Cell Structure, Energy, and Metabolism: Study Guide for BIOL 2120 Module 3

Cell Structure and Function

Major Cell Types: Prokaryotes vs. Eukaryotes

Cells are classified into two major types: prokaryotic and eukaryotic. Understanding their differences is fundamental to cell biology.

• Prokaryotes: Lack a nucleus and membrane-bound organelles. DNA is found in the nucleoid region.

• Eukaryotes: Possess a nucleus and various membrane-bound organelles. DNA is enclosed within the nuclear envelope.

• Example: Bacteria are prokaryotes; plants and animals are eukaryotes.

Cell Structures of Prokaryotes

Prokaryotic cells have unique structures that support their functions.

• Cell wall: Provides structural support and protection.

• Plasma membrane: Controls entry and exit of substances.

• Nucleoid: Region containing the cell's DNA.

• Ribosomes: Sites of protein synthesis.

• Flagella: Used for movement.

Benefits of Organelles in Eukaryotic Cells

Organelles compartmentalize cellular functions, increasing efficiency and specialization.

• Isolation of reactions: Prevents interference between incompatible processes.

• Specialization: Organelles perform specific tasks (e.g., mitochondria for energy production).

Cell Structures of Eukaryotes: Plant and Animal Cells

Eukaryotic cells contain various organelles, each with distinct functions.

• Nucleus: Stores genetic material.

• Mitochondria: Site of cellular respiration.

• Endoplasmic reticulum (ER): Protein and lipid synthesis.

• Golgi apparatus: Modifies, sorts, and packages proteins.

• Lysosomes: Digestion and waste removal (mainly in animal cells).

• Chloroplasts: Photosynthesis (in plant cells).

• Vacuole: Storage and structural support (in plant cells).

Endomembrane System

The endomembrane system coordinates the synthesis, modification, and transport of proteins and lipids.

• Components: ER, Golgi apparatus, lysosomes, vesicles.

• Function: Ensures proper delivery and processing of cellular products.

Molecular Zip Codes

Molecular zip codes direct proteins to their correct cellular locations.

• Nuclear Localization Signal (NLS): Targets proteins to the nucleus.

• ER Signal Sequence: Directs proteins to the endoplasmic reticulum.

• Mannose-6-phosphate: Targets proteins to lysosomes.

Energy and Metabolism

Forms of Energy

Energy exists in various forms, crucial for cellular processes.

• Kinetic energy: Energy of motion (e.g., movement of molecules).

• Potential energy: Stored energy (e.g., chemical bonds).

• Example: ATP stores potential energy in its phosphate bonds.

Entropy (S) and Enthalpy (H)

Thermodynamic properties help predict reaction outcomes.

• Entropy (S): Measure of disorder in a system.

• Enthalpy (H): Total heat content of a system.

Exergonic vs. Endergonic Reactions

Chemical reactions are classified based on energy changes.

• Exergonic: Release energy; spontaneous; $\\Delta G < 0$.

• Endergonic: Require energy input; non-spontaneous; $\\Delta G > 0$.

• Example: Cellular respiration is exergonic; photosynthesis is endergonic.

Gibbs Free Energy (G)

Gibbs free energy determines whether a reaction is spontaneous.

• Formula: $\\Delta G = \\Delta H - T \\Delta S$

• Negative $\\Delta G$: Reaction is spontaneous (exergonic).

• Positive $\\Delta G$: Reaction requires energy (endergonic).

Energetic Coupling

Cells couple exergonic and endergonic reactions to drive necessary processes.

• ATP hydrolysis: Provides energy to power endergonic reactions.

ATP: Structure and Role

ATP is the primary energy currency of the cell.

• Structure: Adenine, ribose, and three phosphate groups.

• Role: Transfers energy to cellular processes.

Enzyme Catalysis

Enzymes accelerate reactions by lowering activation energy.

• Two hurdles: Bringing substrates together and stabilizing the transition state.

Enzyme Regulation

Enzyme activity is regulated to maintain cellular homeostasis.

• Competitive inhibition: Inhibitor binds to active site.

• Allosteric regulation: Inhibitor or activator binds elsewhere, changing enzyme shape.

• Feedback inhibition: End product inhibits an earlier step.

Reaction Energy Diagram

The diagram below illustrates the energy changes during a chemical reaction, including activation energy and Gibbs free energy.

• Forward reaction: Exergonic, $\\Delta G < 0$ (Option b).

• Letter representing $\\Delta G$: d.

• Activation energy without enzyme: c.

• Spontaneity: The reaction is spontaneous.

Cellular Respiration and Fermentation

Mitochondrial Structures

Mitochondria are the site of cellular respiration, with specialized structures.

• Outer membrane: Surrounds the organelle.

• Inner membrane: Contains proteins for the electron transport chain.

• Matrix: Location of the citric acid cycle.

• Cristae: Folds increasing surface area for ATP production.

Aerobic vs. Anaerobic Respiration

Cells can generate energy with or without oxygen.

• Aerobic: Uses oxygen; produces more ATP.

• Anaerobic: Does not use oxygen; less ATP produced.

Fermentation

Fermentation occurs when oxygen is unavailable, regenerating NAD+ and producing products like lactic acid or ethanol.

• Occurs: In absence of oxygen.

• Products: Lactic acid (animals), ethanol (yeast).

Equations for Photosynthesis and Cellular Respiration

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

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

ATP Usage in Cells

ATP powers cellular work, including muscle contraction, active transport, and biosynthesis.

Phosphorylation Mechanisms

• Substrate-level phosphorylation: Direct transfer of phosphate to ADP.

• Oxidative phosphorylation: Uses electron transport chain and chemiosmosis.

Stages of Glucose Oxidation

• Glycolysis: Occurs in cytoplasm; converts glucose to pyruvate.

• Pyruvate processing: Converts pyruvate to acetyl-CoA.

• Citric acid cycle: Occurs in mitochondrial matrix; produces NADH, FADH2, ATP.

• Electron transport chain: Occurs in inner mitochondrial membrane; creates proton gradient for ATP synthesis.

Glycolysis Steps and ATP Yield

• Starting molecule: Glucose.

• Products: 2 pyruvate, 2 ATP (net), 2 NADH.

• Location: Cytoplasm.

• Total ATP: Complete oxidation yields ~30-32 ATP per glucose.

Citric Acid Cycle Main Events

• Acetyl-CoA enters cycle.

• Produces: CO2, NADH, FADH2, ATP (or GTP).

Electron Transport Chain and Chemiosmosis

• ETC: Transfers electrons, pumps protons to create gradient.

• Chemiosmosis: Proton gradient drives ATP synthesis via ATP synthase.

• Proton motive force: Energy stored in gradient.

Regulation of Metabolic Pathways

• Phosphofructokinase: Allosterically inhibited by ATP; slows glycolysis and citric acid cycle when ATP is abundant.

• Correct answer: A) inhibit the enzyme and thus slow the rates of glycolysis and the citric acid cycle.

Photosynthesis

Heterotrophs vs. Autotrophs

• Heterotrophs: Obtain organic molecules from other organisms.

• Autotrophs: Produce their own organic molecules from inorganic sources.

Chloroplast Structures

• Thylakoid membrane: Site of light-dependent reactions.

• Stroma: Site of light-independent reactions (Calvin cycle).

Pigments in Photosynthesis

• Chlorophylls: Absorb light energy.

• Carotenoids: Accessory pigments.

Photosystems

• Components: Antenna complex (captures light), reaction center (converts energy).

• Photosystem I and II: Work together to drive electron flow.

Light-Dependent Reactions

• Steps: Light absorption, electron transport, ATP and NADPH production.

• Products: ATP, NADPH, O2.

Light-Independent Reactions (Calvin Cycle)

• Steps: Carbon fixation, reduction, regeneration of RuBP.

• Products: Glucose, ADP, NADP+.

Chemiosmosis in Photosynthesis

• Role: ATP synthase uses proton gradient to produce ATP.

ATP Synthase Location in Plant Cells

• Correct answer: D) thylakoid membrane and inner mitochondrial membrane.

Additional info: Academic context was added to expand brief points and ensure completeness.