Bioenergetics and ATP Production

Bioenergetics

• Bioenergetics is the transfer and utilization of energy in biological systems.
• Bioenergetics predicts if a process is possible, while kinetics measures the reaction rate.
• Enzymes cannot make a reaction happen by themselves. They speed up reactions by lowering activation energy.

Bioenergetics (cont'd)

• Change in free energy (ΔG) is a measure of spontaneity.
  • ΔG < 0 (negative): The reaction is spontaneous (exergonic).
  • ΔG > 0 (positive): The reaction requires energy input (endergonic).
  • ΔG = 0: The reaction is at equilibrium.
• Enzymes do not change ΔG but help reactions happen under conditions which otherwise would not occur.

ATP Production

• Substrate-level phosphorylation is a metabolic reaction that results in the production of ATP.

• During an enzymatic reaction, a phosphate group is transferred to ADP creating ATP.

• Oxidative phosphorylation is a process that produces a large amount of ATP.

• Electrons from NADH and FADH2 travel through the ETC and the energy from this process is used to pump H+ ions across the membrane to make ATP.

Carbohydrate Metabolism

• Carbohydrates are used to store energy in the form of glycogen (animals) and starch (plants).
• Glycolysis breaks down glucose to pyruvate producing ATP and NADH.
• Gluconeogenesis creates glucose from other sources like amino acids, fatty acids (not glucose).
• Glycogenesis is the synthesis of glycogen from glucose.
• Glycogenolysis is the breakdown of glycogen into glucose.
• Pentose Phosphate Pathway produces NADPH and Ribose 5- Phosphate.

Glycolysis:

• Glycolysis is the breakdown of glucose into pyruvate.
• Glycolysis has two main stages, energy investment and energy harvest. In the energy investment stage, 2 ATP are spent while in the energy harvest stage, 4 ATP are formed; resulting in a net gain of 2 ATP.
• Glycolysis intermediate products can be used in biosynthesis processes.
• Glycolysis has three regulatory steps.

TCA Cycle

• The TCA cycle (or citric acid cycle) is a crucial metabolic pathway.
• It's an aerobic pathway, meaning it requires oxygen to proceed.
• The TCA cycle mainly harvests high-energy electrons from carbon fuels, producing ATP and precursors needed for different biosynthetic processes.

Oxidative Phosphorylation and ETC

• In oxidative phosphorylation, electrons from NADH and FADH2 are used to create ATP.
• The ETC uses energy from these electrons to pump H+ ions, creating a gradient that drives ATP synthesis.

Electron Transport Chain

• Electrons from NADH and FADH2 are transported along a chain of protein complexes in the mitochondrion.
• During this process, protons (H+) are pumped across the inner mitochondrial membrane, generating a proton gradient.
• The energy of the proton gradient is used to synthesize ATP.

Glycogen

• Glycogen is a branched polysaccharide used by animals for glucose storage.
• Skeletal muscle uses glycogen for local and rapid ATP demand.
• Liver's glycogen helps maintain blood glucose levels.

Glycogen Metabolism

• Glycogen synthesis involves activating glucose 1-phosphate with UTP(UDP).
• Glycogen degradation involves cleaving glucose 1-phosphate molecules from the end of glycogen chains.
• One molecule of free glucose is available from branching points.

Pentose Phosphate Pathway

• The pentose phosphate pathway produces NADPH and Ribose 5-Phosphate.
• Ribose 5-phosphate is used for nucleotide and nucleic acid synthesis.
• This pathway also provides intermediates for glycolysis.
• The oxidative reactions produce NADPH and eventually CO2.
• Non-oxidative reactions take this intermediate and go back towards glycolytic intermediates or other sugars.
• The net result is a balance of intermediates which can be converted to other molecules as needed.

Gluconeogenesis

• Gluconeogenesis synthesizes glucose from non-carbohydrate precursors (e.g., pyruvate, lactate and glycerol).
• It's the reverse of glycolysis. It bypasses irreversible steps in glycolysis with unique enzymes.

Transfer of Cytoplasmic NADH to Mitochondria

• Some NADH molecules are located outside the mitochondria, but they cannot enter directly into the mitochondrial matrix.
• Special shuttles, namely the malate-aspartate and glycerol 3-phosphate shuttle, are designed to move electrons (and energy) from NADH across the inner membrane to eventually contribute to ATP production in the mitochondria.

Test your understanding of bioenergetics, the transfer and utilization of energy in biological systems. This quiz covers key concepts such as free energy change, enzyme functions, and ATP production through substrate-level and oxidative phosphorylation. Assess your knowledge of these fundamental biochemical processes.