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LQB388: Medical Physiology 1 > 1 - Membrane Transport > Flashcards

1 - Membrane Transport Flashcards

1
Q

What is the difference between passive and active transport?

A

Active transport requires energy (ATP), while passive transport doesn’t

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2
Q

How does molecular size affect rate of diffusion

A
  • ROD is inversely related to its molecular radius
  • Small molecules bounce further following a collision.
  • So, smaller the molecule, quicker the diffusion
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3
Q

Describe simple diffusion via protein channels

A
  • Small water-soluble substances are repelled by phospholipids, so they use protein channels to allow them to traverse the membrane
  • Only small ions (H+, Na+, K+, Ca2+ )
  • Ion selective: only permit the movement of one ion species
  • May be gated
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4
Q

Describe facilitated diffusion

A
  • For substances too large/lipid soluble to pass through protein channels (glucose, some amino acids)
  • Carrier protein with specific binding site is used
  • Substance binds to carrier protein → protein undergoes conformational change → substance gets transferred
  • Carrier protein is normally specific for particular substance, and sub. can move both directions depending on conc gradient
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5
Q

Describe active transport

A
  • membrane protein acts as a molecular pump to move substances across membrane
  • E.g: Na2+, K+, Ca2+, sugars, amino acids
  • High affinity binding site for particular substance on low conc side of membrane
  • After the substance binds, protein undergoes a conformational change
  • Goes to the opposite side of the membrane and is expelled
  • Powered by ATP
  • Many move more than 1 substance at a time
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6
Q

What are the basic structural components of plasma membrane? How do they regulate movment of materials between ECF and ICF?

A
  • Double layer of phospholipid molecules arranged parallel: hydrophobic tails means it can act as a barrier to prevent the movement of water-soluble substances across the membrane.
  • Membrane Proteins: control the movement of substances (e.g: channels, receptors, pumps)
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7
Q

What is diffusion? How does it occur?

A
  • Tendency for substances to distribute themselves evenly in the environment by moving down their concentration gradient
  • Occurs bc of random molecule motion, due to thermal energy of the system
  • This motion causes particles to collide, ensuring that they become evenly distributed.
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8
Q

How does distance effect ROD

A

greater the distance, slower the rate of diffusion

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9
Q

How does cell size affect ROD?

A
  • Bigger the cell, larger area of plasma membrane available for diffusion, therefore greater ROD
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10
Q

ROD formula

A
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11
Q

Describe exocytosis

A
  • Macromolecules that are synthesized within the cell and stored in membrane-bound vesivles are secreted into extracellular space
    1. Migration of vesicle → plasma mem. where it fuses
    2. Plasma mem. adjacent to vesicle breaks down
    3. Contents are released into extracellular space
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12
Q

What is the significance of the plasma membrane for physiological systems?

A

Acts as an effective barrier between ECF and ICF

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13
Q

Define solvent, solute and aqueous solution

A
  • Solvent: substance that dissolves the solute
  • Solute: substance being dissolved
  • Aq Soln: solute has been dissolved in water
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14
Q

Define concentration gradient

A

Substances moving from an area of high concentration to low.

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15
Q

How does conc gradient affect ROD?

A
  1. Lots of molecules in high conc
  2. Higher frequency of collisions
  3. Progressive migration of molecules from high to low conc until molecules are evenly distributed
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16
Q

Describe simple diffusion via lipid bilayer

A
  • Substances with high lipid solubility (O2, CO2, N2, alcohols, fatty acids)
  • Able to dissolve in phospholipids and diffuse directly through plasma membrane
  • Higher lipid solubility, faster diffusion
17
Q

Describe an experiment that would allow you to determine whether a substance moved across the plasma membrane of a cell by simple or facilitated diffusion.

A

Saturation Kinetics
* Change solute conc outside of cell then measure ROD
* Simple: fairly linear relationship
* Facilitated: plateus because once all carrier proteins are occupied, there can be no more increase in ROD

18
Q

What is bulk transport?

A

Large substances (e.g: macromolecules) enter / leave cells enclosed in membrane-bound vesicles. Powered by ATP.

19
Q

Basic description of endocytosis

A
  • Transfer of large particles, macromolecules and ECF into the cell
  • A fold of the plasma membrane forming around substance to be ingested, forms a membrane bound vesicle
  • 3 ways
20
Q

Hypotonic?

A
  • Lower solute conc in ECF than ICF
  • Water moves into cell
  • Cell swells
21
Q

Hypertonic?

A

Higher solute conc in ECF than ICF
Water moves out of the cell down conc gradient
Cell shrinks

22
Q

What is an isotonic solution?

A

Soln with no net movement of water

23
Q

Osmolarity formula:

A

Molarity x no. molecules

24
Q

What is tonicity?

A

The ability of a solution to affect the fluid volume and pressure in a cell

25
Q

What is osmolarity?

A
  • A measure of the no. of particles in a solution and reflects osmotic pressure more accurately
  • This is because: osmotic pressure is more dependent on total no. rather than total weight
  • Some solutes dissociate into their consituent ions when in soln, so contributes a larger number of solute particles than substances
  • Provides us with a measure of osmotic effectiveness of a solution
26
Q

What is osmotic pressure?

A

Total conc of non-penetrating solutes (driving force for osmosis)

27
Q

Explain the difference between diffusion and osmosis

A
  • Diffusion of solutes doesn’t change volume but osmosis does
  • Membrane is impermeable so water moves down conc gradient by osmosis instead
  • Therefore, increasing the volume
28
Q

What is osmosis?

A
  • movement of water across plasma membrane
  • mem is highly water permeable
  • H2O molecules are small and have sufficient kinetic energy to pass straight through lipid bilayer and protein channels (despite hydrophobic core)
  • Move down conc gradient
29
Q

Describe receptor-mediated endocytosis

A
  • Very selective bc the membrane expresses extracellular receptors to which a particular macromolecule binds
  • Then triggers endocytosis of the portion of mem containing receptor/macromolecule complex
  • E.g: cholesterol, iron and insulin
30
Q

Describe pinocytosis

A
  • Most cells in the body perform this
  • Small volume of ECF being incorporated into a membrane-bound vesicle formed by small fold in plasma mem
31
Q

Describe phagocytosis

A

Few specialised cells (e.g: macrophages) can ingest large solid particles (e.g: cellular debris)
1. Extension of a portion of plasma mem around particle
2. Fusion of these extensions to form a particle-containing vesicle (phagosome)
3. Phagosome fuses with lysosome (contains digestive enzymes)
4. Enzymes break down the ingested debris and release produces into cell’s cytoplasm

LQB388: Medical Physiology 1 (6 decks)

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