Chapter 5: Structure and Function of Plasma Membranes

Question-and-answer flashcards covering membrane structure, components, transport mechanisms, osmosis/osmoregulation, and endocytosis/exocytosis as described in the notes.

What is the Fluid Mosaic Model?

A model describing membranes as fluid and dynamic, with diverse proteins embedded in a phospholipid bilayer, giving selective permeability.

What is the plasma membrane's key transport property?

Selective permeability—the ability to regulate which substances cross the membrane.

What are the major components of the plasma membrane?

Phospholipids, cholesterol, and membrane proteins (with attachments to the cytoskeleton and extracellular matrix).

What are some common functions of membrane proteins?

Enzymatic activity, attachment to ECM/cytoskeleton, receptor signaling, channel transport, active transport, junctions, and glycoprotein roles.

What is the role of channel proteins?

Provide a hydrophilic pathway for specific ions or molecules to cross the membrane.

What is the role of active transport proteins?

Move substances against their concentration gradient using energy (often ATP).

What is the function of glycoproteins?

Serve as identification tags recognized by other cells’ membrane proteins.

What is diffusion?

Net movement of particles from high to low concentration, down their gradient, until dynamic equilibrium is reached.

What is osmosis?

Diffusion of water across a selectively permeable membrane down its concentration gradient.

What does tonicity refer to?

The ability of surrounding solution to cause a cell to gain or lose water.

What happens to animal cells in a hypotonic solution?

Water enters the cell; it may swell and lyse.

What happens to plant cells in a hypotonic solution?

Water enters; cells become turgid (normal due to cell wall).

What happens to animal cells in a hypertonic solution?

Water exits the cell; it shrivels (crenation).

What happens to plant cells in a hypertonic solution?

Water exits; the cell membrane may plasmolyze from the cell wall.

What is osmoregulation?

Control of water balance by an organism.

What is facilitated diffusion?

Passive transport that uses a transport protein to move substances down their concentration gradient.

What is an aquaporin?

A membrane protein channel that facilitates rapid diffusion of water.

What is passive transport?

Diffusion across a membrane with no energy investment.

What is active transport?

Movement of solutes against their concentration gradient requiring energy (ATP).

How does ATP contribute to transport?

ATP provides energy for conformational changes in transport proteins during active transport.

What is exocytosis?

Export of bulky molecules via vesicles that fuse with the plasma membrane.

What is endocytosis?

Uptake of large molecules via vesicle formation; includes phagocytosis and receptor-mediated endocytosis.

What is phagocytosis?

Engulfment of a particle to form a food vacuole.

What is receptor-mediated endocytosis?

Endocytosis initiated by binding of specific solutes to cell-surface receptors, forming a coated vesicle.

What is the role of attachment proteins?

Attach to the extracellular matrix and cytoskeleton to support the membrane and coordinate external/internal changes.

What is the role of junction proteins?

Form intercellular junctions that attach adjacent cells.

What is the role of enzymes as membrane proteins?

Some membrane proteins function as enzymes, often arranged to carry out sequential reactions.

What is spontaneous membrane formation and its significance?

Phospholipids can self-assemble into simple membranes, a critical step in the origin of life.

What is the difference between isotonic, hypotonic, and hypertonic solutions for cells?

Isotonic: no net water movement; hypotonic: water enters; hypertonic: water exits.