Cell Membranes 6
Terms in this set (49)
Fluid Mosaic Model
General structure of membranes. Phospholipids form a bilayer, which is like a "lake" in which a variety of proteins "float".
Phospholipids have a polar what?
Fatty acid "tails"
Phospholipids have a hydrophobic what?
Lipid composition and temperature
Fluidity depends on?
Lipid composition of membranes vary
in fatty acid chain length
degree of saturation
Membrane less fluid:
cholesterol and long-chain
saturated fatty acids pack tightly
Membrane more fluid with:
shorter-chain fatty acids
unsaturated fatty acids (have 'kinks')
Animal cell may be up to what percentage of cholesterol (that is important for membrane integrity)?
Peripheral membrane protein and Integral membrane protein
Two types of membrane proteins
Peripheral Membrane Protein
Lack exposed hydrophobic groups and do not penetrate the bilayer
Integral Membrane Proteins
have hydrophobic and hydrophilic regions or domains. Some extend across the lipid bilayer; others are partially embedded.
INTEGRAL MEMBRANE PROTEINS that extend all the way through the phospholipid bilayer.
Some membrane proteins can move_______within the bilayer, while others are anchored to a specific region.
carbohydrates; outer surface
Membranes also have_____________ on the_______ __________ that serve as recognition sites for other cells and molecules.
(carbohydrate + lipid): any complex lipid with one or more attached carbohydrates residues.
(carbohydrate + protein): molecules often involved in cell recognition and binding
forming, transforming, fusing, and breaking down
Membranes are dynamic and are constantly _______, ___________ ,______________, and _________ __________
Specialized structures that connect and hold cells together
prevent leakage of extra-cellular fluid and help ensure directional movement of materials
Are like "spot welds" that fasten/anchor cells together
allow chemical communication between cells.
Transmembrane protein binds to the matrix outside epithelial cells, and to actin filaments inside the cells.
The binding is noncovalent and reversible.
Fetal development and Metastasis (spread of cancer cells)
Cell detachment allows for cell movement
Cell movement important for:
some substances can pass through but others cant
Passive Transport and Active Transport
Types of Transport across Membrane:
no outside energy required (diffusion)
- Moves substances against a concentration and/or electrical gradient--requires energy.
The energy source is often adenosine triphosphate (ATP)
-The process of random movement of solute toward equilibrium
-It is the net movement of solute from regions of greater concentration to regions of lesser concentration.
-Works very well over short distances
solute continue to move, but there is no net change in distribution.
directional until equilibrium is reached
Diffusion rate depends on:
-Diameter of the molecules or ions
-Temperature of the solution
The membrane is________ to solutes that move easily across it; __________ to those that can't.
Small molecules pass through the lipid bilayer.
-Lipid-soluble molecules can diffuse across the membrane
-Electrically charged and polar molecules cannot pass through easily.
eg. amino acids, sugars and ions
The diffusion of water through specialized channels.
Osmosis depends on the number of solute particles present, not the type of particles.
Equal solute concentration (and equal water concentration)
Higher solute concentration
Lower solute concentration
Plant cells with rigid cell walls build up internal pressure that keeps more water from entering
Animal cells may burst when placed in_________solution
Of polar molecules by two types of transport proteins (passive transport): Channel Proteins and Carrier proteins
have a central pore lined with polar amino acids.
membrane proteins that bind some substances and speed their diffusion through the bilayer
Specific channel proteins with hydrophilic pores
can be closed or open to ion passage
-Gate opens when protein is stimulated to change shape. Stimulus can be a molecule or electrical charge resulting from many ions
Active processes of Membrane transport
Active transport is directional. It involves three kinds pf proteins:
Uniporter, Symporter, and Antiporter
-Active transport: Requires direct hydrolysis of ATP
Macromolecules (proteins, polysaccharides, nucleic acids) are too_____ to cross the membrane.
-They can be taken in or secreted by means of membrane vesicles.
Processes that bring molecules and cells into a eukaryotic cell.
The plasma membrane folds in or invaginates around the material, forming a vesicle.
Molecules or entire cells are engulfed. Some protists feed in this way. Some white blood cells engulf foreign substances
-A food vacuole or phagosome forms, which fuses with a lysosome.
A vesicle forms to bring small dissolved substances of fluids into a cell. Vesicles are much smaller than in phagocytosis.
-is constant in endothelial (capillary) cells.
Receptor mediated endocytosis
-Depends on receptor proteins-integral membrane proteins-to bind to specific substances.
-Sites are called coated pits-coated with other proteins such as clahrin
Material in vesicles is expelled from a cell.
-Indigestible materials are expelled.
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