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24 Cards in this Set
- Front
- Back
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What are most steroids made from?
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cholesterol
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what is a steroid? structurally.
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a terpene: 4 fused rings, usually 6-6-6-5 structure
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What is a structural characteristic of a cholesterol?
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double bond on second ring and -OH group on 3rd carbon of first ring
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How does stereochemistry impact steroid formation?
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A LOT! Isomers are active inactive form.
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What is the starting substrate for steroid synthesis?
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Acetyl CoA
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What is the rate limiting step in steroid synthesis?
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HMG CoA reductase --> enzyme converts HMG CoA to mevalonic acid
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Where does a statin work in the biosynthetic pathway of steroids?
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inhibits HMG CoA reductase (R.L. step)
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What converts acetyl CoA to HMG CoA?
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Thiolase
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What key enzyme converts a molecule to cholesterol in steroid synthesis? (monooxygenase reaction = insertion of O into organic substrate R)
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P450 or CYP (Cytochrome P450)
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What cellular organelle will be abundant in steriodogenic cells?
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smooth ER
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Describe the path of steroid synthesis through the cellular compartments
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1. synthesized in smooth ER or taken from plasma
2. side chain cleavage in mitochondria (resulting in pregnenolone) 3. on to gonads OR adrenal cortex |
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what is the result of side chain cleavage in steroid synth?
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pregnenolone
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what is the primary glucocorticoid? (where made)
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Cortisol (Adrenal Cortex)
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what is the primary mineralocorticoid? (where made)
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Aldosterone (Adrenal Cortex)
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what is the primary androgen? (where made)
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Testosterone (Gonads)
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What is the effect of StAR (steroid acute regulatory protein) in steroid synthesis?
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It is an enzyme that allows the hydrophobic cholesterol to pass the inner and outer mitochondrial membranes for P450scc (side chain cleavage)
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What is the ultimate result of a defect in StAR OR P450cc?
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No steroids can be made
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A male is phenotypically female and experiences salt wasting, what does he have?
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Lipoidal Congenital Adrenal Hyperplasia
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An inherited defect in C7-reductase causes what syndrome?
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Smith-Lemli-Opitz Syndrome (low cholesterol levels, ambiguous male genetalia, abnormal facies)
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What is deficient in patients with Congenital Adrenal Hyperplasia showing ambiguous genitalia for females (why)?
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21-hydroxylase (excess androgen production); also salt-wasting crisis (especially in phenotypic males)
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What is the result of 5-alpha-reductase deficiency?
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46XY individuals, underviralized at birth, viralization at puberty, female organs absent
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Explain the process by which a steroid activates a TF:
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S binds receptor --> hsp release --> phosphorylation of complex --> dimerization of 2 receptor complexes --> SRC (steroid response coactivator) binds --> transcription
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What is the result of a deficiency in androgen receptor?
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Complete Androgen Insensitivity: 46XY, female genetalia, scant pubic hair, gonads = Testes,
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How do steroids "work" if current androgen supply is already saturated?
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increased receptor affinity AND glucocorticoid receptor inhibition
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