Ch 7:

What is the fundamental function of the plasma membrane?

It acts as a selective barrier (selective permeability) separating the cell's internal environment from its surroundings, regulating the movement of substances in and out of the cell.

Amphipathic?

They contain both hydrophilic ("water-loving") head regions and hydrophobic ("water-fearing") tail regions. (e.g phospholipids)

Describe the Fluid Mosaic Model.

The membrane is a fluid structure composed of a phospholipid bilayer with various proteins floating or embedded throughout it.

How do unsaturated vs. saturated fatty acid tails affect membrane fluidity?

• Unsaturated tails: Kinks in the chains prevent tight packing, keeping the membrane more fluid at lower temperatures.

• Saturated tails: Straight chains pack closely together, making the membrane more viscous/solid.

What is the role of cholesterol in animal cell membranes?

It acts as a temperature buffer:

• At high temperatures, it restrains phospholipid movement to reduce fluidity.

• At low temperatures, it prevents tight packing to keep the membrane fluid.

What is the main structural difference between integral and peripheral membrane proteins?

• Integral proteins: (inside) Penetrate the hydrophobic core of the bilayer (transmembrane proteins span all the way through).

• Peripheral proteins: Loosely bound to the outer or inner surface of the membrane.

What secondary protein structure typically forms the hydrophobic region of transmembrane proteins?

An -helix composed of nonpolar amino acids.

List the six major functions of membrane proteins.

• Transport

• Enzymatic activity

• Signal transduction

• Cell-cell recognition

• Intercellular joining

• Attachment to the cytoskeleton and Extracellular Matrix (ECM)

Name the three main types of intercellular junctions in animal cells.

• Tight Junctions: Prevent fluid leakage between cells.

• Desmosomes (Anchoring Junctions): Fasten cells together into strong sheets.

• Gap Junctions: Provide cytoplasmic channels for communication between adjacent cells.

What is passive transport, and what drives it?

The movement of molecules across a membrane without any cellular energy (ATP) input, driven naturally by a concentration gradient.

What is osmosis?

The diffusion of free water across a selectively permeable membrane toward a region of higher solute concentration.

(movement of water from a place where it is watery to a place where it is concentrated (or salty/sugary) through a barrier)

How does a cell react when placed in hypertonic, hypotonic, and isotonic solutions?

• Hypertonic: Is Higher solute outside → water leaves → cell shrivels.

• Hypotonic: Is Lower solute outside → water enters → cell swells/lyses.

• Isotonic: Equal solute concentration → no net water movement.

What is the difference between active transport and facilitated diffusion?

• Facilitated Diffusion: passive transport, meaning the cell lets substances slide down a concentration gradient (from a crowded area to an empty area) through a helper channel or carrier (no energy req)

• Active Transport: Uses transport proteins and energy (ATP) to move substances against their concentration gradient (from an empty area into an already packed room).

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What is the difference between exocytosis and endocytosis?

• Exocytosis: Transport vesicles fuse with the membrane to release materials out of the cell.

• Endocytosis: The cell takes in materials by forming new vesicles from the plasma membrane.