biochem lecture 14

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:

  1. Conversion of macromolecules into monomers.

  2. Transformation of monomers into simpler organic compounds.

  3. Degradation into energy and inorganic compounds.

Page 14 - Overview of Metabolic Pathways

• Metabolism includes:

  1. Glycolysis: Converts glucose into pyruvate.

  2. Oxidative Metabolism: Citric acid cycle requiring oxygen.

  3. 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:

  1. Nucleophilic substitutions.

  2. 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:

  1. Control enzyme concentrations and activity.

  2. 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:

  1. Universally present in living organisms.

  2. Well-characterized enzymes/pathways.

  3. 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.