Chapter 9: Cellular Respiration

Main Structures of the Mitochondria Relevant to Respiration

The mitochondrion is the primary site of cellular respiration in eukaryotic cells. Its structure is specialized to maximize ATP production.

• Outer Membrane: Serves as a barrier between the cytosol and the inner environment of the mitochondrion.

• Inner Membrane: Contains proteins for the electron transport chain and ATP synthase; highly folded into cristae to increase surface area.

• Matrix: The innermost compartment where the citric acid cycle (Krebs cycle) occurs.

• Intermembrane Space: Space between the inner and outer membranes; important for proton gradient formation.

Difference Between Aerobic and Anaerobic Respiration

Respiration can occur with or without oxygen, leading to different pathways and products.

• Aerobic Respiration: Requires oxygen; produces a large amount of ATP, water, and carbon dioxide.

• Anaerobic Respiration: Occurs without oxygen; produces less ATP and byproducts such as lactic acid (in animals) or ethanol (in yeast).

Fermentation

Fermentation is an anaerobic process that allows glycolysis to continue by regenerating NAD+.

• Occurs: When oxygen is not available.

• Products: Lactic acid (in muscle cells), ethanol and CO2 (in yeast).

Equations for Photosynthesis and Cellular Respiration

• Cellular Respiration:

• Photosynthesis:

What ATP is Used for in the Cell

ATP (adenosine triphosphate) is the main energy currency of the cell, used for:

• Active transport of molecules across membranes

• Muscle contraction

• Biosynthesis of macromolecules

• Cell signaling

Substrate-Level Phosphorylation and Oxidative Phosphorylation

• Substrate-Level Phosphorylation: Direct transfer of a phosphate group to ADP from a phosphorylated intermediate; occurs in glycolysis and the citric acid cycle.

• Oxidative Phosphorylation: ATP is produced using energy derived from the electron transport chain and chemiosmosis; occurs in the mitochondria.

Stages of the Complete Oxidation of Glucose

1. Glycolysis

2. Pyruvate Processing

3. Citric Acid Cycle (Krebs Cycle)

4. Electron Transport Chain and Chemiosmosis

Steps of Glycolysis

Glycolysis is the breakdown of glucose into pyruvate, producing ATP and NADH.

• Occurs in the cytoplasm

• Key steps involve phosphorylation, cleavage, and oxidation of glucose

• Net products: 2 ATP, 2 NADH, 2 pyruvate per glucose molecule

Net ATP Produced in Glycolysis vs. Total ATP Produced

• Glycolysis: Net gain of 2 ATP per glucose

• Total Cellular Respiration: Up to 30-32 ATP per glucose (including glycolysis, citric acid cycle, and oxidative phosphorylation)

Main Events of the Citric Acid Cycle

• Acetyl-CoA combines with oxaloacetate to form citrate

• Series of enzyme-catalyzed reactions regenerate oxaloacetate

• Produces 2 CO2, 3 NADH, 1 FADH2, and 1 ATP (or GTP) per acetyl-CoA

Electron Transport Chain (ETC) and Chemiosmosis

The ETC is a series of protein complexes in the inner mitochondrial membrane that transfer electrons and pump protons to create a proton gradient.

• Electrons from NADH and FADH2 pass through complexes I-IV

• Protons are pumped into the intermembrane space, creating an electrochemical gradient

• ATP synthase uses this gradient to synthesize ATP from ADP and Pi (chemiosmosis)

In-Class Activity on Inhibitors of Oxidative Phosphorylation

• Inhibitors can block electron flow or ATP synthase, reducing or stopping ATP production

• Examples: Cyanide (blocks complex IV), oligomycin (blocks ATP synthase)

Theoretical vs. Actual Energy Yields for Respiration

• Theoretical Yield: Maximum possible ATP (about 38 per glucose in prokaryotes, 30-32 in eukaryotes)

• Actual Yield: Lower due to leaky membranes, use of proton gradient for other processes, and transport costs

Regulation of Glycolysis, Pyruvate Processing, and the Citric Acid Cycle

• Key enzymes are regulated by feedback inhibition and allosteric control

• Example: Phosphofructokinase is inhibited by high levels of ATP

Example: Phosphofructokinase is an allosteric enzyme that catalyzes the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate in glycolysis. In the presence of oxygen, an increase in ATP inhibits the enzyme, slowing glycolysis and the citric acid cycle.

Chapter 10: Photosynthesis

Difference Between Heterotroph and Autotroph

• Heterotrophs: Obtain organic molecules by consuming other organisms (e.g., animals, fungi)

• Autotrophs: Produce their own organic molecules from inorganic sources (e.g., plants, algae)

Main Structures of the Chloroplast Relevant to Photosynthesis

• Outer and Inner Membranes: Enclose the chloroplast

• Thylakoid Membranes: Site of the light-dependent reactions; contain chlorophyll

• Stroma: Fluid surrounding thylakoids; site of the Calvin cycle (light-independent reactions)

Pigments Involved in Photosynthesis

• Chlorophyll a: Main pigment; absorbs blue-violet and red light

• Chlorophyll b: Accessory pigment; broadens the spectrum of absorbed light

• Carotenoids: Accessory pigments; protect against photo-damage

The Two Photosystems and Their Components

• Photosystem II (PSII): Absorbs light, splits water, and generates ATP

• Photosystem I (PSI): Absorbs light and generates NADPH

• Each photosystem contains a reaction center and light-harvesting complexes

Main Steps of the Light-Dependent Reaction

• Occurs in the thylakoid membrane

• Light energy excites electrons in chlorophyll

• Water is split, releasing O2

• Electron transport chain produces ATP (via chemiosmosis) and NADPH

Main Steps of the Light-Independent Reaction (Calvin Cycle)

• Occurs in the stroma

• Uses ATP and NADPH to fix CO2 into glucose

• Key steps: carbon fixation, reduction, regeneration of RuBP

Chemiosmosis and Its Role in Photosynthesis

• Proton gradient is established across the thylakoid membrane

• ATP synthase uses the gradient to produce ATP

In-Class Activity on Herbicides

• Herbicides can inhibit photosynthetic electron transport, affecting plant growth

Sample Question: Location of ATP Synthase Complexes in Plant Cells

In a plant cell, ATP synthase complexes are located in:

Correct Answer: D) Thylakoid membrane and inner mitochondrial membrane