Lecture 8 - Hormones Flashcards
Part 2
what are the two classifications of hormones
- membrane solubility
- water solubility
- release
- synthesis
- transport in blood
- examples
Hydrophilic hormones
– Membrane solubility: Not lipid soluble (lipophobic), cannot cross plasma membranes
– Water solubility: Water soluble, can dissolve in plasma
– release: exocytosis
– synthesis: in advance, stored in blood cells
– transport in blood: dissolved
– Examples: peptide hormones, protein hormones and catecholamines
Hydrophobic hormones
– Membrane solubility: Lipid soluble (lipophilic), readily cross plasma
membrane
– Water solubility: Not water soluble, do not dissolve in plasma
– release: diffusion
– synthesis: on demand
– transport in blood: bound to carrier proteins
– Examples: steroid and thyroid hormones
what are the three main types of hormones
for each:
- derived from?
- transport
- examples
- peptide/protein
- derived: chains of 3 or more amino acids
- transport: Hydrophilic, so mix easily with blood plasma
- example: insulin - steroid
- derived: cholesterol
- transport: Hydrophobic, so bind to transport proteins in the blood
- example: sex steroids (estrogen), cortisol - monoamine (derived from single amino acids)
- derived: single amino acid
- transport: Hydrophilic, so mix easily with blood plasma
- example: Catecholamines (epinephrine), thyroxine
peptide and protein hormones
- abudancy
- synthesis
- storage
- release
- half life in plasma
- how to get inside a cell?
- abudancy = most hormones
- synthesis = made in advance like secreted proteins
- storage = in vesicles
- release = exocytosis by signal
- half life in plasma = short
- how to get inside a cell = bind to membrane receptors (next lecture)
Post-translational processing produces biologically active peptide
what is the synthesis, packaging, and release of a peptide hormone in the ER, golgi, and finaly plasma
- ribosome makes. the mRNA protein and attaches to the ER
- ER cleaves the signal sequence from the protein which initiates further processing to the protein with the prohormone embedded
- protein with prohormone transports in vesicles through the golgi apparatus where a number of steps cleave the prohormone/active hormone from the peptide fragment
- through exocytosis it is released from the cytoplasm to the ECF and then enters the plasma (hormone is hydrophilic enters plasma, protein fragments are hydrophobic so don’t enter)
what is a preprohormone?
how does a single preprohormone contain:
- several copies of the same hormone
- more than one type of hormone
what are the active peptides that are cleaved dependent on?
A preprohormone is an inactive precursor to a hormone, containing a signal sequence that directs the protein to be processed and secreted.
several copies of the same hormone
- may have a very long polypeptide with small snippets of active hormones
- it can cleave this very long polypeptide to a small number of hormones + other peptides + signal sequence
more than one type of hormone
- long protein with segments of multiple hormones
- cleaved to separate all of the active hormones + other peptide fragments
Active peptides released depends on specific proteolytic processing enzymes
another example of cleaving proteins for an active hormone:
what are the components of proinsulin?
- proinsulin contains a c-protein and insulin fragments
- when it is cleaved, it cleaves to its fragments of insulin (structure attached by disulfide bonds) and C-peptide (extra fragment)
- ex. Insulin is degraded in the body extremely quickly and is difficult to measure because of this. How else could we indirectly measure insulin release?
- measure the C-peptide levels
steroid hormones
- parent molecule
- synthesis
- storage
- release
- bound to blood
- half life
- how to get inside a cell?
- parent molecule = cholesterol
- synthesis = made on demand
- storage = not in vesicles
- release = cell by simple diffusion (since hydrophobic)
- bound to blood = carries (insoluble)
- half life = long
- how to get inside a cell = are able to go into the cytoplasm or nucleus receptors (can also act on plasma membrane receptors) and diffuse into target cells or be taken up by endocytosis of steroid hormone carrier proteins
use an example to explain how cholesterol is modified based on which organ its in
cholestrol the parent steriord makes different hormones based on what enzymes are present in that organ and cell.
for ex.
cholesterol in ovaries –> estrogen
cholesterol in adrenal cortex –> aldosterone or cortisol
where are amine hormones derived from (2)
what hormone does each derivative make and what class of hormone does that hormone behave like?
synthesized from tryptophan or tyrosine
Tryptophan derivative:
Melatonin (behaves like peptides or steroids)
Tyrosine derivatives:
Catecholamines (behave like peptides –> dopamine, norepinephrine, epinephrine)
Thyroid hormones (behave like steroids –> thyroxine T4, T3)
amine hormone: melatonin - tryp derivative
when and where is it secreted/made?
what is its main function?
when is it made and secreted: at night during sleep
where is it made: pineal gland (also gi tract, leukocytes,
other brain regions)
function:
Transmits information (light-dark cycles to govern the biological clock)
(also Immune modulation Anti-oxidant)
amine hormone: catecholamines - tyrosine derivative
where are catecholamines synthesized? stored? release structure? solubility? binding group?
- synthesis = adrenal medulla in the adrenal gland
- stored = vesicles prior to release
- released = exocytosis
- solubility = water soluble, lipophobic and hydrophilic
- binding = membrane receptors
ex. tyrosine makes epinephrine (adrenaline) via 4 enzymes and 3 intermediates
how do endocrine cells know when to release hormones?
endocrine cells know when to release the hormone when it senses a specific stimuli.
this stimuli can be anything from a metabolite, hormone, neurohormone, or neurotransmitter
how does stimuli trigger hormone release from the endocrine cell? (6)
Act through intracellular pathways to:
* change the membrane potential
* increase free cytosolic Ca2+
* change enzymatic activity
* increase the transport of hormone substrates into the cell
* alter transcription of genes coding for hormones or for enzymes needed for hormone synthesis
* promote survival and in some cases growth of the endocrine cell
explain how hormone insulin is secreted from the cascade of stimuli
the endocrine beta pancreatic cell is able to sense the increase of glucose in the blood stream
- this glucose is uptook from the cell via the GLUT2 channel
- this triggers an increase of ATP/ADP ratio in the cell due to greater glycolysis and respiration
- the ATPs then bind to the K+ channel and thus inhibits K+ ions from leaving the cell –> depolarization (positive charge stays inside thus makes it more positive)
- the depolarization opens up voltage gated Ca++ channels
- Ca++ ions act as the stimuli which when increased concentration in the cell, the insulin vesicles recognize this and releases its contents outside the cell
hormones trigger the release of other hormones. what is an example of this?
Hormones released from the hypothalamus and anterior pituitary regulate the release of several hormones.
ex. hypothalamus –> hypothalamic hormone –> anterior pituitary –> anterior pituitary hormone –>peripheral endocrine gland –> peripheral gland hormone —> reaches target organs (like thyroid, ovary, testes, musculoskeletal, mammary etc.)
there are negative feedback loops from the peripheral gland hormone to the anterior pituitary and hypothalamus.
as well as the anterior pituitary straight to the hypothalamus.
