Structure and Function of Plasma Membranes

Flashcards covering key concepts from the lecture notes on the structure and function of plasma membranes.

What does the plasma membrane define in a cell?

The plasma membrane defines the cell and outlines its borders, determining interactions with the environment.

What is the meaning of selectively permeable in terms of the plasma membrane?

The plasma membrane permits certain molecules to pass through easily while inhibiting others.

What is the fluid mosaic model?

The fluid mosaic model describes the plasma membrane as a mosaic of components—including phospholipids, cholesterol, proteins, and carbohydrates—that gives it a fluid character.

What are phospholipids in the plasma membrane?

Phospholipids form the primary membrane fabric, making them the most abundant component in the plasma membrane.

What characterizes phospholipids as amphipathic molecules?

Phospholipids have a polar (hydrophilic) region and a nonpolar (hydrophobic) region.

What happens to phospholipids when heated in an aqueous environment?

Phospholipids usually spontaneously form small spheres or droplets (micelles or liposomes) with hydrophilic heads forming the exterior and hydrophobic tails on the inside.

How do the polar head groups of phospholipids interact with water?

The polar head groups can form hydrogen bonds with water and other polar molecules.

What stabilizes membranes primarily?

Weak hydrophobic interactions stabilize membranes and allow for dynamic movement within the membrane leaflet.

How do temperatures affect membrane fluidity?

Membranes composed largely of saturated fatty acids become dense and rigid at lower temperatures, while those high in unsaturated fatty acids remain more fluid.

What role does cholesterol play in membrane fluidity?

Cholesterol stabilizes the membrane at higher temperatures by limiting excessive movement of phospholipids and prevents phospholipids from packing too closely together at lower temperatures.

What are peripheral and integral proteins?

Peripheral proteins are found on the inner or outer surface of the membrane, while integral proteins are embedded within the phospholipid layers.

How do carbohydrates contribute to cell-cell recognition?

Carbohydrates form specialized sites on the cell surface that allow for recognition between cells, aiding the immune system.

What is osmosis?

Osmosis is the movement of water molecules across a semi-permeable membrane from an area of high-water concentration to low-water concentration.

What is tonicity?

Tonicity describes how the concentration of solute in the extracellular solution can cause a cell to gain or lose water through osmosis.

What are the three types of endocytosis?

The three types of endocytosis are phagocytosis, pinocytosis, and receptor-mediated endocytosis.

What occurs during phagocytosis?

During phagocytosis, a cell engulfs large particles by surrounding them with its membrane and forming a vacuole.

How does facilitated diffusion differ from simple diffusion?

Facilitated diffusion involves transport proteins to help molecules cross the membrane, while simple diffusion does not.

What is the role of transport proteins?

Transport proteins assist in the movement of hydrophilic substances across the membrane that would otherwise be hindered.

What is active transport?

Active transport is the movement of a substance against its concentration gradient, requiring cellular energy, typically in the form of ATP.

What is osmoregulation?

Osmoregulation is a mechanism that regulates an organism's osmolarity and water balance to prevent osmotic problems.

What is exocytosis?

In exocytosis, transport vesicles containing substances migrate to the plasma membrane and release their contents outside the cell.