7: Inside the Cell

Cell Structure and Function

The cell is the fundamental unit of life, and understanding its internal structure is essential for studying biology. Cells contain various organelles, each with specialized functions that contribute to the cell's survival and activity.

• Prokaryotic Cells: Lack a nucleus; DNA is found in the nucleoid region. Examples include Bacteria and Archaea.

• Eukaryotic Cells: Have a nucleus and membrane-bound organelles such as mitochondria, endoplasmic reticulum, and Golgi apparatus.

• Organelles: Structures within cells that perform specific functions (e.g., mitochondria for energy production, ribosomes for protein synthesis).

• Cell Membrane: A phospholipid bilayer that controls the movement of substances in and out of the cell.

Example: The mitochondrion is known as the "powerhouse" of the cell, generating ATP through cellular respiration.

8: Energy and Enzymes: An Introduction to Metabolism

Metabolic Pathways and Enzyme Function

Metabolism refers to all chemical reactions that occur within living organisms to maintain life. Enzymes are biological catalysts that speed up these reactions without being consumed.

• Metabolic Pathways: Series of interconnected biochemical reactions, such as glycolysis and the citric acid cycle.

• Enzymes: Proteins that lower activation energy, allowing reactions to proceed faster.

• Activation Energy: The minimum energy required to start a chemical reaction.

• Substrate: The molecule upon which an enzyme acts.

Example: Amylase is an enzyme that catalyzes the breakdown of starch into sugars.

Equation:

Where: = change in free energy, = change in enthalpy, = temperature, = change in entropy.

9: Cellular Respiration and Fermentation

Energy Production in Cells

Cells obtain energy from organic molecules through cellular respiration and fermentation. These processes convert glucose into ATP, the energy currency of the cell.

• Cellular Respiration: Aerobic process involving glycolysis, the citric acid cycle, and oxidative phosphorylation.

• Fermentation: Anaerobic process that allows cells to produce ATP without oxygen, resulting in products like lactic acid or ethanol.

• ATP: Adenosine triphosphate, the main energy carrier in cells.

Example: Muscle cells use lactic acid fermentation during intense exercise when oxygen is limited.

Equation:

10: Photosynthesis

Energy Capture and Conversion in Plants

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy, producing glucose and oxygen.

• Light Reactions: Occur in the thylakoid membranes; convert solar energy to chemical energy (ATP and NADPH).

• Calvin Cycle: Occurs in the stroma; uses ATP and NADPH to fix carbon dioxide into glucose.

• Chlorophyll: The pigment responsible for absorbing light energy.

Example: Green plants use photosynthesis to produce food and oxygen, supporting life on Earth.

Equation:

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