Exam 3 Study Guide: Energy, Metabolism, Cellular Respiration, and Photosynthesis

Chapter 8: Energy and Enzymes – An Introduction to Metabolism

8.1 What Happens to Energy in Chemical Reactions?

Chemical reactions involve the transformation of energy. Understanding how energy changes during reactions is essential for studying metabolism.

• Energy is the capacity to do work or produce heat. It exists as kinetic energy (energy of motion) and potential energy (stored energy).

• First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed.

• Second Law of Thermodynamics: Entropy (disorder) of the universe tends to increase.

• Enthalpy (H): Total energy in a molecule, including potential energy and energy in chemical bonds.

• Entropy (S): A measure of disorder or randomness.

• Gibbs Free Energy (G): Determines whether a reaction is spontaneous. Calculated as:

$\Delta G = \Delta H - T \Delta S$

• Exergonic reactions: $\Delta G < 0$, spontaneous, release energy.

• Endergonic reactions: $\Delta G > 0$, non-spontaneous, require energy input.

• Exothermic: Release heat ($\Delta H < 0$); Endothermic: Absorb heat ($\Delta H > 0$).

8.2 Non-spontaneous Reactions May Be Driven Using Chemical Energy

Cells couple exergonic and endergonic reactions to drive processes necessary for life.

• ATP (Adenosine Triphosphate): Main energy currency of the cell. Hydrolysis of ATP is highly exergonic:

$\mathrm{ATP} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{ADP} + \mathrm{P}_i + \text{energy}$

• Phosphorylation: Transfer of a phosphate group to a molecule, often activating or deactivating enzymes.

8.3 How Enzymes Work

Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy.

• Active Site: Region on the enzyme where substrates bind.

• Induced Fit: Enzyme changes shape to better fit the substrate.

• Catalysis: Enzymes stabilize transition states, reducing activation energy ($E_a$).

8.4 What Factors Affect Enzyme Function?

Enzyme activity is influenced by several factors:

• Temperature: Affects molecular movement and enzyme stability.

• pH: Alters enzyme structure and charge properties.

• Substrate concentration: Higher concentrations increase reaction rate up to a maximum (saturation).

• Cofactors: Inorganic ions (e.g., Zn2+), required for enzyme activity.

• Coenzymes: Organic molecules (e.g., vitamins) that assist enzymes.

• Prosthetic groups: Non-protein molecules tightly bound to enzymes.

• Phosphorylation/Dephosphorylation: Addition/removal of phosphate groups regulates enzyme activity.

8.5 Enzymes Can Work Together in Metabolic Pathways

Metabolic pathways are series of enzyme-catalyzed reactions. Pathways can be:

• Catabolic: Break down molecules, releasing energy (e.g., cellular respiration).

• Anabolic: Build complex molecules, requiring energy (e.g., protein synthesis).

Chapter 9: Cellular Respiration and Fermentation

9.1 An Overview of Cellular Respiration

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

• Four main stages:

  1. Glycolysis

  2. Pyruvate Processing

  3. Citric Acid Cycle (Krebs Cycle)

  4. Electron Transport Chain and Chemiosmosis

• Aerobic respiration: Uses oxygen; Anaerobic respiration: Does not use oxygen.

9.2 Glycolysis: Oxidizing Glucose to Pyruvate

• Occurs in the cytosol.

• Glucose (6C) is split into two pyruvate (3C) molecules.

• Net yield per glucose: 2 ATP, 2 NADH.

9.3 Processing Pyruvate to Acetyl CoA

• Occurs in the mitochondrial matrix (eukaryotes).

• Each pyruvate is converted to acetyl CoA, producing NADH and CO2.

9.4 The Citric Acid Cycle: Oxidizing Acetyl CoA to CO2

• Also called Krebs Cycle or TCA Cycle.

• Completes the oxidation of glucose derivatives.

• Per glucose: 2 cycles, producing 2 ATP, 6 NADH, 2 FADH2, and 4 CO2.

9.5 Electron Transport and Chemiosmosis: Building a Proton Gradient to Produce ATP

• Occurs in the inner mitochondrial membrane.

• NADH and FADH2 donate electrons to the electron transport chain (ETC).

• Proton gradient is established across the membrane (proton-motive force).

• ATP synthase uses this gradient to produce ATP (chemiosmosis).

• Ubiquinone (Coenzyme Q): Electron carrier in the ETC.

9.6 Fermentation

• Occurs when oxygen is not available.

• Regenerates NAD+ for glycolysis.

• Produces less ATP than aerobic respiration.

• Examples: Lactic acid fermentation (muscle cells), alcoholic fermentation (yeast).

Comparison: Fermentation vs. Cellular Respiration

Process	Oxygen Required?	ATP Yield (per glucose)
Cellular Respiration	Yes	~30-32
Fermentation	No	2

Chapter 10: Photosynthesis

10.1 Photosynthesis Harnesses Sunlight to Make Carbohydrate from CO2

Photosynthesis is the process by which autotrophs convert light energy into chemical energy stored in carbohydrates.

• Overall equation:

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

• Autotrophs: Organisms that produce their own food (e.g., plants).

• Heterotrophs: Organisms that consume other organisms for energy.

10.2 How Do Pigments Capture Light Energy?

• Pigments: Molecules that absorb specific wavelengths of light (e.g., chlorophyll).

• Chlorophyll: Main pigment in plants, absorbs red and blue light, reflects green.

• Carotenoids: Accessory pigments, absorb other wavelengths, protect chlorophyll.

• Light has both wave-like and particle-like properties.

10.3 The Discovery of Photosystems I and II

• Photosystem II (PSII): Captures light energy, splits water, releases O2.

• Photosystem I (PSI): Captures light energy, produces NADPH.

• Both systems work together to produce ATP and NADPH.

10.4 How Do Cells Capture Carbon Dioxide?

• CO2 is fixed in the Calvin Cycle, which occurs in the stroma of chloroplasts.

• Key enzyme: Rubisco.

10.5 Captured Carbon Dioxide Is Reduced to Make Sugar

• Calvin Cycle has three phases: Carbon fixation, reduction, regeneration of RuBP.

• Uses ATP and NADPH from light-dependent reactions to produce G3P (a sugar).

• Gluconeogenesis: Process of making glucose from non-carbohydrate sources.

Photosynthesis vs. Cellular Respiration

Feature	Photosynthesis	Cellular Respiration
Energy Source	Light	Glucose
Electron Carrier	NADP+/NADPH	NAD+/NADH
Gas Consumed	CO2	O2
Gas Produced	O2	CO2

Lab Classes: Scientific Method and Basic Techniques

Scientific Method and Research

• Primary Research: Original research articles.

• Secondary Research: Reviews, summaries of primary research.

• Plagiarism: Using others' work without proper citation; avoid by using correct citation styles (APA, MLA).

• Scientific Method Steps: Observation, Question, Hypothesis, Experiment, Data Collection, Analysis, Conclusion.

• Variables: Independent (manipulated), Dependent (measured), Controlled (kept constant).

Basic Lab Techniques

• Scientific calculations: Use metric prefixes (kilo-, centi-, milli-, micro-, etc.).

• Units: Mass (grams), Volume (liters), Length (meters), Amount (moles).

• Microscopy: Objective power, total magnification, field of view.

• Enzyme labs: Relationship between oxygen and enzyme activity; importance of controlling variables.

• Fermentation labs: Relationship between CO2 production and yeast activity; importance of variables.

Additional info: Some details (e.g., specific enzyme examples, lab protocols) were inferred based on standard biology curricula and the context of the review notes.