Cellular Respiration: Glycolysis, Krebs Cycle & more

• This lesson is about cellular respiration.
• It discusses mitochondria and aerobic and anaerobic respiration.
• It also discusses the stages of cellular respiration.
• At the end of this lesson, the student should be able to:
• Discuss the structure and role of mitochondria in the process of respiration.
• Differentiate aerobic from anaerobic respiration.
• Differentiate basic features and importance of photosynthesis and cellular respiration.
• Enumerate and describe the stages/processes of cell respiration such as glycolysis, transition reaction, Krebs cycle, electron transport chain and chemiosmosis.
• Determine the number of ATP molecules needed and yielded in each stage of cellular respiration.
• Differentiate lactic acid and alcohol fermentation.
• Key topics to read and study include:
• ATP
• Mitochondria
• Glycolysis
• Krebs Cycle
• Electron transport chain
• Kinds of anaerobic respiration

Mitochondria

• The "powerhouse of the cell".
• The site of cellular respiration.
• Starts in the cytoplasm and is completed in the mitochondria.
• Parts"
• Outer membrane
• Intermembrane space
• Inner membrane
• Cristae – folds of inner membrane
• Matrix – oxidative enzyme

ATP

• Forms of energy: Light, mechanical, thermal, and chemical.
• Chemical energy stored in biomolecules that converted to other forms of energy.
• ATP is a nucleotide made up of adenine, ribose, and 3 phosphate groups.
• The bond between the phosphate group is a high energy bond.

Cell Respiration

• A catabolic set of processes that breaks down organic molecules and converts into chemical energy in the form of ATP.
• Uses electron carriers NADH and FADH2 to form ATP.
• Occurs in 2 main parts.
• Anaerobic respiration occurs in the absence of oxygen; Glycolysis.
• Aerobic respiration occurs in the presence of oxygen; Krebs Cycle.
• Chemical equation: C6H12O6 + 6O2 -> 6 CO2 + 6H2O + ATP

Photosynthesis and Cellular Respiration

• Balanced Equation for photosynthesis is 6 CO2 + 6 H2O --> C6H12O6 + 6 O2. Cellular Respiration is C6H12O6 + 6 O2 --> 6 CO2 + 6 H2O + ATP
• Cell organelle is Chloroplast for photosynthesis, and mitochondria for cellular respiration.
• Raw materials are light, CO2 and H2O for photosynthesis, and glucose and O2 for cellular respiration.
• Main products are C6H12O6 (Glucose) for photosynthesis, and ATP for cellular respiration.
• Source of energy is light energy for photosynthesis, and organic molecules (glucose) for cellular respiration.
• Energy is stored for photosynthesis, and energy is released for cellular respiration.

Stages of Cell Respiration

• Glycolysis - occurs in cytoplasm.
• Pyruvate oxidation/transition reaction – occurs in matrix.
• Krebs Cycle – occurs in matrix.
• Electron transport chain – occurs in cristae.

Glycolysis

• "Sugar splitting"
• Occurs in cytoplasm
• Step 1: Energy investment
• Using 2 ATP, 1 molecule of Glucose becomes 2 molecules of G3P.
• Step 2: Energy Harvesting
• 2 molecules of G3P becomes 2 molecules of Pyruvate.
• It produces 4 ATP and 2 NADH
• Total products:
• 4 ATP and 2 NADH
• Net products:
• 2 ATP, 2 NADH, and 2 molecules of Pyruvate

Transition Reaction

• The carboxyl group is removed and produces carbon dioxide
• Remaining carbon molecules oxidized and give off electrons.
• Electrons picked up by NAD+ to form NADH.
• Oxidized carbon molecules will be attached to Coenzyme A and forms Acetyl CoA.
• Products
• 2 Acetyl CoA
• 2 CO2
• 2 NADH

Krebs Cycle

• Also known as citric acid cycle or Tricarboxylic acid cycle.
• Occurs in matrix.
• Hans Adolf Krebs
• Step 1: Acetyl CoA + Oxaloacetate = Citric acid
• Step 2: Citric acid Alpha-ketoglutarate and (2 CO2 and 2 NADH)
• Step 3: Alpha-ketoglutarate Succinate (and 2 ATP, 2 NADH & 2 CO2
• Step 4: Succinate - Oxaloacetate (and 2 FADH2_& 2 NADH)

Oxidative Phosphorylation

• Occurs in Cristae
• Stage at which most ATP is produced, in 3 Steps.
• Step 1: Electron Transport
• Electron carriers, NADH and FADH2, release elections.
• The released electrons travel along the proteins of Electron transport chain.
• NADH = 3ATP and FADH2 = 2 ATP
• Electrons accepted by oxygen atoms, forming water.
• Step 2: Proton Pump
• The energy of traveling electrons is used to "pump protons."
• This pump moves H+ into the intermembrane space of mitochondria.
• It creates concentration gradient.
• Step 3: Chemiosmosis
  • H+ naturally moves from the intermembrane space to the matrix through ATP synthase.
  • ATP synthase rotates and forms ATP.

Total ATP yield per glucose

• Glycolysis: 2 ATP and 2 NADH (=4/6 ATP)
• Pyruvate Oxidation: 2 NADH = 6 ATP
• Krebs Cycle: 2 ATP, 6 NADH (= 18 ATP) and 2 FADH2 (= 4 ATP)
• Electron transport Chain (Oxidative phosphorylation): TOTAL: 36-38 ATP
• In eukaryotic cells, the theoretical maximum yield of ATP generated per glucose 36 to 38 which varies on how the 2 NADH from glycolysis enter the mitochondria and whether the resulting yield is 2 or 3 ATP per NADH.