General Biology 1: Cellular Respiration

• General Biology 1 is a specialized subject at NU Nazareth School Senior High School.

Learning Competencies (Week 11-12):

• Explain the major features and sequence the chemical events of cellular respiration.
• Distinguish the main features of glycolysis, the Krebs cycle, the electron transport system, and chemiosmosis.
• Describe the reactions that produce and consume ATP.
• Describe the role of oxygen in respiration and electron flow pathways in oxygen's absence.
• Explain the advantages and disadvantages of fermentation and aerobic respiration.

Cellular Respiration Overview:

• Cellular respiration uses glucose to produce energy in the form of ATP.
• The summarized equation is C6H12O6 + 6O2 → 6CO₂ + 6H2O + 36ATP (where C6H12O6 is glucose).
• Cellular respiration can be aerobic (using oxygen) or anaerobic (without oxygen).

Muscle Cramps and Hypoxia:

• Muscle cramps are involuntarily and forcibly contracted muscles that don't relax.
• Hypoxia is an inadequate amount of oxygen in body tissue cells, blood, or breathable air; it's typically below normal levels.
• Muscle cells deprived of oxygen resort to anaerobic metabolism.
• Lactic acid, an acid, is produced when cells produce their own oxygen, causes cramps

Aerobic vs. Anaerobic Respiration:

• Aerobic cellular respiration uses oxygen, with glucose and oxygen as reactants to produce ATP, carbon dioxide, and water.
• Anaerobic cellular respiration (fermentation) generates energy by breaking down sugars without oxygen.
• Examples of fermentation include alcohol fermentation and lactic acid fermentation.

Stages of Aerobic Cellular Respiration:

• There are three stages of aerobic cellular respiration:
• Glycolysis (in the cytosol): It includes substrate-level phosphorylation.
• Krebs Cycle (in the mitochondrial matrix): It includes substrate-level phosphorylation.
• Electron Transport Chain (ETC) (in the inner mitochondrial membrane): It uses oxidative phosphorylation.

Glycolysis

• Glycolysis, the breakdown of glucose, splits a glucose molecule into two 3-carbon pyruvate molecules.
• Enzymes extract potential energy from glucose.
• As a result, the process yields two ATP molecules and two NADH molecules.
• The two steps of Glycolysis, which include an energy investment and extraction step

Glycolysis Step 1: Energy Investment:

• A phosphate is transferred from ATP to glucose.
• A second phosphate is transferred from ATP.
• The 6-carbon molecule splits into two 3-carbon molecules.

Glycolysis Step 2: Energy Extraction:

• A phosphate group is added and NADH is produced.
• ATP is produced.
• Pyruvate is the final product.

Glycolysis Summary:

• Products include two ATP molecules (used by the cell), two NADH (going to ETC), and two pyruvates (entering the Krebs cycle).

Before Krebs Cycle:

• Before the Krebs Cycle, two Pyruvates undergo a transformation to form 2 Acetyl-CoA.
• It enters the following inputs: Two pyruvate molecules, two NAD+, and two Coenzyme A molecules.
• Its outputs include two NADH molecules, two Acetyl CoA molecules, and two carbon dioxide molecules as a byproduct.

Krebs Cycle (Citric Acid Cycle) Summary:

• Two Acetyl CoA molecules are oxidized and interact with 2 ADP, 2 P+, 6 NAD+, and 2 FAD.
• The reaction yields 2 ATP, 6 NADH (+ 2 NADH before Krebs) = 8 NADH, 2 FADH2, and 4 CO2

Krebs Cycle Step 1:

• 2 Acetyl CoA combines with a 4-carbon molecule called oxaloacetate to produce citric acid/citrate.

Krebs Cycle Step 2:

• Citric Acid/Citrate molecules interact with an enzyme to form isocitrate.
• Isocitrate interacts with 2 NAD+, yielding a-ketoglutarate, NADH, and H+

Krebs Cycle Step 3:

• A-ketoglutarate interacts with another enzyme, along with NAD+ and CoASH.
• Succinyl-CoA, NADH, H+, CO2 are produced.

Krebs Cycle Step 4:

• Succinyl-CoA interacts with an enzyme ADP+Pᵢ, and CoASH.
• Succinate, ATP and COASH are produced.

Krebs Cycle Step 5:

• Succinate gets oxidized by FAD to produce Fumarate.
• Oxidation's byproduct is FADH2.

Krebs Cycle Step 6:

• Fumarate interacts with a H₂O and undergoes hydration, producing Malate.

Krebs Cycle Step 7:

• Malate then interacts with an enzyme and NAD+.
• As a result, the cycle goes back to oxaloacetate and NADH is produced.

Krebs Cycle: Overall Summary:

• Glycolysis results in input of 2 NAD+ & 2 ADP, and extraction of 2 NADH & 2 ATP.
• Acetyl CoA formation results in input of 2 NAD+, and extraction of 2 NADH
• Krebs cycle results in input of 6 NAD+ & 2 FAD, and extraction of 6 NADH & 2 FADH₂
• So far, aerobic respiration of one glucose molecule yielded four ATP.

Electron Transport Chain (ETC):

• NADH and FADH2 donate electrons to the electron transport chain.
• Energy released from the electrons is used for ATP production.
• Carrier molecules transport hydrogen ions into the intermembrane compartment.
• Electrons get donated to an oxygen atom, which bonds with hydrogens to form water.
• Hydrogen ions flow down their concentration gradient from the intermembrane compartment to the matrix through ATP synthase, making ATP.
• 32 ATP are produced by the electron transport chain.

Explore the chemical events of cellular respiration, including glycolysis, the Krebs cycle, and the electron transport system. Understand ATP production and consumption, the role of oxygen, and the differences between fermentation and aerobic respiration. Learn about muscle cramps and hypoxia in relation to cellular energy.