General Biology Exam 2 Review: Metabolism, Cellular Respiration, Cell Division, and Photosynthesis

Metabolism and Thermodynamics

Overview of Metabolism

Metabolism encompasses all chemical reactions that occur within a living organism to maintain life. These reactions are organized into metabolic pathways, which are either catabolic (breaking down molecules) or anabolic (building up molecules).

• Catabolic Pathways: Break down complex molecules into simpler ones, releasing energy (e.g., cellular respiration).

• Anabolic Pathways: Build complex molecules from simpler ones, consuming energy (e.g., protein synthesis).

Kinetic and Potential Energy

• Kinetic Energy: The energy of motion. Example: movement of molecules, muscle contraction.

• Potential Energy: Stored energy due to position or structure. Example: chemical energy stored in bonds of glucose.

Thermodynamics in Biology

• First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed (law of energy conservation).

• Second Law of Thermodynamics: Every energy transfer increases the entropy (disorder) of the universe.

• Spontaneity: A reaction is spontaneous if it increases the entropy of the universe and/or releases free energy.

Free Energy and Gibbs Equation

• Gibbs Free Energy ($\Delta G$): The energy in a system available to do work at constant temperature and pressure.

• Equation: $\Delta G = \Delta H - T\Delta S$ Where: $\Delta G$ = change in free energy $\Delta H$ = change in enthalpy (total energy) $T$ = temperature in Kelvin $\Delta S$ = change in entropy

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

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

ATP and Coupled Reactions

• ATP (Adenosine Triphosphate): The primary energy currency of the cell.

• Role of ATP: Powers cellular work by transferring a phosphate group to other molecules (phosphorylation).

• Coupled Reactions: Energy released from exergonic reactions (like ATP hydrolysis) is used to drive endergonic reactions.

Enzymes and Metabolic Regulation

• Enzymes: Biological catalysts that speed up chemical reactions by lowering activation energy.

• Enzyme Specificity: Determined by the shape of the active site; only specific substrates fit.

• Induced Fit Model: Enzyme changes shape slightly to fit the substrate more snugly.

• Enzyme Inhibitors: Molecules that decrease enzyme activity (competitive or noncompetitive).

• Regulation: Enzyme activity is regulated by feedback inhibition, allosteric regulation, and covalent modification.

Activation Energy Diagram

The provided figures likely illustrate the effect of enzymes on activation energy:

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

Redox Reactions and Cellular Respiration

Redox Reactions

• Oxidation: Loss of electrons from a molecule.

• Reduction: Gain of electrons by a molecule.

• Redox Reaction: Chemical reaction involving the transfer of electrons between two species.

• Energy Exchange: Redox reactions are central to energy transfer in cells (e.g., cellular respiration).

Substrate-Level vs. Oxidative Phosphorylation

• Substrate-Level Phosphorylation: Direct transfer of a phosphate group to ADP from a substrate.

• Oxidative Phosphorylation: ATP synthesis powered by the electron transport chain and chemiosmosis.

Cellular Respiration Overview

• Reactants: Glucose and O2

• Products: CO2, H2O, and ATP

• Type of Reaction: Exergonic, catabolic

• Electron Transport Chain: Transfers electrons, pumps protons, creates a proton gradient for ATP synthesis.

• Location: Mitochondria (cytoplasm for glycolysis)

Glycolysis

• Location: Cytoplasm

• Phases: Energy investment and energy payoff

• Reactants: Glucose, 2 ATP, 2 NAD+

• Products: 2 Pyruvate, 4 ATP (net 2 ATP), 2 NADH

• Purpose: Breaks down glucose to pyruvate, generates ATP and NADH

Citric Acid Cycle (Krebs Cycle)

• Location: Mitochondrial matrix

• Reactants: Acetyl-CoA, NAD+, FAD, ADP

• Products: CO2, NADH, FADH2, ATP

• Purpose: Completes the breakdown of glucose, produces electron carriers

Oxidative Phosphorylation

• Electron Transport Chain: Series of protein complexes in the inner mitochondrial membrane

• Proton Gradient: Created by pumping H+ ions across the membrane

• Chemiosmosis: ATP synthase uses the proton gradient to synthesize ATP

• Equation: $\text{NADH} + \text{FADH}_2 + O_2 + ADP + P_i \rightarrow \text{NAD}^+ + \text{FAD} + H_2O + ATP$

Fermentation

• Purpose: Allows ATP production in the absence of oxygen

• Types: Alcohol fermentation (produces ethanol), lactic acid fermentation (produces lactate)

• Comparison to Cellular Respiration: Fermentation yields less ATP and does not use the electron transport chain

Comparison Table: Inputs and Outputs of Major Pathways

	Glycolysis	Oxidation of Pyruvate	Citric Acid Cycle	Oxidative Phosphorylation
Reactants	Glucose, NAD+, ADP	Pyruvate, NAD+, CoA	Acetyl-CoA, NAD+, FAD, ADP	NADH, FADH2, O2, ADP
Products	Pyruvate, NADH, ATP	Acetyl-CoA, NADH, CO2	CO2, NADH, FADH2, ATP	ATP, H2O, NAD+, FAD

Cell Division and the Cell Cycle

Purpose and Phases of Cell Division

• Purpose: Growth, repair, and reproduction of cells

• Phases: Interphase (G1, S, G2), Mitosis (Prophase, Metaphase, Anaphase, Telophase), Cytokinesis

Mitosis

• Definition: Division of a eukaryotic cell's nucleus to produce two genetically identical daughter cells

• Phases:

  • Prophase: Chromosomes condense, spindle forms

  • Metaphase: Chromosomes align at the cell equator

  • Anaphase: Sister chromatids separate to opposite poles

  • Telophase: Nuclear envelope reforms, chromosomes decondense

• Cytokinesis: Division of the cytoplasm, forming two separate cells

Chromosomes and DNA Packaging

• Genome: The entirety of a cell's DNA

• Chromatin: DNA-protein complex that condenses to form chromosomes

• Chromosomes: Structures that carry genetic information

Cell Cycle Regulation

• Checkpoints: Control points (G1, G2, M) where the cell cycle is regulated

• Regulatory Proteins: Cyclins and cyclin-dependent kinases (CDKs)

• Loss of Regulation: Can lead to uncontrolled cell division (cancer)

Photosynthesis and Chloroplasts

Chloroplast Structure

• Outer Membrane: Encloses the organelle

• Inner Membrane: Contains transport proteins

• Stroma: Fluid-filled space containing enzymes for the Calvin cycle

• Thylakoid System: Membranous sacs where light-dependent reactions occur

• Grana: Stacks of thylakoids

• Thylakoid Lumen: Internal space of thylakoids

Autotrophs vs. Heterotrophs

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

• Heterotrophs: Organisms that consume other organisms for energy

Photosynthesis Overview

• Purpose: Convert solar energy into chemical energy (glucose)

• Stages: Light-dependent reactions (in thylakoids), Calvin cycle (in stroma)

• Reactants: CO2, H2O, light energy

• Products: Glucose, O2

• Equation: $6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2$

Light-Dependent Reactions

• Location: Thylakoid membranes

• Key Molecules: NADP+/NADPH, ATP, photosystems

• Photolysis: Splitting of water to provide electrons, releases O2

Calvin Cycle

• Location: Stroma of chloroplast

• Purpose: Fixes CO2 into organic molecules (glucose)

• Reactants: CO2, ATP, NADPH

• Products: Glucose, ADP, NADP+

Comparison: Photosynthesis vs. Cellular Respiration

• Photosynthesis: Converts light energy to chemical energy; stores energy in glucose

• Cellular Respiration: Releases energy from glucose; produces ATP

• Relationship: The products of one process are the reactants of the other

Comparison Table: Photosynthesis and Cellular Respiration

	Photosynthesis	Cellular Respiration
Energy Source	Light	Glucose
Location	Chloroplast	Mitochondria
Reactants	CO2, H2O	Glucose, O2
Products	Glucose, O2	CO2, H2O

Additional info: Some explanations and tables have been expanded for clarity and completeness based on standard General Biology content.