Chapter 6 Flashcards
Hormones
-secreted by ductless endocrine glands to the blood
-travel to target cells
-produced in small amounts
-regulate and direct particular functions
Receptors
-found in target cells
-where hormones will bind
-protein molecules
Hydrophilic Hormones
-highly water soluble
-categorized by length as either: a) peptide hormones or b) catchecholamines
Peptide Hormones
-short length
-short chain of amino acids bound with peptides
-synthesized in rough endoplasmic reticulum
-packaged in the golgi complex
-stored in large amounts in secretory granules
-secreted by exocytosis
-transported freely in the blood
-receptors on surface of target cells
-majority of hormones
-ie. insulin
Mechanism of Peptide Hormones
-channel changes
or
-second messenger system to alter activity of target proteins that produce the effect
Catecholamines (protein) Hormones
-long
-also bound with peptides
-derivatives of the amino acid: tyrosine
-synthesized in cytosol
-stored in chromaffin granules
-released by exocytosis
-receptor side on plasma membrane (surface)
Circulation of Catecholamines
-50% are bound to plasma proteins
-50% freely circulate in the blood
Catecholamine Mechanism of Action
second messenger system alters activity of target proteins that produce the target effect
Adrenal Cortex
-produces cortisol and adrenaline
Catecholamine Examples
-are hormones from the adrenal medulla; the inner part of the adrenal gland
-ie. norepinephrine, epinephrine, dopamine
Adrenal Gland
-above the kidneys
-consists of an inner medulla and an outer cortex
Lipophilic Hormones
-have high lipid solubility and are poorly soluble in water
-categorized by a) steroid hormones and b) thyroid hormones
Steroid Hormones
-derivatives of cholesterol
-synthesized by modification of cholesterol
-not stored (cholesterol is stored in lipid droplets)
-secreted by simple diffusion
-transported via binding to plasma proteins
-receptors are located inside the target cell
Steroid Hormone Mechanism of Action
activation of specific genes to make new proteins that produce the effect
Steroid Hormone Examples
-hormones from the adrenal cortex
-hormones from the gonads (testes and ovaries)
Thyroid Hormones
-also tyrosine derivatives
-secreted by thyroid gland
-synthesized and stored in colloid
-secreted by endocytosis
-transport via binding to plasma proteins
-receptor site is inside target cell
Amine Hormones
catecholamines and thyroid hormones grouped together because they are both tyrosine derivatives
Mechanism of Thyroid Hormones
activation of specific genes that make new proteins to produce the effect
Examples of Thyroid Hormones
-hormones from thyroid follicular cells
Process of DNA copying
-transcription: MRNA goes to cytoplasm where it is decoded (translation)
= brand new protein is made
NASCENT protein
-an original protein that has never been made
-gives a brand new response
-ie. estrogen during puberty
Complexity of Endocrine function
- a single gland may produce multiple hormone
- a single hormone may be secreted by more than one gland
- a single hormone may have more than one type of target cell
- rate of secretion varies
- target cell may be influenced by more than one hormone
Cyclic AMP Second Messenger System
-steps in the cAMP second messenger system to initiate a cellular response in the cell
Step 1: cAMP
-binding of first messenger to its surface membrane receptor
-activates enzyme adenylylcyclase which is located on the cytoplasmic side of the membrane
-G protein found on inner membrane surface acts as the middle man
-unactivated G protein consists of alpha, beta, and gamma subunits
-the G proteins are activated in response to the binding of first messengers on surface receptors
-receptor attaches to the G protein, activating the alpha subunit
-alpha subunit breaks away and moves along inner surface membrane until reaching effector protein
-effector protein is an ion channel or an enzyme
-alpha links with effector (adenylyl cyclase) and alters its activity
Step 2: cAMP
-adenylyl cyclase induced conversion of ATP to cAMP by cleaving off 2 phosphates
Step 3: cAMP
-intercellular 2nd messenger, cAMP, tiggers series of biochemical steps to bring about the response initated by 1st messenger
-to begin, cAMP activates protein kinase A (PKA), an enzyme
Step 4: cAMP
-protein kinase A attaches a phosphate group from ATP (phosphorylation) to a target protein; such as an enzyme
Step 5: cAMP
-phosphorylation causes the protein to change shape and function
-this change is the target cells response to the first messenger
-ie. an enzyme that regulates a metabolic even may be increased or decreased
Step 6: cAMP
-after the response:
-first messenger is removed
-alpha subunit rejoins beta and gamma to restore the inactive G protein complex
-cAMP is inactivated so the message is erased and the response is stopped
key note for cAMP 2nd messenger system
-steps involving the first messenger, receptor, and G protein, and effector protein occur in the plasma membrane
-all these steps lead to the activation of the second messenger
-extracellular messenger cannot enter the cell
-cAMP the 2nd messenger triggers events in the cell to initiate a response
examples where cAMP is used
-modifying heart rate
-forming female sex hormones in ovaries
-breakdown of stored glucose in the liver
-control of water conservation during urine formation
-perceptions of sweet taste via taste bud
Calcium Second Messenger System
-used by some cells instead of cAMP
Step 1: calcium
-binding of the first messenger to surface receptor by means of a G protein
-alpha subunit breaks away
-activates the enzyme phospholipase C (PLC), this is the effector protein
Step 2: calcium
-PLC breaks down phospharidylinositol biphohsphate (PIP2) into either a) IP3 (inositol triphosphate) or b) DAG (diacylglycerol)
Step 3a: calcuim
-IP3 is responsible for mobilizing Ca2+ to increase cytosolic Ca2+
Step 4a: calcium
-calcium takes over the role of second messenger, bringing about the response of the first messenger
-many of the Ca2+ events are triggered by the activation of calmodulin (Ca2+ binding protein)
Step 5a: calcium
-activated calmodulin activates calmodulin dependent protein kinase (CaM kinase)
Step 6a: calcium
-CaM kinase phosphorylates inactive target protein
Step 7a: calcium
-altered protein brings about the desired cellular response
Step 3b-5b: calcium
-DAG simultaneously sets off another second messenger pathway
-DAG activates protein kinase C (PKC) which brings about cellular response by phosphorylating cellular proteins
Cascade of events
-second messenger pathways amplify an initial stimulus
-ie. receptors activate many adenylyl cyclase molecules which activate even more cAMP molecules, influencing many enzymes, producing many products
-so 10 adenylyl cyclase can initiate 10 million molecules of a secretory response
Lipophilic Hormones
-bind with intracellular receptors and primarily produce their effects in their target cells by activating specific genes
-activation of genes cause the synthesis of new proteins
Step 1: lipophilic
-free lipophilic hormone diffused through plasma membrane and binds with receptor (can be in cytoplasm or nucleus)
Step 2: lipophilic
-each receptor has a region for binding with hormone and another region for binding with DNA
-when hormone is bound to receptor, receptor binds with DNA at the hormone response element (HRE)
Step 3: lipophilic
-binding of receptor with DNA turns on a specific gene within the target cell
-the gene contains the code for synthesizing a given protein
-code is transcribed into MRNA
Step 4: lipophilic
-new MRNA leaves nucleus and enters cytoplasm
Step 5: lipophilic
-MRNA binds to a ribosome
-MRNA directs the synthesis of the new proteins
Step 6: lipophilic
-new protein produces the target cells response to the hormone
Nervous System
-rapid response
-brief in duration
-target tissues are muscles, glands, adipose tissue
Endocrine System
-slow response
-longer in duration
-targets many tissues in the body
