Membrane Transport and Structure Vocabulary

Vocabulary flashcards covering key terms related to plasma membrane components, transport mechanisms, diffusion, osmosis, and active transport based on the lecture.

Phospholipid

A molecule featuring a fatty internal portion and an outer head that integrates well with water, forming the core bilayer of the plasma membrane.

Fluid Mosaic Model

A model describing the plasma membrane structure, consisting of a fluid phospholipid bilayer embedded with floating proteins and cholesterol.

Cholesterol

A lipid molecule in animal cell membranes that regulates membrane fluidity and sponginess, preventing it from becoming too liquid or too rigid.

Lipid Rafts

Microdomains in the cell membrane formed when cholesterol aggregates around membrane proteins, allowing them to float together to direct signals.

Sterols

Molecules found in plants and fungi that serve a similar function to cholesterol in maintaining membrane fluidity and sponginess.

Integral Proteins

Proteins embedded in the membrane that can bind tightly to one another, serving as glue to hold cells together in multicellular organisms.

Transmembrane Proteins

Proteins that span across the plasma membrane, facilitating cell communication and the transport of molecules in and out of the cell.

Glycoproteins

Proteins attached to carbohydrate chains on the cell's outer surface, involved in cell-to-cell recognition, such as defining ABO blood types.

ACE-2

An enzyme protein located on host cell surfaces that SARS-CoV-2 specifically attaches to in order to gain entry into the cell.

CD4 and CCR5

Specific surface protein co-receptors found on human T cells that HIV must bind to in order to infect the immune cell.

Nonpolar Molecules

Balanced, nonpolar gases like oxygen ($O_2$) and carbon dioxide ($CO_2$) that can freely slip through the hydrophobic phospholipid membrane without transport proteins.

Diffusion

The passive movement of molecules or solutes from an area of high concentration to an area of low concentration.

Brownian Motion

The random motion of particles suspended in a medium that drives passive diffusion toward equilibrium.

Osmosis

The specific passive movement or diffusion of water across a semipermeable membrane from high water concentration to low water concentration.

Aquaporins

Specialized channel proteins in the plasma membrane that specifically facilitate the rapid passage of water molecules into and out of the cell.

Necrosis

A mechanism of unprogrammed cell death where a cell swells excessively with water, loses structural integrity, and breaks down.

Tonicity

The measure of the effective osmotic pressure gradient or concentration of solutes floating around in a solution relative to the inside of a cell.

Contractile Vacuole

A specialized organelle in organisms like Paramecium that contracts to pump out excess water and maintain proper osmotic balance.

Facilitated Diffusion

The movement of specific molecules across a membrane down their concentration gradient using helper proteins without requiring ATP energy.

Gated Channels

Ion channels in the plasma membrane that open or close in response to specific signals, allowing ions like sodium, potassium, or calcium to flow without directly using ATP.

Active Transport

The movement of substances across a cell membrane against their concentration gradient, requiring energy expenditure in the form of ATP.

Sodium-Potassium Pump

An active transport membrane protein that cleaves one phosphate from ATP to pump three sodium ions out of the cell and two potassium ions into the cell.

Exocytosis

The process by which cells expel internal contents, such as neurotransmitters or insulin, to the outside of the cell via membrane vesicles.

Endocytosis

The cellular process of engulfing external materials by wrapping the plasma membrane around them to form an internal vesicle.

Phagocytosis

A specific form of endocytosis ('cell eating') in which a cell engulfs large particles or organisms, such as a white blood cell consuming a bacterium.