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BMSC 207 > Membrane Dynamics > Flashcards

Membrane Dynamics Flashcards

1
Q

What is the distribution of ions in ECF and ICF

A

Higher in ECF: (few extra positive ions)
-Na+
-Cl-
-Ca2+
-HCO3-
(slightly less proteins than ICF, all located in plasma)

Higher in ICF: (few extra negative ions)
-K+
-Phosphate ions
-Proteins

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2
Q

What is osmolarity?

A

-Describes the number of particles in solution
-Osmotic movement of water can be predicted by knowing the solute particle concentrations of each solution
-Expressed in osmoles per liter (osmol/L or OsM) or milliosmoles/liter (mOsM)

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3
Q

What is Isosmotic?

A

-Equal: solutions have identical osmolarities

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4
Q

What is hyperosmotic?

A

-Greater than: describes the solution with the higher osmolarity

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5
Q

What is hyposmotic?

A

-Less than: describes the solution with the lower osmolarity

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6
Q

What is tonicity?

A

-Term used to describe a solution and how that solution would affect cell volume if a cell were placed in the solution and allowed to come to equilibrium
-Cell swells: hypotonic
-Cell remains: isotonic
-Cell shrinks: hypertonic

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7
Q

What is the difference between tonicity and osmolarity?

A

Osmolarity:
-overall solute concentration of a compartment
-Takes into account all solutes in the compartment (penetrating and non-penetrating)
-Used to compare two solutions

Tonicity:
-Describes a solution relative to a cell, solely on how the cell volume responds to solution
-Only concerned with non-penetrating solutes (determines whether water moves into or out of cell)

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8
Q

What is the difference between osmolarity and osmolality?

A

Osmolarity:
-Osmoles per litre of solution
-Often used when temperature and pressure are relatively constant

Osmolality:
-Osmoles per kg of solvent
-Total solvent weight excludes the solutes

Small concentrations such as in the body have nearly identical values

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9
Q

What is osmosis and osmotic equilibrium?

A

-Osmosis: The movement of water across a membrane in response to a solute concentration gradient
-Osmotic Equilibrium: When fluid concentrations are equal (the amount of solute per volume solution) the ICF and ECF compartments are in osmotic equilibrium

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10
Q

Why is a hyposmotic solution always hypotonic?

A

-The cell will always have a higher concentration of NP solutes than the solution, water will move into the cell

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11
Q

What is osmotic pressure and its purpose?

A

-The force applied to exactly oppose osmosis
-The purpose is to quantitatively measure osmosis by disallowing the water to flow into the higher concentrated compartment

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12
Q

What is diffusion?

A

-Movement of molecules from an area of higher concentration of the molecules to an area of lower concentration of the molecules (down concentration gradient)

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13
Q

What are the 7 properties of diffusion?

A
  1. Passive: uses the kinetic energy of molecular movement and does not require an outside energy source
  2. Molecules diffuse from an area of higher concentration to an area of lower concentration
  3. Diffusion continues until concentrations come to equilibrium. Molecular movement continues after equilibrium has been reached
  4. Diffusion is faster over shorter distances
  5. Directly related to temperature (higher temp=faster molecule movement)
  6. Inversely related to molecular weight and size (smaller = less energy to move = diffuse faster)
  7. Can take place in an open system or across a partition dividing compartments that allows diffusing molecules to cross
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14
Q

What is simple diffusion and its properties?

A

-Diffusion directly across the phospholipid bilayer of a membrane
1. Rate of diffusion depends of the ability of diffusing molecule to dissolve in the lipid bilayer of the membrane or how permeable the membrane is to the diffusing molecule
-Water may diffuse slowly across some phospholipid membranes through protein channels (High cholesterol = less permeable to water)
2. Rate of diffusion is directly proportional to the surface area of the membrane (larger surface area = more molecule diffusion)

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15
Q

What small uncharged lipophilic molecules occur in simple diffusion?

A

-O2, CO2, NH3, lipids and steroids

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16
Q

What is Fick’s Law of Diffusion?

A

Rate of diffusion = surface area x concentration x membrane permeability

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17
Q

What are channel proteins?

A

-Made of membrane spanning protein subunits that create a cluster of cylinders with a pore through the center
-Named according to substance that passes through (mainly smaller substances)
-Open channels (“leak channels”)
-Gated channels normally closed chemically (ligand), voltage, and mechanically
-Facilitated diffusion/osmosis
-Selectivity is determined by size of pore and charge of amino acids that line the protein in the pore

18
Q

What are carrier proteins?

A

-Large complex proteins
-Change conformation to move molecules (never form an open channel between the two sides of the membrane)
-Slow (1000 - 1 million per/sec)
-Can move small organic molecules that cannot pass through channels

19
Q

What is facilitated diffusion?

A

-Use channels or carrier proteins
-Move down their concentration gradient (or electrochemical gradient)
-No energy required (passive)
-Stops once equilibrium is reached (or when the channel closes)

20
Q

What are the 3 types of carrier proteins in membrane transportation?

A

Uniport carriers:
-Transport only one kind of substrate

Symport carriers: (cotransporter)
-Move two or more substratesin the same direction across membrane

Antiport carrier: (cotransporter)
-Move substrates in opposite directions

21
Q

What is active transport?

A

-Moves molecules against their concentration gradients from an area of low concentration to an area of high concentration
-Supports a state of disequilibrium (as seen with certain ions)
-Requires energy
-Uses carrier proteins

22
Q

What is passive transport?

A

-Uses the kinetic energy in molecules and potential energy stored in concentration gradients

23
Q

What are the two types of active transport?

A

Primary active transport:
-Energy to move molecules comes directly from hydrolyzing ATP (referred to as an ATPase)

Secondary active transport:
-Uses the potential energy stored in the concentration gradient of one molecule to push another molecule against their concentration gradient

24
Q

What determines selective permeability of cell membranes?

A

-What crosses depends on the properties of the cell membrane (lipid and protein composition) and the substance (size and lipid solubility)

25
Q

What are the 2 types of transport across membranes?

A

Active:
Vesicular transport (ATP)
-Exocytosis
-Endocytosis
-Phagocytosis
Primary active transport
Secondary active transport

Passive:
-Simple Diffusion
-Facilitated diffusion
-Ion Channel (electrochemical gradient)
-Aquaporin channel (osmosis)

26
Q

What type of membrane transports are protein-mediated?

A

-Primary active transport
-Secondary active transport
-Facilitated diffusion (concentration gradient)
-Ion channel (electrochemical gradient)
-Aquaporin channel (osmosis)

27
Q

What is specificity?

A

-Refers to the ability of a transporter to move one molecule or a closely related group of molecule

28
Q

What is competition?

A

-A carrier may move several members of a related group of substances but these substances compete with one another
-Carrier may have a preference for one family member

29
Q

What is saturation?

A

-Rate of transport depends on concentration and number of transporters
-Transporters normally increase with increasing concentration until transport maximum is reached (all transporters are in use)

30
Q

What is vesicular transport?

A

-Used for macromolecules that cannot fit through a carrier or channel
-Phagocytosis, endocytosis and exocytosis all use bubble like vesicles created from the cell membrane

31
Q

What is phagocytosis?

A

-Created vesicles using the cytoskeleton
-Requires ATP to move the cytoskeleton and for intracellular transport of the vesicle (active transport mechanism)

32
Q

What is endocytosis?

A

-Transport into cell through membrane indents
-Vesicles are much smaller
-Also require ATP

Non-selective:
-Pinocytosis: allows ECF to enter

Selective:
-Receptor mediated transport

33
Q

What is exocytosis?

A

-Transport out of cell
-Vesicles can be filled with large lipophobic molecules such as proteins synthesized in cell or wastes left behind by lysosomes after intracellular digestion
-Can occur continuously or intermittently when initiated by some sort of signal (hormones, electrical)
-Requires ATP
-Can be regulated by CA2+

34
Q

What is epithelial transport?

A

-Substances entering and exiting the body or moving between compartments often must cross a layer of epithelial cells (line lumen or surface of structures in the body)
-Digestive tract, airways, kidneys, etc.

35
Q

What is the process of absorption in epithelial transport?

A

-From lumen of organ to ECF

36
Q

What is the process of secretion in epithelial transport?

A

-From ECF to lumen of organ

37
Q

What is transcellular and paracellular epithelial transport?

A

Transcellular:
-Across epithelial cell

Paracellular:
-Between tight junctions

Transcytosis:
-Plasma proteins are concentrated in caveolae, which then undergo endocytosis and form vesicles
-Vesicles cross the cell with help from the cytoskeleton
-Vesicle contents are released into interstitial fluid by exocytosis

38
Q

What is membrane potential? (resting membrane potential difference)

A

-Vm = -70mV
-The electrical disequilibrium that exists between the ECF and ICF
-Cell is permeable to mutiple types of ions due to the presence of open channels and protein transporters (mainly Na+ and K+ through open channels but to different degrees)
-Cell membrane is about 40x more permeable to K+

39
Q

What is equilibrium potential?

A

-The membrane potential that exactly opposes the concentration gradient of any single ion
-Ena = +60mV
-Ek = -90mV

40
Q

How does a cell maintain the resting membrane potential of -70mV?

A

-Na-K ATPase:
-Sets up concentration gradients that determines membrane potential
-3 Na+ out/ 2 K+ in (electrogenic: generates a negaive intracellular charge)
-Maintains the concentration gradients for Na+ and K+

41
Q

What are the two factors that influence a cell’s membrane potential?

A
  1. The concentration gradients of different ions across the membrane (Na+, K+, Cl- and Ca2+)
    -Changes in concentration gradient alone resulting in an alteration in membrane potential applies to ions with weak channels
  2. The permeability of the membrane to those ions (opening gates channels)
    -Na+ and Ca2+ enter the cell causing depolariztion (less negative than resting potential)
    -K+ leaving the cell causes hyperpolarization (more negative than resting potential)
    -Cl- enters the cell after depolarization and brings resting potential back to normal (repolarization, only after depolarization)

BMSC 207 (14 decks)

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