MCQs

A coenzyme is a non-protein organic molecule that binds transiently to an apoenzyme, allowing it to be separated by dialysis, unlike a prosthetic group.

Substrate binding is mediated by multiple weak, non-covalent forces which are reversible, essential for both binding and product release.

Enzymes lower activation energy by providing an alternative reaction pathway where specific R-groups orient and stress substrates, stabilizing the transition state.

The active site is a specific, flexible 3D pocket formed by a few amino acids that binds the substrate and catalyzes its conversion to product via weak interactions.

A prosthetic group is a non-protein unit that is covalently or very tightly bound to an apoenzyme, making it a permanent part of the functional holoenzyme.

The tertiary structure of an enzyme, which dictates the shape of the active site, is stabilized by hydrogen bonds, ionic interactions, hydrophobic interactions, van der Waals forces, and covalent disulfide bonds.

Enzymes are biological catalysts that accelerate reactions by decreasing the activation energy. They do not provide energy, alter the equilibrium constant, or change the free energy change (ΔG) of the overall reaction.

Pinocytosis is a type of endocytosis where the membrane invaginates to take in fluid.

Its ability to regulate its own composition and environment is a fundamental property of a living membrane.

Immune cells use recognition markers to identify infected or foreign cells (e.g., pathogens).

Cholesterol is a steroid, characterized by its four-ring hydrocarbon structure.

Both facilitated and simple diffusion are passive processes driven by concentration gradients.

Peripheral proteins sit on the outside (or inside) surface of the bilayer.

Carrier proteins bind specific molecules and shift conformation to move them across the membrane.

The phosphate group is negatively charged and highly attracted to water.

Saturated chains pack tightly, resulting in a more rigid, less fluid membrane.

The cell membrane's surface markers are crucial for identifying "self" vs "non-self" cells.

Plasmalemma is essentially the plasma membrane of a cell.

Small, non-polar molecules move easily through the non-polar lipid bilayer.