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Reproduction — Biochemistry MCQs
RMU · 213 MCQs with clinical pearls · Prof Jariya
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Sections in this rmu
- Nucleotide Derivatives — 23 MCQs
- Inhibitors of Nucleotide Synthesis — 22 MCQs
- Purine Degradation and Gout — 21 MCQs
- Gout Clinical Scenarios — 20 MCQs
- Infertility — 20 MCQs
- Pyrimidine Disorders — 12 MCQs
- Nucleotide Structure and Nomenclature — 11 MCQs
- Anticancer Drug Mechanisms — 11 MCQs
- ADA Deficiency SCID — 9 MCQs
- Purine De Novo and IMP Conversion — 8 MCQs
- Pyrimidine Catabolism — 7 MCQs
- Tumour Lysis Syndrome — 7 MCQs
- Lesch-Nyhan Syndrome — 6 MCQs
- Pyrimidine De Novo Synthesis — 6 MCQs
Sample MCQs with clinical pearls
Which of the following is the parent compound of all steroid hormones?
A) Androstenedione
B) Corticosterone
C) Deoxycorticosterone
D) Pregnenolone ✔
E) Progesterone
PREGNENOLONE is the parent of every steroid hormone, formed from cholesterol by DESMOLASE (CYP11A1) cleaving the side chain - the rate-limiting and ACTH-regulated step of steroidogenesis. From pregnenolone the pathways diverge to mineralocorticoids, glucocorticoids and sex steroids. Blocking this first step, as in congenital lipoid adrenal hyperplasia, abolishes all steroid production. MEMORY: 'Cholesterol to pregnenolone opens every steroid pathway.'
A 38-year-old female has stage 2 hormone-responsive breast carcinoma. Which enzyme inhibitor can be used in this patient?
A) 17-20 lyase
B) 17-alpha hydroxylase
C) 21-alpha hydroxylase
D) 21-beta hydroxylase
E) Aromatase ✔
AROMATASE converts androgens to oestrogens, and in the POSTMENOPAUSAL woman adipose aromatase is the main oestrogen source. Aromatase INHIBITORS - anastrozole, letrozole, exemestane - therefore treat hormone-responsive breast cancer effectively after menopause, but NOT before, when ovarian oestrogen dominates and the resulting feedback would simply drive the ovary harder. MEMORY: 'Aromatase inhibitors work only once the ovaries have stopped.'
Deficiency of 3-beta-hydroxysteroid dehydrogenase results in increased levels of which substrate?
A) Cholesterol
B) Hydroxypregnenolone
C) Hydroxyprogesterone
D) Pregnenolone ✔
E) Progesterone
3-BETA-HYDROXYSTEROID DEHYDROGENASE converts pregnenolone to progesterone and the delta-5 steroids to delta-4. Its deficiency causes PREGNENOLONE and the other delta-5 precursors, including DHEA, to accumulate. Because DHEA is a weak androgen, males are UNDER-virilised while females may be mildly virilised - the opposite pattern to 21-hydroxylase deficiency. All three steroid classes are deficient, so salt wasting occurs. MEMORY: 'The delta-5 steroids pile up behind the block.'
213 MCQs are arranged to the learning outcomes of this rmu.
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