BIOL 1151, CH 7

What does amphipathic mean?

Having both hydrophilic and hydrophobic regions.

What part of a phospholipid is hydrophilic?

The phosphate-containing head, which is attracted to water.

What part of a phospholipid is hydrophobic?

The fatty acid hydrocarbon tails, which repel water.

How are phospholipids arranged in the plasma membrane?

In a bilayer, with hydrophilic heads facing the watery environments and hydrophobic tails facing inward toward each other.

How do phospholipids move within a membrane?

They move sideways (laterally) frequently, but rarely flip from one side of the bilayer to the other.

What determines membrane fluidity?

Temperature, cholesterol, and the saturation and length of phospholipid fatty acid tails.

How do unsaturated fatty acid tails affect membrane fluidity?

Their double bonds create bends that prevent tight packing, increasing fluidity.

How do saturated fatty acid tails affect membrane fluidity?

They are straighter and pack more tightly, generally decreasing fluidity.

What is the function of cholesterol in animal cell membranes?

It helps regulate membrane fluidity and stability as temperature changes.

What are the six major functions of membrane proteins?

Transport, enzymatic activity, signal transduction, cell-to-cell recognition, intercellular joining, and attachment to the cytoskeleton and extracellular matrix (ECM).

What is membrane sidedness?

The two sides of a membrane differ in composition and function, including their proteins and lipids.

What is selective permeability?

The ability of a membrane to allow certain substances to cross while restricting others.

What determines which substances can cross a membrane?

The membrane's properties, including its hydrophobic interior, and the presence of specific transport proteins.

What is diffusion?

The net movement of particles from an area of higher concentration to an area of lower concentration.

What is the goal of diffusion?

To reach equilibrium, where particles are evenly distributed overall and there is no net movement.

What is osmosis?

The net movement of water across a selectively permeable membrane toward the side with the higher effective solute concentration.

What is an isotonic solution?

A solution with the same effective solute concentration as the cell, resulting in no net water movement.

What is a hypertonic solution?

A solution with a higher effective solute concentration than the cell, causing water to leave the cell.

What is a hypotonic solution?

A solution with a lower effective solute concentration than the cell, causing water to enter the cell.

What happens to an animal cell in a hypotonic solution?

Water enters the cell, causing it to swell and potentially burst (lyse).

What happens to an animal cell in a hypertonic solution?

Water leaves the cell, causing it to shrink.

What happens to a plant cell in a hypotonic solution?

Water enters the cell, making it turgid; the cell wall helps prevent bursting.

What happens to a plant cell in a hypertonic solution?

Water leaves the cell, causing the membrane to pull away from the cell wall (plasmolysis).

What is passive transport?

Movement across a membrane down a concentration or electrochemical gradient without direct energy input from ATP.

What is facilitated diffusion?

Passive transport in which channel or carrier proteins help substances cross a membrane down their gradient.

What is active transport?

Transport that uses energy to move substances against their concentration or electrochemical gradient.

What is cotransport?

A process in which the downhill movement of one solute provides the energy to move another solute uphill.

What is endocytosis?

The process by which a cell takes in substances using vesicles formed from the plasma membrane.

What is phagocytosis?

A type of endocytosis in which a cell engulfs large particles.

What is pinocytosis?

A type of endocytosis in which a cell takes in extracellular fluid and dissolved substances.

What is receptor-mediated endocytosis?

Selective uptake in which specific ligands bind to receptors, often in coated pits, triggering vesicle formation.

What is a ligand?

A molecule that binds specifically to a receptor.

What is exocytosis?

The process by which a vesicle fuses with the plasma membrane and releases its contents outside the cell.

How does exocytosis differ from endocytosis?

Exocytosis releases substances outside the cell, while endocytosis brings substances into the cell.