Cholesterol Degradation
Key Functions of Cholesterol Degradation
- Bile Acids: Cholesterol is converted into bile acids.
- Vitamin D: Cholesterol aids in vitamin D synthesis.
- Steroid Hormones: Cholesterol is a precursor for steroid hormones.
Bile Acid Synthesis
- Initial Conversion
- Cholesterol is converted to hydroxycholesterol via hydroxylase enzyme.
- Hydroxycholesterol is further converted to 7-hydroxycholesterol.
- Formation of Bile Acids
- 7-hydroxycholesterol transforms into colic acid and chenodeoxycholic acid.
- These acids conjugate with glycine and taurine to form:
- Glycolic acid (glycocolate)
- Taurocholic acid (taurocholate)
- Glycochenodeoxycolate
- Taurochenodeoxycolate
- Primary vs. Secondary Bile Acids
- Primary Bile Acids: Glycocolate, taurocholate, glycochenodeoxycolate, taurochenodeoxycolate.
- Secondary Bile Acids: Deoxycholic acid, lithocolic acid (formed via deconjugation and dehydroxylation)
Function of Bile Salts
- Sodium and potassium salts of bile acids aid in lipid digestion and absorption.
Vitamin D Synthesis
- Starting Compound
- Cholesterol in skin exists as 7-dehydrocholesterol.
- Activation by UV Rays
- UV rays activate 7-dehydrocholesterol, converting it to cholecalciferol.
- Further Conversions
- In the liver: Cholecalciferol is converted to 25-hydroxycholecalciferol by 25-hydroxylase.
- In the kidney: 25-hydroxycholecalciferol is converted to 1,25-dihydroxycholecalciferol (calcitriol, active form of Vitamin D3) by 1-alpha-hydroxylase.
Steroid Hormones Synthesis
- Cholesterol serves as a precursor for cortisol, aldosterone, and sex steroids including estrogen, progesterone, and testosterone.
Summary
- Cholesterol is essential for the production of bile acids, vitamin D, and steroid hormones.
- The degradation process involves multiple steps with conversions and enzymatic actions.
- Understanding these pathways highlights the importance of cholesterol in biochemical processes.
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