26/10/18
Professor Kenneth Linton
Transmembrane Transport
1. Channels
• Used by ions
• To point of equilibrium then stops – passive diffusion
• E.g. CFTR is a chloride channel that stops working
• Can be regulated and selective
• Down electrochemical gradient
• Lots of bulk flow – charges inside channel attract ion
2. Transporters
• Used by amino acids, sugars and drugs
• Up concentration gradient
• E.g. ABCB1 is a drug efflux pump and causes multidrug resistance
• Passive movement with binding sites on one side that switches as it works
• Facilitated diffusion down the concentration gradient at low capacity
3. Integrins, adhesins, connexins, claudins
• Anchored to cytoskeleton or extracellular matrix
• E.g. connexin 26 in cochlear cells that connect gap junctions to allow ion flow
o Causes congenital deafness
4. Receptors
• Used for endocytosis or cell signalling with no ligand movement
• E.g. FGFR3 and FGF are tyrosine receptor kinases
o This gives rise to MAPK that changes gene expression
o Causes less proliferation of bone cells – achondroplasia
5. Enzymes
• Also used in cell signalling
• E.g. phospholipase C activate PKC and iP3
o PKC activates diacyl glycerol in membrane
o iP3 allows Ca2+ release from endoplasmic reticulum
Active Transport
• ATP added on opposite side of membrane – induced by the solute binding
• Net flux dependent on the amount of ATP but can be uphill
• Primary active pump
Professor Kenneth Linton
Transmembrane Transport
1. Channels
• Used by ions
• To point of equilibrium then stops – passive diffusion
• E.g. CFTR is a chloride channel that stops working
• Can be regulated and selective
• Down electrochemical gradient
• Lots of bulk flow – charges inside channel attract ion
2. Transporters
• Used by amino acids, sugars and drugs
• Up concentration gradient
• E.g. ABCB1 is a drug efflux pump and causes multidrug resistance
• Passive movement with binding sites on one side that switches as it works
• Facilitated diffusion down the concentration gradient at low capacity
3. Integrins, adhesins, connexins, claudins
• Anchored to cytoskeleton or extracellular matrix
• E.g. connexin 26 in cochlear cells that connect gap junctions to allow ion flow
o Causes congenital deafness
4. Receptors
• Used for endocytosis or cell signalling with no ligand movement
• E.g. FGFR3 and FGF are tyrosine receptor kinases
o This gives rise to MAPK that changes gene expression
o Causes less proliferation of bone cells – achondroplasia
5. Enzymes
• Also used in cell signalling
• E.g. phospholipase C activate PKC and iP3
o PKC activates diacyl glycerol in membrane
o iP3 allows Ca2+ release from endoplasmic reticulum
Active Transport
• ATP added on opposite side of membrane – induced by the solute binding
• Net flux dependent on the amount of ATP but can be uphill
• Primary active pump
