Anatomy & Physiology: Cellular Processes, Membrane Transport, and Signal Transduction Study Guide

Chapter 4: Cellular Energy and Metabolism

Types of Energy in Biological Systems

Cells utilize various forms of energy to perform biological work, including chemical reactions and transport processes.

• Kinetic Energy: Energy of motion, such as the movement of molecules.

• Potential (Free) Energy: Stored energy, often in chemical bonds or concentration gradients.

• Chemical Energy: Energy stored in the bonds of molecules, especially ATP.

• Activation Energy: The minimum energy required to initiate a chemical reaction.

Open vs. Closed Systems

Biological systems exchange energy and matter with their environment.

• Open System: Exchanges both energy and matter with the surroundings (e.g., the human body).

• Closed System: Exchanges energy but not matter with the surroundings.

Chemical Reactions in Cells

Chemical reactions involve the making and breaking of bonds, with associated energy changes.

• Anabolic Reactions: Build molecules and require energy input (endergonic).

• Catabolic Reactions: Break down molecules and release energy (exergonic).

• Activation Energy: Required to start most reactions; enzymes lower this barrier.

Enzymes and Reaction Rates

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

• Enzymes can also position reactants and increase the kinetic energy of molecules.

• Enzyme activity can be regulated by various factors, including temperature, pH, and inhibitors.

Types of Chemical Reactions

• Dehydration (Condensation): Water is removed to form a bond; requires energy.

• Hydrolysis: Water is added to break a bond; releases energy.

• Oxidation-Reduction (Redox): Transfer of electrons; the molecule losing electrons is oxidized, the one gaining is reduced.

• Phosphorylation: Addition of a phosphate group, often catalyzed by kinases.

Metabolic Pathways and Regulation

Cells regulate metabolism through enzyme activity, feedback inhibition, compartmentalization, gene expression, and substrate availability.

• Glycolysis: Occurs in the cytoplasm; anaerobic; converts glucose to pyruvate, producing 2 ATP per glucose.

• Citric Acid Cycle (Krebs Cycle): Occurs in mitochondria; aerobic; processes acetyl-CoA, producing NADH, FADH2, and 2 ATP per glucose.

• Electron Transport Chain: Occurs in mitochondrial inner membrane; aerobic; uses NADH/FADH2 to generate ~28-32 ATP per glucose.

Total ATP yield per glucose: Approximately 30-36 ATP (varies by cell type and conditions).

Genetic Information Flow

DNA is transcribed to mRNA, which is then translated into protein.

• Transcription: DNA → mRNA (in nucleus)

• Translation: mRNA → Protein (in cytoplasm, at ribosome)

• Codons: Triplets of nucleotides on mRNA specify amino acids.

• tRNA: Brings amino acids to ribosome, matching codons via anticodons.

• Post-translational Modifications: Proteins may be modified (e.g., phosphorylation, glycosylation) before becoming functional.

Chapter 5: Membrane Transport and Homeostasis

Equilibrium Concepts

• Osmotic Equilibrium: Water concentration is equal on both sides of a membrane.

• Chemical Disequilibrium: Unequal distribution of solutes across a membrane.

• Electrical Disequilibrium: Difference in charge across a membrane (membrane potential).

Osmolarity and Tonicity

• Isosmotic: Solutions have equal osmolarity.

• Hyperosmotic: Solution has higher osmolarity than another.

• Hyposmotic: Solution has lower osmolarity than another.

• Isotonic: No net water movement; cell volume remains constant.

• Hypertonic: Cell loses water and shrinks.

• Hypotonic: Cell gains water and swells.

Membrane Transport Mechanisms

Cells use various mechanisms to move substances across membranes.

Type of Transport	Passive or Active?	Membrane Proteins/Vesicles?	Type of Molecule Transported	Other Details
Osmosis	Passive	Sometimes (aquaporins)	Water	Driven by concentration gradient
Bulk Flow (Filtration)	Passive	No	Water, solutes	Driven by pressure gradient
Facilitated Diffusion	Passive	Yes (carrier/channel proteins)	Ions, glucose, amino acids	Specificity, saturation, competition
Active Transport	Active	Yes (pumps)	Ions, large molecules	Requires ATP
Endocytosis	Active	Yes (vesicles)	Large particles, fluids	Phagocytosis, pinocytosis, receptor-mediated
Exocytosis	Active	Yes (vesicles)	Proteins, neurotransmitters	Fusion with plasma membrane
Transcytosis	Active	Yes (vesicles)	Macromolecules	Transport across cell

Factors Affecting Diffusion

• Increased by higher temperature, larger surface area, and steeper concentration gradient.

• Ions are affected by both concentration and electrical gradients (electrochemical gradient).

Transport Proteins

• Channel Proteins: Form pores for ions/water (e.g., aquaporins).

• Carrier Proteins: Bind and transport specific molecules.

• Uniport: Transports one substance in one direction.

• Symport: Transports two substances in the same direction.

• Antiport: Transports two substances in opposite directions.

Primary vs. Secondary Active Transport

• Primary Active Transport: Direct use of ATP (e.g., Na+/K+ pump).

• Secondary Active Transport: Uses energy from an ion gradient established by primary active transport.

Endocytosis and Exocytosis

• Endocytosis: Uptake of materials via vesicles (includes phagocytosis, pinocytosis, receptor-mediated).

• Exocytosis: Release of materials via vesicle fusion with the membrane; involves proteins like clathrin and SNAREs.

Membrane Potential

• Resting Membrane Potential: The voltage difference across the membrane, typically -70 mV in neurons.

• Depolarization: Membrane potential becomes less negative.

• Repolarization: Return to resting potential after depolarization.

• Hyperpolarization: Membrane potential becomes more negative than resting.

Chapter 6: Cell Communication and Signal Transduction

Types of Cell Signaling

• Paracrine: Signals affect nearby cells.

• Autocrine: Signals affect the same cell that secreted them.

• Neurocrine: Includes neurotransmitters, neuromodulators, and neurohormones; travel via synapses or blood.

• Hormones: Distributed via circulation; can affect distant cells.

Signal Transduction Pathways

• Signal Transduction: Transfer of information from outside to inside the cell via membrane receptors.

• Signal Amplification: One signal molecule leads to a cascade, amplifying the response.

• Receptors: G-protein coupled, receptor-enzymes, receptor-channels, integrin receptors.

G-Protein Coupled Receptors (GPCRs)

• Activate second messengers like cAMP or IP3.

• Can alter enzyme activity or open ion channels.

Second Messengers

• cAMP: Activates protein kinase A.

• IP3: Releases Ca2+ from intracellular stores.

Ligand Binding and Regulation

• Down-regulation: Decrease in receptor number or sensitivity in response to high ligand concentration.

• Up-regulation: Increase in receptor number or sensitivity.

Neural vs. Endocrine Reflexes

• Neural reflexes are faster, more specific, and shorter in duration.

• Endocrine reflexes are slower, less specific, and longer-lasting.

• Neural signals use neurotransmitters; endocrine signals use hormones.

• Neural reflexes have a direct pathway; endocrine reflexes may involve multiple steps.

• Neural responses are typically all-or-none; endocrine responses can be graded.

Example: Epinephrine Response

The effect of epinephrine depends on the type of receptor and target cell (e.g., vasoconstriction in some vessels, vasodilation in others).

Key Terms and Definitions

• Osmotic Equilibrium: Equal water concentration across a membrane.

• Chemical Disequilibrium: Unequal solute distribution.

• Electrical Disequilibrium: Unequal charge distribution.

• Depolarization: Membrane potential becomes less negative.

• Repolarization: Return to resting potential.

• Hyperpolarization: Membrane potential becomes more negative.

Additional info: This study guide expands on the original questions by providing definitions, context, and examples for each major topic, as well as a summary table for membrane transport mechanisms. Equations and more detailed mechanisms (e.g., for glycolysis or signal transduction) can be added as needed for further study.