1.2 The Cell Membrane

Hydrophilic

Refers to molecules that are attracted to water; they are polar and tend to be soluble in water.

Hydrophobic

Refers to molecules that repel water; they are non-polar and typically insoluble in water.

Amphipathic

Molecules that have both hydrophilic and hydrophobic properties.

Phospholipid bilayer

A double layer of phospholipids that makes up the cell membrane; it is selectively permeable.

Integral proteins

Proteins that are permanently embedded in the membrane and may span across it.

Peripheral proteins

Proteins that temporarily associate with the membrane and are usually located on its surface. They can be monotopic or attach to the surface.

Cholesterol

A type of lipid that stabilizes the cell membrane, regulating its fluidity and flexibility. It makes the phospholipids pack more tightly and regulates the fluidity and flexibility of the membrane. It stabilizes membranes at higher temperatures and prevents stiffening at lower temperatures.

Saturated fatty acids

Fatty acids with straight chains that can pack tightly, reducing membrane fluidity and permeability.

Unsaturated fatty acids

Fatty acids with one or more kinks that pack loosely, increasing membrane fluidity and permeability.

Glycolipids

Lipids with a carbohydrate attached, playing roles in cell recognition.

Glycoproteins

Proteins with a carbohydrate as the non-polypeptide component, involved in cell communication and recognition.

Conjugated protein

A protein that is combined with a non-protein component, such as a carbohydrate in glycoproteins.

Fluid mosaic model

A model describing the cell membrane structure as flexible and composed of various molecules that can move laterally.

Facilitated diffusion

A process that allows substances to cross membranes with the assistance of special proteins.

Active transport

The movement of molecules across a membrane that requires energy input, often against a concentration gradient.

Endocytosis

The process by which cells engulf external substances, bringing them into the cell.

Exocytosis

The process of expelling materials from the cell using vesicles that fuse with the plasma membrane.