Study Guide: Cell Structure, Enzymes, Cellular Respiration, and Photosynthesis

Chapter 4: The Function and Structure of the Organelles of the Cell

Major Eukaryotic Organelles

This section covers the main organelles found in eukaryotic cells, their structures, and their functions.

• Mitochondria: Known as the "powerhouse" of the cell, mitochondria are responsible for producing ATP through cellular respiration.

• Chloroplasts: Organelles found in plant cells and some protists; they conduct photosynthesis by converting solar energy into chemical energy.

• Lysosomes: Membrane-bound vesicles containing digestive enzymes that break down waste materials and cellular debris.

• Golgi Apparatus: A series of flattened membranes involved in modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles.

• Nucleus: The control center of the cell, containing most of the cell's genetic material (DNA) and coordinating activities like growth, metabolism, and reproduction.

• Endoplasmic Reticulum (ER): A network of membranes involved in protein and lipid synthesis. The rough ER is studded with ribosomes and synthesizes proteins, while the smooth ER is involved in lipid synthesis and detoxification.

Chapter 5: The Functions of Enzymes

Enzyme Basics

Enzymes are biological catalysts that speed up chemical reactions in living organisms.

• Energy Barriers and Catalysis: Enzymes lower the activation energy required for reactions, allowing them to proceed more rapidly.

• Specificity: Each enzyme is specific to particular substrates and reactions due to the unique shape of its active site.

• Role in Reactions: Enzymes facilitate biochemical reactions without being consumed in the process.

Activation Energy

• Definition: The minimum amount of energy required to start a chemical reaction.

• Enzyme Function: Enzymes lower the activation energy, making it easier for reactions to occur at cellular temperatures.

Energetic Reactions

ATP and Metabolic Pathways

ATP (adenosine triphosphate) is the primary energy carrier in cells. Metabolic pathways are series of chemical reactions occurring within a cell.

• ATP Structure and Function: ATP consists of adenine, ribose, and three phosphate groups. It stores and transfers energy within cells.

• Exergonic vs. Endergonic Reactions: Exergonic reactions release energy (e.g., cellular respiration), while endergonic reactions require energy input (e.g., photosynthesis).

• Metabolic Pathways: Sequences of enzyme-catalyzed reactions where the product of one reaction becomes the substrate for the next.

Photosynthesis and Respiration

• Reactants and Products:

  • Photosynthesis: Reactants: CO2, H2O, light energy. Products: glucose (C6H12O6), O2.

  • Respiration: Reactants: glucose, O2. Products: CO2, H2O, ATP.

• Subcellular Locations:

  • Photosynthesis: Occurs in chloroplasts (plants and algae).

  • Respiration: Occurs in mitochondria (all eukaryotes).

• Oxidation and Reduction:

  • Oxidation: Loss of electrons from a molecule.

  • Reduction: Gain of electrons by a molecule.

Chapter 6: Cellular Respiration

Overview of Cellular Respiration

Cellular respiration is the process by which cells extract energy from glucose and other organic molecules to produce ATP.

• Mitochondria Structure: Double-membraned organelle with inner folds called cristae, increasing surface area for ATP production.

• Role of Glucose: Primary fuel molecule broken down during glycolysis and subsequent steps to release energy.

• Role of Oxygen: Final electron acceptor in the electron transport chain, allowing for efficient ATP production.

• Pumping of Hydrogen Ions and Chemiosmosis: Hydrogen ions (protons) are pumped across the inner mitochondrial membrane, creating a gradient used by ATP synthase to generate ATP (chemiosmosis).

• Chemical Equation for Cellular Respiration:

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

• General Steps: Glycolysis, Krebs cycle (citric acid cycle), and electron transport chain.

Chapter 7: Photosynthesis

Chloroplast Structure and Function

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

• Chloroplast Structure: Contains an outer membrane, inner membrane, and internal stacks of thylakoids (grana) surrounded by stroma.

• Role of CO2 and H2O: Carbon dioxide and water are the raw materials for photosynthesis.

• Photosynthesis Equation:

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

• Two Stages of Photosynthesis:

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

  • Calvin Cycle (Dark Reactions): Occur in the stroma; use ATP and NADPH to fix CO2 into glucose.

• Role of Chlorophyll: Pigment that absorbs light energy, initiating the process of photosynthesis.

• Photosynthetic Reaction Centers and NADPH: Specialized protein complexes where light energy is converted to chemical energy; NADPH is an electron carrier produced in the light reactions.

Comparison Table: Cellular Respiration vs. Photosynthesis

The following table summarizes the main differences between cellular respiration and photosynthesis.

Feature	Cellular Respiration	Photosynthesis
Location	Mitochondria	Chloroplasts
Reactants	Glucose, O2	CO2, H2O, light
Products	CO2, H2O, ATP	Glucose, O2
Energy Conversion	Chemical energy (glucose) to ATP	Light energy to chemical energy (glucose)
Electron Carriers	NADH, FADH2	NADPH