Metabolism & Energy

Introduction to Metabolism

Metabolism is a central concept in biology, referring to the sum of all chemical reactions that occur within living organisms to sustain life. These reactions enable cells to grow, reproduce, maintain their structures, and respond to environmental changes.

• Metabolism: The complete set of chemical reactions in a living body.

• Living things use energy for processes that sustain life, such as growth, repair, and movement.

• According to the law of conservation of matter, matter cannot be created or destroyed, but it can be transformed by living beings through multi-step reactions.

Metabolic Pathways

Metabolic pathways are sequences of chemical reactions, each catalyzed by a specific enzyme, that transform molecules stepwise to produce a final product.

• Metabolic pathway: A series of chemical reactions where a specific molecule undergoes stepwise changes to become a final product.

• Each step is catalyzed by an enzyme, which speeds up the reaction.

• Example: Enzyme 1 converts molecule A to B (Reaction 1), Enzyme 2 converts B to C (Reaction 2), and so on.

Types of Metabolic Pathways

Metabolic pathways are classified as either catabolic or anabolic, depending on whether they break down or build up molecules.

• Catabolic pathways: Break down complex molecules into simpler compounds, releasing energy in the process.

• Anabolic pathways: Build complex molecules from simpler ones, consuming energy in the process.

Example:

• Catabolic: Cellular respiration breaks down glucose into carbon dioxide and water, releasing energy.

• Anabolic: Protein synthesis builds proteins from amino acids, requiring energy input.

Coupling of Pathways

Catabolic pathways are 'downhill' reactions that release energy, which can be used to power the 'uphill' reactions of anabolic pathways.

• Energy released from catabolism is often used to drive anabolic processes.

• This coupling is essential for maintaining cellular functions.

What is Energy?

Energy is the capacity of a system to cause change in itself or its surroundings. In biological systems, energy exists in various forms and is essential for performing work.

• Energy: The ability to do work, such as moving objects against opposing forces (gravity, friction).

• The study of how energy flows through and is used by living organisms is called bioenergetics.

Forms of Energy

Energy in biological systems can be classified into several types:

• Kinetic energy: Energy of motion; objects in motion impart energy to other objects.

• Thermal energy: Kinetic energy at the atomic level; transferred as heat between objects.

• Potential energy: Energy due to location or structure; can be converted into kinetic energy.

• Chemical energy: Potential energy stored in chemical bonds; released through chemical reactions.

Example: Water at high altitude has high potential energy due to its position; glucose has chemical energy stored in its bonds.

Summary Table: Forms of Energy

Additional info:

• Bioenergetics is a subfield of biochemistry that focuses on energy flow and transformation in living systems.

• Enzymes are biological catalysts that lower activation energy, increasing the rate of metabolic reactions.