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
requires interaction of a carrier protein
facilitated diffusion
aids passage of the molecules or ions through the membrane
carrier proteins
One of the most important factors that determines how rapidly a substance diffuses through the lipid bilayer
lipid solubility
total amount of water that diffuses in each direction through the red cell membrane during each second
100 times as the volume of red cell itself
composed of integral cell membrane proteins that form open tubes through the membrane and are always open
pores
provide selectivity that permits only certain molecules to pass through pores
diameter, electrical charge
narrow pore that permits water molecules to diffuse through the membrane in single file
aquaporins/ water channels
permit passage of potassium ions across the cell membrane about 1000 times
potassium channels
structure of potassium channels
tetrameric structure
form a narrow selectivity filter
pore loops
Lines the selectivity filter
carbonyl oxygens
sodium channel’s inner surfaces are lined with amino acid that are
strongly negatively charged
provides a means of controlling ion permeability of the channels
gating of protein channels
molecular conformation of the gate or of its chemical bonds responds to the electrical potential across the cell membrane
voltage gating
opened by the binding of a chemical substance with the protein
chemical (ligand) gating
exceedingly important for the transmission of nerve signals from one nerve cell to another and from nerve cells to muscle cells to cause muscle contraction
acetylcholine channel
carrier-mediated diffusion
facilitated diffusion
Among the most important substances that cross cell membranes by facilitated diffusion
glucose, amino acids
glucose transporter 4 (GLUT4) is activated by
insulin
cell membrane moves molecules or ions “uphill” against a concentration gradient (or “uphill” against an electrical or pressure gradient)
active transport
energy is derived directly from breakdown of adenosine triphosphate (ATP) or of some other high-energy phosphate compound
primary active transport
energy is derived secondarily from energy that has been stored in the form of ionic concentration differences of secondary molecular or ionic substances
secondary active transport
substances that are transported by primary active transport
sodium, potassium, calcium, hydrogen, chloride
active transport mechanism that has been studied in greatest detail
sodium-potassium pump
responsible for maintaining the sodium and potassium concentration differences across
the cell membrane
sodium-potassium pump
establish negative electrical voltage inside the cells
sodium potassium pump
60-70 % of the cells’ energy requirement devoted to pumping Na+ out of the cell and K+ into the cell
nerve cells
it controls the volume of each cell
Na+-K+ pump
2 places primary active transport of hydrogen ions is important
(1) in the gastric glands of the stomach and
(2) in the late distal tubules and cortical collecting ducts of the kidneys
have the most potent primary active mechanism for transporting hydrogen ions of any part of the body
parietal cells
late distal tubules and cortical collecting ducts that also transport hydrogen ions by primary active transport
intercalated cells
