Lecture 14 – Metabolism: An Overview
Lecture 14 – Metabolism, an overview
Date: March 11th, 2025
Reading Material: Biochemistry: Concepts and Connections, Chapter 11, Pages 342 - 363
Page 1 - Introduction
Focus on an overview of metabolism.
Importance of understanding how food is digested and converted into smaller components.
Page 2 - Overview of Metabolism
Discusses the process of digestion, emphasizing:
Breakdown of carbohydrates, proteins, and fats.
Role of the small intestine as the primary site for absorption.
Accessory organs involved in digestion (liver, gallbladder, pancreas).
Overview of:
Monomers and smaller molecules.
Biochemical reactions in metabolism.
ATP as the universal energy converter and its functions in cells.
Page 3 - Ingestion of Foodstuffs
Main biological macromolecules, focusing on:
Fats, carbohydrates, proteins; neglecting nucleic acids.
Pathway of food digestion:
Stomach: Minor role, mainly absorbs alcohol and aspirin.
Small intestine: Divided into duodenum, jejunum, and ileum, playing a major role in absorption.
Colon (large intestine): Final absorption before waste excretion.
Page 4 - Carbohydrate Digestion
Carbohydrate breakdown begins in the mouth:
Salivary amylase acts on complex starches, producing oligosaccharides.
Further digestion occurs in the small intestine:
Pancreatic amylase converts oligosaccharides into disaccharides.
Brush border cells digest disaccharides into monosaccharides for absorption.
Page 5 - Protein Digestion
Initial protein breakdown occurs in the stomach:
Pepsin activated by low pH, leading to the creation of water-soluble components.
Further digestion in the small intestine:
Pancreatic enzymes transform small pieces into di-peptides.
Brush border absorbs amino acids from these peptides.
Page 6 - Fat Digestion
Occurs primarily in the small intestine, in two main stages:
Emulsification by bile due to the non-polar nature of fats.
Digestion by pancreatic lipases, breaking down fats into fatty acids and glycerol.
Page 7 - Small Intestine Components
Approximately 5-6 metres long, consisting of three parts:
Duodenum: Shortest segment, initiates nutrient absorption; connects to the stomach.
Jejunum: Site for the majority of nutrient absorption, including amino acids and fats.
Ileum: Longest section, absorbs bile salts and vitamin B12; transitions into the large intestine.
Page 8 - Microscopic Overview of the Small Intestine
Nutrient absorption occurs at the brush border:
Villi: Projections that increase surface area for absorption.
Structure includes columnar cells with microvilli and lamina propria (connective tissue).
Page 9 - Large Intestine
Approximately 1.5m long; comprises five structural components:
Caecum, ascending colon, transverse colon, descending colon, sigmoid colon.
Main functions include reabsorption of ions/water and fecal matter production.
Page 10 - Supporting Organs
Supporting organs help produce chyme:
Liver: Produces bile for fat digestion, involved after nutrient absorption.
Gallbladder: Stores bile, releases it post-meal for fat digestion.
Page 11 - The Pancreas
Involved in both endocrine (hormone production) and exocrine (enzyme secretion) functions:
Secretes digestive enzymes (proteases, amylases, lipases) directly to the duodenum via pancreatic duct.
Page 12 - Pancreatic Enzyme Activation
Inactive enzyme precursors are activated in duodenum:
Example enzymes include trypsinogen, proelastase, chymotrypsinogen.
Page 13 - Metabolism Beginnings
Breakdown of nutrients occurs in three steps:
Conversion of macromolecules into monomers.
Transformation of monomers into simpler organic compounds.
Degradation into energy and inorganic compounds.
Page 14 - Overview of Metabolic Pathways
Metabolism includes:
Glycolysis: Converts glucose into pyruvate.
Oxidative Metabolism: Citric acid cycle requiring oxygen.
Electron Transport Chain: Main site of ATP production.
Page 15 - Metabolic Pathways Diagram
Illustrates flow from polysaccharides to ATP production through glycolysis, citric acid cycle and oxidative phosphorylation.
Page 16 - Catabolism vs. Anabolism
Catabolism focuses on breakdown of molecules for energy; pathways also allow for reverse processes (anabolism) to synthesize biomolecules.
Page 17 - Biochemical Reactions Overview
Essential terms: nucleophile (electron donor) and electrophile (electron acceptor).
Reaction types include:
Nucleophilic substitutions.
Nucleophilic additions.
Page 18 - Additional Reactions
Discusses: 3. Carbonyl Condensations: Formation of carbon chain groups. 4. Eliminations: Formation of double bonds (e.g., in unsaturated fatty acids). 5. Oxidations and Reductions: Changes in energy states, e.g. NAD+ to NADH.
Page 19 - Energy Production and ATP
Energy from metabolism arises from oxidation processes.
Intermediate reactions necessary for glucose oxidation to produce useful ATP rather than just heat.
Page 20 - ATP Functionality
ATP as an energy currency in cells, used for various biological functions.
High energy compound due to phosphate groups; can couple with other reactions.
Page 21 - Metabolic Component Segregation
Importance of keeping metabolic processes separate:
Control enzyme concentrations and activity.
Manage substrate and product levels through membrane segregation.
Page 22 - Levels of Metabolism Study
Different levels of analysis:
Whole organism (e.g., glucose tolerance tests).
Organs with fluid analysis (PBS flush).
Cellular analysis through FACS for specific cell types.
Page 23 - Glycolysis as a Starting Point
Justification for focusing on glucose:
Universally present in living organisms.
Well-characterized enzymes/pathways.
Central role in metabolic pathways.
Page 24 - Energy Investment vs. Return in Glycolysis
Glycolysis involves:
Initial investment of 2 ATP.
Return of 4 ATP and 2 reduced NADH.
Quick return on investment, popular in various organisms, including cancer cells.
Page 25 - Lecture Summary and Next Class
Next session will focus on Chapter 12: Glycolysis and Gluconeogenesis.