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PHYL2062 > Cell Physiology L2/3: Osmosis and Diffusion > Flashcards

Cell Physiology L2/3: Osmosis and Diffusion Flashcards

1
Q

What is homeostasis?

A

maintain a stable internal environment for all those critical physiological processes to occur

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2
Q

How is homeostasis maintained?

A
  • Each cell contributes by the exchange of nutrients to and from the intra- and extra-cellular fluid in specialised ways.
  • Done by cell membrane
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3
Q

What does the phospholipid bilayer consist of?

A
  1. Hydrophilic (polar heads)
  2. Hydrophobic (non-polar tails)
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4
Q

What is the structural function of the phospholipid bilayer?

A

Gives cells shape

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5
Q

Is the phospholipid layer flexible? Explain.

A

Yes, is flexible

  • Allows cells to change shape
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6
Q

Does the phospholipid layer acts as a barrier? Explain.

A

Yes, is a barrier

  • Prevents water soluble substances passing through
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7
Q

What is the phospholipid layer permeable to? Explain.

A

Permeable to:

  • Lipid-soluble molecules (eg. steroid)
  • Small uncharged molecules (eg. O2, CO2, urea can move freely between phospholipids)
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8
Q

What is the phospholipid layer impermeable to? Explain.

A

Impermeable to:

  • ions & large molecules (e.g. sodium, proteins, glucose)
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9
Q

Is the phospholipid layer permeable to H20?

A

Yes, but is a bit more tricky- thorough osmosis

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10
Q

What simple diffusion?

A

Anything which passes directly through the bilayer

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11
Q

How does simple diffusion occur?

A
  • Driven by concentration gradient
    • The bigger the gradient (difference) –> faster the molecules will pass through
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12
Q

What are the 2 things that the movement across a membrane depends on?

A
  1. Concentration gradient
  2. Permeability of membrane
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13
Q

What is Fick’s Law?

A

All factors affect simple diffusion through a membrane

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14
Q

What is osmosis?

A

Movement of water from a high water concentration to a low water concentration

  • Water moves from high [water] low [water]
  • Low [solute] –> high [solute]
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15
Q

Why would osmosis not occur?

A
  • Water moves down its (concentration) activity gradient o No activity = no osmosis
  • Water activity same on both sides because [solute] same on both sides.
    • No net flux
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16
Q

For osmosis, in the presence of solutes, there will be _____ (increased/decreased activity)? Why?

A

Decreased; water is a solvent

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17
Q

If there is a non-penetrating solute occurring on one side of the membrane, will osmosis occur? How?

A

Yes, water activity gradient

  • Net flux to the side of the non-penetrating solute
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18
Q

Do all solutes behave the same in terms of influencing water activity, and thus osmosis?

A

No- differ in 2 ways

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19
Q

What are the 2 different ways that solutes behave, which influences water activity and in turn osmosis?

A
  1. Whether they are (as already considered)
    • membrane penetrating (e.g. urea), or
    • non-penetrating (e.g. glucose and ions).
  2. Whether they dissociate in solution.
    • e.g. compare solutions of glucose and sodium chloride (NaCl)
    • Break apart = more particles in water = eg. NaCl = Na+2 + Cl- = higher solute concentration = need twice as much water = water activity is lowest and every molecule dissociates into 2 ions.
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20
Q

How do we describe the difference between solutions that contain solutes that dissociate in solution and those that do not?

A

Osmolarity of solution

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21
Q

What is osmolarity (equation)? Use glucose and NaCl as examples.

A

Osmolarity of a solution = ∑ {(solute concentration) x (#dissociated species)}

E.g.

  • 1M glucose = (1M x 1) = 1 Osmolar (OsM)
  • 1M NaCl = (1M x 2) = 2 Osmolar (OsM)
  • 2M CaCl2 + 0.5M KCl = (2M x 3) CaCl2 + (0.5M x 2) KCl = 7 OsM

N.B. Water activity is inversely proportional to osmolarity (i.e. water activity is low when osmolarity is high)

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22
Q

Water activity is __________(proportional/inversely proportional) to osmolarity.

A

inversely proportional (i.e. water activity is low when osmolarity is high)

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23
Q

What is the importance of osmosis?

A

Cell volume (keep shape)

24
Q

Intracellular fluid (ICF) is normally _____ mOsM

A

300mOsM

25
Q

Explain if any processes occur with 0.15M of NaCl?

A

(i) as ions, Na+ and Cl- are non-penetrating solutes
(ii) the osmolarity of this solution is: (0.15M x 2) = 0.3 OsM = 300 mOsM* *same as normal ICF

  • –> no osmolarity gradient
  • –> no water activity gradient – no osmosis
  • –> no change in cell volume

**Intracellular fluid (ICF) is normally 300 mOsM**

26
Q

What is tonicity?

A

Effect of bathing solutions on cell voume

27
Q

What are the 3 types of tonicity?

A
  1. Isotonic: no change on cell volume
  2. Hypotonic: cells swell
  3. Hypertonic: cells shrink
28
Q

What is the cause of the 3 types of tonicity?

A

If ECF in body is too weak or too concentrated (i.e hydration) your cells swell or shrink

29
Q

What is an isotonic cell?

A

no change on cell volume

30
Q

What is a hypotonic cell?

A

cells swell

31
Q

What is a hypertonic cell?

A

cells shrink

32
Q

Specialised membrane proteins enable trans-membrane solute movement (carrier-mediated transport). What are the 4 types?

A
  1. Simple diffusion (of ions, through channels) 2
  2. Facilitated diffusion (larger molecules)
  3. Primary active transport
  4. Secondary active transport
    • (both requiring energy to move solutes against their concentration gradient)
    • [low] = [high]

All display: specificity, saturation and competition

33
Q

The 4 types of carrier-mediated transport all display ___, _____ and ______.

A

specificity, saturation and competition

34
Q

What is specificity in terms of carrier-mediated transport?

A

Each carrier protein is specialised to transport one or, at most, a few closely related substances

35
Q

What is saturation in terms of carrier-mediated transport?

A

Limited number of carriers in the membrane + limited number of binding sites for a particular substance, therefore can become ‘full’ - known as the transport maximum (Tmax)

36
Q

What is competition in terms of carrier-mediated transport?

A

If closely related substances can use the same carrier they will compete for the use of that carrier

37
Q

Carrier-mediated transport: What is simple diffusion?

A

Channels are an easy way to go ions

They come in many types, depending on:

  • Ion selectivity (e.g. for Na+,K+, Cl-, etc.)
  • Gating
    • ungated: always open (leak in/out)
    • gated: voltage, ligand (hormones) or mechanically-gated (move, change shape)
38
Q

What are the typical ion concentrations in simple diffusion?

A
39
Q

Carrier-mediated transport: What is facilitated diffusion? What are the 4 steps?

A

Step 1: Transported solute binds weakly to a carrier protein (trans-membrane protein, but no pore)

Step 2: Binding of the solute molecules induces change in conformation of carrier protein Once molecule is full = Flip and change shape

Step 3: Transported solute detaches from carrier protein in area of low concentration

Step 4: Carrier protein reverts to original shape

40
Q

Carrier-mediated transport: What is step 1 of facilitated diffusion?

A

Step 1: Transported solute binds weakly to a carrier protein (trans-membrane protein, but no pore)

41
Q

Carrier-mediated transport: What is step 2 of facilitated diffusion?

A

Step 2: Binding of the solute molecules induces change in conformation of carrier protein

Once molecule is full = Flip and change shape

42
Q

Carrier-mediated transport: What is step 3 of facilitated diffusion?

A

Step 3: Transported solute detaches from carrier protein in area of low concentration

43
Q

Carrier-mediated transport: What is step 4 of facilitated diffusion?

A

Step 4: Carrier protein reverts to original shape

44
Q

Carrier-mediated transport: What is active transport in primary and secondary active transport?

A
  • “uphill” movement, thus work to be done …needs energy
  • energy direct from ATP hydrolysis: …primary active transport
  • energy derived from existing concentration
  • gradient of another solute: … secondary active transport
  • both involve a protein carrier that binds one or more solutes, thus substrate specific & saturable
45
Q

Uphill movement of active transport needs _____.

A

Energy

46
Q

Primary active transport means that energy in active transport is direct from _________.

A

ATP hydrolysis

47
Q

Energy in active transport is derived from _________ (new/existing) concentration.

A

Existing

48
Q

Secondary active transport means that the _____ of another solute.

A

gradient

49
Q

Active transport both involve a protein carrier that binds one or more solutes, thus______ and _______.

A

substrate specific; saturable

50
Q

What is the most important thing about primary active transport? Why?

A
  • Most important is Na2+/K+ pump
    • Maintain low Na2+ and high K+ (inside cells)
    • Pump out 3 Na2+
    • Pump in 2 K+
51
Q

What is secondary active transport?

A
  • Similar steps as those in facilitated diffusion but ‘extra’ solute transported against concentration gradient
  • Example: Na+/glucose symport
  • Moves glucose from intestine into epithelial cells
  • Na+ concentration gradient used to drive glucose ‘uphill’
52
Q

What are 6 important active transporters?

A
  1. Na+/K+ – ubiquitous sodium/potassium pump
  2. K+/H+ – gastric acid pump (stomach)
  3. Ca2+ – ubiquitous calcium extrusion pump
  4. H+ – ubiquitous acid extrusion pump
  5. Na+/H+ antiport – renal tubules (removes acid from body, makes urine acidic)
  6. Na+-coupled amino acid transporters (allow cells to take in amino acids to make proteins)
53
Q

In secondary active transport, there are similar steps as those in ____ diffusion but ‘extra’ solute transported ______ (towards/against) concentration gradient

A

facilitated; against

54
Q

In secondary active transport, moves glucose from ______ into _______ cell.

A

intestine; epithelial cell

55
Q

Water moves from an area of ___ (high/low)osmolarity to an area of ____ (high/low) osmolarity.

A

low; high

PHYL2062 (17 decks)

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