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Endocrine system > Biochemistry > Flashcards

Biochemistry Flashcards

1
Q

What are the hypothalamic hormones and their chemical classes?

A
  • Growth hormone–releasing hormone (GHRH): polypeptide
  • Somatostatin: polypeptide
  • Corticotropin-releasing hormone (CRH): polypeptide
  • Gonadotropin-releasing hormone (GnRH): polypeptide
  • Thyrotropin-releasing hormone (TRH): polypeptide
  • Dopamine: catecholamine (tyrosine derivative)
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2
Q

What is the smallest polypeptide hormone?

A

Thyrotropin-releasing hormone (TRH): three residues

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3
Q

How are growth hormone–releasing hormone (GHRH) and somatostatin structurally unique?

A

They each have two different functional forms due to alternative splicing

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4
Q

What is the precursor molecule of adrenocorticotropic hormone (ACTH)?

A

pro-opiomelanocortin (POMC)

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5
Q

What are the hormones/biomolecules synthesized from pro-opiomelanocortin (POMC)?

A
  • Adrenocorticotropic hormone (ACTH)
  • Melanocyte-stimulating hormones (MSHs; melanotropins)
  • Enkephalins
  • Endorphins
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6
Q

Which hypothalamic hormone is the largest?

A

Growth hormone–releasing hormone (GHRH)

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7
Q

What are the adenohypophyseal (anterior pituitary) hormones and their chemical classes?

A
  • Growth hormone (somatotropin): straight-chain protein
  • Prolactin (PRL): straight-chain protein
  • Adrenocorticotropic hormone (ACTH): small peptide
  • Follicle-stimulating hormone (FSH): αβ glycoprotein
  • Luteinizing hormone (LH): αβ glycoprotein
  • Thyroid-stimulating hormone (TSH): αβ glycoprotein
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8
Q

How is thyrotropin-releasing hormone (TRH) chemically and structurally distinct?

A
  • It is the smallest peptide hormone (3 amino acids)
  • It contains pyroglutamate, a modified glutamate residue derived from glutathione
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9
Q

How are follicle-stimulating hormone (FSH), luteinizing hormone (LH), and thyroid-stimulating hormone (TSH) similar?

A
  • They are all αβ glycoproteins
  • Their α-subunits are identical and have a structural role (whereas the β-subunits provide the functional distinction)
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10
Q

How are the different derivatives of pro-opiomelanocortin (POMC) produced?

A

Alternative splicing of the POMC mRNA

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11
Q

Which adenohypophyseal (anterior pituitary) hormone is the smallest?

A

Adrenocorticotropic hormone (ACTH)

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12
Q

Which adenohypophyseal (anterior pituitary) hormone is the largest?

A

Prolactin (PRL)

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13
Q

What are the neurohypophyseal (posterior pituitary) hormones and their chemical classes?

A
  • Oxytocin: modified nonapeptide
  • Antidiuretic hormone (ADH; vasopressin): modified nonapeptide
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14
Q

How are antidiuretic hormone (ADH; vasopressin) and oyxtocin similar?

A
  • They are both modified nonapeptides
  • They share their amino acid structure, except at residues 3 and 8
  • They each have an amidated glycine at their C-terminus (the carboxyl is replaced by an amide group, —CONH2)
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15
Q

What are the different forms of antidiuretic hormone (ADH; vasopressin)?

A
  • Arginine vasopressin (AVP): Arg at residue 8
  • Lysine vasopressin (LVP): Lys at residue 8

In humans, LVP is not typically found

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16
Q

What are the thyroid hormones and their chemical classes?

A
  • Thyroxine (tetraiodothyronine; T4): modified tyrosine
  • Triiodothyronine (T3): modified tyrosine
  • Calcitonin: polypeptide with amidated Pro at C-terminus
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17
Q

What are the pancreatic hormones and their chemical classes?

A
  • Insulin: large AB polypeptide
  • Glucagon: smaller polypeptide
  • Somatostatin: polypeptide
  • Pancreatic polypeptide (PP): polypeptide
  • Gastrins: polypeptides
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18
Q

Which pancreatic hormone is the largest?

A

Insulin

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19
Q

Which pancreatic hormone is the smallest?

A

Pancreatic polypeptide (PP)

20
Q

What are glucagon-like peptides (GLPs)?

A

Hormones of different sizes produced from proglucagon by alternative splicing

21
Q

What are the calcium-regulating hormones, their source glands, and their chemical classes?

A
  • Parathyroid hormone (PTH): parathyroid glands; polypeptide
  • Calcitonin: thyroid gland; polypeptide
  • Fibroblast growth factor 23 (FGF23): mainly osteocytes and osteoblasts; very large protein
  • Vitamin D: kidney (1,25(OH)2D3) steroid
22
Q

What is the largest peptide hormone?

A

Fibroblast growth factor 23 (FGF23)

23
Q

What is the source tissue and structure of melatnonin?

A

Pineal gland; indolamine Trp derivative (N-acetyl-5-methoxytryptamine)

24
Q

How is nitric oxide synthesized?

A

arginine + 2O2 + NADPH + H+ → citrulline + NO + NADP+

Catalyzed by nitric oxide synthase (NOS)

25
Q

What are the isozymes of nitric oxide synthase (NOS)?

A
  • Neuronal NOS (nNOS; NOS-I): expressed constitutively in CNS neurons to produce NO as a neurotransmitter
  • Inducible NOS (iNOS; NOS-II): expressed predominantly in macrophages upon encountering a pathogen
  • Endothelial NOS (eNOS; NOS-III): expressed constitutively in endothelial cells to produce NO as a vasodilator

Tip: the numbering of the isozymes runs in reverse alphabetical order

26
Q

What is nitroglycerin (glyceryl trinitrate)?

A

A nitrate compound used to treat angina. It forms nitric oxide, which leads to vasodilation.

27
Q

What is thyroglobulin (Tg)?

A

A large, glycosylated protein formed in the rER of thyrocytes. It has 115 Tyr residues, some of which are iodinated and coupled to form bound thyroid hormones and their precursors.

28
Q

What are the steps of iodine metabolism in thyroid hormone synthesis?

A
  1. Iodine trapping: I– is actively transported into the thyrocyte cytoplasm by the sodium–iodide symporter
  2. Iodide is pumped into the colloid lumen by a chloride antiporter (pendrin)
  3. Oxidation: iodide is oxidized using hydrogen peroxide by the enzyme thyroid peroxidase (TPO)
  4. Organification of tyrosine: TPO catalyzes the addition of iodine to the tyrosine residues of thyroglobulin
  5. Recycling: uncoupled MIT and DIT residues, or released T4/T3 have their iodine atoms cleaved by a cytoplasmic deiodinase
29
Q

What are the inhibitors of thyroid hormone synthesis and their sites of action?

A
  • Thiocyanate (SCN–): inhibits the sodium–iodide symporter
  • Perchlorate (ClO4–): inhibits the sodium–iodide symporter
  • Methimazole: inhibits oxidation of iodide by thyroid peroxidase (TPO)
  • Propylthiouracil: inhibits organification of Tg by TPO
30
Q

How are T4 and T3 degraded?

A
  • T4: deiodinated to T3 (active) or rT3 (inactive) by a cytoplasmic deiodinase in target cells
  • T3:
    • Deiodination
    • Conjugation to bile acids in the liver
    • Decarboxylation/oxidative deamination
31
Q

What is the pathway of catecholamine synthesis?

A

[phenylalanine → tyrosine; hydroxylase]

  1. tyrosine → ʟ-DOPA; tyrosine hydroxylase
  2. ʟ-DOPA → dopamine; DOPA decarboxylase
  3. dopamine → norepinephrine; dopamine β-hydroxylase
  4. norepinephrine → epinephrine; N-methyltransferase (occurs in adrenal medulla only)

(enzyme names given in italics)

32
Q

How are the catecholamines degraded?

A

Action of catecholamine-O-methyltransferase (COMT) and monoamine oxidase (MAO), in either order, to give vanillylmandelic acid (EPI/NE) or homovanillic acid (DA)

33
Q

What are the functions of catecholamine-O-methyltransferase (COMT) and monoamine oxidase (MAO)?

A
  • COMT: transfers a methyl to the catecholamine ring
  • MAO: oxidizes the amine backbone of the catecholamine
34
Q

What is the synthetic pathway of melatonin?

A
  1. tryptophan → 5-hydroxytryptophan; hydroxylase
  2. 5-hydroxytryptophan → 5-hydroxytryptamine (5-HT; serotonin); decarboxylase
  3. serotonin → N-acetylserotonin; N-acetyltransferase
  4. N-acetylserotonin → melatonin; O-methyltransferase
35
Q

How is melatonin degraded?

A
  • Deacetylation
  • Demethylation
  • Oxidation of amine backbone (by monoamine oxidase; MAO)
36
Q

How is insulin synthesized?

A
  1. Preproinsulin is synthesized from the insulin mRNA
  2. preproinsulin → proinsulin + 23-a.a. signal sequence (rER)
  3. proinsulin → insulin + C-peptide (Golgi)
37
Q

What is the structure of proinsulin?

A

An A-chain and B-chain separated by a long connecting (C-) peptide. The A- and B- chains form two disulfide bridges, while the A-chain forms one internal disulfide bridge

38
Q

What is the function of connecting (C-) peptide in proinsulin?

A

It places the A- and B-chains in a suitable orientation for forming disulfide bonds

39
Q

How is the cleavage of connecting (C-) peptide in insulin clinically useful?

A

C-peptide and insulin are produced in equimolar concentrations, so insulin concentration can be measured by measuring the level of C-peptide

40
Q

Which hormones bind to intracellular receptors?

A
  • Androgens
  • Calcitriol
  • Estrogens
  • Glucocorticoids
  • Mineralocorticoids
  • Thyroid hormones
41
Q

Which hormones use cAMP as a second messenger?

(11)

A

Neurohormones

  • Catecholamines (α2- and β-receptors)

Hypothalamic

  • CRH
  • Somatostatin

Pituitary

  • ACTH
  • ADH
  • FSH
  • LH
  • TSH (i.e. all except LH and GH, the acidophil secretions)

Other

  • Calcitonin
  • Glucagon
  • PTH
42
Q

Which hormones use calcium or phosphoinositols as second messengers?

(3)

A
  • Catecholamines (α1-receptor)
  • ADH
  • TRH
43
Q

Which hormones use a kinase/phosphatase cascade (e.g. receptor tyrosine kinases, janus kinases) as second messengers?

A
  • Epidermal growth factor (EGF)
  • Fibroblast growth factor (FGF)
  • Platelet-derived growth factor (PDGF)
  • Growth hormone (GH)
  • Insulin and IGFs
  • Prolactin
44
Q

Which hormones use a receptor tyrosine kinase (RTK)?

A
  • Insulin and IGFs
  • EGF
  • FGF
  • PDGF
45
Q

Which hormones use the Jak/STAT pathway?

A
  • Growth hormone
  • Prolactin

Endocrine system (2 decks)

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