Lecture 21-23

Lecture 21-23 - BIOCHEMISTRY 120 Spring, 2009 Lectures #...

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Unformatted text preview: BIOCHEMISTRY 120 Spring, 2009 Lectures # 21,22,23 REPRODUCTION I, II, III Helen L. Henry REPRODUCTION I. Biosynthesis and Catabolism of Androgens and Estrogens II. Hormonal Influences on Sexual Differentiation III. Male Reproduction IV. Female Reproduction V. Hormones of Pregnancy VI. Parturition VII. Lactation BIOSYNTHESIS OF ANDROGENS Fig. 2-22 Synthesis of androgens by the interstitial (Leydig) cells of the testis is by extension the same pathway as in the adrenal cortex for glucocorticoids and mineralcorticoids. 5 pathway : Cleavage of carbons 20, 21 before A-ring modification 4 pathway: A-ring modification before removal of carbons 20, 21 CSCC is the rate-limiting step, regulated by LH 17 -OHase/C17 - C20 lyase 17 -OHSDH 3 -OHSDH/ 5 - 4 Isomerase Androgens Fig. 2-22 (error in DHT structure at C17) The 5 -Reduction of Testosterone In some target tissues of androgens, testosterone is converted to dihydrotestosterone which interacts with the androgen receptor. 5 -Reductase Since DHT has a higher affinity for AR than T does and since it cannot be aromatized, 5 -reduction amplifies the androgen signal in target tissues BIOSYNTHESIS OF ESTROGENS Fig. 2-23 Fig. 2-30 Aromatase 17 -OHSDH 16 -OHase Estriol Estrone 17 -estradiol In the ovarian follicle, androgens are produced from cholesterol by the same pathway as in the testis. Estrogen production in the ovary is regulated by LH at the step of CSCC. [ details of the aromatase reaction ] The C19 androgens are converted to C18 estrogens by aromatase, a microsomal cytochrome P450-dependent enzyme. STEROID ACUTE REGULATORY PROTEIN (StAR) StAR is rapidly induced by ACTH in the adrenal and by LH in the ovary and testis. ACTH/LH StAR mediates the transfer of cholesterol to the inner mitochondrial membrane Also see Fig 2.33; AWN lecture notes The purposes of steroid hormone catabolism are to: inactivate the active hormone make it H 2 O-soluble through conjugation with sulfate or a monosaccharide so it can be excreted Catabolism of Steroid Hormones Most steroid hormone catabolism takes place in the liver. The main pathway of androgen catabolism is reduction of A-ring Reduction is usually at the 3 and 5 positions and may be either or - O 3 S 17 -OHSDH Androstanediol Bioavailability of active hormone to target tissues depends on both synthesis and degradation Catabolism of Steroid Hormones, cont Estrogens are catabolized by hydroxylation at carbon 2 and/or 16 and conjugation at carbons 2, 3, or 16 REPRODUCTION II. Hormonal Influences on Sexual Differentiation A. Components of Sexual Differentiation B. Embryonic Development C. Endocrine Disorders of Sex Differentiation D. Puberty Hormonal influences on Sexual Differentiation and Development Genotype XY XX Gonad TESTIS OVARY Hormone production: Hormones ANDROGENS ESTROGENS Regulation TONIC CYCLIC Internal and external genitalia Sexual identity, behavior Components of sexual differentiation Hormonal Influences on Sex Differentiation...
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Lecture 21-23 - BIOCHEMISTRY 120 Spring, 2009 Lectures #...

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