Permeability Barriers (2) Flashcards Preview

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Flashcards in Permeability Barriers (2) Deck (32)
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0

What types of molecules can cross lipid bilayers. Give 2 examples of each.

- Hydrophobic: O2/CO2
- Small uncharged polar: H20/urea

1

What type of molecules can't cross lipid bilayers? Give 2 examples of each.

- Large uncharged polar: Glucose/Sucrose
- Ions: H+/Na+

2

What 2 things is passive transport dependent on?

- Permeability
- Concentration gradient.

3

Passive transport increases linearly with what?

- Concentration gradient.

4

What are some of the roles of transport in cells?

- Maintenance of ionic composition
- Maintenance of Intracellular pH
- Regulation of cell volume
- Concentration of fuels and building blocks
- Extrusion of waste products
- Generation of ion gradients necessary for the electrical excitability of nerve and muscle.

5

What is 'ping pong' transport?

- Substrate enters carrier protein
- Carrier protein changes shape to release substrate on other side of membrane.

6

What is facilitated diffusion?

- Channel proteins are open or closed.
- When open, allows large insoluble molecules to cross membrane.
- Opens in response to a ligand binding.

7

Give examples of ligand gated ion channels.

- Nicotinic acetylcholine receptor (Ach for Na+)
- ATP sensitive K+ channel (ATP for K+)

8

What are voltage gated ion channels?

- Membrane depolarisation allows channels to open

9

What are the differences between passive and active transport?

- Passive: down conc gradient, -delta G (release of energy)
- Active: against conc gradient, +delta G (requires energy)

10

What does active transport allow?

- Transport of molecules against an unfavourable conc and or electrical gradient.
- Energy is supplied directly or indirectly from ATP.

11

What are the Extracellular amounts of Na/Cl/Ca/K?

- Na: 145mM
- Cl: 123mM
- Ca: 1.5mM
- K: 4mM

12

What are the Intracellular values for Na/Cl/Ca/K?

- Na: 12mM
- Cl: 4.2mM
- Ca: 1x10^-7M
- K: 155mM

13

What does primary active transport mean?

- Gets its energy from ATP directly.

14

What is co-transport?

- More than one type of ion or molecule may be transported on a membrane transporter per reaction cycle.

15

What are the different types of transport through a membrane?

- Uniport: Only one molecule transported in one direction
- Symport: Two molecules transported in the same direction
- Antiport: Two molecules transported, one in each direction.

16

What is the Na/K pump?

- Antiport, primary active transport.
- Plasma membrane associated pump
- P type ATPase: ATP phosphorylates aspartate, producing a phosphoenzyme intermediate.

17

- The Na/K pump is made up of two subunits, what are these and what are their roles?

- Alpha: K/Na/ATP ouabin binding site
- Beta: Glycoprotein directs pump to surface.

18

What proportion of BMR is used for the Na/K pump?

- 25%

19

What is the role of K being pumped through the membrane?

- Responsible for membrane potential

20

What are the two types of Ca transport?

- Uniport: Ca-Mg ATPase.
- High affinity, low capacity

- Antiport: Na-Ca exchanger.
- Low affinity, high capacity.

21

What are the main two sodium transport systems?

- Na-H+ exchange: inward flow of Na down conc gradient, causing cell alkalisation by removing H+ (antiport)
- Na-glucose co-transport: entry of Na provides energy for entry of glucose against conc gradient (symport)

22

What is the role of transport proteins in diarrhoea?

- CFTR is overstimulated by protein kinase A
- Cl outflow increased so does H2O as it follows.

23

What are the intracellular and extracellular Ca concentrations?

- Intracellular: 50-100 nM
- Extracellular: 2mM

24

What are the 6 different ways of controlling resting Ca?

- Na/K pump using ATP
- Ca ion channel
- NCX (Na/Ca exchange)
- PMCA (Ca/H exchange)
- SERCA (Ca/H exchange in sarcoplamic reticulum)
- Ca facilitated transport (mitochondria)

25

How can NCX work in both directions?

- As Na enters this causes depolarisation, membrane potential reverses mode of operation.

26

How is the NCX pump affected in ischaemia?

- Decrease in ATP
- Na pump inhibited
- Na accumulates, cell depolarises
- NCX reverses, Na is exchanged for Ca
- High Ca levels is toxic causing cell damage.

27

What are the ways in which cell pH is controlled?

- Acid extrusion: Na/H exchange -NHE
Na dependent Cl/HCO3 exchanger -NBC
- Base extrusion: Cl/HCO3 exchange (Cl in) -AE

28

How is cell volume regulated?

- Transport of osmotically active ions (Na/K/Cl/organic osmolytes)
- Water follows
- Cell swelling (extrude ions)
- Cell shrinkage (influx ions)
- Conductive and co-transport systems to maintain electroneutrality

29

Outline how bicarbonate reabsorption occurs in the proximal tubule.

- NaHCO3 splits into Na and HCO3-
- Na is transported into the tubule from the lumen by NHE (Na/H)
- Na pump, pumps Na into the capillary. (K opposite direction, but diffuses back into capillary)
- In the proximal tubule H20 and CO2 from metabolism are combined to form H2CO3
- This splits into HCO3- and H+
- HCO3- is transported into the capillary by an AE pump (Cl the other way)
- H+ is used in the NHE pump to be transported to the lumen.
- H+ and HCO3- combine to form H2CO3
- This can be changed into CO2 and H2O by carbonic anhydrase
- These can be transported into the tubule.