Lecture on Insulin by Armando Hasurugan

Introduction

• Insulin is a polypeptide hormone.
• Major role in the regulation of macromolecules and metabolism.
• Main role: storing excess energy (fats, lipids, carbohydrates, proteins) during the fed state.

Organs Affected by Insulin

• Intestines
• Blood
• Liver
• Skeletal muscle
• Lymphatic circulation
• Adipose tissue
• Pancreas

Insulin's Role During the Fed State

• After eating, macromolecules like glucose, amino acids, and fats run through the intestines.

Effects on Glucose

• Absorbed by the blood.
• Pancreas secretes insulin, promoting:
  • Uptake of glucose from blood to liver.
  • Conversion of glucose to glycogen.
  • Conversion of glucose to pyruvate, then to acetyl-CoA, and further to triacylglycerols.
  • Storage of triacylglycerol in adipose tissue as very low-density lipoproteins (VLDLs).

Effects on Amino Acids

• Absorbed by the blood.
• Insulin promotes uptake of amino acids to the liver and protein synthesis.

Effects on Fats

• Absorbed through lymphatic circulation.
• Insulin promotes fat storage in skeletal muscle and triacylglycerol synthesis in the liver.

Insulin Synthesis

• Occurs in pancreas' beta cells.

Process

• Ribosome translates mRNA to form pre-proinsulin.
• Pre-proinsulin transported to endoplasmic reticulum, forming proinsulin (segments A, C, B).
• Proinsulin travels to Golgi apparatus, forming insulin (A and B connected by disulfide bonds) and C-peptide.
• C-peptide plays role in cell membrane for G-protein signaling.

Insulin Receptor: Tyrosine Kinase Receptor

• Consists of two alpha subunits, two beta subunits, and tyrosine kinase.
• Inactive when not phosphorylated.

Mechanism

• Insulin binds to alpha subunits, activating tyrosine kinase.
• Phosphorylates target protein, initiating intracellular effects.

Effects of IRS1 Activation

• Promotes growth and gene expression.
• Promotes glycogen and fat synthesis.
• Stimulates protein synthesis and increases glucose transporter expression.

Insulin Resistance

• Condition where insulin can't bind to receptor, leading to high blood glucose levels.

Main Functions of Insulin

• Lowers blood glucose levels.
• Inhibits glycogen degradation.
• Promotes glucose conversion to glucose-6-phosphate and glycogen synthesis.
• Increases glucose transporter expression, enhancing glucose uptake.
• Stimulates protein synthesis and inhibits protein degradation.
• Promotes glycolysis and fatty acid synthesis.
• Inhibits hormone-sensitive lipase and prevents beta-oxidation.

Conclusion

• Insulin is crucial for storing excess energy as glycogen, triglycerols, and proteins.
• Encouraged to watch related video on glucagon.