Chapter 4 Flashcards
rate of diffusion is determined by
- amount of substance available
- velocity of kinetic motion
- number and sizes of openings in the membrane through which the molecules or ions can move
Simple diffusion can occur through the cell membrane by two pathways
(1) through the interstices of the lipid bilayer
(2) through watery channels that penetrate all the way through some of the large transport proteins
High lipid solubles
oxygen, nitrogen, carbon dioxide, alcohol
2 important characteristics of protein channels
(1) Selectively permeable
(2) Opened or closed by gates regulated by voltage-gated channels or ligand-gated channels
opening and closing of gates are controlled in two principal ways
- Voltage gating
- Chemical (ligand) gating
Substances transported by primary active transport
- Sodium
- Potassium
- Calcium
- Hydrogen
- Chloride
carrier protein is a complex of
two separate globular proteins
- larger one called the α subunit
- a smaller one called the β subunit
3 specific feature of larger unit (a subunit)
- 3 receptor sites for binding calcium
- 2 receptor sites for potassium ions
- inside portion of this protein near the sodium binding sites has ATPase activity
Two especially important counter-transport mechanisms
- sodium-calcium counter-transport
- sodium-hydrogen counter-transport
Active Transport Through Cellular Sheets
(1) intestinal epithelium
(2) epithelium of renal tubules
(3) epithelium of all exocrine glands, (4) epithelium of the gallbladder
(5) membrane of the choroid plexus of the brain and other membranes
basic mechanism for transport of a substance through a cellular sheet
(1) active transport
(2) either simple diffusion or facilitated diffusion
Na+ in ECF
142
Na+ in Intracellular fluid
10
K+ in ECF
4
K+ in Intracellular fluid
140
random molecular movement of substances molecule by molecule
diffusion
energy that causes diffusion
energy of the normal kinetic motion of matter
movement of ions or other substances across the membrane in combination with a carrier protein
active transport
requires an additional source of energy besides kinetic energy
active transport
continual movement of molecules among one another in liquids or in gases
diffusion
diffuse far less rapidly than molecular substances because of their large size
colloids
kinetic movement of molecules or ions occurs through a membrane opening or through intermolecular spaces
simple diffusion