BPK 205 Study Guide - Midterm Guide: Immunoglobulin M, Botulinum Toxin, Homeostasis
10 May 2018
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Lecture 11: Un-Assisted Transport
Membrane: The plasma membrane has a dual function;
- it can retain content and allow material in and out of cell.
- The membrane is selectively permeable meaning only some stuff can come in and come out of the membrane.
Unassisted Membrane Transport: Ions can penetrate plasma membrane by themselves
- passively driven across a membrane by diffusion down gradient or movement along gradient
Passive Diffusion: The greater the concentration of the solution, the greater the chance of a collision.
- The difference between two adjacent cells is called a concentration gradient
- Diffusion occurs when one area has a greater concentration than the other, allowing the higher concentration solutions
to go to the lower concentration area.
- Net Diffusion: is the difference between two movements (If 4 molecules move from Side 1 Side 2, while 2
molecules moves from Side 2 Side 1, the net diffusion is 2)
- Steady State is when the diffusion between both areas are equal.
Fick’s Law of Diffusion
- Magnitude of Gradient: The greater the difference in concentration, the faster the net diffusion rate.
- Permeability of membrane of Substance: The more permeable the membrane is to the substance, the more rapid it
can diffuse down the gradient.
- Surface area of Membrane: The greater the surface area, the greater the rate of diffusion.
- Molecular Weight: The lighter the molecules, the faster it can diffuse.
- The Distance which diffusion takes place: The greater the distance is the slower the rate of diffusion can take place.
Passive Diffusion of Ions: Movement of ions is affected by electrical charge.
- Cations move to the negative side,
- Anions move to the positive side
Osmosis: Water can permeate the plasma membrane.
- Slips between phospholipids between the bilayer
- When adding a solute to pure water, it decreases the concentration of the gradient. Solute displaces water
- If solutions of an unequal solute are separated by membrane that permits the passage of water, than it will move from
its own gradient of higher concentration to lower concentration.
- Water has Aquaporin, which provide channels for the passage of water.
Osmosis when membrane separates unequal solutions of a penetrating solute: Membrane permits the passage of water and
solute
- allowing both to go down its gradient
- This continues until both the solute and water are evenly distributed across the membrane.
Osmosis when membrane separates unequal solutions of a non-penetrating solute: Membrane is permeable to water but not
to the solute
- Due to this, the solute will not be able to move so the volume of Side 2 will be higher.
- The loss of water on Side 1 will increase the solute concentration, while the addition of water to Side 2 will reduce the
solutes concentration creating an even balance.
Osmosis when membrane of pure water is separated from a solution of non-penetrating solute:
- Osmosis will occur but the concentration will not be equal.
- Due to the pure water, Side 2 will not become pure nor can Side 1 ever acquire any solute.
- Hydrostatic pressure (Pressure exerted by a standing fluid on an object. Greater on Side 2 and tends to push fluids
from Side 2 to Side 1) between Side 1 and 2 is created as the volume expands in Side 2.
- Osmotic Pressure (the measure of the tendency for water to move into that solution because of its concentration of
non-penetrating solutes and water).
- Net movement of water continues until hydrostatic pressure counteracts the osmotic pressure.
Tonicity: Has an effect on cell volume.
- Isotonic Solution: Same concentration of non-penetrating solute in and out of the cell.
- Hypertonic Solution: Low solute and water moves in causing swelling.
- Hypotonic Solution: High level of solute, cells shrink as they lose water by osmosis.
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Lecture 12: Assisted Membrane Transport.
Assisted Membrane Transport: Large molecules cannot cross the membrane on their own, must have mechanism help to help
molecule move in or out of cell.
- Carrier Mediated and Vesicular transport.
Carrier Mediated: Spans the membrane which is passive-down gradient or active against the gradient. It has 3 characteristics.
- Specificity: Each carrier protein is specialized to transport specific substances.
- Saturation: A limited number of binding sites are available within the membrane for a substance. This limit is called
the Transport Maximum
- Until Tm is reached the carrier won’t be saturated, and once it becomes saturated the sites will not be available. Insulin
increases the carrier mediated transport of glucose
- Competition: Several related components may compete for the specific carrier.
Active Transport: Facilitated Diffusion and active transport are used.
Facilitated Diffusion: Does not require energy.
- uses a carrier to assist the transfer of a particular substance across the membrane from high concentration to low
concentration.
Active Transport: Requires carrier to expand energy to transfer the passenger against the gradient from low to high
concentration.
- The process requires the use of protein carriers to transfer a specific substance across the membrane
- The binding site gets attached to a phosphate which creates phosphorylation causing the protein to flip its position so
the passenger is now exposed to higher concentration.
- Dephosphorylation reduces affinity so passenger goes to the higher concentration area.
- Examples: The Na+ and K+ pump: Na+ moves out of the cell and picks up K+ from the outside. ATP splitting and
phosphorylation increases affinity Na+ leading to a drop-off to the exterior. The dephosphorylation moves K+ into the cytoplasm
Secondary Active Transport: Energy is not used to run the pump
- but uses energy in the form of concentration gradient to move molecules uphill.
- Downhill travel is coupled by another substance against the gradient.
Vesicular Transport: Materials unable to cross membrane so it is wrapped by the membrane-enclosed vesicle.
- Energy is needed to finish vesicle formation/movement.
- Endocytosis: Membrane fuses over surface pinching off membrane so material is trapped within the cell. 3 forms:
- Pinocytosis – uptake of ECF
- Receptor mediated endocytosis – uptake of larger molecule selectively.
- Phagocytes – uptake of the particle.
- Exocytosis: Membrane enclosed vesicle within cell fuses with membrane opens and releases its content to exterior.
- Enables the cell to add compounds to the membrane,
- provides a mechanism for secreting large polar molecules which are put in the membrane.
Lecture 13: Membrane Potential
Membrane Potential: Separation of charges across the membrane establishes this potential or the number of cations/anions
present in the ICF/ECF.
- When oppositely charged particles have been separated the electrical force of the attraction can be harnessed to
perform work when changes come together.
- Potential occurs due to the charges waiting to come together in the membrane.
- Once the membrane is removed the ions will attract.
- The unit in which potential is measure in is millivolt (mV)
- A membrane potential exists when there are more cations on one side and more anions on the other side.
Concentration and Permeability of Ions: Cells of nerves/muscles have the ability to produce rapid and transient changes when
excited.
- Serve as electrical signals
- When they are not producing electrical signals it is known as the resting potential.
- The body has important ions that carry electrical charges
Ions: The ions are K+ and Na+.
- The concentration among the Na+/K+ is maintained by the Na+/K+ pump at the expense of ATP
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- It is easier for K+ than Na+ to get though the membrane because more channels open passively for K+.
- Therefore the resting potential of a nerve cell is 50-75 times more permeable for K+ than Na+.
- K+ moves outward while Na+ goes inwards.
Effect of Na+- K+ pump on potential: because Na+ and K+ are positive, a membrane potential is generated on the inward or
outward side of the membrane.
Effect of K+ on potential: Since potassium is positive, an electrical gradient would be present
- Occurs because there are more cations outside than inside of the cell membrane.
- K+ would attract negative ions in the interior because K+ moves to the exterior.
- As K+ increases and moves down the gradient out of the cell, the inside becomes more negative.
- As K+ keeps moving out down the gradient, the inward gradient would increase in strength.
- When the concentration gradient and net outward movement balances no further movement of K+ would occur.
- This is the Potassium equilibrium potential
Potassium Equilibrium Potential: As this point there is a high K+ concentration gradient but no movement of K+ would occur
- At the EK+ the membrane potential is -90mV
- This means that the potential of magnitude is 90mV with the inside being negative relative to the outside
Effect of Na+ on potential: The concentration would move Na+ into the cell.
- Negative outside with positive inside
- Net movement occurs until equilibrium is reached. ENa+ is +60mV
Concurred Potassium/Sodium Effect:
- the membrane at rest is more permeable to K+ than Na+ the potassium influences resting potential to a greater extent.
- It establishes its resting potential of -90mV and is somewhat permeable to Na+
- some Na+ enters the cells to reach its equilibrium of +60mV
- When it does this it cancels some of the potential produced by K+.
- The typical resting potential is -70mV which is much closer to the Ek+ than the ENa+.
Balance of passive leak and active Pumping:
- to get the counteraction of concentration, the K+ concentration needs to be at -90mV
- K+ slowly exists through its leak channels down its gradient.
- Concentration and electrical gradient do not oppose each other but favor Na+ movement.
- Na+ continues to leak inward due to the electrochemical gradient.
- The pump counterbalances the rate of leakage. It transports back the same number of K+ that left and Na+ that entered.
Chloride Movement:
- Cl- would produce an opposing electrical gradient
- it is an anion in ECF and is drawn out by K+.
Lecture 14: Graded and Action Potential
Membrane electrical States:
- Polarization changes separates across the membrane so a potential is present. If the potential is not 0mV it is in a
state of polarization
- Depolarization is the Reduction in magnitude of negative membrane potential. Moves closer to 0mV and goes in a
positive direction
- Repolarization when the membrane returns to resting potential after have been depolarized. Movement is in the
negative direction
- Hyperpolarization is an increase in the magnitude of negative potential. More polarized and is in the negative
direction
Electrical Signal/Ion Movement:
- Changes in the membrane potential is brought by change in ion movement.
- Change in ion movement is brought by change in response to membrane permeability.
- Water-soluble ions use channels to penetrate the plasma bilayer.
2 types of channels:
- Leak channels: Open all the time
- Gated Channels: can be open to allow ion passage or closed to prevent ion passage
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Document Summary
Membrane: the plasma membrane has a dual function; It can retain content and allow material in and out of cell. The membrane is selectively permeable meaning only some stuff can come in and come out of the membrane. Unassisted membrane transport: ions can penetrate plasma membrane by themselves. Passively driven across a membrane by diffusion down gradient or movement along gradient. The difference between two adjacent cells is called a concentration gradient. Diffusion occurs when one area has a greater concentration than the other, allowing the higher concentration solutions. Passive diffusion: the greater the concentration of the solution, the greater the chance of a collision. to go to the lower concentration area. molecules moves from side 2 side 1, the net diffusion is 2) Steady state is when the diffusion between both areas are equal. Net diffusion: is the difference between two movements (if 4 molecules move from side 1 side 2, while 2.
