Biology Chapter on Respiration

Respiration

• Process where energy stored in carbohydrates is released in a controlled manner
• Energy is used to synthesize ATP
• ATP is essential for plant cell maintenance, growth, and development

Aerobic Respiration

• Chemical Reaction: C6H12O6 + 6O2 + 6H2O → 6CO2 + 12H2O + energy (ATP)
• 1 mole of glucose yields 36 ATP

Efficiency of Aerobic Respiration

• Energy released from breaking an ADP-P bond is -7.6 kcal/mol ATP
• Theoretical energy yield of burning 1 mole of glucose is -686 kcal/mol
• Practical energy yield of burning 1 mole of glucose in the cell with oxygen is 36 ATP
• Efficiency: (274 kcal/mol glucose / 686 kcal/mol glucose) * 100 = 40%

Efficiency of Anaerobic Respiration

• Energy released from breaking an ADP-P bond is -7.6 kcal/mol ATP
• Theoretical energy yield of burning 1 mole of glucose is -686 kcal/mol
• Practical energy yield of burning 1 mole of glucose in the cell without oxygen is 2 ATP
• Efficiency: (15.2 kcal/mol glucose / 686 kcal/mol glucose) * 100 = 2.2%

3 Stages of Respiration

• Glycolysis
  • Occurs in the cytoplasm
  • Happens with or without oxygen
  • Breaks down glucose (6C) into 2 pyruvates (3C)
• TCA Cycle
  • Occurs in the mitochondrial matrix
  • Requires oxygen
  • Converts pyruvate via acetyl CoA into CO2, generates NADH and FADH2
• Electron Transport Chain
  • Occurs in the mitochondrial cristae
  • Transfers electrons from NADH and FADH2 to reduce O2 to H2O and generate ATP

Mitochondria

• Spherical to oval shape
• Approximately 1 micron in diameter
• Number of mitochondria per cell increases with respiration demand (300-1000/root tip cell)
• Double-membrane bound
  • Outer membrane is smooth
  • Inner membrane folds into cristae, controlling movement in and out of the organelle
  • Inner membrane is the site of electron transport

Glycolysis

• Found in all living organisms
• The only stage that can occur without oxygen
• Oldest stage of respiration, operating for billions of years in anaerobic organisms
• Converts glucose to 2 pyruvates in the cytosol
• With oxygen: pyruvate goes to the TCA cycle
• Without oxygen: pyruvate is converted to lactate or ethanol (fermentation)
• Yields 2 ATP/mole glucose in the absence of oxygen

Glycolysis Flowchart

Glucose (6C) 

2 Pyruvate (3C)
CO2     -O2            -O2
                +O2
Ethanol                        Lactate
                TCA Cycle

Chemiosmotic Theory (Peter Mitchell)

• The transport of protons from the matrix to the intermembrane space generates a proton gradient across the membrane.
• Protons accumulate in the intermembrane space, creating an electrochemical potential difference known as the proton motive force (PMF).
• This PMF drives ATP synthesis by the ATP synthase complex.

Inner Mitochondrial Membrane (IMM)

• IMM - Inner mitochondrial membrane
• IMS- Inter membrane space
• OMM- outer mitochondrial membrane

ATP Synthase

• Protein assembly in the inner mitochondrial membrane
• Uses the proton gradient to make ATP
• Protons are pumped through a channel on the enzyme from the intermembrane space into the matrix
• Approximately 4 H+ are required for every ATP produced

NADH and FADH2

• NADH yields 2.5 (3) ATP molecules
• FADH2 yields 1.5 (2) ATP molecules

ATP Synthase Units

• F1
  • Projects into the matrix
  • Contains 3 α, 3 β, gamma, delta, and epsilon chains
  • Catalyzes ATP synthesis
  • Peripheral catalytic sites are present on the beta subunits.
• Fo
  • Embedded in the membrane
  • Acts as a channel for transport of H+

ATP Production

• ADP + Pi → ATP
• 34 H+ are required to produce one ATP molecule (34 protons are pumped from the intermembrane space to the matrix)

Alternate Fates of Glucose Carbon (C)

• Not all carbon from glucose is respired to CO2
• Intermediates of respiration branch off to synthesize:
  • Amino acids
  • Pentoses for cell wall structure
  • Nucleotides
  • Porphyrin biosynthesis
  • Fatty acid synthesis
  • Lignin precursors
  • Precursors for carotenoid synthesis, hormones

Factors Affecting Respiration Rate

• Substrate concentration
• ATP concentration
• Oxygen concentration
• Temperature
• Plant type
• Plant organ
• Plant age