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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
What are the isozymes of nitric oxide synthase (NOS)?
* 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 ## Footnote Tip: the numbering of the isozymes runs in reverse alphabetical order
26
What is nitroglycerin (glyceryl trinitrate)?
A nitrate compound used to treat angina. It forms nitric oxide, which leads to vasodilation.
27
What is thyroglobulin (Tg)?
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
What are the steps of iodine metabolism in thyroid hormone synthesis?
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
What are the inhibitors of thyroid hormone synthesis and their sites of action?
* 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
How are T4 and T3 degraded?
* 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
What is the pathway of catecholamine synthesis?
[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
How are the catecholamines degraded?
Action of *catecholamine-*O*-methyltransferase* (COMT) and *monoamine oxidase* (MAO), in either order, to give vanillylmandelic acid (EPI/NE) or homovanillic acid (DA)
33
What are the functions of catecholamine-*O*-methyltransferase (COMT) and monoamine oxidase (MAO)?
* COMT: transfers a methyl to the catecholamine ring * MAO: oxidizes the amine backbone of the catecholamine
34
What is the synthetic pathway of melatonin?
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
How is melatonin degraded?
* Deacetylation * Demethylation * Oxidation of amine backbone (by monoamine oxidase; MAO)
36
How is insulin synthesized?
1. Preproinsulin is synthesized from the insulin mRNA 2. preproinsulin → proinsulin + 23-a.a. signal sequence (rER) 3. proinsulin → insulin + C-peptide (Golgi)
37
What is the structure of proinsulin?
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
What is the function of connecting (C-) peptide in proinsulin?
It places the A- and B-chains in a suitable orientation for forming disulfide bonds
39
How is the cleavage of connecting (C-) peptide in insulin clinically useful?
C-peptide and insulin are produced in equimolar concentrations, so insulin concentration can be measured by measuring the level of C-peptide
40
Which hormones bind to intracellular receptors?
* Androgens * Calcitriol * Estrogens * Glucocorticoids * Mineralocorticoids * Thyroid hormones
41
Which hormones use cAMP as a second messenger? | (11)
**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
Which hormones use calcium or phosphoinositols as second messengers? | (3)
* Catecholamines (α1-receptor) * ADH * TRH
43
Which hormones use a kinase/phosphatase cascade (e.g. receptor tyrosine kinases, janus kinases) as second messengers?
* Epidermal growth factor (EGF) * Fibroblast growth factor (FGF) * Platelet-derived growth factor (PDGF) * Growth hormone (GH) * Insulin and IGFs * Prolactin
44
Which hormones use a receptor tyrosine kinase (RTK)?
* Insulin and IGFs * EGF * FGF * PDGF
45
Which hormones use the Jak/STAT pathway?
* Growth hormone * Prolactin

Endocrine system (2 decks)

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