Deck 22: Biochemistry of Hormones

Question 1

Which one of the following statements BEST describes the action of the parathyroid hormone?

A) it lowers calcium and phosphorus levels in plasma upon prolonged administration
B) its secretion is inhibited by high levels of plasma calcium
C) it lowers serum calcium levels and raises serum phosphate levels
D) it causes (or enhances) precipitation of calcium salts in bone
E) it stimulates reabsorption of phosphate from the kidney

Answer 1

its secretion is inhibited by high levels of plasma calcium

Question 2

Which one of the following statements concerning the formation of estrogens is FALSE?

A) Androgens can be converted to estrogens in adipose tissue.
B) NADPH and oxygen are required.
C) The conversion of androgens to estrogens involves the aromatization of the "A" ring and the loss of two methyl groups.
D) Testosterone can be a precursor of estrogens.
E) The placenta can convert DHEA-sulfate into estrogens.

Answer 2

The conversion of androgens to estrogens involves the aromatization of the "A" ring and the loss of two methyl groups.

Question 3

Specificity in the action of a peptide hormone is determined at the level of

A) the receptor, cyclic AMP and the cyclic AMP-dependent protein kinase.
B) the receptor, cyclic AMP and the substrates to be phosphorylated.
C) the receptor and the substrates to be phosphorylated.
D) the cyclic AMP-dependent protein kinase and the substrates to be phosphorylated.
E) none of these.

Answer 3

the receptor and the substrates to be phosphorylated.

Question 4

Thyroxine

A) is synthesized by iodination of free tyrosine molecules in the thyroid gland
B) is the only hormone synthesized by the thyroid gland
C) binds to plasma membrane receptors and activates adenylate or guanylate cyclase
D) is transported to its target tissue free in solution in the blood
E) synthesis requires iodination of a cellular protein in the thyroid

Question 5

Which of the following occurs subsequent to administration of parathyroid hormone?

A) hypercalcemia and hyperphosphatemia
B) hypocalcemia and hypophosphatemia
C) hypercalcemia and hypophosphatemia
D) hypocalcemia and hyperphosphatemia
E) none of the above is correct

Question 6

Which of the following enzymes is involved in the metabolism (breakdown) of epinephrine?

A) Phenylethanol amine-N-methyl transferase
B) Catechol-o-methyl transferase
C) Dopamine-beta-hydroxylase
D) Aromatic decarboxylase
E) Cyclic AMP phosphodiesterase

Question 7

Which vitamin is a secosteroid and acts through a steroid receptor?

A) Vitamin A
B) Vitamin C
C) vitamin D
D) Vitamin E
E) Vitamin K

Question 8

The thyroid hormone found in highest concentration in blood is

A) thyroglobulin.
B) monoiodotyrosine.
C) diiodotyrosine.
D) triiodothyronine.
E) thyroxine.

Question 9

Cortisol has primarily

A) estrogen activity.
B) mineralocorticoid activity.
C) androgen activity.
D) glucocorticoid activity.
E) None of the above is true.

Question 10

Of the following statements concerning human hormones, which one, if any, is true?

A) Adrenocorticotropic Hormone (ACTH) is a steroid hormone.
B) Hormones do not enter the blood but act locally on surrounding cells.
C) Initially, all hormones are synthesized in the cell as a prohormone.
D) Excess/abnormal thyroid hormone produced by a thyroid carcinoma is termed ectopic production.
E) None of the above.

Question 11

The catabolism and excretion of steroid hormones

A) occurs primarily as the bile salts.
B) usually involves transmethylation reactions.
C) requires reduction and cleavage of the steroid nucleus.
D) may involve conjugation of a metabolite with sulfate or glucuronate.
E) produces carbon dioxide.

Question 12

Which one of the following statements does not describe a characteristic of hormones?

A) synthesized in endocrine glands
B) have specific metabolic effects
C) are considered to be secondary messengers
D) act on one or more target tissues
E) bind either to cell surface or to intracellular receptors

Question 13

As regards the insulin receptor, which of the following statements, if any, is/are true?

A) The active receptor is made up of 1 alpha chain and 1 beta chain.
B) The alpha chain spans the membrane while the beta chain binds the insulin molecule.
C) In addition to activating the intrinsic tyrosine kinase of the receptor, insulin binding also activates a phospholipase c and induces production of the phosphatidylinositol second messengers.
D) A and C only.
E) None of the above.

Question 14

All of the following statements regarding the mechanism of action of the steroid hormones are true EXCEPT which one?

A) steroid hormones are lipid-soluble, therefore Can readily traverse the cell membranes.
B) In general, the steroid hormones act by affecting the rate of protein synthesis.
C) steroid hormones combine with a cytoplasmic receptors and stimulate the production of cAMP.
D) In general, steroid hormones take a rather long time (1-8 hours) to produce an effect.

Question 15

Which of the following best describes the mechanism by which steroid hormones increase the relative abundance of specific proteins?

A) steroids increase the half-life of specific proteins.
B) steroids increase the half-life of the mRNAs that encode specific proteins.
C) steroids increase the rate of synthesis of specific mRNAs.
D) steroids increase the translatability of specific mRNAs.
E) steroids increase RNA polymerase II activity.

Question 16

Thyroxine

A) decreases tissue oxygen consumption
B) circulates bound to thyroglobulin
C) biosynthesis and secretion by the thyroid is directly stimulated by thyrotropin releasing hormone (TRH).
D) decreases TRH secretion by the hypothalamus
E) secretion is increased by thyrocalcitonin

Question 17

In normal animals and an, the rate-limiting step in the biosynthesis of the catecholamine neurotransmitters dopamine and norepinephrine is

A) the transport of L-tyrosine across the blood brain barrier.
B) the decarboxylation of dihydroxyphenylalanine by DOPA decarboxylase.
C) the 3-0-methylation of the catechol nucleus by catechol-0-methyl transferase.
D) the hydroxylation of L-tyrosine by tyrosine hydroxylase.
E) the action of monoamine oxidase on the beta-phenethylamine nucleus.

Question 18

Pregnanediol is a metabolite of

A) cortisol.
B) progesterone.
C) 17-hydroxyprogesterone.
D) estradiol.
E) androstenedione.

Question 19

The insulin? receptor has in common with other growth?
Factor receptors such as epidermal growth factor

A) the ability to phosphorylate tyrosine residues on certain proteins.
B) the ability to phosphorylate serine residues on certain proteins.
C) their location in the cytosol.
D) the ability to bind steroid hormones.
E) the presence of a bound GTP.

Question 20

Specificity in the action of a peptide hormone is determined at the level of

A) the receptor, cyclic AMP and the cyclic AMP-dependent protein kinase.
B) the receptor, cyclic AMP and the substrates to be phosphorylated.
C) the receptor and the substrates to be phosphorylated.
D) the cyclic AMP-dependent protein kinase and the substrates to be phosphorylated.
E) none of these.

Question 21

Examples of hormones have been found which belong to each of the following chemical families EXCEPT which one?

A) steroids
B) Peptides
C) Amines
D) Purines
E) Glycoproteins

Question 22

The glucocorticoid hormones act

A) at the cell surface by binding to specific membrane-bound receptors.
B) by directly activating a protein kinase.
C) by blocking expression from target genes.
D) through an intracellular receptor that binds to DNA.
E) by directly binding to glucocorticoid responsive elements (GREs) near the ' end of target genes.

Question 23

Which of the following hormone combinations is NOT regulated by a negative feedback loop?

A) LH - androgen
B) TSH - thyroid hormone
C) ACTH - glucocorticoid
D) prolactin - estrogen
E) FSH - inhibin

Question 24

Which statement BEST describes the regulatory action of steroid hormones on cellular metabolic events?

A) steroid hormones serve as signals to alter cellular metabolism in response to environmental changes.
B) steroid hormones are capable of specific interactions with the genomes of their target cells.
C) steroid hormones act as an independent regulatory system relative to cyclic nucleotide systems.
D) steroid hormone action involves specificity at the levels of both cytosolic receptor and chromatin sites.
E) All of the other s are correct.

Question 25

Vasopressin (ADH)

A) acts on uterine smooth muscle.
B) acts on the distal part of the nephron.
C) is secreted in response to elevated blood pressure.
D) is secreted in response to decreased plasma osmolality.

Question 26

Parathyroid hormone

A) produces, in intestinal epithelial cells, new mRNA which codes for calcium ion transport protein
B) lowers the concentration of free calcium ion in blood
C) stimulates reabsorption of phosphate by the kidney
D) stimulates osteoclasts to break down bone mineral
E) counteracts the effect of the active metabolite of vitamin D on the kidney

Question 27

Biological conversion of testosterone

A) never results in the formation of estrogens.
B) leads only to the production of 17-ketosteroids.
C) does not take place.
D) may lead to even more active androgens being formed.
E) does not occur in androgen target tissues.

Question 28

Which of the following is/are characteristic of the transmembrane domain of a typical tyrosine kinase receptor?

A) It functions as an anchor for the receptor
B) It contains a regulatory sequence which produces a low affinity ligand binding site.
C) It controls negative feedback upon ligand binding.
D) It has some intrinsic catalytic kinase activity.
E) A and B only.

Question 29

Which of the following enzymes catalyzes the rate controlling step in cortisol biosynthesis?

A) HMG-CoA reductase.
B) the one converting cholesterol to 7-dehydrocholesterol.
C) the one converting cholesterol to delta-5-pregnenolone.
D) 11-hydroxylase.
E) 18-hydroxylase.

Question 30

Aldosterone is only produced in which portion(s) of the adrenal gland?

A) Zona glomerulosa of the cortex
B) Corticosterone
C) Aldosterone
D) Dehydroepiandrosterone
E) Testosterone

Question 31

The estradiol receptor Erb can inhibit the activity of ERA. What is the mechanism of this inhibition?

A) Blockage of transport of ERa into the nucleus
B) Dissociation of the ligand from ERa
C) ERb binds the ERa ligand
D) Formation of heterodimers of the two receptors
E) Inhibition of synthesis of ERa

Question 32

The following are TRUE statements concerning catecholamines EXCEPT

A) dopamine cannot pass the blood brain barrier and is provided to patients with Parkinson's disease in the form of DOPA
B) the synthesis of epinephrine requires tetrahydrobiopterin, pyridoxal phosphate and SAM as cofactors
C) synthesis of epinephrine and norepinephrine takes place in the adrenal medulla
D) tyrosinase is one of the enzymes involved in catecholamine biosynthesis
E) catabolism of catecholamines involves oxidative removal of the amino groups by monoamino oxidase (MAO) and methylation of OH-groups by catechol-O-methyltransferase (cOMT)

Question 33

Specificity in the action of steroid hormones is determined at the level of

A) non-histone proteins.
B) DNA.
C) histone proteins.
D) RNA polymerase.
E) the nuclear membrane.

Question 34

Insulin

A) stimulates the phosphodiesterase enzyme which breaks down cAMP.
B) decreases the concentration of fructose-2,6-bisphosphate in liver.
C) inhibits hepatic glycolysis.
D) stimulates glucose transport into the liver.
E) has the same effect on glycolysis in the liver as glucagon.

Question 35

Which of the following statements is false?

A) Hormones exert their effects by interacting/binding to specific receptors which may be in the cell membrane or intracellular.
B) Phosphorylation plays an important role in many hormonal effects.
C) In humans, there exists known protein kinases that phosphorylate proteins on serine.
D) In humans, there exists known protein kinases that phosphorylate proteins on methionine.
E) In humans, there exists known protein kinases that phosphorylate proteins on tyrosine.

Question 36

Estrogen is thought be exert its metabolic effects by which one of the following?

A) Decreasing the production of cyclic AMP.
B) Increasing the permeability of cell membranes to molecules such as glucose and amino acids.
C) Reaction with a specific receptor protein which in turn affects DNA metabolism.
D) Alteration of the phosphorylation of histones.

Question 37

Thyroid hormone is produced in the thyroid gland

A) in a process that involves the iodination of single tyrosine molecules prior to incorporation into thyroglobulin
B) after which T4 and T3 are stored as active hormones in the colloid of the thyroid follicles
C) stored in the follicle, and released into the blood stream after proteolysis of thyroglobulin in phagolysosomes of the thyroid cell
D) with a ratio of T3 to T4 of approximately 151
E) C and D

Question 38

Which one of the following is a pro-vitamin D?

A) 25-hydroxycholecalciferol
B) 7-hydroxycholesterol
C) 7-dehydrocholesterol
D) ergocalciferol
E) cholestanone

Question 39

All of the following compounds could serve as androgen precursors EXCEPT which one?

A) cortisol
B) 11-desoxycortisol
C) 17 alpha-hydroxy progesterone
D) 17 alpha-hydroxy pregnenolone
E) pregnenolone

Question 40

Aldosterone

A) would circulate in the blood primarily as the free hormone.
B) binds to a cytoplasmic protein receptor and is transported to the nucleus of its target cell.
C) is released from the adrenal cortex by ACTH.
D) results in the activation of certain enzymes by stimulating their phosphorylation.
E) results in increased glucose in the blood.

Question 41

The major actions of parathyroid hormone are

A) enhancement of calcium excretion by direct effect on the kidney tubules
B) direct promotion of bone resorption with increased osteoclastic activity
C) enhancement of renal clearance of phosphate
D) A and C above
E) B and C above

Question 42

Thyroid hormone receptors

A) are histone proteins localized in the chromatin of target cells.
B) are intrinsic non-histone chromosomal proteins.
C) initially bind triiodothyronine in the cytoplasm and after undergoing a conformational change translocate to the nucleus.
D) are enzymes that deiodinate thyroxine to triiodothyronine.
E) have higher affinity for thyroxine than triiodothyronine.

Question 43

Hypothalamic hormones which regulate the synthesis and secretion of anterior pituitary hormones include all of the following EXCEPT

A) TRH (thyrotropin releasing hormone)
B) GnRH (gonadotropin releasing hormone)
C) somatomedin c
D) somatostatin
E) CRH (corticotrophin releasing hormone)

Question 44

Aldosterone

A) contains 20 carbons.
B) is the major regulator of sodium ion retention in the kidney in man.
C) is regulated by ACTH.
D) is produced primarily in the adrenal medulla.
E) is a 19-nor compound.

Question 45

All of the following would be caused by or would be the result of increased levels of epinephrine in the circulatory system EXCEPT

A) production of cyclic-AMP.
B) activation of a protein kinase.
C) phosphorylation in liver cells of sidechains of specific serine units of certain proteins.
D) stimulation of a phosphoprotein phosphatase.
E) increased breakdown of liver glycogen.

Question 46

Which of the following steroids serves as the immediate precursor for the synthesis of estradiol?

A) Cortisol
B) Testosterone
C) Progesterone
D) Dehydroepiandrosterone
E) Pregnenolone

Question 47

The insulin receptor

A) is a transmembrane protein composed of alpha and beta subunits
B) transports glucose into the cell after insulin binding
C) initiates tyrosine kinase activity after insulin binds to the beta-subunit
D) all of the above
E) A & C only

Question 48

Regarding the endocrine system and hormone feedback, which of the following statements is false?

A) The feedback of thyroid hormone is an example of a short?loop feedback system.
B) The feedback of insulin is an example of a long?loop feedback system.
C) For the most part, the hormones of the endocrine system utilize positive feedback.
D) Tight control of hormone levels and their actions is important in normal human homeostasis.
E) Many hormones exert their feedback either directly on the gland that produces them, on a gland that controls their synthesis/secretion or some combination of these.

Question 49

O-Hydroxylation of progesterone gives rise to

A) deoxycorticosterone.
B) corticosterone.
C) cortisol.
D) deoxycortisol.
E) dehydroisoandrosterone.

Question 50

Which of the following statements is CORRECT?

A) Catabolism of steroids involves reduction, conjugations and a final breakdown of the steroid nucleus to acetoacetate.
B) The main organ of steroid catabolism is the adrenal gland.
C) The major precursor of urinary 17-ketosteroids is cortisol.
D) All of the above.
E) None of the above.

Question 51

Triiodothyronine (T3)

A) is less potent in vivo than T4.
B) is the predominant thyroid hormone produced by thyroid gland.
C) is converted in peripheral tissues directly to reverse T3 (3,3'5' triiodothyronine).
D) decreases basal metabolic rates of most tissues.
E) binds to a nuclear receptor.

Question 52

Which of the following is a precursor of both adrenocortical and gonadal steroid hormones?

A) corticosterone
B) dihydroxycholecalciferol
C) estradiol
D) pregnenolone
E) testosterone

Question 53

The insulin receptor is regulated by (auto) phosphorylation of one or more _______________ residues.

A) cysteine
B) histidine
C) serine
D) threonine
E) tyrosine

Question 54

All of the following are potential actions of hormones EXCEPT which one?

A) Control of differentiation
B) Control of growth
C) Control of metabolism
D) Control of extracellular fluid volume and composition
E) None of the above; all are potential mechanisms.

Question 55

In eukaryotic cells, adrenal corticosteroids regulate gene expression by binding to

A) allosteric effector sites on an inactive enzyme.
B) a receptor that, in turn, interacts with DNA and activates transcription.
C) a receptor that, in turn, migrates to the nuclear matrix and blocks RNA degradation.
D) ribosomes and stimulating translation.

Question 56

All of the following biologically active peptides are potentially derivable from the pituitary K dalton glyco-protein proopiomelanocortin EXCEPT

A) CLIP (corticotropin-like intermediate lobe peptide)
B) alpha-MSH (alpha-melanocyte stimulating hormone)
C) beta-endorphin
D) angiotensin II
E) beta-MSH

Question 57

Which of the following statements is false?

A) insulin is made by the pancreatic beta cells and stimulates liver glycogen, fat and albumin synthesis and simulates lipogenesis in adipocytes.
B) Glucagon is made by the pancreatic alpha cells and stimulates liver glycogenolysis, gluconeogenesis and ketogenesis and stimulates lipolysis in adipocytes.
C) The rate controlling step/enzyme in the synthesis of epinephrine by the adrenal medulla is the formation of dopamine from DOPA via DOPA decarboxylase.
D) In the adrenal medulla, DOPA decarboxylase requires pyridoxal phosphate as a cofactor.
E) In the adrenal medulla, epinephrine is broken down by two enzymes, monoamine oxidase and catechol O-methyl transferase.

Question 58

Regulation of FSH and LH secretion by the anterior pituitary is effected by

A) testosterone and inhibin respectively
B) inhibin and testosterone respectively
C) estrogen and inhibin respectively
D) cortisol and testosterone respectively
E) inhibin and activin respectively

Question 59

Down-regulation of insulin receptors is due to

A) irreversible binding of insulin to its receptor.
B) negative cooperativity of insulin binding.
C) insulin-stimulated pinocytosis of the insulin-receptor complex.
D) insulin-stimulated proteolysis of its receptor.
E) insulin-stimulated release of inhibitory prostaglandins.

Question 60

Which of the following is a major mineralocorticoid in man?

A) cortisol
B) corticosterone
C) aldosterone
D) androsterone
E) vasopressin

Question 61

The feature of target cells for steroid hormones which gives tissue specificity for steroid hormone action is

A) plasma-membrane associated receptor-adenylate cyclase complex.
B) cholesterol to phospholipid ratio of the plasma membrane.
C) ability to carry out reverse pinocytosis.
D) a soluble cytoplasmic polypeptide receptor for the steroid.
E) a steroid transport system coupled to a specific steroid hydroxylase.

Question 62

Angiotensin converting enzyme catalyzes conversion of

A) angiotensinogen to angiotensin I
B) angiotensin I to angiotensin II
C) angiotensin II to angiotensin III
D) bradykinin to an inactive form
E) renin to its active form

Question 63

The biochemical mechanism by which parathyroid hormone exerts its effect on sensitive tissues is by activation of a(n)

A) adenylyl cyclase.
B) phosphodiesterase.
C) nuclear hormone receptor.
D) tyrosine kinase.
E) voltage-gated Ca²⁺ channel.

Question 64

A peptide hormone which is located both in the hypothalamus and in the pancreas is

A) cholecystokinin
B) proinsulin
C) somatostatin
D) neurophysin
E) none of the above

Question 65

ACTH has all of the following effects on the adrenal cortex EXCEPT which one?

A) increased blood flow
B) depletion of cholesterol esters
C) development of adrenal hypertrophy
D) increased activity of the desmolase complex
E) preferential synthesis of progesterone

Question 66

Signal transduction initiated by insulin leads to all of the following EXCEPT

A) activation of a G protein-coupled receptor.
B) guanine nucleotide exchange.
C) multiple protein?protein interactions.
D) phosphorylation of one or more proteins.
E) increased secretory vesicle trafficking.

Question 67

Which of the following statements concerning steroid hormones is correct

A) a 17-ketosteroid (e.g. androstenedione) has exactly 17 carbons
B) the difference between pregnenolone and progesterone is the presence of a hydroxyl group on C17
C) removal of the C18 Carbon of corticosterone is an important step in the synthesis of aldosterone
D) aromatization of androstenedione produces beta-estradiol
E) none of the above

Question 68

Human growth hormone (HGH), in vivo, in specific tissues

A) Causes an increase in the size of cells.
B) Causes a decrease in the size of cells.
C) increases the rate of cell proliferation.
D) decreases the rate of cell proliferation.
E) Can be replaced therapeutically by other mammalian growth hormones.

Question 69

The receptor protein for steroid hormones occurs principally in the

A) cytoplasm.
B) mitochondria.
C) plasma membrane.
D) nuclear membrane.
E) Golgi membrane.

Question 70

Endocrine, paracrine, neuronal, and contact-dependent are all forms of

A) Extracellular signaling.
B) Intracellular signaling.
C) Nerve impulse transmission.
D) Hormone signaling.

Question 71

All of the following statements regarding the second messenger concept of hormone action are true EXCEPT which one?

A) The hormone itself is the first messenger.
B) Hormones act through receptors to stimulate the production of the second messenger.
C) Cyclic AMP is a leading candidate for the second messenger of lipid-soluble hormones such as steroids.
D) None of the above are exceptions; all statements are true.

Question 72

Beta-endorphin is derived fro

A) ACTH
B) enkephalin
C) beta-lipotropin
D) beta-MSH
E) gamma-endorphin

Question 73

Which one of the following would be ost useful in determining whether ovulation has occurred?

A) urinary 17-ketosteriod level
B) urinary gonadotrophin level
C) serum estradiol level
D) serum testosterone level
E) serum prolactin level

Question 74

Which of the following statements concerning steroid hormone synthesis is correct

A) although cells in the adrenal cortex can synthesize cholesterol, most of the cholesterol used for steroid hormone synthesis comes from the plasma
B) the enzymes for 17-alpha-hydroxylase and 17,20-desmolase are segregated to different compartments in the cell
C) the side chain cleavage complex that Catalyzes the conversion of cholesterol to pregnenolone requires NADPH, a flavoprotein, a P450, and molecular oxygen
D) A, B and C
E) A and C

Question 75

Each of the following is derived by the proteolytic processing of a larger protein molecule EXCEPT

A) melanocyte stimulating hormone.
B) glucagon.
C) growth hormone.
D) parathyroid hormone.
E) adrenocorticotrophic hormone.

Question 76

In target sites such as prostate, testosterone appears to act via one of its metabolites which is

A) a 17-ketosteroid.
B) delta 4-androstenedione.
C) 17 beta-estradiol.
D) dehydroepiandrosterone.
E) 5 alpha-dihydrotestosterone.

Question 77

Which of the following statements is CORRECT?

A) The pituitary hormone ACTH controls to a large part the biosynthesis of cortisol.
B) The adrenal secretion of cortisol and the pituitary secretion of ACTH both depend on the secretion of corticotropin releasing factors by the hypothalamus.
C) Increased plasma cortisol levels inhibit the release of corticotropin releasing factors.
D) All of the above.
E) None of the above.

Question 78

Which of these statements concerning parathyroid hormone (PTH) is CORRECT?

A) its secretion is inhibited by high levels of plasma calcium
B) it lowers calcium and phosphorus levels in plasma
C) it lowers serum calcium levels and raises serum phosphate levels
D) it causes (or enhances) precipitation of calcium salts in bone
E) it stimulates reabsorption of phosphate from the kidney

Question 79

All of the following biologically active peptides are potentially derivable fro beta-lipotropin (beta-LPH) EXCEPT

A) methionine enkephalin
B) alpha-endorphin
C) beta melanocyte stimulating hormone (beta-MSH)
D) beta-endorphin
E) antidiuretic hormone (ADH)

Question 80

The most prominent second messenger involved in the actions of LH, FSH and ACTH is

A) Ca²⁺
B) cGMP
C) inositol triphosphate (IP3)
D) steroid receptor protein
E) cAMP