Cellular Bioenergetics Overview

Pyruvate Fermentation Products

• Pyruvate fermentation in human muscle produces lactate.
• In yeast and bacteria, pyruvate fermentation results in ethanol.

Pyruvate Metabolism

• Pyruvate is converted to acetyl CoA during aerobic oxidation.

Anaerobic Reduction of Pyruvate

• Reactants for lactic acid fermentation: NADH and pyruvate.
• Products for lactic acid fermentation: lactate and NAD+.

Photosynthesis and Cellular Respiration

• Photosynthesis occurs within specific structures (labeled H).
• Molecules in spaces A and B include glucose and oxygen, produced by photosynthesis.
• Mitochondria (indicated by letter C) are the cellular respiration sites.
• Carbon dioxide and water are by-products of cellular respiration, found in spaces E and F.

Glycolysis Overview

• Glycolysis takes place in the cytosol and converts glucose to 2 pyruvates.
• ATP is produced through substrate-level phosphorylation during glycolysis.
• Glycolysis yields a net gain of 2 ATP and generates 2 NADH.

Importance of NAD+

• Upon gaining a hydrogen atom, NAD+ is reduced to NADH.
• The electron donor in glycolysis is glucose, which is oxidized to pyruvate.

Citric Acid Cycle Insights

• Acetyl CoA enters the citric acid cycle, where it is oxidized to CO2.
• The cycle produces ATP, NADH, and FADH2, but not acetyl CoA.
• Substrate-level phosphorylation in the citric acid cycle also generates ATP.

Oxidative Phosphorylation

• The most ATP (about 26 molecules) is produced in the electron transport chain and chemiosmosis.
• Oxygen serves as the final electron acceptor, forming water when combined with electrons and hydrogen.
• NADH and FADH2 donate electrons to the electron transport chain, creating a proton gradient used for ATP synthesis.

Role of Cellular Respiration Components

• Glycolysis and citric acid cycle produce intermediates for further energy extraction in oxidative phosphorylation.
• The proton gradient generated by the electron transport chain drives ATP synthase to phosphorylate ADP into ATP.

Mitochondrial Processes

• Glycolysis occurs in the cytosol, while acetyl CoA formation and the citric acid cycle occur in the mitochondrial matrix.
• Oxidative phosphorylation takes place in the inner mitochondrial membrane, where electron transport and ATP synthesis occur.
• A decrease or absence of oxygen halts electron transport and ATP production.

ATP Yield Sources

• Each glucose molecule produces two acetyl CoA, leading to 6 NADH from the citric acid cycle.
• Oxidative phosphorylation is the main contributor to ATP production, requiring NAD+, ADP, and O2.

Importance of NADH vs. FADH2

• More ATP is synthesized from NADH compared to FADH2 due to the point of entry in the electron transport chain; NADH enters at Complex I while FADH2 enters at Complex II, resulting in fewer protons being pumped.

Effects of Gramicidin

• If gramicidin is added, it affects proton permeability, likely disrupting proton pumping and ATP synthesis in oxidative phosphorylation, without influencing NADH and FADH2 production from earlier processes.### Proton Gradient and ATP Synthesis
• Proton pumping rate, electron transport rate, and oxygen uptake remain constant with gramicidin's effect.
• Gramicidin increases membrane permeability, disrupting the proton gradient and halting ATP synthesis.
• Leakiness of the membrane does not affect the efficiency of electron transport.

Fermentation in Muscle Cells

• Fermentation produces lactate and NAD+ in muscle cells.
• Pyruvate is reduced to lactate or ethanol, while NADH is oxidized back to NAD+ during fermentation.

Coupling in Cellular Respiration

• Cellular respiration stages are interconnected; outputs of one stage serve as inputs for others.
• NAD+ and NADH play crucial roles in this coupling, with NAD+ accepting electrons during glucose oxidation.
• NADH generated in earlier stages is oxidized during oxidative phosphorylation to regenerate NAD+.

Anaerobic Conditions and Pyruvate Conversion

• Lack of oxygen halts the conversion of pyruvate to acetyl CoA due to stopped electron transport.
• Without NAD+ regeneration, essential for glycolysis, the oxidative phosphorylation process ceases.

Regulation of Cellular Respiration

• ATP acts as a feedback inhibitor for phosphofructokinase (PFK), impacting glycolysis and ATP production.
• Increased ATP demand leads to initial drops in ATP levels, decreasing PFK inhibition, thus enhancing glucose utilization and ATP production.

Importance of Glycolysis and Fermentation

• Under anaerobic conditions, glycolysis persists while oxidative phosphorylation halts, relying on fermentation.
• Fermentation leads to a net gain of 2 ATP per glucose; to meet ATP needs under anaerobic conditions, glucose utilization must increase significantly.

Electron Transport Chain Function

• Energy from NADH and FADH2 is harnessed to pump hydrogen ions into the intermembrane space during electron transport.
• This process contributes to establishing a proton gradient necessary for ATP synthesis.

ATP Synthase Role

• ATP synthase phosphorylates ADP to produce ATP, functioning as the primary enzyme in ATP generation.

Acetyl CoA Production

• Each glucose molecule entering glycolysis results in the formation of two acetyl CoA for the citric acid cycle.

Energy Currency in Cells

• Glucose is primarily metabolized for energy in the form of ATP within cells.

Potential Energy in ATP

• The energy potential of ATP molecules originates from their three phosphate groups, facilitating cellular energy transfer.

ATP Production in the Citric Acid Cycle

• ATP molecules are generated through substrate-level phosphorylation when a phosphate group is transferred from GTP to ADP during the citric acid cycle.

Citric Acid Cycle Products

• The citric acid cycle yields products such as ATP, FADH2, and NADH, but acetyl CoA is not a product of this cycle.