Biochemical Synthesis of Steroid Hormones
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Questions and Answers

Which hormone is involved in the stress response and stimulates the adrenal cortex?

  • Progesterone
  • Glucocorticoids
  • Corticotropin-releasing hormone (correct)
  • 18-Hydroxydehydrogenase

    • What reaction does the enzyme 21α-hydroxylase catalyze?

  • Hydroxylation of progesterone (correct)
  • Formation of aldosterone
  • Oxidation of cholesterol
  • Reduction of glucocorticoids

    • What does oxidation refer to in biochemical terms?

  • Addition of hydrogen atoms
  • Loss of oxygen atoms
  • Loss of electrons (correct)
  • Loss of hydrogen atoms

    • Which of the following is a product of hydroxylation on the 21st carbon of progesterone?

    <p>17-Hydroxyprogesterone</p> Signup and view all the answers

    What is produced as an intermediate in the synthesis of aldosterone?

    <p>18-Hydroxycorticosterone</p> Signup and view all the answers

    What is the primary role of glucocorticoids in metabolism?

    <p>Stimulating the breakdown of stored nutrients</p> Signup and view all the answers

    Where are hormone response elements (HREs) typically located in relation to the transcription initiation site?

    <p>Upstream of the transcription initiation site</p> Signup and view all the answers

    Which of the following is NOT a primary function of steroid hormones?

    <p>Protein synthesis promotion</p> Signup and view all the answers

    Cortisol is primarily involved in managing which process in the body?

    <p>Mediating the stress response</p> Signup and view all the answers

    What triggers the secretion of mineralocorticoids?

    <p>High extracellular fluid volume and high potassium concentration</p> Signup and view all the answers

    Which enzyme converts 11-deoxycortisol to cortisol?

    <p>11-β-hydroxylase</p> Signup and view all the answers

    What is the role of aldosterone in the steroid hormone pathway?

    <p>It is produced from deoxycorticosterone.</p> Signup and view all the answers

    In the action of steroid hormones, which location serves as the site for hormone-receptor complex binding?

    <p>The nucleus</p> Signup and view all the answers

    Which enzyme is responsible for catalyzing the conversion of corticosterone to aldosterone?

    <p>18-hydroxylase</p> Signup and view all the answers

    What type of receptor do estrogen hormones bind to in the target cells?

    <p>Intracellular receptors</p> Signup and view all the answers

    What is a common result of 21α-hydroxylase deficiency?

    <p>No cortisol and no aldosterone</p> Signup and view all the answers

    What is a key characteristic of CAH due to 3β-OH dehydrogenase deficiency?

    <p>Ambiguous genitalia in affected males</p> Signup and view all the answers

    What symptom might indicate a deficiency in 17α-hydroxylase?

    <p>Hypertension due to fluid retention</p> Signup and view all the answers

    How does adrenal insufficiency affect the HPA axis?

    <p>Causes loss of negative feedback to HPA axis</p> Signup and view all the answers

    What is NOT typically produced in significant amounts in 3β-OH dehydrogenase deficiency?

    <p>Androgens</p> Signup and view all the answers

    What enzyme deficiency leads to increased aldosterone levels and low sex hormones?

    <p>17α-hydroxylase</p> Signup and view all the answers

    What is the inheritance pattern of Congenital Adrenal Hyperplasia (CAH)?

    <p>Autosomal recessive</p> Signup and view all the answers

    What is formed as a consequence of the lack of cortisol due to adrenal insufficiency in CAH?

    <p>Excessive adrenal androgens</p> Signup and view all the answers

    What is the primary deficiency in the salt-wasting form of congenital adrenal hyperplasia (CAH)?

    <p>Mineralocorticoids</p> Signup and view all the answers

    Which of the following clinical effects is directly caused by aldosterone deficiency in CAH?

    <p>Hyponatremia</p> Signup and view all the answers

    What is a consequence of the overproduction of deoxycorticosterone in CAH?

    <p>Fluid retention</p> Signup and view all the answers

    What results from the deficiency of 11-β-hydroxylase (CYP11B1) in CAH?

    <p>Increased production of androgens</p> Signup and view all the answers

    What gender-specific effect can result from excess androgen production in females with CAH?

    <p>Virilization</p> Signup and view all the answers

    What is an important step in the management of CAH?

    <p>Daily glucocorticoid and mineralocorticoid replacement</p> Signup and view all the answers

    Which hormone's deficiency contributes to poor response to stress in CAH?

    <p>Cortisol</p> Signup and view all the answers

    What is a major electrolyte imbalance associated with aldosterone deficiency in CAH?

    <p>Hyperkalemia</p> Signup and view all the answers

    What is the first step in steroid hormone synthesis?

    <p>Conversion of cholesterol to pregnenolone</p> Signup and view all the answers

    Which enzyme is responsible for converting pregnenolone to progesterone?

    <p>3β-OH dehydrogenase</p> Signup and view all the answers

    What role does the steroidogenic acute regulatory protein (StAR) play in steroid synthesis?

    <p>It controls the uptake of cholesterol into mitochondria.</p> Signup and view all the answers

    Which hormone is formed from the conversion of progesterone through a series of hydroxylation reactions?

    <p>Aldosterone</p> Signup and view all the answers

    What is the rate-limiting step in the synthesis of steroid hormones?

    <p>Conversion of cholesterol to pregnenolone</p> Signup and view all the answers

    Which of the following enzymes is not involved in the synthesis of cortisol from progesterone?

    <p>3β-OH dehydrogenase</p> Signup and view all the answers

    What type of molecule is a steroid hormone?

    <p>Amphipathic</p> Signup and view all the answers

    Which of the following statements about steroid hormone synthesis is true?

    <p>Steroid hormone synthesis requires NADPH and oxygen.</p> Signup and view all the answers

    What modification is made to progesterone to form cortisol?

    <p>Hydroxylation and subsequent oxidation</p> Signup and view all the answers

    Where does the modification process for steroid synthesis predominantly occur?

    <p>Endoplasmic reticulum and mitochondria</p> Signup and view all the answers

    What is the process that replaces a hydrogen atom with a hydroxyl group in a substrate molecule called?

    <p>Hydroxylation</p> Signup and view all the answers

    Which reaction involves the removal of hydrogen atoms and is a common oxidation process in biochemistry?

    <p>Oxidation</p> Signup and view all the answers

    Which molecule is a precursor to both glucocorticoids and mineralocorticoids in steroid hormone synthesis?

    <p>Cholesterol</p> Signup and view all the answers

    What type of enzymes are primarily responsible for catalyzing hydroxylation reactions in biological systems?

    <p>Cytochrome P450 enzymes</p> Signup and view all the answers

    What is the product formed through the oxidation of the 18-hydroxyl group in 18-Hydroxycorticosterone?

    <p>Aldosterone</p> Signup and view all the answers

    Which enzyme directly catalyzes the conversion of 11-deoxycortisol to cortisol?

    <p>CYP11B1</p> Signup and view all the answers

    What is the role of the hormone-receptor complex in the mechanism of steroid hormone action?

    <p>To bind to hormone response elements in the DNA</p> Signup and view all the answers

    In the synthesis of aldosterone, which precursor is converted by the enzyme 18-hydroxylase?

    <p>Deoxycorticosterone</p> Signup and view all the answers

    Which location within the cell signifies where steroid hormones typically exert their function?

    <p>Cytoplasm or nucleus</p> Signup and view all the answers

    What type of steroid hormone does aldosterone primarily regulate electrolyte levels for?

    <p>Mineralocorticoids</p> Signup and view all the answers

    What clinical feature is most directly related to an excess of deoxycorticosterone in patients with CAH?

    <p>Fluid retention</p> Signup and view all the answers

    Which electrolyte imbalance is characteristic of aldosterone deficiency in congenital adrenal hyperplasia?

    <p>Hyponatremia</p> Signup and view all the answers

    What is the primary hormonal deficiency in the salt-wasting form of congenital adrenal hyperplasia?

    <p>Mineralocorticoids</p> Signup and view all the answers

    What physiological effect results from the absence of negative feedback in the hypothalamic-pituitary-adrenal axis in CAH?

    <p>Increased ACTH production</p> Signup and view all the answers

    Which of the following symptoms is likely associated with cortisol deficiency in CAH?

    <p>Hyperpigmentation</p> Signup and view all the answers

    What is a consequence of increased androgen production in females with congenital adrenal hyperplasia?

    <p>Masculinization of external genitalia</p> Signup and view all the answers

    Which treatment is essential for managing congenital adrenal hyperplasia effectively?

    <p>Daily glucocorticoid and mineralocorticoid replacement</p> Signup and view all the answers

    What cardiac issue can arise from aldosterone deficiency in congenital adrenal hyperplasia?

    <p>Hypotension</p> Signup and view all the answers

    What is the first product formed when cholesterol is converted during steroid hormone synthesis?

    <p>Pregnenolone</p> Signup and view all the answers

    Which enzyme is directly responsible for the conversion of pregnenolone to progesterone?

    <p>3β-OH dehydrogenase</p> Signup and view all the answers

    Where does the hydroxylation of progesterone occur to produce 11-deoxycorticosterone?

    <p>Endoplasmic Reticulum</p> Signup and view all the answers

    Which step in steroid hormone synthesis is considered the rate-limiting step?

    <p>Cholesterol side-chain cleavage to pregnenolone</p> Signup and view all the answers

    Which of the following statements about steroid hormones is correct?

    <p>They have both hydrophilic and hydrophobic properties.</p> Signup and view all the answers

    What is the final product of the steroid synthesis pathway starting from progesterone that involves 17α-hydroxylase?

    <p>Cortisol</p> Signup and view all the answers

    Which enzyme is involved in the conversion of corticosterone to aldosterone?

    <p>18-hydroxylase</p> Signup and view all the answers

    What is required for the activity of cytochrome P450 enzymes during steroid synthesis?

    <p>NADPH and oxygen</p> Signup and view all the answers

    Which of the following is a product of hydroxylation at C-21 of progesterone?

    <p>Corticosterone</p> Signup and view all the answers

    Which modification occurs to pregnenolone to form progesterone during steroid synthesis?

    <p>Oxidation of the 3-hydroxyl group</p> Signup and view all the answers

    What happens to sodium levels in the condition associated with 17α-hydroxylase deficiency?

    <p>Sodium levels increase due to mineralocorticoid overproduction.</p> Signup and view all the answers

    What is a common genetic characteristic of patients with 3β-OH dehydrogenase deficiency?

    <p>Affected genetic males may have ambiguous genitalia.</p> Signup and view all the answers

    What is the primary clinical consequence of virtually no cortisol production in individuals with 21α-hydroxylase deficiency?

    <p>Hyponatremia due to increased sodium excretion.</p> Signup and view all the answers

    What is the impact of 21α-hydroxylase deficiency on hormone levels?

    <p>Decrease in glucocorticoids, decrease in mineralocorticoids, increase in androgens.</p> Signup and view all the answers

    Which statement accurately describes the syndrome associated with 3β-OH dehydrogenase deficiency?

    <p>There is an absence of both glucocorticoids and mineralocorticoids.</p> Signup and view all the answers

    In patients with 17α-hydroxylase deficiency, what effect does excess mineralocorticoid production have?

    <p>Leads to sodium and fluid retention.</p> Signup and view all the answers

    What differentiates the classic form of CAH from the non-classic forms?

    <p>Classic form involves a complete deficiency of mineralocorticoids and glucocorticoids.</p> Signup and view all the answers

    What is a major consequence of congenital adrenal hyperplasia in both sexes?

    <p>Infertility</p> Signup and view all the answers

    Which zone of the adrenal cortex is primarily responsible for synthesizing aldosterone?

    <p>Zona glomerulosa</p> Signup and view all the answers

    Which of the following enzyme deficiencies is associated with the overproduction of adrenal androgens?

    <p>21α-hydroxylase deficiency</p> Signup and view all the answers

    What clinical manifestation in infants may suggest the presence of congenital adrenal hyperplasia?

    <p>Ambiguous genitalia</p> Signup and view all the answers

    Which mechanism best describes how steroid hormones exert their effects on target cells?

    <p>They bind directly to DNA and regulate gene transcription.</p> Signup and view all the answers

    How does the deficiency of aldosterone affect an individual's electrolyte balance?

    <p>Reduced sodium reabsorption</p> Signup and view all the answers

    What is one consequence of the overproduction of androgens in females suffering from CAH?

    <p>Development of male secondary sexual characteristics</p> Signup and view all the answers

    Which hormone regulates blood pressure and fluid balance through its effects on the kidneys?

    <p>Aldosterone</p> Signup and view all the answers

    What is the primary impact of glucocorticoids like cortisol on metabolism?

    <p>Increasing blood glucose levels</p> Signup and view all the answers

    What condition results from the accumulation of steroid hormones due to enzymatic deficiencies in their synthesis pathways?

    <p>Congenital adrenal hyperplasia</p> Signup and view all the answers

    Study Notes

    Biochemical Synthesis of Steroid Hormones

    • Steroid hormones are derived from cholesterol.
    • The synthesis of steroid hormones occurs in the adrenal cortex and gonads.
    • The adrenal cortex has three distinct zones: glomerulosa, fasciculata, and reticularis. Each zone produces different types of steroid hormones.
    • The adrenal medulla produces catecholamines (adrenaline and noradrenaline).
    • Steroid hormones are lipid-soluble, so they diffuse across cell membranes.
    • They bind to intracellular receptors in the cytoplasm or nucleus, and bind to DNA triggering the transcription of a target gene to mRNA.
    • There are hormone response elements within the DNA sequence, located near the transcription initiation site.
    • These elements bind to the activated steroid hormone-receptor complex, which in turn affects the expression of target genes.

    Learning Objectives

    • The biochemical pathway of glucocorticoid and mineralocorticoid synthesis from cholesterol is described.
    • The key enzymes involved in each pathway are differentiated.
    • The mechanism of action for steroid hormones is clarified.
    • The impact of deficiencies in these hormones, leading to congenital adrenal hyperplasia (CAH), is outlined.
    • How these deficiencies result in congenital adrenal hyperplasia (CAH) is outlined.

    Congenital Adrenal Hyperplasia (CAH)

    • Inherited autosomal recessive disorders.
    • Mutations in the genes encoding enzymes involved in mineralocorticoid.
    • Glucocorticoids or sex steroids synthesis.
    • Enlarged adrenal glands (hyperplastic adrenomegaly) result.
    • Reduced levels of cortisol or aldosterone result with overproduction of androgen.

    Clinical Presentation of Classic CAH

    • (In Infants):*

    • Ambiguous genitalia in females.

    • Enlarged genitalia in males.

    • Poor weight gain.

    • Adrenal crisis (dehydration, vomiting, hypoglycemia, and circulatory collapse)

    • (In Children and Adults):*

    • Early onset of puberty.

    • Rapid growth during childhood.

    • Premature completion of growth (short stature).

    • Irregular menstrual cycles.

    • Infertility in both sexes.

    Classification of Steroid Hormones

    • Steroids:
      • Adrenal Cortical Hormones (Corticoids)
        • Glucocorticoids (e.g., cortisol)
        • Mineralocorticoids (e.g., aldosterone)
      • Sex hormones
        • Female sex hormones (e.g., estrogens, progesterone)
        • Male sex hormones (e.g., androgens, testosterone)
    • Peptide hormones: (e.g., insulin, glucagon)
    • Amino acid derivatives: (e.g., thyroid hormones)

    Steroid Hormone Functions

    • Glucocorticoids (e.g., cortisol): Regulate metabolism, mood, blood pressure, immunity, and pain sensation.
    • Mineralocorticoids (e.g., aldosterone): Regulate electrolyte and fluid balance, and blood volume, and Reabsorb sodium in the kidney at the expense of potassium and H+
    • Estrogens and Progesterone: Female secondary sexual characteristics, regulation of the menstrual cycle, regulation ovulation, maintains pregnancy.
    • Androgens (e.g., testosterone): Male reproductive development

    Metabolic Functions of Glucocorticoids

    • Carbohydrate Metabolism: Stimulates hepatic gluconeogenesis, increases glycogen deposition in the liver, and antagonizes the peripheral action of insulin on glucose uptake.
    • Protein Metabolism: Inhibits amino acid uptake and protein synthesis in extrahepatic tissues, is a potent protein catabolic agent in peripheral tissues (muscle, skin, and bone), and stimulates amino acid uptake by the liver for gluconeogenesis.
    • Fat Metabolism: Increases the mobilization of fatty acids, stimulates lipolysis in adipose tissue, and increases fat deposition in facial and truncal areas

    Actions of Mineralocorticoids

    • Secreted in response to increased extracellular fluid (ECF) and high potassium (K+) concentration.
    • Stimulates the transcription of the sodium-potassium ATPase.
    • Increases the number of sodium pumps in the basolateral membranes of tubular epithelial cells.
    • Facilitates sodium (and water) uptake from the tubular lumen.
    • Reabsorbs sodium in the kidney at the expense of potassium and H+.

    Disorders of Adrenal Gland Insufficiencies: Congenital Adrenal Hyperplasia (CAH)

    • Autosomal recessive disorders of cortisol biosynthesis resulting in failure of cortisol secretion and loss of negative feedback to the hypothalamic-pituitary-adrenal (HPA) axis.
    • Classified based on the specific enzyme step involved.
      • 3β-hydroxysteroid dehydrogenase deficiency
      • 17α-hydroxylase deficiency
      • 21-hydroxylase deficiency
      • 11β-hydroxylase deficiency

    Deficiency in 3β-OH dehydrogenase

    • Virtually no glucocorticoids, mineralocorticoids, active androgens or estrogens.
    • Salt excretion in urine
    • Affected genetic males (46, XY) have ambiguous genitalia.
    • Autosomal recessive.

    Deficiency in 17α-hydroxylase

    • Virtually no sex hormones or cortisol are produced.
    • Increased production of mineralocorticoids causes sodium and fluid retention, leading to hypertension.
    • Genetic males (46, XY) have female-like genitalia.

    Deficiency in 21-α-hydroxylase

    • Partial and virtually complete deficiencies are known.
    • Classic form: deficiency in the production of mineralocorticoids and glucocorticoids. Salt wasting severe; with virtually absent mineralocorticoids and glucocorticoids.
    • Non-classic form: mineralocorticoids might be normal to slightly reduced, while glucocorticoids can be deficient to varying degrees.
    • Overproduction of androgens leads to masculinization of external genitalia in females and early virilization in males.

    Deficiency in 11β-hydroxylase

    • Decrease in serum cortisol, aldosterone and corticosterone.
    • Increased production of deoxy-corticosterone causing fluid retention
    • Hypertension and hypokalemia.
    • Overproduction of androgens leads to masculinization of external genitalia in females and early virilization in males.

    Clinical Effects of CAH

    • (Cortisol deficiency):*
    • Poor response to stress.
    • Hypoglycemia.
    • Hyperpigmentation.
    • (Aldosterone deficiency):*
    • Hyperkalemia.
    • Hyponatremia.
    • Disturbances in cardiac rhythm.
    • Hypotension.
    • (Combined deficiency):*
    • Vascular collapse, shock, and death.

    Clinical Effects of CAH (Additional Notes)

    • Absence of negative feedback to the hypothalamus.
    • Overproduction of ACTH
    • Adrenal hyperplasia.
    • Excess androgen production causing masculinization of external genitalia in females.
    • Absence of active androgens results in female-like genitalia.

    Treatment for CAH

    • Daily glucocorticoid and mineralocorticoid replacement.
    • Restore volume, electrolyte, and glucose imbalances.

    Hormone Synthesis Summary

    • Shortening of cholesterol hydrocarbon tail.
    • Hydroxylation of steroid nucleus.
    • Cytochrome P450 (CYP) mixed function oxidases.
    • NADPH and oxygen are required.
    • Modification occurs in endoplasmic reticulum (ER) and mitochondria of adrenal gland, ovary, and testes

    First Step in Steroid Synthesis

    • StAR (steroidogenic acute regulatory protein) controls the uptake of cholesterol into mitochondria.
    • Cholesterol is converted to pregnenolone, catalyzed by cytochrome P450 side chain cleavage enzyme (CYP11A1).
    • NADPH and oxygen are required.

    Progesterone Synthesis from Pregnenolone

    • 3β-hydroxysteroid dehydrogenase oxidises the 3-hydroxyl group to a 3-keto group.
    • Δ5,4 isomerase isomerises the Δ5 double bond to a Δ4 double bond.

    References

    • Provided in the document.

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    Biochemical Synthesis of Steroid Hormones PDF

    Description

    This quiz covers the biochemical synthesis pathways of steroid hormones derived from cholesterol. It explores the role of the adrenal cortex and gonads in hormone production, detailing the three zones of the cortex and the mechanisms of hormone-receptor interactions affecting gene expression.

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