BIOS3010 - week 31 Energy metabolism

Introduction

Good afternoon, everyone! Today's session will cover energy metabolism and its significance to biological functions and daily activities.

Overview of Metabolism

Metabolism is an umbrella term that encompasses all chemical reactions within organisms involving energy transfer, which is essential for sustaining life. It is divided into two primary categories:

• Catabolism: The process of breaking down larger, complex molecules into smaller, simpler ones to release energy. This stage includes the degradation of nutrients, such as carbohydrates, fats, and proteins, which provides the energy required for various biological functions.

• Anabolism: This involves the building of complex molecules from simpler ones, requiring energy input. It encompasses processes like protein synthesis, DNA replication, and the synthesis of cellular components necessary for growth and repair.

Key topics today:

• The energy currency of cells, ATP (Adenosine Triphosphate)

• Mechanisms for energy generation in the body

ATP (Adenosine Triphosphate)

ATP: The Energy Currency

ATP Structure:

ATP is a nucleotide composed of three fundamental parts: adenine (a nitrogenous base), ribose sugar (a five-carbon sugar), and three phosphate groups. The high-energy bonds between the second and third phosphate groups store energy that is released upon hydrolysis.

ATP Hydrolysis:

The process of breaking down ATP into ADP (Adenosine Diphosphate) and inorganic phosphate (Pi) releases energy, which is utilized by cells for various metabolic processes. The chemical reaction is as follows:

• ATP → ADP + PiThe energy released is approximately -32 kilojoules per mole under standard conditions, but this value can fluctuate in different cellular environments due to factors such as ion concentrations and temperature.

Cellular ATP Concentrations

Typical ATP concentrations in resting skeletal muscle cells include:

• ATP: 8 millimolar

• ADP: 9 micromolar

• Inorganic phosphate (Pi): 4 millimolarThese concentrations provide a more significant energy yield per cell compared to standard assay measurements (which range from -52 to -75 kilojoules per mole), indicating how efficient ATP utilization can be in maintaining active cellular processes.

Daily ATP Production

The human body produces approximately 6 kilograms of ATP daily, highlighting the necessity for continuous energy replenishment. Constant recycling of ATP enables energy availability without significant weight gain, as ATP is rapidly converted back and forth between ADP and ATP.

Energy Generation Mechanisms

Energy generation in the body involves various pathways, each suited to different types of physical activity and energy demands:

Creatine Phosphate System:

This system allows for rapid ATP regeneration, providing energy for short bursts of high-intensity activity lasting approximately 10 seconds. Creatine phosphate donates a phosphate group to ADP, regenerating ATP through an enzyme called creatine kinase. This mechanism is essential in activities like sprinting or weightlifting.

Glycolysis:

Glycolysis is an anaerobic pathway occurring in the cytoplasm that breaks down glucose into pyruvate, yielding ATP in the process. This pathway can function without oxygen, making it particularly important for quick energy demands when oxygen supply may be limited, such as during intense exercise.

Glycolysis Details

• Initial Glucose Entry into Cells: Due to its polar nature, glucose cannot pass through the phospholipid bilayer directly and requires specific transporters (e.g., GLUT transporters) to enter cells.

• First Step in Glycolysis: The conversion of glucose into glucose-6-phosphate (G6P) using hexokinase requires ATP. This phosphorylation step prevents glucose from leaving the cell, thereby maintaining a high concentration of glucose for further energy production.

Regulation of Glycolysis

The regulation of glycolysis occurs through allosteric mechanisms that ensure cellular energy balance:

• Allosteric Regulation: Hexokinase is activated by AMP when cellular energy levels are low, signifying a need for increased ATP production. Conversely, it is inhibited when ATP levels are high, ensuring that glycolysis is only utilized when necessary. This feedback mechanism helps the cell conserve energy and utilize it efficiently based on immediate energy needs.

Conclusion

Glycolysis plays a crucial role in energy production within cells, especially under anaerobic conditions. Key regulatory mechanisms exist to ensure that energy is conserved and used efficiently according to the cellular environment and requirements, enabling the organism to thrive under various conditions.