Bch 441 androgens
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BCH441 GROUP 2BIOCHEMISTRY OF
ANDGROGENS
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GROUP MEMBERSAdjekukor Ufuoma CynthiaAkpata PatrickKayode KazeemOkechukwu EmekaOrakpo AnabelUdechukwu Treasure
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CONTENTSIntroductionTypes of AndrogensTestosteroneAndrostendedioneDehydroepiandrosteroneBiosynthesis of AndrogensTransport , Metabolism and ExcretionBiochemical FunctionsClinical Disorders of Androgen SecretionConclusion
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INTRODUCTIONAndrogen is a type of sex steroid
hormone.
They are mostly produced by the Leydig cells of testes, though a smaller amount originates from the adrenal glands.
The theca cells at the periphery of the ovarian follicles also produce a small amount of androgens.
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TYPES OF ANDROGENSThey are majorly three types of the
androgens namely:
Testosterone
Androstendedione
Dehydroepiandrosterone
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TESTOSTERONEThis is the major androgen
synthesized in tetses.
It has 19 carbon atoms in its structure.
Other subsidiary sources include: adrenal cortex and the ovary.
Its plasma level is about 0.7 μg/dl in males and < 0.1 μg/dl in females.
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Testosterone
Fig. 1 Structure of testosterone
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ANDROSTENDEDIONEIt has 19 carbon atoms in its
structure.
It is synthesized primarily in the adrenal cortex.
Other, subsidiary sources include: ovary and testis.
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Androstendedione
Fig 2 Structure of androstendedione
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DEHYDROEPIANDROSTERONE
It has 19 carbon atoms in its structure.
It is primarily synthesized testis.
It can also be synthesized in adrenal cortex and the ovary
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Dehydroepiandrosterone
Fig 3 Structure of dehydroepiandrosterone
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BIOSYNTHESIS OF ANDROGENS
Cholesterol is the biosynthetic precursor of all steroid hormones, including androgens.
Pregnenolone, initially formed from cholesterol is converted to progesterone by microsomal and cytoplasmic enzyme.
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13Fig. 4 Biosynthetic pathway of pregnenolone
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Biosynthesis of AndrogensPregnenolone is converted to 17-
hydroxypregnenolone by the enzyme 17- hydroxylase.
17-hydroxypregnenolone is cleaved by the enzyme 17-20 lyase to give dehydroepiandrosterone (an androgen).
Dehydroepiandrosterone is then reduced by the enzyme 3β–Hydroxysteroid dehydrogenase to yield androstendedione.
Or pregnenolone is converted to progesterone by 3β- Hydroxysteroid dehydrogenase.
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Biosynthesis of AndrogensThen the synthesis starts with the
hydroxylation of progesterone at C-17 by 17-Hydroxylase to give 17-hydroxyprogesterone .
The side chain consisting of C-20 and C-21 is then cleaved by the enzyme 17-20 Lyase to yield androstendedione (an androgen).
Testosterone, another androgen is formed by the reduction of the 17-keto group of androstendedione which is catalyzed by 17-keto-reductase.
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Fig 5 Biosynthetic pathway of dehydroepiandrosterone and androstenedione
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Fig. 6 Biosynthetic pathway of testosterone
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Biosynthesis of AndrogensTestosterone is reduced by 5α–
reductase to yield dihydrotestosterone (DHT).
It is a powerful embryonic androgen that instigates the development and differentiation of the male phenotype.
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Fig 7 Biosynthetic pathway of dihydrotestosterone
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TRANSPORT, METABOLISM AND EXCRETION
Testosterone circulates in blood in association with two proteins: sex hormone-binding globulin (SHBG) and testosterone-oestrogen-binding globulin (TEBG).
Both these proteins are formed in the liver.
The liver metabolizes androgens to 17-ketosteroids, which are excreted in urine.
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BIOCHEMICAL FUNCTIONSTestosterone promotes appearance of
secondary sexual characteristics, such as Deeping voice and masculine distribution of body hair, libido and potency.
Testosterone in association with follicle-stimulating hormone (FSH) is required for normal spermatogenesis.
Androgens promote RNA synthesis and protein synthesis thereby causing positive nitrogen balance.
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Biochemical FunctionsThe production of D-fructose from D-
glucose in seminal vesicles is increased by androgens. The androgens synthesis of aldolase, thereby enhancing glycolysis.
Androgens increase renal retention of sodium chloride and water , though to a much smaller extent than mineralocorticoids.
Androgens promote formation of bone matrix proteins.
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CLINICAL DISORDERS OF ANDROGEN SECRETION
Hypogonadism (under secretion)In primary hypogonadism, there is failure of
testes to produce testosterone.
Hypergonadism (over secretion)It is seen in precocious puberty.
A rare disorder resulting either from early maturation of the normal hypothalamo-pituitary-gonadal axis or as a result of a tumour that secretes androgen (or HCG).
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THANK YOU FOR
LISTENING