Biology: Membrane Structure and Function Flashcards

Practice questions covering membrane structure, fluidity, transport mechanisms (passive, active, bulk), and tonicity based on Campbell Biology lecture materials.

What is the property of the plasma membrane that allows some substances to cross more easily than others?

Selective permeability

What are the most abundant lipids in the plasma membrane?

Phospholipids

What does it mean for a molecule to be amphipathic?

The molecule contains both hydrophobic and hydrophilic regions.

What is the Fluid Mosaic Model?

A model stating that the membrane is a fluid structure with a "mosaic" of various proteins embedded in it.

How do unsaturated fatty acids affect membrane fluidity?

Membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids because unsaturated tails prevent packing.

What is the effect of cholesterol on membrane fluidity at warm temperatures ($37^\circ\text{C}$)?

Cholesterol restrains the movement of phospholipids, reducing fluidity.

How does cholesterol affect membrane fluidity at cool temperatures?

It maintains fluidity by preventing tight packing.

What is the difference between integral and peripheral proteins?

Integral proteins penetrate the hydrophobic core (often as transmembrane proteins), while peripheral proteins are bound to the inner surface of the membrane.

What are the six major functions of membrane proteins?

1. Transport, 2. Enzymatic activity, 3. Signal transduction, 4. Cell-cell recognition, 5. Intercellular joining, 6. Attachment to the cytoskeleton and extracellular matrix (ECM).

What specific cell surface protein and co-receptor must HIV bind to in order to infect an immune cell?

HIV must bind to the receptor CD4 and the co-receptor CCR5.

How do cells recognize each other?

By binding to molecules, often containing carbohydrates (glycolipids or glycoproteins), on the extracellular surface of the plasma membrane.

Where is the asymmetrical distribution of proteins, lipids, and carbohydrates in the plasma membrane determined?

In the ER and Golgi apparatus when the membrane is being built.

Which type of molecules can dissolve in the lipid bilayer and pass through the membrane rapidly?

Hydrophobic (nonpolar) molecules, such as hydrocarbons.

What are channel proteins called that specifically facilitate the passage of water?

Aquaporins

What is the mechanism of a carrier protein?

They bind to molecules and undergo a subtle change in shape to shuttle the solute-binding site across the membrane.

What is diffusion?

The tendency for molecules to spread out evenly into the available space, moving from an area of high concentration to an area of lower concentration.

Why is the diffusion of a substance across a biological membrane called passive transport?

Because no energy is expended by the cell for the process to occur.

What is osmosis?

The diffusion of water across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration.

What happens to an animal cell placed in a hypertonic solution?

The cell will lose water and shrivel.

What happens to a plant cell in a hypotonic solution?

The cell swells until the wall opposes uptake, making the cell Turgid (firm).

What is osmoregulation and what organism uses a contractile vacuole for it?

Osmoregulation is the control of solute concentrations and water balance; the protist Paramecium uses a contractile vacuole as a pump.

What is plasmolysis?

A lethal effect in plant cells in a hypertonic environment where the plasma membrane pulls away from the cell wall, causing the plant to wilt.

What are gated channels?

Ion channels that open or close in response to a stimulus.

What is the primary requirement for active transport?

Energy, usually in the form of ATP, to move solutes against their concentration gradients.

What is membrane potential?

The voltage difference across a membrane created by the distribution of positive and negative ions.

What two forces make up the electrochemical gradient driving ion diffusion?

A chemical force (the ion's concentration gradient) and an electrical force (the effect of the membrane potential).

What is the main electrogenic pump in plants, fungi, and bacteria?

The proton pump ($H^+$ ions).

What is cotransport?

A process where the active transport of a solute indirectly drives the transport of other substances.

What is the difference between exocytosis and endocytosis?

Exocytosis is the release of content outside the cell via vesicle fusion, while endocytosis is the intake of macromolecules by forming vesicles from the plasma membrane.

What are the three types of endocytosis?

Phagocytosis ("cellular eating"), Pinocytosis ("cellular drinking"), and Receptor-mediated endocytosis.

What is a ligand?

Any molecule that binds specifically to a receptor site of another molecule.