Lecture 5 - transporters Flashcards
(18 cards)
Forces Influencing Ion and Solute Movement
Biological membranes have a membrane voltage (electrical gradient) due to selective permeability and ion gradients.
Ion movement is influenced by:
Chemical (concentration) gradients: Ions move from high to low concentration.
Electrical gradients: Ions are attracted to opposite charges.
The electrochemical gradient is the combination of both forces.
Rules of movement:
Negative membrane potential → positive ions move inward.
Positive membrane potential → positive ions move outward
To calculate equilibrium potential (E):
- Find ion concentrations inside and outside.
- Take the ratio ([outside]/[inside]) and calculate the log base 10.
- Multiply by a constant (~58 mV at room temperature).
This tells you whether ion movement is passive (downhill) or requires energy (uphill).
General Types of Membrane Transporters and their features
Pumps:
Low turnover rate, high abundance. Use primary energy (e.g., ATP) to transport ions uphill.
Carriers:
Intermediate rates. Couple movement of solutes with driver ions (e.g., Na+ or H+). Secondary active transport.
Channels:
Very high rates. Allow passive movement down gradients. Highly selective and regulated (“gated”).
Specific Transport Mechanisms: Primary pumps
Use ATP for primary active transport.
Pump ions like H+ or Na+ against their gradients.
Are electrogenic: they create and maintain electrochemical gradients.
Specific Transport Mechanisms: Carriers
Secondary active transport.
Powered by pre-existing ion gradients (e.g., Na+ or H+).
Can be:
Symporters (co-transporters): move two things in the same direction.
Antiporters (counter-transporters): move two things in opposite directions.
Can be electrogenic or electroneutral.
Specific transport mechanisms: Channels
Always passive.
Highly selective (e.g., Ca²⁺ channels, K⁺ channels).
Regulated by gating mechanisms.
Distinct transport strategies in animals: pumps
Pumps:
Na⁺/K⁺ ATPase: 3 Na⁺ out, 2 K⁺ in. Creates a strong Na⁺ gradient for Na⁺ influx.
Distinct transport strategies in plants: pumps
Pumps:
H⁺-ATPase: expels H⁺ out of the cytosol, using ATP. Builds strong H⁺ gradient.
Distinct transport strategies in bacteria: pumps
Pumps:
H⁺ pump driven by electron transport chain, expelling H⁺.
Distinct transport strategies in endomembranes (Inside cells): pumps
Pumps:
V-type H⁺-ATPase: pumps H⁺ into lumen of vesicles (e.g., vacuoles, lysosomes).
Distinct transport strategies in animals: carriers
Carriers:
Facilitators: e.g., GLUT1 (glucose transporter).
Antiporters: e.g., Na⁺/Ca²⁺ antiporter (expels Ca²⁺).
Symporters: e.g., Na⁺-dependent uptake of sugars and amino acids in intestines.
Distinct transport strategies in animals: channels
Channels:
Na⁺ and K⁺ channels: mediate action potentials in neurons.
Resting K⁺ channels: maintain membrane voltage.
Cl⁻ channels: involved in osmoregulation.
Ca²⁺ channels: involved in signalling.
Distinct transport strategies in plants: Carriers
Carriers:
Antiporters: e.g., Na⁺/H⁺ antiporter for salinity tolerance (expels Na⁺).
Symporters: e.g., K⁺, PO₄²⁻, SO₄²⁻ uptake in roots coupled to H⁺ influx.
Distinct transport strategies in plants: Channels
Channels:
K⁺ channels: dominant for membrane voltage regulation and guard cell control.
Ca²⁺ channels: elevate cytosolic Ca²⁺ for signalling.
Cl⁻ channels: involved in membrane voltage regulation
Distinct transport strategies in bacteria: carriers
Carriers:
Symporters: nutrients like K⁺, PO₄²⁻, lactose coupled to H⁺ influx.
Na⁺/H⁺ antiporters: expel Na⁺ and create Na⁺ influx gradients.
Distinct transport strategies in bacteria: channels
Channels:
Non-selective cation channels: important for osmoregulation
Distinct transport strategies in endomembranes: carriers
Carriers:
Antiporters: couple H⁺ influx with nutrient or waste product transport.
Example: neurotransmitters stored in vesicles in neurons.
Distinct transport strategies in endomembranes: channels
Channels:
Ion channels regulate membrane voltage and signalling (e.g., Ca²⁺ channels).
