Membranes as Permeability Barriers Flashcards
What is a semi-permeable membrane?
A layer through which only allowed substances can pass
Name 2 molecules that move easily and 2 that have difficulty permeating through the lipid bilayer
Easy - respiratory gases, water, urea
Hard - glucose, sucrose, ions
What is a permeability co-efficient?
Ability of a molecule to pass through a membrane
What is passive transport dependent on?
- Permeability
- Concentration gradient
Name 3 roles of membrane transport processes
- Maintenance of ionic composition
- Maintenance of intracellular pH
- Cell volume regulation
- Concentration of metabolic fuels and building blocks
- Extrusion of waste products
- Generation of ion gradients
Which kind of membrane transport exhibits conformational change?
Gated pore channel
Name the 4 types of facilitated diffusion via ion channels
Gated pore
Ligand-gated - binding opens channel
Ligand-gated - binding closes channel
Voltage-gated
How does a voltage-gated ion channel work? Give an example
- Contains Voltage sensor
- Acts on the membrane potential
- Na+ channel
What is the difference between active and passive transport?
Active - requires energy to create a gradient
Passive - concentration gradient drives direction of transport
Name the 2 types of passive diffusion and 1 type of active transport
Passive - simple diffusion, facilitated diffusion
Active - transport against an unfavourable concentration/electrical gradient
Which 2 ions are most prevalent outside cells and what are their concentrations?
Na+ - 145mM
Cl- - 123mM
What are the extracellular concentrations of Ca2+ and K+?
Ca2+ - 1.5mM
K+ - 4mM
Name 3 types of plasma membrane ion transporters
- PMCA - Plasma membrane Ca2+ ATPase
- ATP Synthetase
- Na+ Pump
- NHE - sodium H+ exchanger
- SGLT - sodium glucose transporter
What is the action of a PMCA?
- Primary active transporter
- Powered by ATP hydrolysis
- Energy used to move calcium out of the cell
- High affinity and low capacity
What is the action of ATP Synthetase in ATP synthesis and where does it occur?
- Reverse active transport
- Drives ATP synthesis and is reliant on H+ gradient
- Reversible
- Occurs in mitochondria
Describe the action of a Na+ pump and what type of transport does it use?
- Active transport
- 3 Na+ ions expelled for every 2 K+ ions in
- Creates ion gradients
What does a sodium/H+ exchanger do?
Creates a sodium gradient to enable extrusion of acid
What is a uniport transport mechanism?
Movement of a single ion in one direction through the membrane
What are the 2 types of co-transporter mechanisms and what do they mean in terms of ion movement?
Symport - Movement of two ions through a membrane in one direction
Antiport - Movement of two ions through a membrane in different directions
Give 2 examples of co-transporter ion channels and what is their effect?
Na+ pump - Maintains cellular concentration of Na+ and K+
NCX - Inward flow of Na+ pushes Ca2+ out up a concentration gradient
NHX - Inward of flow of Na+ leads to alkalinisation by removing H+
How do deficient ion channels contribute to Cystic Fibrosis?
- Defective CFTR gene inhibits Cl- transport out of the cell
- Osmotic pull for water connected with Cl-
- Less water to dilute mucous
How does PKA contribute to Cholera?
- PKA activated by Gs
- PKA increases Cl- flow out of the cell
- Water follows Cl- out of the cell causing diarrhoea
