Physiological functions of transporters Flashcards Preview

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Flashcards in Physiological functions of transporters Deck (20):
1

Cell shape

-Highly variable
-Depends on cell type and its function

2

Cytoskeleton

-Supports cell shape
-Enables cell movement
-But is not rigid (shape can be changed by external factors)

3

Osmotic pressure

Pressure generated when two compartments separated by a semi-permeable membrane contain different solute concentrations.

4

van't Hoff's law

Osmotic pressure π=nCRT
n: no. of dissociable particles, e.g. 2 for NaCl
C: total conc
R: gas constant
T: temp in K

5

Osmolarity

Number of osmoles of solute per 1 L of solvent (Osm/L).

6

Osmolality

Number of osmoles of solute per 1 kg of solvent (Osm/kg).

7

Osmole

Dissolved particle

8

Why is osmolality a better measure than osmolarity?

It is temperature independent as volume varies with temp but mass does not.

9

Oncotic pressure

-Osmotic pressure that is caused by proteins
-Proteins (and other large molecules) in solution produce larger osmotic pressure than expected
-van't Hoff's law only applies to small molecules

10

Tonicity

The effective osmolality and is equal to the sum of the concentrations of the solutes which have the capacity to exert an osmotic force across the membrane.

11

How is the cell regulatory volume controlled

-Regulatory volume decrease (RVD)- mainly loss of KCl (cell conc of these ions is very high)
-Regulatory volume increase (RVI)- mainly NaCL uptake, but Na+ exchanged for K+ via Na+/K+ ATPase (3:2 ratio)

12

What membrane transport proteins maintain cellular pH

-Na/H exchanger (acid extruder)
-Anion exchanger (base extruder)

13

Na+/H+ exchanger (NHE)

-Antiport- exchanges extracellular Na+ for intracellular H+ -> alkalises cytoplasm
-Secondary active transport driven by Na+ gradient
-Also regulates cell volume

14

Anion exchanger (AE)

-Antiport- exchanges extracellular Cl- for intracellular HCO3- -> acidifies cytoplasm
-Secondary active transport driven by Cl- gradient

15

Co-ordination of acid and base extrusion

Rates of acid and base extrusion from cytoplasm are pH sensitive:
-Acidification activates Na+/H+ exchanger
-Alkalisation activates anion exchanger
-Only works with small disturbances

16

Cellular calcium homeostasis

-Steep calcium concentration gradient: ~4-5 orders of magnitudes
-Small changes in cytosolic [Ca2+] play important role in cell signalling e.g. calcium-dependent enzyme activity & vesicular release (e.g. synapses)
-Large changes in cytosolic [Ca2+] are toxic to cells -> important to maintain low cytosolic [Ca2+]

17

Sources of Ca2+ to increase cytosolic [Ca2+]

-Extracellular membrane via Ca2+ channels
-Release from intracellular stores

18

Removal of excess cytosolic Ca2+ via active transport

-Plasma membrane Ca2+ ATPase (PMCA)
-Sarco/endoplasmic reticulum Ca2+ ATPase (SERCA)
-High Ca2+ affinity, but low capacity
-Remove residual calcium

19

Removal of excess cytosolic Ca2+ via secondary active transport

-Na+Ca2+ exchanger
-Low Ca2+ affinity, but high capacity
-Removal of most Ca2+

20

Removal of excess cytosolic Ca2+ via mitochondria

-Mitochondrial Ca2+ uniporters
-Facilitated diffusion
-Operate at high [Ca2+]cyt
-Mitochondria -ve charged -> driven via electrical gradient against conc gradient