Sterols

Sterols (Steroids)

  • Distinguished from other lipids by their unique structure:

    • Lack fatty acid chains and long tails.

    • Characterized by a four-ring hydrocarbon structure.

Cholesterol

  • Most abundant steroid in animals.

  • Functions:

    • Component of plasma membranes and organelle membranes.

      • Contributes to membrane structure and integrity.

    • Precursor for all steroid hormones.

      • Cholesterol is modified to produce various steroid hormones like testosterone by altering its functional groups

Steroid Hormone Families

  • Three primary families of steroid hormones:

Mineralocorticoids

  • Role: Regulate mineral balance (e.g., sodium, calcium) and water levels.

    • Influence kidney function to control fluid retention and excretion.

  • Example: Aldosterone

    • Mechanism: Increases sodium reabsorption in the kidneys, leading to water retention.

      • High aldosterone levels promote sodium uptake from kidney filtrate, drawing water back into the body, thus preventing excessive water loss through urine.

Glucocorticoids

  • Role: Increase glucose levels in the body.

  • Example: Cortisol

    • Commonly known as the "stress hormone."

    • Elevated cortisol levels can raise blood glucose.

    • Also suppress the immune system.

      • Used medically to prevent the immune system from overreacting.

      • Example: Corticosteroid creams for itchy skin are glucocorticoids that reduce inflammation.

Sex Hormones (Gonadocorticoids)

  • Examples: Testosterone, estrogen, and progesterone.

  • Structural Similarity:

    • All possess the four-ring steroid structure.

    • Differ in the arrangement of methyl groups, hydroxyl groups, and double bonds.

      • Differences in functional groups on the four-ring structure determine the specific hormone.

  • Genetic Basis:

    • Genes encode enzymes that modify cholesterol into different steroid hormones, rather than directly encoding the hormones themselves.

      • Lipids are not directly encoded by genes; instead, genes code for the proteins (enzymes) responsible for their synthesis and modification.

Synthesis

  • Cholesterol is the base molecule for all steroid hormones.

  • Enzymes modify cholesterol to produce different hormones.

Equations

  • Steroid Synthesis:\text{Cholesterol} + \text{Enzymes} \rightarrow \text{Steroid Hormones}