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Endocrine System > Synthesis of Steroid Hormones > Flashcards

Synthesis of Steroid Hormones Flashcards

1
Q

The steroid hormone-receptor complex enhances the synthesis of ______________ .

A

mRNA through transcription

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2
Q

Transcription of the human ______ gene encoding _______ in adult tissues is largely limited to the adrenal and gonad, although it may also be expressed in skin.

A

CYP17A1

P450c17

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3
Q

____________ are important beyond the context of male genital differentiation and androgen action.

A

5α-reductases

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4
Q

______________ mediate the interconversions of androstenedione and testosterone, DHEA and androstenediol, estrone and estradiol.

A

17β-hydroxysteroid dehydrogenases (17βHSDs)

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5
Q

Wich enzyme catalyze the following reactions?

  • Converts pregnenolone to progesterone
  • 17α-hydroxypregnenolone to 17α- hydroxyprogesterone (17OHP)
  • DHEA (dehydroepiandrostedione) to androstenedione
  • Androstenediol to testosterone
A

3βHSD

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6
Q

The _________ use NAD+ as their cofactor to oxidize hydroxysteroids to ketosteroids, and the __________ mainly use NADPH to reduce ketosteroids to hydroxysteroids.

A

Dehydrogenases

Reductases

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7
Q

The enzyme present in the Endoplasmic Reticulum that catalyzes 21- hydroxylation in the synthesis of both glucocorticoids and mineralocorticoids are:

A

P450c21

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8
Q

______________ result in the loss of all steroidogenesis, indicating that all steroidogenesis is initiated by this one enzyme.

A

P450scc mutations

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9
Q

________increasing blood sugar and acting as an immunosuppressant.

A

Cortisol (Glucocoticoid)

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10
Q

____________ activate molecular oxygen using their heme center and add electrons from the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH).

A

All P450 enzymes

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11
Q

What property made the stereoid hormones to diffuse through the cell membrane of the target cell), interacting once inside with soluble nuclear receptors?

A

Lipid Soluble

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12
Q

A cytochrome P450 may be either type 1 when its found in ______________

A

Mitochondria

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13
Q

__________ is the enzymatic rate- limiting step in steroidogenesis.

A

P450scc

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14
Q

_________ is the microsomal P450 enzyme that catalyzes both 17α- hydroxylase and 17,20-lyase activities, principally in the adrenal and gonads.

A

P450c17

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15
Q

The enzyme present in the Endoplasmic Reticulum that catalyzes aromatization of androgens to estrogens are:

A

P450aro

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16
Q

The first and rate-limiting step in steroidogenesis is the conversion of cholesterol to pregnenolone by which single enzyme?

A

P450scc (CYP11A1)

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17
Q

Within mitochondria, _________ is converted to _________ by an enzyme in the inner membrane called CyP11A1.

A

Cholesterol

Pregnelone

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18
Q

__________ is the first, rate-limiting, and hormonally regulated step in the synthesis of all steroid hormones. This process involves oxidative scission of the __________ to yield __________.

A
  • Conversion of cholesterol to pregnenolone in mitochondria
  • C20-22 bond
  • Pregnenolone
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19
Q

Steroid hormones are all synthesized from cholesterol and hence have closely related structures based on:

A

Cyclopentanophenanthrene 4-ring structure

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20
Q

In wich disorder affected females are phenotypically normal but fail to undergo adrenarche and puberty, and males have absent or incomplete development of the external genitalia?

A

Male Pseudohermaphroditism (46,XY disorder of sex development)

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21
Q

If it expresses the cholesterol side-chain cleavage enzyme, P450scc, which catalyzes the first step in steroidogenesis, is said that the cell is:

A

Steroidgenic

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22
Q

___________ is the cholesterol side-chain cleavage enzyme catalyzing the series of reactions formerly termed “20,22 desmolase.”

A

Mitochondrial P450scc

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23
Q

_________is expressed in steroidogenic tissues (ovarian granulosa cells, placenta), in brain, and in nonsteroidogenic tissues, especially fat and bone

A

P450aro

24
Q

21- hydroxylase deficiency has an incidence of 1 in 15,000 to 1 in 20,000 births, causing more than 90% of all cases of:

A

Congenital Adrenal Hyperplasia (CAH)

25
Q

Deficient 17α-hydroxylase activity results in decreased in__________ and over prodction of ___________.

A

Cortisol

ACTH

26
Q

_________ participate in regulating CYP17A1 transcription, linking the regulation of steroidogenesis with the regulation of cholesterol biosynthesis.

A

SREBP1c

27
Q

Expression of P450scc is induced by:

A

cAMP in:

  • The adrenal zona fasciculata/reticularis
  • Testis and ovary

And by the calcium/protein kinase C system in

  • Zona glomerulosa.
28
Q

____________regulates the cyclical changes of the endometrium of the uterus, and the maintenance of pregnancy.

A

Progesterone

29
Q

Because insufficient free cholesterol is available to P450scc, there is adrenal insufficiency, causin a disease named:

A

Wolman Disease

30
Q

_________is derived from cholesterol, this has a double bond between carbons # 5 and 6

A

Pregnelone

31
Q

__________ is rare cause of glucocorticoid and mineralocorticoid deficiency that may be fatal if not diagnosed early in infancy

A

3βHSD deficiency

32
Q
  • In Females:
    • May occur clitoromegaly and mild virilization because the fetal adrenal overproduces large amounts of DHEA, a small portion of which is converted to testosterone
A

3βHSD deficiency

33
Q

_______________is a generic term for a group of oxidative enzymes, all of which have about 500 amino acids and contain a single heme group.

A

Cytochrome P450

(Because all absorb light at 450 nm)

34
Q

Severe deficiency of _______decreases the secretion of cortisol, causing CAH and virilization of affected females.

It results in accumulation of 11-deoxycortisol, and the defect in the 17-deoxy pathway in the synthesis of corticosterone in the fasciculata leads to overproduction of DOC, potentially leading to mineralocorticoid-based hypertension.

A

P450c11β

35
Q

A cytochrome P450 may be type 2 when its found in ______________

A

Endoplasmic Reticulum

36
Q

The final steps in the synthesis of glucocorticoids and mineralocorticoids are catalyzed by wich two closely related mitochondrial enzymes?

A

P450c11β and P450c11AS

37
Q

The receptor-steroid hormone complex travels into the nucleus and binds to a ___________

A

Hormone- response element (HRE) of an enhancer region on DNA

38
Q

________ contributes to the development and maintenance of female secondary sex characteristics.

A

Estrogens

39
Q

The absence of 17α-hydroxylase and 17,20- lyase activities in complete P450c17 deficiency prevents:

A

The synthesis of adrenal and gonadal sex steroids

40
Q

___________ moves this double bond from the B ring to carbons 4 and 5 in the A ring, forming Δ4 compounds.

A

3β-hydroxysteroid dehydrogenase/isomerase

41
Q

Wich protein is only found in the adrenals and catalyzes the 21-hydroxylation of the Δ4 steroids progesterone to DOC and 17OHP to 11- deoxycortisol in the biosynthesis of mineralocorticoids and glucocorticoids, respectively?

A

P450c21

42
Q

_________ contributes to the regulation of blood pressure

A

Aldosterone

43
Q

The enzyme present in the Endoplasmic Reticulum that catalyzes both 17α- hydroxylase and 17,20-lyase activities are:

A

P450c17

44
Q

____________ may belong to either the aldo-keto reductase or short-chain dehydrogenase/reductase families.

A

Hydroxysteroid Dehydrogenase

45
Q

__________ is a cytosolic reductive enzyme that uses NADPH as its cofactor to catalyze reductase activity.

A

17βHSD type 1

46
Q

Extraglandular aromatase expression, especially in fat, can convert:

A

Androgens to Estrogens

47
Q

The two isozymes of mitochondria that catalyze 11β- hydroxylase, 18-hydroxylase, and 18-methyl oxidase activities are:

A

P450c11:

  • P450c11β (11β-hydroxylase)
  • P450c11AS (aldosterone synthase)
48
Q

______________do not have heme groups, and require NADH/NAD+ or NADPH/NADP+ as cofactors to either reduce or oxidize a steroid

A

Hydroxysteroid dehydrogenases (HSDs)

49
Q

How many carbons have:

  • Corticosteroids
  • Androgens
  • Estrogens
A
  • Corticosteroids (C-21)
  • Androgens (C-19)
  • Estrogens (C-18)
50
Q

Most of the major biologically active steroid hormones are ___________ compounds.

A

Δ4

51
Q

____________ are produced by the aromatization of androgens, including those derived from adrenal steroidogenesis, by a complex series of reactions catalyzed by ___________.

A

Estrogens

Aromatase P450aro

52
Q

Wich is the rate limiting step of biosynthesis of streoid hormones?

A

The transport of free cholesterol from the cytoplasm into mitochondria

53
Q

Who is the mmediate precursor for the synthesis of all of the steroid hormones?

A

Pregnelone

54
Q

Once pregnenolone is produced from cholesterol, it may undergo 17α-hydroxylation by ________ to converted to progesterone (first biologically important steroid in the pathway).

A

P450c17

55
Q

__________ catalyzes both conversion of the hydroxyl group to a keto group on carbon 3 and the isomerization of the double bond from the B ring (Δ5 steroids) to the A ring (Δ4 steroids).

A

3βHSD

56
Q

Who transport the free cholesterol from cytoplasm to membrane?

A

StarD4

57
Q

Who is responsible for the rapid transport of cholesterol from the outer mitochondrial membrane to the inner mitochondrial membrane?

A

StAR

Endocrine System (2 decks)

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