Hormone metabolism

Introduction

Hormone metabolism is a fundamental process in the regulation of various physiological and developmental processes in living organisms. This course aims to provide an in-depth understanding of hormone metabolism, focusing on the biosynthesis, secretion, transport, action, degradation, and catabolism of hormones.

Biosynthesis of Hormones

Overview

The biosynthesis of hormones involves several steps that are specific to each hormone type. This section will focus on the synthesis mechanisms for various hormones such as steroid hormones, peptide hormones, and amino acid-derived hormones.

Steroid Hormones Biosynthesis

Overview

Steroid hormones are synthesized from cholesterol in a process that takes place mainly in the gonads and adrenal cortex. The biosynthetic pathway of steroid hormones will be discussed, along with the enzymes involved and their regulatory mechanisms.

Key Enzymes and Regulatory Mechanisms

Cholesterol Side-Chain Cleavage Enzyme (P450scc)

The cholesterol side-chain cleavage enzyme initiates the biosynthesis of steroid hormones by catalyzing the conversion of cholesterol to pregnenolone.

3β-Hydroxysteroid Dehydrogenase (3β-HSD)

3β-Hydroxysteroid dehydrogenase is responsible for converting pregnenolone to progesterone and other steroids. The enzyme's regulation will be discussed, including its role in the feedback mechanism of hormone production.

Peptide Hormones Biosynthesis

Overview

Peptide hormones are synthesized as pre-propeptides within the rough endoplasmic reticulum (RER) and undergo a series of processing steps to produce the mature, biologically active hormone. This section will focus on the biosynthesis pathway for peptide hormones and the post-translational modifications involved.

Key Post-Translational Modifications

Proteolytic Cleavage

Proteolytic cleavage is a crucial step in the maturation of peptide hormones, during which the precursor molecule is cleaved into smaller fragments to produce the active form.

Glycosylation

Glycosylation is another post-translational modification that may occur in some peptide hormones. This process involves the addition of sugar residues to the hormone, which can affect its stability and biological activity.

Secretion of Hormones

Overview

The secretion of hormones is tightly regulated and involves various transport mechanisms. This section will focus on the different modes of hormone secretion and the factors that control their release.

Modes of Hormone Secretion

Exocytosis

Exocytosis is the primary mode of hormone secretion, during which hormones are released from the secreting cell by fusion of the cell membrane with the secretory vesicle. The mechanism and regulation of exocytosis will be discussed.

Regulated Exocytosis

Regulated exocytosis is a specialized form of exocytosis that allows for precise control over hormone release. This process involves calcium signaling and the interaction between specific proteins on the cell membrane and the secretory vesicle.

Transport of Hormones

Overview

Hormones can be transported through the bloodstream to reach their target tissues, or they may use specialized transport mechanisms for localized delivery. This section will focus on the modes of hormone transport and the factors that affect their distribution.

Bloodstream Transport

Bloodstream transport is a simple method by which hormones are carried throughout the body to interact with their receptors in various target tissues. The kinetics of hormone transport, including binding to plasma proteins and clearance mechanisms, will be discussed.

Action of Hormones

Overview

Hormones exert their effects by binding to specific receptors on the target cell surface or inside the cell. This section will focus on the mechanisms of hormone action, the types of hormone receptors, and the signal transduction pathways activated by hormone-receptor interactions.

Signal Transduction Pathways

Signal transduction pathways are complex networks of proteins that transmit signals from hormone-bound receptors to the nucleus, ultimately leading to changes in gene expression and cellular responses. The various signaling pathways activated by different hormones will be discussed.

Degradation and Catabolism of Hormones

Overview

Hormones are subjected to degradation mechanisms that help regulate their levels and prevent excessive effects. This section will focus on the enzymes responsible for hormone degradation, the pathways involved, and the factors that affect hormone catabolism.

Enzymes Involved in Hormone Degradation

Aromatase

Aromatase is an enzyme that converts androgens to estrogens, playing a crucial role in hormonal balance. The structure, regulation, and physiological roles of aromatase will be discussed.

Peptidases

Peptidases are responsible for the degradation of peptide hormones. This section will focus on various types of peptidases and their specificity towards different hormone types.

Factors Affecting Hormone Catabolism

Metabolic Enzymes

Metabolic enzymes are involved in the degradation of steroid hormones, catalyzing reactions that break down the hormone molecules into smaller, inactive forms. The role and regulation of these enzymes will be discussed.

Clearance Mechanisms

Clearance mechanisms play a crucial role in removing hormones from the circulation. This section will focus on the renal clearance of hormones and their binding to plasma proteins, which affects their elimination rate.