Plasma Membrane and Cell Extensions Review

Flashcards covering plasma membrane structure, lipid and protein components, transport mechanisms, cell surface extensions, glycocalyx, and intercellular junctions.

What proportion of plasma membrane lipid molecules are phospholipids?

About $75\%$ of membrane lipid molecules are phospholipids.

What is the function of cholesterol in the plasma membrane?

Cholesterol is found at the surface of phospholipids and holds them in place, which can stiffen the membrane.

What are glycolipids and where are they located?

Glycolipids are phospholipids with short carbohydrate chains bound to them, located on the extracellular side of the plasma membrane.

What structural regions allow transmembrane proteins to pass completely through the phospholipid bilayer?

Transmembrane proteins have both hydrophilic regions and hydrophobic regions, and they are anchored to the cytoskeleton.

How do receptor proteins in the plasma membrane function?

Hormones or neurotransmitters bind to receptors on the membrane to trigger a physiological change inside the cell.

What role do enzyme proteins play in the plasma membrane?

They carry out chemical reactions to break down messages that have already been received.

What molecules act as cell-identity markers and what is their function?

Glycoproteins and glycolipids act as identification markers that distinguish self cells from foreign entities like bacteria.

What is the function of cell-adhesion molecules (CAMs)?

CAMs are membrane proteins that allow cells to stick together and to extracellular material, which is essential for cell survival.

What is the distinction between constantly open channel proteins and gated channel proteins?

Constantly open channel proteins allow solutes or water to pass freely, whereas gated channels open or close only when stimulated.

How does filtration work across a membrane?

Filtration uses pressure to force water and small solutes through tiny openings in a membrane, while preventing large particles like blood cells from passing.

How does simple diffusion differ from facilitated diffusion?

Simple diffusion moves molecules from high to low concentration directly through the bilayer or channels without transport proteins, whereas facilitated diffusion moves molecules from high to low concentration using transport proteins without ATP.

How does active transport move solutes across the plasma membrane?

Active transport uses a transport protein and ATP energy to move molecules from low to high concentration against their concentration gradient, changing the protein's shape as ATP is broken down.

What is osmosis?

Osmosis is the ATP-independent movement of water across a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration to balance solute concentrations.

What happens during pinocytosis?

During pinocytosis, the cell engulfs a sample of interstitial fluid containing ions and molecules.

How does phagocytosis carry out the chemical breakdown of engulfed particles?

Pseudopodia extend to surround a particle and form a vesicle, which then fuses with lysosomes containing digestive enzymes to break down the particle.

What structure surrounds vesicles during receptor-mediated endocytosis?

The vesicles are surrounded with clathrin-coated pits (proteins) that act as identification markers for the internal substance.

What is the structure and main function of microvilli?

Microvilli form a brush border supported by actin microfilaments to increase surface area for absorption, such as absorbing nutrients in the small intestine.

What is the function of cilia in the trachea?

Cilia allow movement and work in the trachea to move mucous in order to trap certain matter.

What composes the glycocalyx and what are its primary functions?

The glycocalyx is composed of sugar chains belonging to glycolipids and glycoproteins. It protects the plasma membrane from physical and chemical injury and aids in cell identity.

What is the function of tight junctions?

Tight junctions are proteins that join cells and tissues together, sealing the space between cells to keep extracellular matter out.

What are desmosomes?

Desmosomes are proteins that hold cells together.

What is the structure and function of gap junctions?

Gap junctions are formed by $6$ proteins known as a connexon, which creates a pore or channel connecting the cytoplasms of adjacent cells.