Bioenergetics I
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Questions and Answers

Which of the following statements accurately describes the role of NADH in glycolysis?

  • NADH is primarily involved in the breakdown of glucose into pyruvate.
  • NADH acts as a reducing agent, carrying electrons from glycolysis to the electron transport chain. (correct)
  • NADH is a substrate for the enzyme pyruvate kinase in the final step of glycolysis.
  • NADH is directly used to generate ATP during glycolysis.

    • What is the net gain of ATP from the breakdown of glycogen through glycolysis, considering the initial glucose 6-phosphate formed?

  • 3 ATP (correct)
  • 7 ATP
  • 5 ATP
  • 2 ATP

    • Which of the following enzymes is NOT considered a rate-limiting enzyme in glycolysis?

  • Hexokinase
  • Phosphofructokinase
  • Glyceraldehyde-3-phosphate dehydrogenase
  • Phosphoglycerate mutase (correct)

    • During anaerobic metabolism, the fate of pyruvate is to be converted into lactate. What is the primary reason for this conversion?

    <p>To regenerate NAD+ for continued glycolysis. (C)</p> Signup and view all the answers

    What is the effect of the 'committed step' in glycolysis on the process?

    <p>It irreversibly commits glucose to the glycolytic pathway. (D)</p> Signup and view all the answers

    What critical role does lactate serve during high-intensity exercise?

    <p>It acts as a buffer for excess H+ ions. (A)</p> Signup and view all the answers

    Why does lactate build-up occur when the demand for ATP exceeds the mitochondrial capacity?

    <p>The shuttles cannot keep up with NADH production. (B)</p> Signup and view all the answers

    Which enzyme is responsible for the conversion of pyruvate to lactate?

    <p>Lactate dehydrogenase (C)</p> Signup and view all the answers

    What happens to NADH during glycolysis under low ATP demand?

    <p>It is oxidized and shuttled to the mitochondria. (C)</p> Signup and view all the answers

    How does the presence of high lactate levels correlate with muscle fatigue?

    <p>Lactate is simply a byproduct of fatigue due to insufficient oxygen. (D)</p> Signup and view all the answers

    What is the main consequence of inadequate regeneration of NAD during glycolysis?

    <p>Slowed down glycolysis. (C)</p> Signup and view all the answers

    What is the significance of the lactate shuttle in energy metabolism?

    <p>It helps transport lactate to cells in need of energy. (C)</p> Signup and view all the answers

    During maximal exercise, how high can skeletal muscle lactate levels rise?

    <p>20 mmol/kg (B)</p> Signup and view all the answers

    What occurs to pyruvate in the presence of sufficient oxygen after glycolysis?

    <p>It is transformed into Acetyl-CoA. (D)</p> Signup and view all the answers

    What did Otto Meyerhof contribute to the understanding of lactate?

    <p>He linked lactate production to muscle fatigue. (D)</p> Signup and view all the answers

    Which of the following statements accurately describes the relationship between glycolysis and oxygen availability?

    <p>Glycolysis is independent of oxygen availability, and can occur in both aerobic and anaerobic conditions. (A)</p> Signup and view all the answers

    Which of these is NOT a product of glycolysis under anaerobic conditions?

    <p>Pyruvate (A)</p> Signup and view all the answers

    What is the function of the 'rate-limiting enzyme' phosphorylase in glycogenolysis?

    <p>Phosphorylase regulates the rate of glycogen breakdown into glucose 1-phosphate. (D)</p> Signup and view all the answers

    What is the role of Glut-4 receptors in glucose uptake during exercise?

    <p>Glut-4 receptors transport glucose from the blood into muscle cells. (C)</p> Signup and view all the answers

    Which of the following correctly describes the process of glycogenolysis?

    <p>The breakdown of glycogen into glucose 1-phosphate using phosphorylase. (A)</p> Signup and view all the answers

    How does the relative activity of glycolytic and mitochondrial processes influence the outcome of glycolysis, particularly in terms of pyruvate and lactate production?

    <p>High glycolytic activity and low mitochondrial activity lead to lactate production. (B)</p> Signup and view all the answers

    Why are the terms 'anaerobic glycolysis' and 'aerobic glycolysis' considered inaccurate?

    <p>The terms are inaccurate because oxygen is not directly involved in glycolysis. (A)</p> Signup and view all the answers

    What is the primary role of the hexokinase reaction in the glycolysis pathway?

    <p>Hexokinase converts glucose into glucose 6-phosphate. (C)</p> Signup and view all the answers

    Considering the energy yield of glycolysis, why is it considered a relatively 'fast' energy system?

    <p>Glycolysis utilizes readily available glucose and glycogen, providing quick energy. (B), Glycolysis involves only a few steps, making it a quick process. (D)</p> Signup and view all the answers

    What is the primary difference between the glucose entry pathway during exercise versus resting conditions?

    <p>During exercise, glucose entry is independent of insulin, relying on exercise intensity. (C)</p> Signup and view all the answers

    Flashcards

    Glycolysis Phases

    Glycolysis consists of two phases: Phase I (steps 1-4) and Phase II (steps 5-10).

    Phase I

    Phase I of glycolysis includes steps 1-4 and requires two ATP molecules to produce isomers.

    Rate Limiting Enzymes

    Key enzymes in glycolysis that control the pathway: hexokinase, phosphofructokinase, glyceraldehyde phosphate dehydrogenase, phosphoglycerate kinase, pyruvate kinase.

    Byproducts of Glycolysis

    Glycolysis produces pyruvate, ATP (net gain of 2), and NADH (net gain of 2).

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    Aerobic vs Anaerobic Metabolism

    Aerobic metabolism uses NADH in ETC for ATP; anaerobic converts pyruvate to lactate without ATP generation.

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    Protein

    Complex molecules made of amino acids, containing nitrogen.

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    Energy yield of protein

    Protein provides a small energy yield of 4 kcal/g.

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    Immediate Energy System

    Energy system using ATP and phosphocreatine for very short bursts of effort.

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    Phosphocreatine (PCr)

    High-energy phosphate that re-phosphorylates ATP for quick energy.

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    Glycolysis

    Process of breaking down glucose to generate ATP.

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    Fast Glycolysis

    Anaerobic pathway producing ATP quickly, resulting in lactate.

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    Glycogenolysis

    Breakdown of glycogen into glucose 6-phosphate for energy.

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    Glycogen storage

    Glycogen serves as a stored form of glucose in muscles and liver.

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    Glut-4 receptors

    Transporters that help glucose enter muscle cells, stimulated by insulin or exercise.

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    Energy Systems Overview

    Three systems: Immediate, Non-oxidative, and Oxidative, each producing ATP differently.

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    Lactate

    A product derived from glucose during high ATP demand when oxygen is limited.

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    Otto Meyerhof

    The scientist known as the father of glycolysis; Nobel Prize winner in 1922.

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    NAD and NADH

    NAD is an electron acceptor; NADH is its reduced form, crucial in glycolysis.

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    Glycolysis Step 6

    The step where NADH is produced, linking glycolysis to lactate formation.

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    Lactate dehydrogenase (LDH)

    The enzyme that converts pyruvate to lactate when H+ accumulates.

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    Pyruvate Transport

    Pyruvate moves to mitochondria to be converted into Acetyl-CoA for more ATP.

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    NADH Shuttle

    Pathways that transport NADH into mitochondria, essential when ATP demand is low.

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    Acidosis

    Increase in acidity, particularly in muscles, during high-intensity exercise.

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    Lactate as Marker

    While lactate levels indicate fatigue, it primarily helps buffer H+ ions.

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    ATP Demand Increase

    Higher activity levels lead to increased glycolytic rates and lactate production.

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    Study Notes

    Bioenergetics I

    • All systems in the body are constantly active.
    • Homeostasis and allostasis are important concepts.
    • Energy supply and demand are crucial.
    • The location of energy breakdown and synthesis varies.
    • The number and yield of reactions are significant.
    • Photosynthesis in plants and combustion/cellular respiration in animals release/capture energy.

    Introduction

    • Metabolism is the sum of all chemical reactions in the body.
    • Anabolic reactions synthesize molecules.
    • Catabolic reactions break down molecules.
    • Bioenergetics converts foodstuffs to energy.
    • Chemical energy (e.g., glucose, fatty acids) is transformed into mechanical energy for work.

    Cellular Respiration

    • Cellular respiration (reverse of photosynthesis) breaks down glucose to release energy as ATP.
    • Glucose + oxygen → carbon dioxide + water + ATP
    • ATP provides energy for mechanical, chemical, and transport work.

    Bioenergetics

    • Metabolic reactions generate free energy used for work and heat release.
    • Measuring heat production is done in kilocalories (kcal).
    • 1 kcal is the heat required to raise 1 kg of water by 1°C.
    • The rate of energy production is influenced by substrate availability and enzyme activity.
    • Rate-limiting enzymes control entire biochemical pathways.
    • ATP turnover rate is influenced by the activity demands.

    ATP

    • ATP is the universal energy carrier in cells.
    • ATP is constantly resynthesized with both oxidative and non-oxidative reactions.
    • Intracellular ATP concentration is low (80-100 g).
    • A decrease in ATP and an increase in ADP trigger metabolic processes to resynthesize ATP.
    • The enzyme ATPase is vital in this ATP breakdown process.

    Main Nutrients for Energy Metabolism

    • Carbohydrates (stored glycogen and blood glucose) are the primary energy source.
    • Fats (stored lipids) are an important energy source as well.
    • Proteins, used during prolonged intense fasting.
    • Protein is not a primary energy source under resting conditions.

    Carbohydrates

    • Carbohydrates consist of carbon, hydrogen, and oxygen atoms.
    • They are a primary energy source in the body (approximately 4 kcal/g).
    • Carbohydrates enter the bloodstream as glucose.
    • They are stored as glycogen in muscle and liver.
    • Monosaccharides, oligosaccharides, and polysaccharides are the different carbohydrate categories.

    Lipids

    • Lipids are insoluble molecules with high energy density.
    • Lipids provide even more energy than carbohydrates (approximately 9 kcal/g).
    • Types of lipids include fatty acids, triacylglycerols, phospholipids, and steroids.
    • Triacylglycerols and fatty acids provide energy for the body.

    Proteins

    • Proteins contain nitrogen and consist of amino acids.
    • The energy yield is low (approximately 4 kcal/g).
    • Proteins are not a primary fuel source, except under intense long lasting exercise or prolonged fasting
    • Nitrogen is removed during protein use for energy.
    • Breakdown products can be converted to glucose or fatty acids or enter energy pathways

    Oxidation-Reduction Reactions

    • Oxidation involves the removal of electrons, while Reduction involves the gain of electrons.
    • Reactions involving hydrogen atom transfer are common in cells.
    • Molecules that lose hydrogen atoms also lose electrons, and hence are oxidized.
    • Key molecules involved in oxidation-reduction include NAD and FAD.

    Glycolysis/Glycogenolysis

    • Glycolysis breaks down glucose to create ATP.
    • Glycogen is broken down to glucose-6-phosphate, which can then be used in glycolysis.
    • Glucose and glycogen sources for glycolysis.
    • Glycolysis rate is higher during exercise and activity, but there is variation depending on intensity of activity.
    • The end result of glycolysis is either pyruvate or lactate.

    Nonaerobic Glycolysis/Glycogenolysis

    • Occurs in the cytosol of muscle cells.
    • Glucose/glycogen enters the pathway as Glucose 6-phosphate.
    • Steps in how glucose is processed.
    • Two molecules of ATP are initially used
    • Two Pyruvate molecules and Two NADH molecules are produced

    Fast vs Slow Glycolysis

    • Fast glycolysis is also called anaerobic glycolysis, while Slow is called aerobic glycolysis.
    • Fast and slow glycolysis are defined as relative to the activity demands.
    • These terms also refer to whether the activity depends on mitochondrial or glycolytic activity.

    Glycogen

    • Glycogen is a storage form of glucose.
    • Glycogen breakdown to glucose-1-phosphate is essential for glycolysis.
    • Phosphorylase is the rate-limiting enzyme in glycogen breakdown.
    • The breakdown occurs faster during higher activity levels.

    NADH shuttle

    • Mitochondrial membrane cannot easily pass the high demand of NADH during intense exercise.
    • Needs a pathway or shuttle for NADH transport.
    • Two main shuttles are available
    • Aspartate/Malate
    • Glycerol/phosphate

    Lactate

    • Lactate in terms of ATP demand being high, and shuttling not quickly enough.
    • Lactate can be recycled to generate more NAD, allowing more glycolysis.
    • Lactate is a byproduct of glycolysis and acts as a vital buffer of H+ ions. Lactate production increases with higher intensity exercise .

    Lactate Utilization

    • Lactate can be used in 3 ways by muscles
    • Used by the mitochondria to generate ATP in the cytoplasm
    • Lactate transportation to other cells for oxidation
    • Recirculated to the liver to generate glucose.

    Lactate Removal

    • Lactate is shuttled out of muscle cells and into other tissues, like blood, liver and skeletal muscle.

    Lactate Threshold

    • The amount of exercise where lactate production rates exceed the rate it's cleared out by the body.
    • At this threshold, the energy demand surpasses the ability for the body to buffer the increase of lactate. This threshold is characterized by an increase in blood lactic acid levels.

    Cori Cycle

    • The Cori Cycle is crucial mechanism in energy metabolism and in maintaining blood glucose levels during exercise and recovery.
    • This is the process occurring in the liver that converts lactate back into glucose. The glucose can then be re-enter the muscle and used to generate ATP through glycolysis or transported through the blood stream to other cells. Glucose is a key metabolite in glycolysis.

    Monocarboxylate Transporters (MCTs)

    • Facilitated diffusion transporters moving lactate and pyruvate across cell membranes.
    • Important in shuttling lactate for other functions.

    Benefits/Liabilities of ATP-PCr System

    • The ATP-PCR system is the most rapid form of generating ATP.
    • It is not reliant on long chain reactions, making it a more immediate energy source for the body.
    • Only provides a limited amount of energy for the body, and is only good for high intensity short duration activities.

    Next Week

    • Oxidative phosphorylation
    • ATP production from fats
    • Relationship between energy metabolism, exercise, and performance

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    Description

    Test your understanding of glycolysis with this quiz focused on key concepts such as the role of NADH, ATP yield, rate-limiting enzymes, and the fate of pyruvate. Answer questions that cover essential metabolic pathways and understand the committed step in glycolysis.

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