Chapter 5/6 Biology Study Notes: The Working Cell

Chapter 5: The Working Cell

Introduction to Cellular Processes

This chapter explores the fundamental processes that occur within cells, focusing on energy transformation, enzyme function, and the molecular mechanisms that drive cellular activities.

• Kinetic Energy: The energy of motion, which is utilized by cells to perform work.

• Potential Energy: Stored energy, often found in chemical bonds within molecules.

• Endergonic Reaction: A chemical reaction that absorbs energy from its surroundings.

• Exergonic Reaction: A chemical reaction that releases energy.

• Hydrocarbon: Organic molecules consisting entirely of carbon and hydrogen; important in energy storage.

• ATP (Adenosine Triphosphate): The primary energy carrier in cells.

Example: The breakdown of ATP to ADP releases energy for cellular work.

Equation:

$\text{ATP} \rightarrow \text{ADP} + \text{Phosphate} + \text{Energy}$

Enzymes and Their Function

Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required. They are essential for both the breakdown and synthesis of molecules in cells.

• Definition: An enzyme is a protein that accelerates chemical reactions without being consumed.

• Substrate: The specific reactant that an enzyme acts upon.

• Active Site: The region on the enzyme where the substrate binds.

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

Example: The enzyme sucrase catalyzes the breakdown of sucrose into glucose and fructose.

Enzyme Reaction Diagram:

• Enzymes lower the activation energy barrier, allowing reactions to proceed faster.

Factors Affecting Enzyme Activity:

• pH: Each enzyme has an optimal pH range for activity.

• Temperature: Enzyme activity increases with temperature up to a point, after which it declines due to denaturation.

Example: Human enzymes typically function best at body temperature (37°C) and neutral pH.

Chapter 6: How Cells Harvest Chemical Energy

Introduction to Cellular Energy Harvesting

This chapter focuses on how cells obtain and utilize energy, emphasizing the differences between cell types and the processes of cellular respiration and photosynthesis.

Characteristics of All Cells

• DNA: Genetic material present in all cells.

• Cytoplasm: The fluid interior where cellular processes occur.

• Cell Membrane: The boundary that regulates entry and exit of substances.

Prokaryotic vs. Eukaryotic Cells

Cells are classified based on the presence or absence of a nucleus and other organelles.

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	Absent	Present
Organelles	Few or none	Many (e.g., mitochondria, chloroplasts)
Examples	Bacteria	Plants, animals, fungi

Cellular Respiration

Cellular respiration is the process by which cells convert glucose and oxygen into ATP, the energy currency of the cell, along with carbon dioxide and water as byproducts.

• Definition: The metabolic pathway that breaks down glucose to produce ATP.

• Word Formula: Glucose + Oxygen → Carbon Dioxide + Water + ATP (energy)

Equation:

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$

Photosynthesis

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

• Occurs in: Chloroplasts

• Inputs: Carbon dioxide, water, light energy

• Outputs: Glucose, oxygen

Equation:

$6\text{CO}_2 + 6\text{H}_2\text{O} + \text{light energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$

Stages of Cellular Respiration

• Stage 1: Glycolysis – Occurs in the cytoplasm; produces 2 ATP molecules.

• Stage 2: Pyruvate Oxidation – Occurs in mitochondria; produces no ATP directly.

• Stage 3: Citric Acid Cycle – Occurs in mitochondria; produces 2 ATP molecules.

• Stage 4: Oxidative Phosphorylation (Electron Transport Chain) – Occurs in mitochondria; produces the majority of ATP.

Example: The electron transport chain uses electrons from NADH and FADH2 to generate ATP.

Redox Reactions in Cellular Respiration

• Oxidation: Loss of electrons or hydrogen atoms.

• Reduction: Gain of electrons or hydrogen atoms.

• During cellular respiration, glucose is oxidized and oxygen is reduced.

Equation:

$\text{Glucose} \rightarrow \text{CO}_2$ (oxidation) $\text{O}_2 \rightarrow \text{H}_2\text{O}$ (reduction)

Factors Affecting Cellular Respiration and Enzyme Activity

• pH: Affects enzyme structure and function; optimal pH varies by enzyme.

• Temperature: Influences reaction rates; extreme temperatures can denature enzymes.

Example: The optimal temperature for human enzymes is around 37°C, while the optimal pH varies (e.g., pepsin in the stomach works best at pH 2).

Additional info: These notes expand upon the provided review sheet by including definitions, equations, and examples for key concepts in cellular energetics and enzyme function, ensuring a comprehensive study guide for exam preparation.