Cellular Respiration Quiz

Cellular Respiration Overview

• Cellular respiration is a process that harvests chemical energy
• Organisms use it to derive and utilize energy
• The process consists of 3 stages: glycolysis, Krebs cycle, oxidative phosphorylation

Learning Objectives

• Understand the structure and function of mitochondria
• Locate the different stages of cellular respiration in animal cells
• Explain the process of how organisms derive and utilize energy through cellular respiration with focus on 3 stages: glycolysis, Krebs cycle, oxidative phosphorylation
• Describe the process of chemiosmosis in mitochondria including the electron transport chain and ATP production
• Understand the processes of alcohol fermentation and lactic acid fermentation
• Compare the processes of aerobic and anaerobic respiration

Cellular Respiration: Harvesting Chemical Energy

• Cells require energy from external sources to perform various tasks
• These include: synthesis of macromolecules, active transport, movement, and reproduction
• Catabolic pathways breakdown organic compounds to generate energy (e.g., cellular respiration)
• Anabolic pathways consume energy to build organic compounds (e.g., photosynthesis)
• Mitochondria and chloroplasts are organelles involved in energy production and conversion

Sunlight as Ultimate Energy Source

• Sunlight is the ultimate source of energy for all ecosystems
• Energy enters an ecosystem as sunlight and exists as heat
• Photosynthesis takes place in chloroplasts, converting light energy into chemical energy
• Cellular respiration takes place in mitochondria, releasing energy stored in organic molecules

Catabolic Pathways: Production of ATP

• Cells need to produce ATP to remain functional
• Catabolic pathways break down organic fuels to generate energy
• The breakdown of organic molecules is exergonic (releases energy as ATP)
• Reactants are more energy-rich than products
• Cellular respiration is the most prevalent and efficient catabolic pathway for degrading carbohydrates in the presence of oxygen (aerobic)
• Anaerobic respiration (fermentation) is a partial degradation of carbohydrates in the absence of oxygen which yields less ATP

Cellular Respiration: Details

• Involves transfers of energy in glucose bonds to phosphate bonds in ATP
• The released energy in ATP hydrolysis is used for cellular work(e.g. endergonic reactions)

Photosynthesis and Cellular Respiration

• Photosynthesis: CO2 + H2O + sunlight = C6H12O6 + O2 (produces organic molecules and oxygen)
• Cellular respiration (aerobic): C6H12O6 + O2 = CO2 + H2O + ATP + energy (releases stored energy as ATP and heat)
• ATP: A nucleotide that stores energy in phosphate bonds

Mitochondria and Chloroplasts

• Energy production and conversion organelles
• Cellular respiration: energy production from oxidation of organic compounds
• Chloroplasts: photosynthesis, light and dark reactions
• Mitochondria: 2 phases of Cellular Respiration (GLYCOLYSIS, Kreb's Cycle, oxidative phosphorylation)

Mitochondria: Structure

• Diameter: 1-10 μm
• Structure: outer & inner membrane, intermembrane space, cristae, matrix containing mtDNA and free ribosomes
• Inner membrane: cristae formation (contains ETC complexes, ATP synthase)

Redox Reactions:

• Redox reactions transfer electrons. Oxidation releases electrons, reduction gains electrons.
• Catabolic pathways yield energy through electron transfer

Examples of redox reactions

• Na + Cl => Na+ + Cl- (Na becomes oxidized, Cl becomes reduced)
• X + Y => X- + Y+ (X is oxidized, Y is reduced)

Oxidation of Organic Fuels During Cellular Respiration

• Glucose is oxidized and O2 is reduced
• C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (ATP)

The Stages of Cellular Respiration

• Respiration consists of three metabolic stages:
  • Glycolysis: the anaerobic stage, in the cytosol
  • The citric acid cycle
  • Oxidative phosphorylation process in the mitochondria.

Production of ATP during cellular respiration

• Glycolysis and the citric acid cycle generate a small amount of ATP (10% of total) by substrate-level phosphorylation.
• Most ATP (90%) is generated by oxidative phosphorylation (by ATP synthase).

Overview of cellular respiration stages

• Glycolysis breaks down glucose into pyruvate
• The citric acid cycle converts pyruvate to acetyl-CoA, producing CO2
• Oxidative phosphorylation involving electron transport chain (ETC) leading to chemiosmosis and ATP synthesis

Energy transfer via the redox coenzymes NAD+ and FAD

• Cells release energy from organic compounds in the form of electrons
• Redox coenzymes NAD+ and FAD carry electrons
• Electrons released from oxidizing organic compounds are transferred to NAD+ and FAD, reducing them to NADH and FADH2, which then carry these electrons to ETC
• These electrons are then transferred to O2, resulting in the production of water.

Redox Coenzymes NAD and FAD

• NAD = Nicotinamide adenine dinucleotide
• FAD = Flavine adenine dinucleotide
• NADH and FADH2 are carriers of electrons to the electron transport chain

NAD and FAD: redox coenzymes

• Each electron is co-transferred with a proton (H+)
• Dehydrogenases remove these electrons, transferring them to NAD+ or FAD, converting them to NADH and FADH2; this process is used to transport electrons to the ETC.

Cellular Respiration Stages Summary

• Glycolysis
• Citric Acid Cycle
• Oxidative Phosphorylation

Cellular Respiration Localization

• Glycolysis: happens in the cytosol
• Krebs cycle: occurs in the mitochondrial matrix
• Oxidative phosphorylation: occurs in the inner mitochondrial membrane

Glycolysis

• Glycolysis is the splitting of sugar
• Breaks down glucose (6C) into 2 molecules of pyruvate (3C)
• Occurs in the cytosol
• Anaerobic stage (doesn't require oxygen)
• Products: 2 ATP, 2 NADH, 2 pyruvate molecules
• ATP is produced by substrate-level phosphorylation

Glycolysis: Two Major Phases

• Energy Investment Phase: requires ATP
• Energy Payoff Phase: produces ATP and NADH

Citric Acid Cycle (Krebs Cycle/TCA Cycle)

• Happens in the mitochondrial matrix
• Completes oxidation of organic molecules (e.g., CO2 and energy production)
• Converts pyruvate (a glycolysis product) into acetyl-CoA before beginning the citric acid cycle
• Acetyl-CoA is produced from glycolysis or beta-oxidation of fatty acids.
• Acetyl-CoA enters the Krebs cycle.

Pyruvate Conversion to Acetyl-CoA

• Pyruvate is converted to Acetyl CoA in the mitochondria, generating NADH and CO2
• This is a crucial step connecting glycolysis to the Citric Acid Cycle

Citric Acid Cycle (Krebs Cycle)

• Pyruvate is broken down into CO2
• Acetyl-CoA binds to oxaloacetate
• Citric acid is produced
• NADH and FADH2 are created and transferred to the ETC

Krebs cycle (Krebs Cycle/TCA Cycle)

• Krebs cycle products: Each acetyl-CoA that enters the cycle is converted into 2 CO2, 3 NADH, 1 FADH2, and 1 ATP
• Krebs cycle energy gain: 1 ATP, 3 NADH, 1 FADH2
• Net energy profit: 12 molecules of ATP from one Krebs cycle

Overview of the citric acid cycle

• 1 glucose molecule generates 2 pyruvates = 2 acetyl-CoA molecules
• One glucose molecule and 2 citric acid cycles produce:
  • 4 CO2, 2 ATP
  • 6 NADH
  • 2 FADH2

Oxidative Phosphorylation

• NADH and FADH2 donate electrons to the ETC
• ETC powers ATP synthesis
• Oxidative phosphorylation is coupled with chemiosmosis; this creates an H+ gradient across the inner mitochondrial membrane
• Chemiosmosis uses energy in the H+ gradient to form ATP

Electron Transport Chain (ETC)

• Electrons enter via NADH or FADH2
• 2 ways electrons enter ETC: NADH oxidation by complex I (NADH dehydrogenase), FADH2 oxidation through complex II (succinate dehydrogenase)
• Stepwise energy transfer
• Each electron carrier is more electronegative than the previous one, allowing for energy to be released gradually

Oxidative Phosphorylation: Electron Transport Chain

• Oxygen accepts ETC electrons, producing water
• ETC pumps H+ into the intermembrane space, creating an electrochemical gradient

Oxidative Phosphorylation: Chemiosmosis

• ETC causes H+ pumping to the intermembrane space, creating a H+ concentration gradient that generates a membrane potential.
• Chemiosmosis uses energy for H+ flow through ATP synthase, driving ATP synthesis within the mitochondrial matrix.

Oxidative Phosphorylation: ATP Production

• The H+ concentration is greater in the intermembrane space than the matrix.
• Chemiosmosis involves H+ flow down the gradient through ATP synthase
• ATP synthase uses energy from the H+ flow to produce ATP

Proton-motive force (PMF)

• A gradient of protons is created by the flow of electrons in the ETC.
• Drives chemiosmosis
• Stores energy => drives ATP production by ATP synthase, located in the inner mitochondrial membrane

Chemiosmosis: The Energy-Coupling Mechanism

• ATP synthase functions reversely as a pump running in reverse
• Each H+ flowing through ATP synthase causes 120° rotation
• Every 3 H+ flowing through ATP synthase results in the synthesis of 1 ATP molecule

ATP synthase (FoF1 ATPase)

• Enzyme responsible for synthesizing ATP from ADP and Pi
• Located in the inner mitochondrial membrane
• Found in mitochondria, chloroplasts, and bacteria
• A proton pump (H+) that uses proton gradient for ATP synthesis
• It has 2 parts: Fo(transmembrane), F1(matrix)
• Proton flow causes changes in binding affinity of ATP/ADP.

Anaerobic Respiration

• Cellular (aerobic) respiration produces large amounts of ATP in the presence of oxygen.
• Anaerobic respiration occurs in the absence of oxygen
• It utilizes an electron transport chain but with a different electron acceptor from oxygen (e.g., sulfate)

Fermentation

• An anaerobic respiration process:
• Uses phosphorylation instead of an electron transport chain to make ATP
• Two types are: alcohol fermentation (yeasts produce ethanol and CO2); lactic acid fermentation (animal cells produce lactic acid)

Anaerobic Cellular Respiration

• Produces less ATP compared to aerobic respiration (only 2 ATP molecules)
• Two phases include glycolysis and fermentation

Aerobic and Anaerobic Respiration

• Both start with glycolysis, breaking down glucose into pyruvate
• Different final products (organic compounds vs. water)
• Aerobic respiration yields significantly more ATP (38 ATP per glucose molecule) while anaerobic respiration (fermentation) produces a much lower yield (2 ATP per glucose molecule)

Comparison of Aerobic Respiration vs Anaerobic Respiration

• Obligate anaerobes: microorganisms that carry out fermentation or anaerobic respiration, and can't survive with oxygen.
• Facultative anaerobes: microorganisms that can survive in both the presence and absence of oxygen.

Catabolic Pathways Connection

• Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration.
• Glycolysis and the citric acid cycle connect to many other metabolic pathways.
• Excess amino acids from proteins, glycerol from fats, and fatty acids from fats enter different stages of cellular respiration (e.g., glycolysis, acetyl-CoA, citric acid cycle)

Anabolic Pathways: Biosynthesis

• The body uses ATP to synthesize other substances
• Small molecules from food or glycolysis/citric acid cycle are used for biosynthesis.

Regulation of Cellular Respiration

• Metabolism is tightly regulated by: supply and demand of intermediates, and energy status
• Cellular respiration is controlled by allosteric enzymes and feedback inhibition by ATP, among other mechanisms

Control of Cellular Respiration

• Phosphofructokinase (PFK) is a crucial control point in glycolysis
• It's an allosteric enzyme
• Inhibited by ATP and citrate
• Stimulated by AMP

Clinical Correlations

• Diseases linked to insufficient ATP synthesis are often severe (neuromuscular disorders, encephalopathy)
• Some diseases may arise from ATP synthase mutations
• Example include: Leigh syndrome, MELAS syndrome, and Leber's optic neuropathy.

Summary

• Mitochondria are crucial for cellular respiration.
• Cellular respiration has three stages: glycolysis, Krebs cycle, and oxidative phosphorylation
• Anaerobic respiration includes alcohol and lactic acid fermentation
• Aerobic vs anaerobic respiration yields different amounts of ATP

Videos (URLs Provided)

Glycolysis Animation (URLs Provided)

Oxidative Phosphorylation Animation (URLs Provided)

Test your understanding of cellular respiration processes, including the energy investment and payoff phases, as well as the roles of ATP and NAD+. This quiz covers key concepts, from glucose breakdown to the final products of aerobic respiration. Perfect for biology students looking to enhance their knowledge of metabolism.