Chapter 4: Movement of molecules Flashcards
1
Q
Purposes of membranes
A
- membranes serve as boundaries between the cell interior and extracellular fluid (plasma membrane) and between organelle interiors and the cytosol
- -> regulate what substances enter and leave cells/organelles, how much and how fast
2
Q
Passive mechanisms of membrane transport
A
- don’t require energy
- diffusion, osmosis, facilitated diffusion
3
Q
active mechanisms of membrane transport
A
- require energy
- active transport, exocytosis, endocytosis
- exo and endocytosis are both bulk transport
4
Q
Active transport and facilitated diffusion
A
- both require carrier molecules and are considered transport mechanisms
5
Q
Diffusion
A
- movement of molecules from one location to another as a result of random thermal motion; movement of molecules from higher to lower concentration (decrease the concentration gradient)
- used to move substances in and out of capillaries and blood and cells
- most common process most likely
- may or may not occur across a semi-permeable membrane
- uniform concentration is eventually reached
6
Q
Flux
A
- amount of material crossing a surface in a unit of time
- magnitude determined by concentration gradient
7
Q
net flux
A
- the difference between two one-way fluxes
- the net amount of material transferred from one location to another
- net flux always occurs from regions of higher concentration to regions of lower concentration
- concentration difference determines the magnitude of net flux
- at a given concentration gradient, also influenced by temperature, mass, surface area, and medium
8
Q
diffusion rate
A
affected by distance
9
Q
diffusion time
A
square of the distance over which molecules diffuse
10
Q
diffusion through lipid bilayer
A
- plasma membrane is semipermeable/differentially permeable
- some, not all, molecules can diffuse across the plasma membrane
- small, uncharged, lipid-soluble molecules diffuse easily across lipid bilayer (nonpolar)
- charged (polar) molecules have more difficulty diffusing across lipid bilayer…slowly or not at all
- macromolecules can’t freely cross membrane
11
Q
Polar molecules and membrane
A
- lower permeability and harder to cross membrane
12
Q
Protein Channels
A
- used by ions because harder for them to pass because charge
- made of integral membrane proteins, either a single one or usually a protein aggregate
- small diameters
- ion selectivity
13
Q
Electrochemical gradient
A
- intracellular fluid is usually negatively charged
- extracellular fluid usually positively charged
- influences ion movement
- direction and magnitude of ion fluxes across membranes depend on both the concentration difference and membrane potential (electrical difference)
14
Q
membrane potential
A
- separation of electrical charge across the plasma membrane
15
Q
regulation of diffusion through ion channels
A
channel gating
- ligand-gated channels
- voltage-gated channels
- mechanically-gated channels
16
Q
ligand-gated channels
A
- open and close in response to a certain binding chemical ligate to protein of channel
17
Q
voltage-gated channels
A
- open and close in response to membrane potential
18
Q
mechanically-gated channels
A
- open and close due to the stretching of the membrane
19
Q
Mediated transport mechanisms
A
- responsible for the transport of some ions, and for polar molecules such as amino acids and glucose that are too large to move through channels
- use transporters/carrier molecules (integral mem proteins, undergo conformational change, can move molecules in either direction across mem, chemical specificity)
20
Q
how mediated transport mechanisms work
A
- the solute binds to a specific site on the transporter protein
- the protein changes shape, and the solute is released on the other side of the membrane
