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8. steroid hormones Essay Example
8. steroid hormones Essay Example

8. steroid hormones Essay Example

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  • Pages: 3 (671 words)
  • Published: November 28, 2017
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question

terpene
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a steroid is a terpene. a terpene is a hydrocarbon derived from isoprene.
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animal steroids include (3)
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sterols (cholesterol), bile acids, steroid hormones
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4 important parent ring structures
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cholestane, androstane, pregnane, estrane.
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5beta-dihydrotestosterone
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has no biological activity because it cannot interact with androgen

...

receptor. active stereochemical form is 5alpha-dihydrotestosterone

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cholesterol is synthesized where? (4)
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virtually all tissues, but especially in liver, adrenal cortex and gonads and placenta.
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cholesterol synthesis requires (2)
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reducing equivalents (provided by NADPH) and energy derived from CoA and ATP
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where in cell is cholesterol synthesized?
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cytoplasm - cytosol and er
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HMG Coa synthase is ____ for cholesterol synthesis and ____ for ketoacid synthesis
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answer

cytosolic, mitochondrial
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key rate limiting reaction in cholesterol synthesis
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HMG CoA reductase > makes mevalonate, which makes IPP which condenses to squalene, which cyclizes (hydroxylation) into lanosterol > cholesterol
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how is HMG CoA reductase controlled
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predominantly at the expression level (regulation of mRNA abundance) and at the activity level (reversible phosphorylation)
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precursor for steroid hormone synthesis
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cholesterol, except for vitamin D (whose precursor is 7-dehydrocholesterol) (need light to make vitamin D)
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progesterone makes
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cortisol and aldosterone and androstenedione
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testosterone makes
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estradiol
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androstenedione makes
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estrone and testosterone
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cholesterol makes
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progesterone
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cholesterol degradation
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align="center">excreted as bile salts and bile acids
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steroid hormone biosynthesis
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cholesterol from sER transported to mitochondria for side chain cleavage, makes pregnenolone, which returns to sER for further synthetic steps
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steroid hormone biosynthesis in the gonads
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pregnenolone -> androgens, estrogens and progestins
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steroid hormone biosynthesis in adrenal cortex
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pregnenolone goes back to mito for production of glucocorticoids and mineralocorticoids
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steroid-secreting cells have abundant
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sER and tubular-vesicular cristae
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cytochrome p450
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cyp, p450, cyp450. a large and diverse family of hemoproteins that often form electron transfer chains
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most common reaction catalyzed by cyp
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monooxygenase reaction: R + O2 + NADPH = R-OH + H20 + NADP+
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p450scc / old names / regulation
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p450 side-chain cleavage enzyme. catalyzes cholesterol > progesterone. also referred to

as CYP11A1 or 20-22 desmolase. regulated by LH in gonads and by ACTH in adrenal cortex
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StAR
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steroid acute regulatory protein: facilitates transfer of hydrophobic cholesterol across the OMM to the IMM
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IMM
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location of p250scc; this is where metabolism of cholesterol to pregnenolone occurs
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lipoidal congenital adrenal hyperplasia
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mutations in StAR. no steroid hormones can be synthesized. all individuals are phenotypic females with salt-wasting crises. fatal if not treated during infancy
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smith-lemli-opitz
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lack of c7-reductase to make cholesterol from 7-dehydrocholesterol. retardation, ambiguous genitalia in males, abnormal face, low circulating cholesterol
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CAH
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no c21-hydroxylase to make cortisol or aldosterone from progesterone. => abundance of androgens, > virilization of female infants, salt-wasting crises. can be treated with glucocorticoid and mineralocorticoid replacement.
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5alpha-reductase deficiency
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AR mutation in 5alpha-reductase-2. males are undervirilized but virilize at puberty. born with blind vaginal pouch, no mullerian derivatives, normal testes

and wolffian derivatives.
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biological actions of steroid hormones are determined by
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specificity and tissue localization or steroid hormone receptors
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major course of vitamin d metabolites
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skin, diet
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major source of retinoic acid
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diet
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major sources of progestins, estrogens, androgens
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p: ovary, placenta. e: ovary, placenta, testis. a: ovary, testis.
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action of steroid hormone receptors requires (3)
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hsp70,90; coactivators (SRC); and a specific DNA binding element (zinc finger) = HIGHLY specific
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complete androgen insensitivity / old name
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old name - testicular feminization. x-linked recessive disorder expressed in 46XY. mutation in androgen receptor gene. breasts, no pubic/axillary hair, primary amenorrhea, blind vaginal pouch. testes. wolffian derivatives absent, mullerian derivatives absent or vestigial.
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anabolic steroids (2)
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2-5% increase in androgen receptor saturation; competitively inhibiting

function of glucocorticoid receptor in muscle stops cortisol from breaking down muscle = higher net positive nitrogen balance
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lanosterol>
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14-demethylation of lanosterol = cholesterol
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ligand activated transcription factors
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steroid hormone receptors

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