Human Biochemistry and Nutrition Overview

I. Introduction to Carbohydrates

  • Date: January 12, 2025
  • Faculty: Dr. Dominguez

II. Schedule and Topics

  • January 12 (M): Introduction to Carbohydrates
  • January 13 (T): Glycolysis
  • January 15 (Th): Glycolysis
  • January 16 (F): Glycolysis
  • January 19 (M): Gluconeogenesis
  • January 20 (T): Gluconeogenesis
  • January 22 (Th): Glycogen Metabolism
  • January 23 (F): Glycogen Metabolism
  • January 26 (M): Long Quiz I (50 points)
  • January 29 (Th): Monosaccharide and Disaccharide Metabolism
  • January 30 (F): Monosaccharide and Disaccharide Metabolism
  • February 2 (M): Pentose Phosphate Pathway
  • February 3 (T): Insulin and Glucagon
  • February 5 (Th): Insulin and Glucagon
  • February 6 (F): Diabetes Mellitus
  • February 9 (M): Diabetes Mellitus
  • February 10 (T): Diabetes Mellitus
  • February 12 (Th): Long Quiz II (50 points)
  • February 19-20, 24-26: Prelim Examinations (100 points)

III. Quizzes Overview

  • 1st Prelim Quiz:
    • Topics: Introduction to Carbohydrates; Glycolysis; Gluconeogenesis; Glycogen Metabolism
    • Date: January 27, 2026
  • 2nd Prelim Quiz:
    • Topics: Monosaccharide and Disaccharide; Pentose Phosphate Pathway; Insulin and Glucagon; Diabetes Mellitus
    • Date: February 16, 2026

IV. Definitions and Key Concepts

A. Carbohydrates

  • General Definition: Organic compounds consisting of carbon, hydrogen, and oxygen. They include sugars, starches, and cellulose.
  • Empirical Formula: Typically represented as (CH₂O)n, where n is a number representing the number of carbon atoms in the molecule.
  • Functions of Carbohydrates:
    • Provide energy (calories) for most organisms.
    • Serve as storage forms of energy (e.g., glycogen in animals, starch in plants).

- Act as structural components in cells (cell walls in bacteria, cellulose in plants).

B. Classification of Carbohydrates

  • Monosaccharides: Simple sugars with 1 unit (e.g., glucose, galactose, fructose).
  • Disaccharides: Composed of 2 monosaccharide units (e.g., sucrose, lactose, maltose).
  • Oligosaccharides: Composed of 3 to 10 monosaccharide units.
  • Polysaccharides: Composed of more than 10 monosaccharide units (e.g., starch, cellulose).

C. Glycolysis

  1. Overview: The metabolic pathway that converts glucose into pyruvate, releasing energy stored in glucose for ATP production.
  2. Location: Occurs in the cytosol of cells.
  3. Steps:
    • Glucose is phosphorylated to glucose-6-phosphate by the enzyme hexokinase or glucokinase.
    • Conversion of glucose-6-phosphate to fructose-1,6-bisphosphate by phosphofructokinase-1 (PFK-1).
    • Breakdown into two three-carbon sugars (trioses) which enter further glycolytic reactions.
  4. Products: During glycolysis:
    • Net gain of 2 ATP molecules per glucose.
    • Generation of 2 NADH.

D. Gluconeogenesis

  1. Definition: The process of synthesizing glucose from non-carbohydrate precursors, essential during fasting or low-carbohydrate intake.
  2. Key Precursors: Amino acids, lactate, and glycerol.
  3. Significance: Helps maintain blood sugar levels, especially for the central nervous system (CNS) and red blood cells (RBCs) during fasting states.

E. Glycogen Metabolism

  1. Glycogen: The main storage form of glucose in the body, found mainly in the liver and skeletal muscles.
  2. Synthesis (Glycogenesis): Conversion of glucose to glycogen through a series of enzymatic reactions, primarily driven by insulin.
  3. Breakdown (Glycogenolysis): The conversion of glycogen back into glucose, primarily through the action of glucagon when blood sugar levels fall.

F. Pentose Phosphate Pathway (PPP)

  1. Function: Generates NADPH (for reductive biosynthesis) and ribose-5-phosphate (for nucleotide synthesis).
  2. Phases:
    • Oxidative Phase: Converts glucose-6-phosphate into NADPH and ribulose-5-phosphate.
    • Non-Oxidative Phase: Interconverts sugars and supports nucleotide synthesis.
  3. Importance: Crucial in tissues needing NADPH for biosynthesis (e.g., fatty acid synthesis in adipose tissue).

G. Hormonal Regulation of Glycolysis and Gluconeogenesis

  1. Insulin: Promotes glucose uptake and storage, stimulates glycogenesis, and reduces blood sugar levels.
  2. Glucagon: Stimulates gluconeogenesis and glycogenolysis when blood sugar levels are low.
  3. Counterregulatory Hormones: Includes epinephrine that acts during stress to increase glucose availability.

V. Clinical Correlations

A. Diabetes Mellitus

  1. Type 1 Diabetes: Characterized by autoimmunity targeting pancreatic beta cells, leading to insulin deficiency.
  2. Type 2 Diabetes: Involves insulin resistance and is often accompanied by metabolic syndrome.
  3. Symptoms: Frequent urination, excessive thirst, increased hunger, fatigue.

B. Glycogen Storage Diseases (GSD)

  1. Von Gierke Disease (Type I): Deficiency of glucose-6-phosphatase leading to severe fasting hypoglycemia.
  2. Pompe Disease (Type II): Deficiency of lysosomal alpha-1,4-glucosidase.
  3. Cori Disease (Type III): Deficiency in debranching enzyme, resulting in abnormal glycogen structure.
  4. Andersen Disease (Type IV): Deficiency in the branching enzyme, leading to abnormal glycogen formation.
  5. McArdle Disease (Type V): Deficiency of skeletal muscle glycogen phosphorylase, leading to exercise intolerance.

VI. Quizzes Overview

A. Key Quiz Topics

  1. Carbohydrates
  2. Glycolysis
  3. Gluconeogenesis
  4. Glycogen Metabolism
  5. Monosaccharide and Disaccharide Metabolism
  6. Pentose Phosphate Pathway

B. Example Quiz Questions

  1. What is the rate-limiting enzyme in glycolysis?

    • Answer: Phosphofructokinase-1 (PFK-1).

  2. What stimulates insulin release from the pancreas?

    • Answer: Elevated blood glucose levels.

  3. Which enzyme is deficient in Von Gierke disease?

    • Answer: Glucose-6-phosphatase.

VII. Summary

  • Carbohydrates play crucial roles in energy metabolism.
  • Understanding glycolysis, gluconeogenesis, and storage/release of glucose through glycogen metabolism is essential for grasping human biochemistry.
  • Hormonal regulation by insulin and glucagon is vital for maintaining blood glucose homeostasis, impacting various physiological and pathophysiological states.

VIII. References

  • Ferrier, D.R. (2017). Lippincott Illustrated Reviews: Biochemistry (7th ed.). Wolters Kluwer.
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