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Chapter 1: Problem 44

Which of the following regarding the steroid synthetic pathway is not correct? a. cholesterol is converted to pregnenolone b. 11 deoxycortisol is converted to cortisol c. pregnenolone is converted to progesterone d. androstenedione is converted to testosterone e. 17 hydroxyprogesterone is converted to aldosterone

Short Answer

Expert verified
e. 17 hydroxyprogesterone is converted to aldosterone

Step by step solution

01

Understanding the Steroid Synthesis Pathway

Review the steps and intermediates involved in the steroid synthesis pathway. The pathway includes several conversions of cholesterol into different steroid hormones like cortisol, aldosterone, testosterone, among others.
02

Conversion from Cholesterol to Pregnenolone

Verify if cholesterol is converted to pregnenolone, which is a correct step in the steroid synthesis pathway.
03

Conversion from 11-Deoxycortisol to Cortisol

Check if 11-deoxycortisol converts to cortisol. This transformation occurs in the adrenal cortex and is correct.
04

Conversion from Pregnenolone to Progesterone

Determine if pregnenolone converts to progesterone. This conversion is also a correct step in the pathway.
05

Conversion from Androstenedione to Testosterone

Confirm if androstenedione is converted to testosterone. This is another correct process in the pathway.
06

Conversion from 17-Hydroxyprogesterone to Aldosterone

Review the pathway to check if 17-hydroxyprogesterone converts to aldosterone. This conversion is not correct; 17-hydroxyprogesterone is involved in the pathway that leads to cortisol and androgens, not aldosterone.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Cholesterol Conversion
The steroid synthesis pathway begins with cholesterol. Cholesterol is a type of lipid molecule that serves as the precursor to all steroid hormones. The first step in the pathway is the conversion of cholesterol into pregnenolone. This process occurs in the mitochondria of steroid-producing cells, such as those found in the adrenal cortex and gonads. Enzymes called cytochrome P450scc (side-chain cleavage enzyme) facilitate this crucial transformation. This initial step is vital because pregnenolone is the precursor from which all other steroid hormones are synthesized.
Cortisol Synthesis
Cortisol is a steroid hormone produced in the adrenal cortex. Its synthesis starts with the conversion of 17-hydroxyprogesterone into 11-deoxycortisol. Following this, 11-deoxycortisol undergoes an enzymatic change facilitated by 11尾-hydroxylase, resulting in cortisol. Cortisol plays key roles in metabolism, immune response, and stress management. The correct sequence of enzymatic transformations ensures proper cortisol production, impacting a wide array of physiological processes.
Progesterone Synthesis
Progesterone synthesis involves the conversion of pregnenolone into progesterone. Pregnenolone is first produced from cholesterol and then converted to progesterone through a dehydrogenation process involving the enzyme 3尾-hydroxysteroid dehydrogenase. Progesterone serves as a precursor for other steroid hormones, such as cortisol, aldosterone, and sex steroids. It also plays a central role in the menstrual cycle and in maintaining the early stages of pregnancy.
Testosterone Synthesis
Testosterone synthesis involves the transformation of androstenedione to testosterone. Androstenedione is first synthesized from cholesterol through several enzymatic steps involving intermediates like pregnenolone and DHEA (dehydroepiandrosterone). The enzyme 17尾-hydroxysteroid dehydrogenase converts androstenedione into testosterone. Testosterone is vital for the development of male secondary sexual characteristics and plays a role in muscle mass and bone density maintenance.
Hormonal Pathways
Hormonal pathways in steroid synthesis are complex and involve multiple interconnected steps. These pathways start with cholesterol and lead to the production of various steroid hormones. For instance, cholesterol is converted to pregnenolone, which then can follow different paths 鈥� toward progesterone production, cortisol production, or the creation of sex steroids like testosterone and estradiol. Each pathway is tightly regulated by specific enzymes. Understanding these pathways is crucial for grasping how different enzymes and intermediates contribute to the diverse functions of steroid hormones in the body.

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Most popular questions from this chapter

Use the following Key to answer Questions. a. 1,2 , and 3 are correct b. 1 and 3 are correct c. 2 and 4 are correct d. 4 only is correct e. all are correct Which of the factors regarding a drug screen are true? 1\. Results should be reviewed by a medical review officer. 2\. Are always randomly performed. 3\. Are used as part of a contingency contract. 4\. Never need confirmation testing of the results.

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A patient with confirmed Cushing's sydrome has the following results. The urine free cortisol and serum cortisol measurements are elevated but suppress by more than \(90 \%\) after being given \(8 \mathrm{mg}\) of dexamethasone. The plasma ACTH concentration is slightly higher than the upper limit of normal. These results are suggestive of which cause of Cushing's syndrome? a. adrenal adenoma b. pituitary adenoma c. bronchial carcinoid d. bronchial carcinoma e. ectopic secretion of ACTH

The best test to assess adrenal reserve in a patient withdrawn from long term glucocorticoid therapy is which of the following? a. morning serum cortisol b. urine free cortisol c. insulin hypoglycemia stimulation test d. ACTH stimulation test e. aldosterone

A healthy individual may occasionally have __ RBC/high powered field in a random urine specimen: a. zero b. 2-4 c. 8-10 d. 15-25 e. 25-30
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