaction rate, transport of ions or molecules across cell membranes, gene expression and protein synthesis
bind to target receptors
termination of action
half-life indicates length of activity
how does termination of action work
hormones bound to membrane receptors are degraded by plasma enzymes (endocytosis), intracellular enzymes metabolise hormones in cell
what is the classification of hormones
peptide - 3 amino acids, large proteins, glycoproteins
steroid - derived from cholesterol
amine - derived from tryptophan or tyrosine
what is the preprohormone in relation to peptide hormones
large inactive form
mRNA in the ribosome binds amino acids into a peptide hormone called a preprohormone, the chain is directed in the ER lumen by a signal sequence of amino acids
what is the prohormone
enzymes in the ER chop off the signal sequence, creating an inactive prohormone, this passes from the ER through the Golgi complex and undergoes post-translational modification
what is the function of the secretory vesicles
secretory vesicles containing enzymes and prohormone bud off the Golgi, the enzymes chop the prohormone into one or more active peptides plus additional peptide fragments the secretory vesicles releases its contents by exocytosis into the extracellular space
what occurs after the hormone is released into the extracellular space
hormone moves into circulation for transport to its target, when it reaches its target it forms a peptide hormone-receptor complex and signal transduction occurs
what are the features of peptide hormones
water soluble
short half-life (minutes)
bind to membrane receptors as they are lipophobic
signal transduction occurs through production of cAMP (insulin transduction method is tyrosine kinase)
where is aldosterone and cortisol made
adrenal cortex
what steroid hormones are made in the gonads
oestrogen, progesterone, testosterone and androgens
what is different about steroid hormone producing cells
unusually large amounts of smooth ER
smooth ER is responsible for synthesis of cholesterol
how do steroid hormones move around the body
simple diffusion
they are not stored in vesicles as they are lipophilic and cannot be contained in a lipid-based vesicle instead they are synthesised as required
what are features of steroid hormones
cholesterol derived
cytoplasmic or nuclear receptors (mostly) activate DNA for protein synthesis
slower acting, longer half life
what is the mechanism of action for steroid hormones
most hydrophobic steroids are bound to plasma protein carriers, only unbound hormones can diffuse into the target cell
the receptor complex binds to DNA and activates or represses one or more genes
activated genes create new mRNA that moves into the cytoplasm
translation produces new proteins for cell processes
