Chapter 7: Cellular Respiration

• Cellular Respiration


  The process by which cells break down glucose into carbon dioxide and water, releasing energy
• Cellular Respiration


  1. Balanced Chemical Equation: C6H12O6(s) + O2(g) → CO2(g) + H2O(l) + energy

  2. Word Chemical Equation: Glucose + oxygen → carbon dioxide + water + energy
• Once a plant produces glucose through photosynthesis, it can either be used right away, stored, transported to cells, or used to make molecules that can store long-term energy
• Animal and fungal cells join glucose molecules from their food to form a storage compound called glycogen
• Intermediate products used by cells

  • NADH
  • FADH2
  • ATP
• ATP (Adenosine triphosphate)


  A molecule containing three high-energy phosphate bonds that act as the primary energy-transferring molecule in living organisms
• ATP formation


  1. Formed by the addition of an inorganic phosphate group (PO43- or Pi) to a molecule of lower-energy ADP

  2. When ATP loses a phosphate group, it forms ADP and releases energy which is used for cellular processes
• ADP (adenosine diphosphate)


  A molecule containing two high-energy phosphate bonds that may be formed by breaking one of the phosphate bonds in ATP
• Electron Carrier Molecules: NADH, NAD+, FADH2, FAD+


  • Functions like NADPH in photosynthesis, and transfer electrons through redox reactions
  • When the electron transport chains transfer electrons between molecules, energy is released at each step, which can be used to form ATP (forms when a phosphate group attaches to ADP)
• NADH


  • An electron carrier, DONATES H+ and electrons in cellular processes
  • Reduced form of NAD+
  • Its Oxidation process: NADH → NAD+ + H+ + 2e-
• NAD+ (nicotinamide adenine dinucleotide)


  • An electron carrier, ACCEPTS H+ and electrons in cellular processes
  • Its Reduction process: NAD+ + H+ + 2e- → NADH
• FADH2


  • An electron carrier, DONATES H+ and electrons in cellular processes
  • Reduced form of FAD+
  • Its Oxidation process: FADH2 → FAD + 2H+ + 2e-
• FAD+ (flavin adenine dinucleotide)


  • An electron carrier, ACCEPTS H+ and electrons in cellular processes
  • Its reduction process: FAD + 2H+ + 2e- → FADH2
• Functions Require ATP: Motion


  1. ATP makes specialized muscle fibres in cells to contract, causing movement

  2. Examples: Chromosome movements, Cytoplasmic streaming, beating of cilia and flagella
• Functions Require ATP: Transport of Ions + Molecules


  1. ATP Powers active transport

  2. Active Transport: the movement of substances through a membrane against a concentration gradient using a membrane-bound carrier protein and energy from ATP

  3. Examples: Sodium-Potassium pump, Hydrogen ion pump (Carrier proteins are called pumps)
• Functions Require ATP: Building Molecules

  1. ATP Provides energy for molecule building

  2. Examples: Making proteins from amino acids, Building DNA in DNA replication
• Functions Require ATP: Switching Reactions On/Off


  1. ATP Changes a molecule's shape, changing its function too

  2. Example: This switches enzymes on and off to maintain equilibrium, which is important for digestion and metabolism
• Functions Require ATP: Bioluminsescence


  1. ATP Reacts with a molecule called luciferin and O2

  2. Example: Produces light for fireflies
• ATP and Glucose


  • All cells use ATP energy to meet their energy demands, but ATP is not abundant in food and only provides a small amount of energy per molecule
  • Molecules with higher energy content (i.e. glucose) are useful for long term chemical energy storage
• ATP as Money Analogy

  • A cell is a factory where all operations are performed by vending machines that only take $1
  • To perform a task (or cellular action), one or more coins must be inserted into the vending machine
  • ATP molecule is $1 coin and Glucose is a $100 bill
  • A glucose molecule has about 100 times more energy than one ATP molecule
  • The $100 must be exchanged for $1 coins to be used
  • Glucose must be converted into the energy of many ATP molecules to perform cellular activities
• Glucose is relatively small and highly soluble so it is ideal for transportation within and between cells and throughout the body
• Cellular respiration fundamentally transfers the energy content of food molecules into the energy content of ATP
• Since glucose has a large energy content, a single molecule can be used to form many lower-energy molecules
• Efficiency of Cellular Respiration


  • At best, about 36% of the energy content of one glucose molecule is converted into ATP energy while the remaining 64% is lost to heat energy
  • Cellular respiration involves many complex chemical pathways within cells
  • Warm-blooded organisms need to use this heat to maintain a constant body temperature
• Aerobic Cellular Respiration


  • The set of reactions that takes place in the cell in the presence of oxygen and releases energy stored in glucose
  • Requires Oxygen and involves the complete oxidation of glucose
  • Only four stages: Glycolysis, Pyruvate Oxidation, The Krebs Cycle, Electron Transport Chain and Chemiosmosis
  • Final products: Carbon dioxide, water, and 36 ATP molecules
  • Balanced Chemical Equation: C6H12O6 + 6O2 + 36 ADP + 36 Pi → 6CO2 + 6H2O + 36 ATP
  • Word Chemical Equation: Glucose + Oxygen + ADP + Inorganic Phosphate → Carbon Dioxide + Water + ATP
  • Produces more ATP molecules than anaerobic respiration
• Anaerobic Cellular Respiration


  • The set of reactions that takes place in the cell in the absence of oxygen and releases energy stored in glucose
  • Takes place when oxygen is absent and glucose is not fully oxidized
  • Takes place in the cytoplasm of the cell
  • Only two stages: Glycolysis and Fermentation
  • Two main types: Alcoholic fermentation and Lactic acid fermentation
• Alcoholic fermentation


  1. Balanced Chemical Equation: C6H12O6 + 2 ADP + 2 Pi → 2 C2H5OH + 2 CO2 + 2 ATP

  2. Word Chemical Equation: Glucose + ADP + Inorganic Phosphate → Ethanol + Carbon Dioxide + ATP
• Lactic acid fermentation


  1. Balanced Chemical Equation: C6H12O6 + 2 ADP + 2 Pi → 2 C3H6O3 + 2 ATP

  2. Word Chemical Equation: Glucose + ADP + Inorganic Phosphate → Lactic Acid + ATP
• Glycolysis


  A process for harnessing energy in which a glucose molecule is broken into two pyruvate molecules in the cytoplasm of a cell
• Glycolysis

  Means "splitting of sugar"
• Aerobic and Anaerobic cellular respiration begins with glycolysis
• Glycolysis is technically an anaerobic process since it does not require oxygen
• Glycolysis

  An inefficient form of energy production since only small amounts of ATP are produced
• Glucose contains 6 carbon atoms (C6H12O6); in glycolysis, it's split into 2 pyruvate molecules (C3H4O3)
• Glycolysis


  1. 2 ATP molecules are used up (activation energy) to start the process

  2. 4 ATP molecules are produced (net gain of 2 ATP molecules)
• Glycolysis also includes 2 NAD+, and 2 H+ ions
• Glycolysis only transfers about 2.2% of available energy in glucose to ATP, the rest of the energy being trapped in the pyruvate molecules and NADH
• Net equation for glycolysis

  1 glucose + 2 ADP + 2 Pi + 2 NAD+ → 2 pyruvate + 2 ATP + 2 NADH + 2H+
• Some single-celled organisms use glycolysis but multicellular organisms can't rely on glycolysis alone
• When oxygen is present, pyruvate will be transported to the mitochondria for pyruvate oxidation