Cell Membrane (1.2)

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Cell Membrane

A selectively permeable boundary; surrounding the entire cytoplasm and separating it from the extracellular environment; composed of a phospholipid bilayer with embedded proteins and cholesterol.

cilia

Hair-like motile projections; located on the apical (top) surface of certain epithelial cells; composed of a "9+2" arrangement of microtubules made of tubulin.

intracellular fluid

The aqueous environment inside the cell; located within the boundaries of the plasma membrane; composed of water (cytosol); dissolved ions; and organic molecules.

phospholipid molecules

The fundamental building blocks of the membrane; located throughout the entire plasma membrane and organelle membranes; composed of a hydrophilic phosphate head and two hydrophobic fatty acid tails.

extracellular fluid

The fluid environment outside the cell; located immediately exterior to the plasma membrane; composed of water; electrolytes; and nutrients.

membrane proteins

Functional molecules of the cell boundary; located embedded within or attached to the surface of the phospholipid bilayer; composed of chains of amino acids.

selectively permeable

A regulatory property of the cell boundary; located at the site of the plasma membrane; determined by the chemical arrangement of the phospholipid bilayer and specific transport proteins.

flagella

A long whip-like tail; located extending from the posterior end of cells like sperm; composed of long bundles of microtubules.

microvilli

Small finger-like folds; located on the apical surface of cells specialized for absorption (like the intestines); composed of plasma membrane extensions with a core of actin filaments.

integral

Proteins that span the membrane; located passing through the hydrophobic core of the phospholipid bilayer; composed of amino acids with nonpolar side chains.

peripheral

Proteins on the membrane surface; located attached to the inner or outer surface of the phospholipid bilayer; composed of hydrophilic amino acids.