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AP biology - cell transport notes

Cell Transport
Passive transport
Specialized exchange
Gibbs free energy
Integral proteins
Peripheral proteins
Proteins channels
Hydrogen bonds
The movement of ions and other atomic or molecular substances across
cell membranes without need of energy input.
The amount of substance in a defined space
the process of particles, which are sometimes called solutes, moving
through a solution or gas from an area with a higher number of particles
to an area with a lower number of particles.
The movement of atoms or molecules from an area of higher
concentration to an area of lower concentration
the spontaneous net movement of solvent molecules through a selectively
permeable membrane into a region of higher solute concentration, in the
direction that tends to equalize the solute concentrations on the two
a length of open-meshed material made of twine, cord, rope, or
something similar, used typically for catching fish or other animals.
productive of desired effects
the places that substances are moved across membranes in an organism,
via mechanisms such as diffusion or active transport
A thermodynamic quantity equal to the enthalpy (of a system or process)
minus the product of the entropy and the absolute temperature.
has the same concentration of solutes as another solution across a
semipermeable membrane.
A solution that contains fewer dissolved particles
a particular type of solution that has a greater concentration of solutes on
the outside of a cell when compared with the inside of a cell.
Receptor mediated
Video notes:
Video 1: (passive) Diffusion – simple and facilitated
 There are two types of passive diffusion; simple Diffusion and facilitated diffusion
Simple diffusion:
 Molecules move down the concentration gradient
 Net diffusion; high concentration  low concentration
Facilitated diffusion:
 Diffusion of polar molecules or ions (solutes) by a protein.
 They balance out to equilibrium
 Types of proteins; channel proteins, carrier proteins.
Channel proteins:
o Solute moves down the concentration gradient
o Simple channel protein allows solutes to move through.
o Gated channel protein: opened by a chemical or electrical stimulus
Carrier proteins:
o Allows a specific solute to bind to a binding site on the carrier protein.
o When it binds, the carrier proteins flip over releasing it to move inside
Diffusion is a spontaneous solution, but it does require energy.
As the solute first passes through the leaflet the Gibbs free energy is positive and so
energy is required, as it slowly passes through he fatty acid tails it decrease slightly, then it
increase after it leaves the leaflet; you could say that it’s in equilibrium.
 With a transporter, the Gibbs free energy is much lower in comparison to simple
diffusion. So, it saves energy.
Mechanics of facilitated diffusion:
 Decreases pack to its initial position afterward
Video 2: Passive transport and selective permeability
 In passive transport, molecules move down their concentration gradient
 The membrane is selectively permeable; it allows certain molecules to enter.
 Small molecules that have no charge can easily diffuse through the membrane.
e.g. carbon dioxide, not attracted, not repelled.
e.g. molecular oxygen, small and non-charged. (indifferent to the membrane)
 In both examples, there is a net inflow. They diffuse naturally
 Ions and charged molecules have trouble diffusing through simple diffusion.
e.g. K+ and Na+ (they use channel proteins)
 Water does not have a charge but is polar, or the in between of the two cases made
 It slowly is diffusing through.
 It can also pass by facilitated diffusion through aquaporins.
 Larges proteins and molecules cannot diffuse through
Video 3: Introduction to passive and active transport
 going against the concentration gradient requires energy.
 Passive transport:
o Molecules move from high to low concentrations
Positives repel positives, and negatives repel negatives, while positives attract
negatives. And negatives attract positives
So, molecules move through their electrical gradient.
You can have both as an electrochemical gradient.
No energy is needed in the above cases, it is done naturally.
Active transport:
o Molecules go against the concentration gradient
o Molecules go against their electrical gradient
o Most common is the sodium potassium pump.
o You have many K+ and Na+ ions in the inside of the cell but many more on the
o If there was a channel protein it would normally move through its concentration
o The sodium potassium pump uses energy to go against the concentration gradient
Video 4: Sodium potassium pump
(to be done later)
Kaplan notes:
Passive transport:
Passive transport does not require the cell to use ATP energy and plays a role in both the
import of resources and the export of waste.
1. Simple Diffusion
 In diffusion, a substance moves down its concentration gradient from an area of higher
concentration to an area of lower concentration.
 Substances moved are small, uncharged molecules (e.g., carbon dioxide and oxygen).
 Substances move directly across the lipid bilayer.
2. Facilitated Diffusion
 In facilitated diffusion, transport proteins move charged molecules (e.g., potassium ions)
and larger molecules (e.g., glucose) into and out of the cell.
 As with diffusion, facilitated diffusion moves a substance down its concentration gradient
from an area of higher concentration to an area of lower concentration without the use of
 Unlike diffusion, however, the substance moves with the help of carrier proteins or
through a channel protein.
 Examples of facilitated diffusion include glucose transport and Na+/K+ transport.
3. Osmosis
 Osmosis causes water to move across the plasma membrane from a hypotonic solution to
a hypertonic solution.
 Hypotonic solution —has lower concentration of solutes (dissolved substances) than a
hypertonic solution.
 If two solutions have equal concentrations of solutes, they are called isotonic and there is
no net movement of water across the plasma membrane. This is called dynamic
 In osmosis, the solute molecule is not able to cross the selectively permeable plasma
Active transport:
 Requires the cell to use ATP
 Involves movement against the concentration gradient, which is why active transport
requires the use of ATP.
Specific membrane proteins are used in active transport.
Na+-K+ pump is an example of a protein that uses active transport to move ions through
the cells’ membrane.
Exocytosis and Endocytosis:
 Exocytosis and endocytosis move large molecules and food particles across the plasma
membrane with the expenditure of ATP; in other words, they utilize active transport.
 Exocytosis —fusion of vesicles and molecules with the plasma membrane; secretes
materials to the outside of the cell.
 Endocytosis —the cell takes in the molecules via vesicles that fuse with the plasma
 Pinocytosis —uptake of liquids
 Phagocytosis —uptake of solids