Intro To Cell Physiology And Pharmacology Flashcards
Define a semi-permeable membrane
A layer through which only allowed substances can pass
What molecules pass freely through the membrane?
Hydrophobic molecules
Small uncharged polar molecules (less freely)
What molecules don’t pass freely through the membrane?
Large uncharged polar molecules (small amount pass through)
Ions
What is fick’s law?
J = P(C1 -C2)
Where:
J = net rate of transport
P = permeability coefficient
C1 and C2 = concentration gradients on side 1 and 2
Rate of passive transport (cm/sec) increases linearly with increasing concentration gradient
Compare and contrast simple diffusion, facilitated diffusion and active transport
Simple diffusion: no proteins involved, no energy required, solute moves by diffusion down concentration or electrical gradient.
Facilitated diffusion: channel or carrier protein involved. No energy required. Solute moves by diffusion down concentration or electrical gradients.
Active transport: carrier protein involved. Cellular energy required. Solute moves across the membrane against its concentration gradient.
Describe non-gated and gated pores/channels
Gated channels (pores) - conditionally open
Non-gated pores (channels)- always open
Both have hydrophilic centres
Pores allow bi-directional transport
Some channels are ligand-gated, requiring the binding of a molecule to enable ions to pass through (such as ACh in nicotinic acetylcholine receptor in neuromuscular junction)
Some channels are voltage-gated, requiring membrane depolarisation to allow ions through (e.g. Ca2+ channels)
What is a uniport transport protein
Transports one substance in one direction
Can be passive or active transport
What is a symport transport protein?
Transports 2 different substances in same direction
Can be passive or active transport
What is an antiport transport protein?
Transports 2 different substances in opposite directions
Can be passive or active transports
What is included in co-transporters?
Symports and antiports can both be considered co-transporters
Give an example of 1º active transport
Na+ K+ ATPase - maintains cellular concentrations of Na+ and K+ (antiport)
Give an example of 2º active transport
Na+ Ca2+ exchange - inwards flow of Na+ down conc. gradient drives outward flow of Ca2+ up its conc gradient (ANTIPORT)
Na+/H+ exchanger - inward flow of Na+ down its conc gradient leads to cell alkalisation by removing H+ (ANTIPORT)
Give an example of a symport
Na+/glucose co-transport (small intestine and kidney) - entry of 1 or 2 Na+ ions provides the energy for the entry of 1 glucose molecule against the conc gradient
Give some examples of important physiological roles of transport processes
Maintenance of ionic composition
Maintenance of intracellular pH
Regulation of cell volume
Concentration of metabolic fuels and building blocks
Expulsion of metabolic waste products and toxic substances
Generation of ion gradients necessary for the electrical excitability of nerve and muscle (excitable tissues)
Where does the energy for active transport come from?
Directly or indirectly ATP hydrolysis - some cells spend 30-50% of their ATP on active transport e.g. nerves, muscle cells, erythrocytes, enterocytes, hepatocytes
What does the sodium potassium pump do?
Transports 3Na+ out and 2K+ in per ATP molecule hydrolysed
Moves both Na+ and K+ against conc gradient
Necessary for electrical excitability - only generates approx 5-10mV of resting membrane potential. Drives 2º active transport - control of pHi, regulation of cell volume and [Ca2+], absorption of Na+ in epithelia, nutrient uptake e.g. glucose or amino acids from the small intestine
What is 1º active transport?
Uses ATP as direct energy source
What is 2º active transport?
Uses energy present in an electrochemical gradient
Give some features of the sodium-potassium pump (Na+ K+ ATPase)
Antiport protein
1º active transport
25% basal metabolic rate used to keep this pump working
Known as a P-type ATPase - ATP phosphorylates aspartate, producing a phosphoenzyme intermediate
Beta subunit glycoprotein directs pump to cell surface
