VIDEO 5.1 Cell Visualization: Membranes, hormones, and receptors
See Figure 5.1
Figure 7.13 The water balance of living cells
Figure 7.16, 1–6 The sodium-potassium pump: a specific case of active transport
Bio 189 cell_membranes_and_signaling_spr
BIOLOGY 189Cell Membranes and Signaling
Biological Membranes• General structure: fluid mosaic model.• Phospholipids form a bilayer• Two regions: Hydrophilic regions—“heads” that associate with water molecules Hydrophobic regions—nonpolar fatty acid “tails” that do not dissolve in water
Biological Membranes • May differ in lipid composition as there are many types of phospholipids. • Phospholipids may differ in: Fatty acid chain length Degree of saturation Kinds of polar groups present
Biological Membranes• Two important factors in membrane fluidity: Lipid composition—types of fatty acids can increase or decrease fluidity Temperature—membrane fluidity decreases in colder conditions
Biological Membranes• Membranes contain proteins Peripheral membrane proteins lack hydrophobic groups and are not embedded in the bilayer. Integral membrane proteins are partly embedded in the bilayer.
Biological Membranes • Anchored membrane proteins have lipid components that anchor them in the bilayer. • Transmembrane proteins extend through the bilayer on both sides
Biological Membranes• Plasma membrane carbohydrates located on the outer membrane serve as recognition sites. Glycolipid—a carbohydrate bonded to a ________ Glycoprotein—a carbohydrate bonded to a ______
Selective Permeability • Biological membranes allow some substances to pass or not. Passive transport does not require energy. Active transport requires energy.
Diffusion Passive transport • Two types of diffusion: Simple diffusion Facilitated diffusion through channel proteins or aided by carrier proteins
Diffusion• Speed of diffusion depends on Diameter of the molecules—smaller molecules diffuse faster Temperature of the solution—higher temperatures lead to faster diffusion The concentration gradient the greater the concentration, the faster a substance will diffuse
Diffusion Higher concentration inside the cell causes the solute to diffuse out, and a higher concentration outside causes the solute to diffuse in, for many molecules.
Osmosis• Diffusion of water across membranes.• Depends on the concentration of solute molecules on either side of the membrane.• Water passes through special membrane channels.
Hypertonic, Isotonic, HypotonicWhen comparing two solutions separated by a membrane:• A hypertonic solution has a higher solute concentration• Isotonic solutions have equal solute concentrations• A hypotonic solution has a lower solute concentration
Facilitated Diffusion Diffusion aided by • Channel proteins. Integral membrane proteins that form channels across the membrane. • Substances can also bind to carrier proteins to speed up diffusion.
A Ligand-Gated Channel Protein Opens in Response to a Stimulus
Diffusion• Water crosses membranes with the help of Aquaporins (specific channels)• They allow large amounts of water to move against its concentration gradient• I t may “hitchhike” with ions such as Na+ as they pass through channels.
Active transport• requires energy to move substances against their concentration gradients.• energy source: ATP.• A substance moves in the direction of the cell’s needs, usually by means of a specific carrier protein.
Active transport Two types • Primary active transport involves hydrolysis of ATP for energy. • Secondary active transport uses the energy from an ion concentration gradient, or an electrical gradient.
Active Transport • The sodium–potassium (Na+–K+) pump is an integral membrane protein that pumps Na+ out of a cell and K+ in. • One molecule of ATP moves two K+ and three Na+ ions.
EXTRACELLULAR [Na+] high Na+ FLUID [K+] low Na+ Na+ Na+ Na+ Na+ Na+ Na+ [Na+] low ATP Na+ PCYTOPLASM [K+] high P ADP 1 2 3 K+ K+ K+ + K+ K P K+ P 6 5 4
Endocytosis and Exocytosis • Macromolecules are too large or too charged to pass through biological membranes and instead pass through vesicles. • Cells use endocytosis or exocytosis