BIO 110 Exam 3 Study Guide: Membrane Structure, Transport, and Cellular Respiration

Membrane Structure and Function

Fluid Mosaic Model

The fluid mosaic model describes the structure of the plasma membrane as a dynamic and flexible layer composed of a mosaic of proteins floating in or on a fluid phospholipid bilayer.

• Phospholipid bilayer: Provides the basic structure, with hydrophilic heads facing outward and hydrophobic tails facing inward.

• Proteins: Embedded within the bilayer, serving various functions such as transport, signaling, and structural support.

• Carbohydrates: Attached to proteins and lipids on the extracellular surface, involved in cell recognition.

Selective Permeability

Selective permeability refers to the ability of the plasma membrane to allow certain molecules to pass through while restricting others.

• Small, nonpolar molecules (e.g., O2, CO2) pass easily.

• Ions and large polar molecules require transport proteins.

Structure of the Plasma Membrane

• Phospholipids: Amphipathic molecules with hydrophilic heads (face outward toward water) and hydrophobic tails (face inward, away from water).

• Proteins: Integral (span the membrane) and peripheral (attached to the surface).

• Cholesterol: Maintains membrane fluidity.

• Carbohydrates: Glycoproteins and glycolipids for cell recognition.

Functions of the Plasma Membrane

• Regulates transport of substances in and out of the cell.

• Facilitates communication with other cells.

• Provides structural support and maintains cell shape.

• Enables cell recognition and adhesion.

Membrane Transport Mechanisms

Passive Transport

Passive transport is the movement of substances across the membrane without energy input from the cell.

• Diffusion: Movement of molecules from high to low concentration.

• Facilitated diffusion: Diffusion of molecules via transport proteins.

• Osmosis: Diffusion of water across a selectively permeable membrane.

Active Transport

Active transport requires energy (usually ATP) to move substances against their concentration gradient.

• Uses transport proteins (pumps).

• Example: Sodium-potassium pump.

Endocytosis and Exocytosis

• Endocytosis: Process by which cells take in large molecules by engulfing them in vesicles.

• Exocytosis: Process by which cells expel materials in vesicles that fuse with the plasma membrane.

• Phagocytosis: "Cell eating"; a type of endocytosis where large particles are engulfed.

Osmosis and Tonicity

• Osmosis: Movement of water from an area of low solute concentration to high solute concentration.

• Hypotonic solution: Lower solute concentration outside the cell; water enters the cell, which may swell or burst.

• Hypertonic solution: Higher solute concentration outside the cell; water leaves the cell, causing it to shrink.

• Isotonic solution: Equal solute concentration; no net movement of water.

Direction of Water Movement in Different Solutions

Solution Type	Water Movement	Effect on Cell
Hypotonic	Into cell	Cell swells
Hypertonic	Out of cell	Cell shrinks
Isotonic	No net movement	No change

Energy and Enzymes

Kinetic and Potential Energy

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

• Potential energy: Stored energy due to position or structure.

• Chemical energy: A form of potential energy stored in chemical bonds.

Comparison Table: Kinetic vs. Potential Energy

Type	Description	Example
Kinetic	Energy of motion	Flowing water, moving car
Potential	Stored energy	Chemical bonds, stretched bow

Enzymes

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

• Active site: Region on the enzyme where the substrate binds.

• Phosphorylation: Addition of a phosphate group to a molecule, often regulating enzyme activity.

How Enzymes Work

• Substrate binds to the enzyme's active site.

• Enzyme lowers the activation energy required for the reaction.

• Products are released, and the enzyme is unchanged.

Factors Affecting Enzyme Functionality

• Temperature

• pH

• Substrate concentration

• Presence of inhibitors

Enzyme Inhibitors

• Competitive inhibitors: Bind to the active site, blocking substrate binding.

• Noncompetitive inhibitors: Bind to another part of the enzyme, changing its shape and reducing activity.

Cellular Respiration

Overview

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

• Occurs in three main stages: Glycolysis, Citric Acid Cycle, and Oxidative Phosphorylation.

• Overall products: ATP, CO2, and H2O.

Chemical Equation for Cellular Respiration

$\mathrm{C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + ATP}$

Redox Reactions in Cellular Respiration

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

• During respiration, glucose is oxidized and O2 is reduced to form H2O.

Stages of Cellular Respiration

Stage	Location	Inputs	End Products	Oxygen Required?
Glycolysis	Cytoplasm	Glucose	2 Pyruvate, 2 ATP, 2 NADH	No
Citric Acid Cycle	Mitochondrial matrix	Acetyl-CoA	CO2, NADH, FADH2, 2 ATP	Yes
Oxidative Phosphorylation	Inner mitochondrial membrane	NADH, FADH2, O2	ATP, H2O	Yes

Glycolysis

• Occurs in the cytoplasm.

• Net gain: 2 ATP, 2 NADH, 2 pyruvate per glucose.

• Does not require oxygen (anaerobic).

Citric Acid (Krebs) Cycle

• Occurs in the mitochondrial matrix.

• Inputs: Acetyl-CoA.

• End products: CO2, NADH, FADH2, ATP.

• Intermediate molecules: Citrate, succinate, fumarate, malate, oxaloacetate.

Oxidative Phosphorylation

• Occurs in the inner mitochondrial membrane.

• Includes the electron transport chain and chemiosmosis.

• ATP synthase uses the H+ gradient to produce ATP.

Electron Transport Chain (ETC)

• Series of protein complexes in the inner mitochondrial membrane.

• NADH and FADH2 donate electrons at the beginning.

• O2 is the final electron acceptor, forming H2O.

Aerobic vs. Anaerobic Respiration

• Aerobic respiration: Requires oxygen; produces more ATP.

• Anaerobic respiration: Does not require oxygen; less efficient ATP production.

• Types of anaerobic respiration:

  • Alcohol fermentation: Produces ethanol and CO2 (e.g., yeast).

  • Lactic acid fermentation: Produces lactic acid (e.g., muscle cells).

Evolutionary Significance of Glycolysis

• Occurs in almost all organisms.

• Does not require oxygen or membrane-bound organelles.

• Considered evolutionarily "old" because it likely evolved before atmospheric oxygen was abundant.

Summary Table: Cellular Respiration Stages

Stage	ATP Produced (Net)	Location
Glycolysis	2	Cytoplasm
Citric Acid Cycle	2	Mitochondrial matrix
Oxidative Phosphorylation	~28-34	Inner mitochondrial membrane

Example: During strenuous exercise, muscle cells switch to lactic acid fermentation when oxygen is scarce, allowing ATP production to continue anaerobically.

Additional info: The study of membrane structure and cellular respiration is fundamental for understanding how cells maintain homeostasis and generate energy necessary for life processes.