BI108 Membrane Transport

Passive transport

any movement of ions or molecules that does NOT require an input of energy

• occurs DOWN a concentration gradient (high concentration → lower concentration)

• spontaneous process

Active transport

any movement of ions or molecules that requires an input of energy

• nonspontaneous process

• occurs AGAINST a concentration gradient (low concentration → higher concentration)

Channel proteins

transmembrane proteins that function as tunnels and allow ions and other small molecules to pass

• have open and closed configurations that are highly regulated

Ligand

chemical signal

Conformational change

when a protein changes shape

Carrier proteins

proteins that temporarily bind to substances to move them across the membrane creating conformational changes in the protein

Membrane pumps

transport substances against—or up—a concentration gradient (and/or electrical gradient) → active transport

Vesicle

encloses fluid and materials in a lipid bilayer

Exocytosis

material in vesicles is expelled from the cell

Endocytosis

vesicles brings materials into a eukaryotic cell