part 1

Chapter 26: Metabolism

Section 26.2: General Overview

• The food we eat is our only energy source for performing biological work.

  • **Functions of Food: **

  • Supply Energy: Provides the necessary energy for biological processes.

  • Building Blocks: Serves as raw materials to produce essential biomolecules.

  • Storage: Can be stored for future use, typically converted to fat or glycogen.

Basal Metabolic Rate (BMR)

• The basal metabolic rate (BMR) can most effectively be defined as:

  • B. Amount of energy needed to maintain life.

• Other options discussed:

  • A. Lowest point of energy used by the body.

  • C. Maximal energy used by the body.

  • D. Energy required to digest a meal.

Overview of Metabolism

• Metabolism consists of:

  • Chemical Reactions: Depend on energy transfer from one molecule to another.

  • ATP: Typically carries out energy transfer.

• **Types of Metabolic Reactions: **

  • Catabolism:

  • Definition: Reactions that break down complex molecules.

  • Characteristic: Exergonic, releasing energy.

  • Anabolism:

  • Definition: Reactions that synthesize complex molecules.

  • Characteristic: Endergonic, consuming energy.

• ATP as Energy Currency:

  • Acts as a short-term energy storage molecule.

  • Energy distribution: 40% for maintenance and 60% for activity.

ATP as a Rechargeable Battery

• Structure of ATP: Composed of 3 phosphates when charged and energized.

• Energy Utilization: To use ATP energy, the bond between the last two phosphates must be broken, releasing necessary energy for the body.

• Recharging ADP: Involves converting food into energy via cellular respiration.

• Key Processes:

  • Phosphorylation: Adding of phosphate.

  • Dephosphorylation: Removal of phosphate.

Food Digestion vs. Molecule Synthesis

• In general metabolic terms:

  • Food digestion is catabolism, while building new proteins and carbohydrates is anabolism.

• Example question: A. metabolism; B. anabolism; C. cellular respiration; D. catabolism.

Characteristics of Catabolic Reactions

• Which of these apply to catabolic reactions? Select all that apply:

  • A. They are exergonic reactions.

  • C. They produce more energy than they consume.

  • F. They result in the breakdown of complex molecules to form simple ones.

REDOX Reactions and Energy Transfer

• Definition of REDOX Reaction: Involves oxidation and reduction processes crucial for energy transfer.

  • Oxidation: Loss of electrons (e-), resulting in a decrease in potential energy (PE).

  • Reduction: Gain of electrons (e-), resulting in an increase in potential energy (PE).

• Mnemonic for remembering: "LEO the lion says GER" (Loss of Electrons is Oxidation, Gain of Electrons is Reduction).

Importance of Glucose in REDOX Reactions

• Glucose as a Substrate: Contains many high-energy carbon-hydrogen (C-H) bonds that are ideal for oxidation reactions.

• Energy Transfer in Cellular Respiration:

  • Energy from glucose is transferred via REDOX reactions to coenzymes (electron carriers).

  • Electrons are carried until converted into ATP.

• Chemical formula for glucose: $C<em>6H</em>{12}O_6$.

Electron Carriers: NAD+ and FADH2

• NAD+ (Nicotinamide adenine dinucleotide):

  • Accepts 2 electrons and 1 proton (H+) to become reduced to NADH (1 H+ released).

• Process of Energy Storage: Hydrogens and electrons taken from organic molecules, such as glucose, to temporarily store energy.

• Chemical Representation: 2 H atoms can be rewritten as $2H^+ + 2e^-$.

Mechanisms of Generating ATP in Eukaryotic Cells

• Three mechanisms:

  • Substrate-Level Phosphorylation: Transfers high-energy phosphate groups directly to ADP from an intermediate.

  • Oxidative Phosphorylation: Electrons are removed and passed through the electron transport chain (ETC) to oxygen gas (O2).

  • Photophosphorylation: Occurs only in chlorophyll-containing plant cells.

Substrate-Level Phosphorylation Explained

• Process: Formation of ATP occurs by an enzyme directly transferring a phosphate group to ADP from an intermediate substrate.

• Location: Occurs in the cytosol.

• Role of Kinases: Kinases are enzymes that modify proteins by adding phosphate groups during phosphorylation.

Electron Transport Chain (ETC) and Oxidative Phosphorylation

• Oxidative Phosphorylation:

  • Removes electrons from organic compounds and transfers them to oxygen through a series of electron acceptors (the ETC).

  • Location: Inner mitochondrial membrane.

• Electron Transport: Each transfer allows for the pumping of protons (H+) against their concentration gradient.

• Role of Oxygen: Final electron acceptor in the chain; essential for ATP production.

• Formation of ATP: Proton motive force created via H+ gradient drives ATP synthesis in the mitochondria.

Photosynthesis: Photophosphorylation Overview

• Occurrence: Only in chlorophyll-containing plant cells or bacteria with light-absorbing pigments.

• Function: Converts photons (light energy) into chemical energy (ATP).

Carbohydrate Metabolism

• Polysaccharides Breakdown: Converts to disaccharides and then monosaccharides.

  • Key Monosaccharides: Galactose, Fructose, Glucose.

• Function of the Liver: Converts monosaccharides into glucose.

• Fate of Glucose in the Body:

  • Used for ATP production, amino acid synthesis, glycogen synthesis, and triglyceride synthesis.

  • Digestive enzymes assist in breaking down carbohydrates.

Glucose Absorption Mechanisms

• GI Tract: Absorption occurs via secondary active transport using Na+ - glucose symporters.

• Other Body Cells: Uses GluT transporters for facilitated diffusion.

  • Insulin enhances the insertion of these transporters, increasing glucose entry into the cells.

• Phosphorylation: Traps glucose within cells after absorption.

Cellular Respiration Process

• Definition: The process living organisms employ to turn food into usable energy.

• Chemical Reaction Overview: Oxidation of one glucose molecule leads to the production of approximately 30 – 32 ATP.

• Aerobic Process: Requires the presence of oxygen.

Phases of Cellular Respiration

• There are 4 phases:

  1. Glycolysis

  2. Transition Reaction (Pyruvate Oxidation)

  3. Citric Acid Cycle (Krebs Cycle)

  4. Electron Transport Chain (ETC)

• **Continuous occurrence in cells.

Phase 1: Glycolysis

• Location: Takes place in the cytoplasm.

• Purpose:

  • Splits a single glucose molecule into two pyruvate molecules.

  • Consumes 2 ATP but ultimately produces 4 ATP via substrate-level phosphorylation, resulting in a net gain of 2 ATP.

  • Donates electrons to NAD+ carriers, forming NADH to be used in the ETC.

• Anaerobic Capability: Can occur in the absence of oxygen through fermentation.

• Steps in Glycolysis: Consists of 10 enzymatic reactions each requiring distinct enzymes.

Glycolysis Overview

• Chemical Representation of Reactions: Illustrates breaking down one glucose molecule.

  • Cleavage occurs, turning a six-carbon sugar into two three-carbon sugars.

  • End of the glycolysis process yields 2 molecules of pyruvate.

ATP Production and Overhead Costs in Glycolysis

• ATP Produced Directly:

  • Substrate-Level Phosphorylation: Net gain of 2 ATP.

  • Reduced Coenzymes: 2 NADH formed, leading to 5 ATP during oxidative phosphorylation via ETC.

• Total ATP Tally from Glycolysis: Net ATP = 7.

Fate of Pyruvate

• Aerobic Conditions: Converted to acetyl CoA when oxygen is plentiful.

• Anaerobic Conditions: Converted to lactic acid under low oxygen supply.

Phase 2: Transition Reaction (Pyruvate Oxidation)

• Location: Occurs in mitochondria.

• Purpose:

  • Produces CO2 as a byproduct.

  • Forms 2 acetyl CoA molecules for the Citric Acid Cycle.

  • Transports electrons to carriers, forming NADH.

• Decarboxylation Process: Involves removal of carbon dioxide.

Glycolysis ATP Accounting

• Direct ATP Production: Glycolysis yields a net of 2 ATP.

• Coenzyme Production: Produces 2 NADH leading to 5 ATP via oxidative phosphorylation.

Citric Acid (Krebs) Cycle Overview

• Location: Occurs in the mitochondrial matrix.

• Completion of Glucose Oxidation: All 6 carbons from glucose are converted to CO2, exhaled as waste.

Phase 3: Citric Acid Cycle

• Purpose:

  • Completes glucose breakdown and turns twice for every acetyl CoA received.

  • Produces small amounts of ATP, CO2, and donates electrons through NAD+ and FAD carriers to the ETC.

• Reactions Involved: Series of 8 redox reactions.

Citric Acid Cycle ATP Accounting

• Byproducts:

  • Each cycle produces 2 ATP, 6 NADH, and 2 FADH2 for further processing in oxidative phosphorylation.

• Role of Acetyl CoA: Released from the breakdown of glucose into pyruvate, entering the Krebs cycle.

Final ATP Tally from Oxidation of Glucose

• Total ATP yield includes contributions from glycolysis, the transition reaction, and the Krebs cycle leading to potential 32 ATP.

• Process Breakdown:

  1. Glycolysis: 2 ATP, 2 NADH

  2. Oxidation of Pyruvate: 2 NADH

  3. Krebs Cycle: 2 ATP, 6 NADH, 2 FADH2 through substrate-level phosphorylation.

Phase 4: Electron Transport Chain (ETC)

• Definition: Mechanism through which ATP is generated linked to the pumping of protons (H+).

• Chemical Driving Force: Energy derived from the concentration gradient across the membrane assisting ATP synthase enzyme function.

Role of Oxygen in ATP Production

• Key Function of Oxygen Acquired via Lungs: Serves as the final electron acceptor in cellular respiration.

• Oxygen’s critical role: Vital for high energy yield from oxidation of food sources.

Consequences of Mitochondrial Membrane Damage

• Effect of Virus on ATP Production: A virus creating holes in the mitochondrial membrane would lead to decreased ATP production due to the inability to establish a hydrogen ion gradient.

• Correct option: C. ATP production would decrease because a hydrogen ion gradient could not be established.

Summary of Cellular Respiration

• Overview of main phases leads to ATP production and the cycling of electrons and protons, establishing the foundations of energy generation in cells.

Lactic Acid Fermentation (Anaerobic Respiration)

• Function: Converts glucose to lactic acid without oxygen; occurs during intense exercise when O2 levels are low.

• Impact: Lactic acidosis can result from the buildup of lactic acid, causing pain and cramps.

• Cori Cycle: Lactate is transported to the liver, converted back to pyruvate, playing an essential role in recirculating energy.

Glycogen and Related Processes

• Glycogen Storage and Breakdown:

  • Process to create glycogen is termed A. glycogenesis.

  • Process to break down glycogen for energy termed B. glycogenolysis.

Hormonal Regulation of Glucose Levels

• Hormones Influencing Blood Sugar Levels:

  • Glucagon promotes glucose release (glycogenolysis) from stored sources.

  • Enhanced by epinephrine during stress situations.

• Question about hyperglycemia: Hormones include glucagon and B. epinephrine.

Summary of Glycogen Synthesis Processes

• GP Synthesis Process:

• Glycogenesis: Formation of glycogen for storage in liver and skeletal muscle, mainly regulated by insulin.

• Glycogenolysis: Breakdown of glycogen to glucose for ATP synthesis, stimulated by glucagon due to energy demand.