Chapter 3 Flashcards
plasma membrane (plasmalemma)
forms the cell’s flexible outer surface, separating the cell’s internal environment (everything inside the cell) from the external environment (everything outside the cell).
Selective barrier
Key role in communication between cells
-contains the cytoplasm
Cytoplasm
consists of all the cellular contents between the plasma membrane and the nucleus. This compartment has two components: cytosol and organelles
nucleus
- is a large organelle that houses most of a cell’s DNA.
a flexible yet sturdy barrier that surrounds and contains the cytoplasm of a cell, is best described by using a structural model called the
Fluid mosaic model
fluid mosaic model
According to this model, the molecular arrangement of the plasma membrane resembles a continually moving sea of fluid lipids that contains a mosaic of many different proteins
basic structural framework for the plasma membrane
is the lipid bilayer: two back-to-back layers made up of three types of lipid molecules—phospholipids, cholesterol, and glycolipids
The bilayer arrangement occurs because the
lipids are amphipathic molecules, which means that they have both polar and nonpolar parts.
hydrophobic and hydrophilic
In phospholipids, the polar part is the phosphate-containing “head,” which is hydrophilic (water loving). The nonpolar parts are the two long fatty acid “tails,” which are hydrophobic
Integral proteins (which are amphipathic)…
extend into or through the lipid bilayer and are firmly embedded in it. Most integral proteins are transmembrane proteins, which means that they span the entire lipid bilayer and protrude into both the cytosol and extracellular fluid.
peripheral proteins
are not as firmly embedded in the membrane
- help support the plasma membrane, anchor integral proteins, and participate in mechanical activities such as moving materials and organelles within cells, changing cell shape during cell division and in muscle cells, and attaching cells to one another.
ion channels
Some integral proteins form ion channels, pores or holes that specific ions can flow through to get into or out of the cell.
carriers
Other integral proteins act as carriers, selectively moving a polar substance or ion from one side of the membrane to the other.
receptors
Integral proteins called receptors serve as cellular recognition sites. Each type of receptor recognizes and binds a specific type of molecule
enzymes
Some integral proteins are enzymes that catalyze specific chemical reactions at the inside or outside surface of the cell.
linkers
Integral proteins may also serve as linkers that anchor proteins in the plasma membranes of neighboring cells to one another or to protein filaments inside and outside the cell. Peripheral proteins also serve as enzymes and linkers.
cell identity markers
Membrane glycoproteins and glycolipids often serve as cell-identity markers. They may enable a cell to (1) recognize other cells of the same kind during tissue formation or (2) recognize and respond to potentially dangerous foreign cells.
Membranes are fluid structures; that is,
most of the membrane lipids and many of the membrane proteins easily rotate and move sideways in their own half of the bilayer.
Plasma membranes are: selectively permeable
The lipid bilayer is always permeable to: small, nonpolar uncharged molecules
Transmembrane proteins that act as channels or transporters: increase the permeability of the membrane
Macromolecules are only able to pass through the plasma membrane by: vesicular transport
Gradients Across the Plasma Membrane
-concentration gradient is the difference in the concentration of a chemical between one side of the plasma membrane and the other
-An electrical gradient is the difference in concentration of ions between one side of the plasma membrane and the other
-Together, these gradients make up an electrochemical gradient
which processes are passive
Simple diffusion, facilitate diffusion, osmosis
In passive processes,
a substance moves down its concentration or electrical gradient to cross the membrane using only its own kinetic energy (energy of motion).
In active processes
cellular energy (normally ATP) is used to drive the substance “uphill” against its concentration or electrical gradient.
the way that some substances may enter and leave cells is an active process in which tiny, spherical membrane sacs referred to as vesicles are used.
types of active processes
P : primary and secondary transport
V : vesicular transport
diffusion
Diffusion is a passive process in which the random mixing of particles in a solution occurs because of the particles’ kinetic energy. Both the solutes, the dissolved substances, and the solvent, the liquid that does the dissolving, undergo diffusion. If a particular solute is present in high concentration in one area of a solution and in low concentration in another area, solute molecules will diffuse toward the area of lower concentration—they move down their concentration gradient. After some time, the particles become evenly distributed throughout the solution and the solution is said to be at equilibrium. The particles continue to move about randomly due to their kinetic energy, but their concentrations do not change.
Simple diffusion
is a passive process in which substances move freely through the lipid bilayer of the plasma membranes of cells without the help of membrane transport proteins
Nonpolar, hydrophobic molecules move across the lipid bilayer
facilitated diffusion
Solutes that are too polar or highly charged to move through the lipid bilayer by simple diffusion can cross the plasma membrane by a passive process called facilitated diffusion. In this process, an integral membrane protein (channel or carrier protein) assists a specific substance across the membrane.
