2 ATP-dependent pumps and Ion exchangers Flashcards
Name 3 properties that means molecules cannot passively move through a membrane. Give 4 examples
Large, uncharged polar molecules and ions
Glucose, sucrose, H+, Cl-
Name 3 properties of molecules that allows them to passively move through a membrane and give 4 examples
Hydrophobic, small, uncharged
H2O, O2, CO2, urea
List the important functions of transport proteins (6)
Maintenance of ionic composition Maintenance of intracellular pH Regulation of cell volume Concentration of metabolic fuels The extrusion of waste products of metabolism The generation of ion gradients
Describe Ping-Pong transport
A membrane protein will go through a conformational change to allow a molecule through the membrane
Explain how ‘Ligand-Gated Channels’ work
When a ligand such as ATP or ACh binds to the protein, the channel opens.
Explain how ‘Voltage-Gated Channels’ open
The channel opens when the membrane becomes depolarised.
Define ‘Active Transport’
Active transport allows the transport of molecules or ions against the concentration gradient and/or electrical gradient. It requires energy from ATP hydrolysis.
What is the extracellular concentration of Na+?
145mM
What is the extracellular concentration of Cl-?
123mM
What is the extracellular concentration of Ca2+?
1.5mM
What is the extracellular concentration of K+?
4mM
Define Co-transport
More than 1 type of ion or molecule can be transported on a protein carrier per cycle.
Describe the difference between a ‘symport’ and an ‘antiport’
A symport takes two molecules or ions from one side of the membrane to the other
An antiport moves one molecule or ion IN and one molecule or ion OUT of a cell.
Describe the workings of the Na-K-ATPase pump.
3 Na+ ions are moved OUT of the cell. 2 K+ ions are moved IN to the cell. This movement is against the concentration gradients so ATP is required.
What ions are moved by the PMCA protein? What is its affinity and capacity?
PMCA: plasma membrane calcium ATPase
Calcium is moved OUT of the cell against the concentration gradient so ATP is required. It has a high affinity for calcium but a low capacity.
Describe and explain the actions of the Na-Ca-exchanger (NCX)
Exchanges 3Na+ IN for 1Ca2+ OUT in an antiport.
It works via the electrogenic current of Na+ ions. It helps to expel Ca2+ after depolarisation. The movement reverses during depolarisation.
It has a low affinity for Ca2+ but a high capacity.
Describe the actions of the Na-H-exchanger (NHE)
1 Na+ is moved IN as 1H+ is moved out
Describe the actions of the Na-glucose co-transport pump and explain how the energy is acquired.
1 Na+ ion and 1 glucose molecule move IN together. The movement of Na+ IN provides the energy for glucose entry against its concentration gradient.
Explain why sufferers of CF have thick mucus
In CF, the CFTR gene is not present. This restricts Cl- from leaving the cell so water also remains in the cell. The mucus is therefore, very thick.
Explain how diarrhoea occurs
Protein kinase A increases the expression of Cl- transport proteins. More Cl- moves OUT and so more water also moves OUT of the cell and into the gut. This results in diarrhoea.
List 2 important functions of Na+ pumps
Forms Na+ and K+ gradients essential for electrical impulses
Drives secondary active transport for control of pH and regulation of cell volume.
Describe and explain the functions of the SERCA protein
SERCA: Sarco/Endoplasmic Reticulum Calcium ATPase
1 Ca2+ moves IN as 1 H+ moves OUT of the SER
ATP is required as it is against the concentration gradient
It has a high affinity but a low capacity
What is the function of mitochondrial Ca2+ uniports?
Act as a buffer at high concentrations of Ca2+
Explain how ischaemia can result in toxic consequences to as cell.
ATP levels are depleted so the sodium pump is inhibited. Na+ accumulated in the cell and the cell depolarises. This reverses the NCX protein and Ca2+ is moved into the cell. This can be toxic to the cell.
