Chapter 4 – Cell Energy & Membrane Transport

Vocabulary flashcards covering energy concepts, enzyme function, plasma membrane structure, and transport mechanisms.

Energy

The capacity to do work or cause change in matter

Kinetic Energy

Energy of motion (e.g., a sperm’s flagellum or a bicycle rushing downhill)

Potential Energy

Stored energy based on position or chemical bonds (e.g., energy in glucose bonds, runners waiting at the start line)

Chemical Energy

Potential energy stored within chemical bonds of molecules like food or ATP

ATP (Adenosine Triphosphate)

The cell’s main energy carrier; composed of adenine, ribose sugar, and three phosphate groups

ADP (Adenosine Diphosphate)

ATP after losing one phosphate group; can be re-phosphorylated to store energy again

ATP Hydrolysis

Reaction in which ATP → ADP + Pi, releasing usable free energy

Energy Coupling

The transfer of energy from ATP-releasing reactions to energy-requiring reactions

Ribose

Five-carbon sugar found in ATP

Enzyme

Protein catalyst that speeds specific biochemical reactions without being consumed

Substrate

The reactant molecule(s) on which an enzyme acts

Product (Enzymatic Reaction)

Molecule(s) produced after an enzyme converts its substrate

Enzyme Specificity

Property whereby each enzyme catalyzes only one particular reaction or type of reaction

Denaturation

Loss of a protein’s three-dimensional structure (and function) due to changes in pH, temperature, or solute concentration

Optimal Conditions (Enzyme)

The specific pH, temperature, and ionic environment where an enzyme functions best

Plasma Membrane

Selective, semi-permeable boundary of cells made of a phospholipid bilayer with proteins and cholesterol

Phospholipid Bilayer

Double layer of phospholipids forming the core of all biological membranes

Membrane Protein

Integral or peripheral protein that assists in transport, signaling, or structural support

Concentration Gradient

Difference in the concentration of a substance across a space or membrane

Passive Transport

Movement of substances down their concentration gradient without energy input (e.g., diffusion, osmosis)

Simple Diffusion

Passive movement of small non-polar molecules (O₂, CO₂) directly through the lipid bilayer

Facilitated Diffusion

Passive transport of ions or polar molecules via membrane proteins

Osmosis

Diffusion of water across a selectively permeable membrane from hypotonic to hypertonic solution

Tonicity

Relative solute concentration of two solutions separated by a membrane

Hypertonic Solution

Solution with higher solute concentration; water moves toward it

Hypotonic Solution

Solution with lower solute concentration; water moves away from it

Isotonic Solution

Solutions with equal solute concentration; no net water movement

Active Transport

Movement of substances against their concentration gradient that requires ATP and membrane proteins

Na⁺/K⁺ Pump

Membrane protein that uses ATP to export 3 Na⁺ and import 2 K⁺ ions against their gradients

Endocytosis (Phagocytosis)

Active transport process where a cell engulfs large particles or bacteria; requires ATP

Exocytosis

Active transport process that exports materials in vesicles fusing with the plasma membrane; uses ATP

Transport Vesicle

Membrane-bound sac that moves proteins and other molecules within or out of the cell