Chapter 5: Cell Signaling & Membrane Transport
Terms in this set (22)
Why are phospholipids amphipathic?
All of the lipid molecules in cell membranes are amphipathic (or amphiphilic)—that is, they have a hydrophilic ("water-loving") or polar end and a hydrophobic ("water-fearing") or nonpolar end. The most abundant membrane lipids are the phospholipids. These have a polar head group and two hydrophobic hydrocarbon tails.
What is the fluid mosaic model?
membrane of protein molecules bobbing in fluid bilayer of phospholipids.
How is the fluidity of a cell membrane by temperature?
membrane remains fluid as temperature decreases until phospholipids settle into close packed arrangement and membrane solidifies.
temperature at which membrane solidifies depends on the type of lipid it is made out of
What is cholesterol doing in membranes?
- cholesterol helps membranes resist changes in fluidity when the temperature changes.
- reduces phospholipid movement at low temperature. It hinders solidification by disrupting regular packing of phospholipids.
What is a peripheral membrane protein?
- NOT embedded in lipid bilayer
- loosely bounded to surface of membrane, often exposed to part of integral protein.
What is a integral membrane protein?
- penetrates hydrophobic interior of lipid bilayer
- extends only partway into hydrophobic interior
What are the six major functions of membrane proteins?
1. transport: a protein that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute.
2. enzymatic activity: a protein built into the membrane may be an enzyme with its active site exposed to substances in the adjacent solution.
3. attachment to the cytoskeleton and ecm: microfilaments or other elements of the cytoskeleton may be noncovalently bound to membrane proteins, a function that helps maintain cell shape and stabilizes the location of certain membrane proteins.
4. cell-cell recognition: some glycogen proteins serve as identification tags that are specifically recognized by membrane proteins of other cells.
5. intercellular joining: membrane proteins of adjacent cells may hook together in various kinds of junctions such as gap junctions or tight junctions.
6. signal transduction: a membrane protein (receptor) may have a binding site with a specific shape that fits the shape of a chemical messenger such as a hormone.
What is the role of membrane carbohydrates in cell-cell recognition?
The ability of a cell to distinguish other cells based on recognition of membrane carbohydrates. The glycolipids and glycoproteins attached to the outside of plasma membranes varies.
How does hydrophobic molecules cross cell membrane?
through FACILITATED DIFFUSION
Certain compounds important to the functioning of the cell, such as ions, cannot enter the cell through simple diffusion because they cannot pass through the cell membrane. As with water, these substances "want" to enter the cell if the concentration gradient demands it. For that reason, cells have developed a way for such compounds to bypass the cell membrane and flow into the cell on the basis of concentration. The cell has protein channels through the phospholipid membrane. The channels can open and close based on protein membranes. When closed, nothing can get through. When open, the protein channels allow compounds to pass through along the concentration gradient, which is diffusion.
High to low concentration
random movement of particles from an area of high concentration to areas of low concentration until they reach an equilibrium
Low to high concentration
diffusion of water in selectively permeable membrane.
What is a hypertonic, hypotonic or isotonic solution?
Hypertonic- when a cell loses water, shrivels and dies.
Hypotonic- when water enters the cell, gets swollen and bursts.
Isotonic- no net movement of water across the plasma membrane.
Why does a concentration gradient of a substance across a membrane represent potential energy?
- a concentration gradient is a condition where, for example, the concentration of sodium ions is higher on one side of the membrane than on the other. This represents potential energy because ions (all molecules, actually) move *
* their concentration gradient--from higher to lower concentration, in an attempt to "even things out". This movement can be used by cells as an energy source (think of water falling down a waterfall making a turbine spin).
a concentration gradient, therefore, requires work--such as active transport. Active transport takes molecules from a
concentration (like when cells take in nutrients), but since it's against the normal flow in a gradient, it takes work--energy--to make this happen.
How does living cells without walls regulate water balance?
Cells without cell walls rely on tonicity (the ability of gain or lose water), isotonic cells result in no net movement as it is equal throughout, hypotonic cells will result in the entering of water, hypertonic will result in the loss of water.
What is paramecium?
a unicellular ciliated protozoan, commonly studied as a representative of the ciliate group. Paramecia are widespread in freshwater, brackish, and marine environments and are often very abundant in stagnant basins and ponds.
Paramecium typically lives in a hypotonic environment ( water diffuses from the outside to the inside of the animal by osmosis ).
Distinguish between osmosis, facilitated diffusion and active transport?
Osmosis is the diffusion of water across a such a selectively permeable membrane. In facilitated diffusion, transport proteins speed the passive movement of molecules across the plasma membrane. Active transport allows cells to move substances against their concentration gradients.
How does large molecules transport across a cell membrane?
Large molecules, such as polysaccharides and proteins, cross the membrane in bulk via vesicles. Bulk transport requires energy.
What is the role of the membrane in signaling?
What are receptors?
Receptors are proteins embedded in the cell membrane. They are proteins that bind to specific signal molecules, which enables the cell to respond to the signal molecule.
What is signal transduction pathway?
signal transduction pathway definition. A set of chemical reactions in a cell that occurs when a molecule, such as a hormone, attaches to a receptor on the cell membrane. The pathway is actually a cascade of biochemical reactions inside the cell that eventually reach the target molecule or reaction.
What type of responses do cells have to signals?
Distinguish between exocytosis and endocytosis.
In exocytosis, transport vesicles migrate to the membrane, fuse with it, and release their contents. In endocytosis, the cell takes in macromolecules by forming vesicles from the plasma membrane.
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