Membrane Transport - Passive (overview)
- no energy required
- solute moves down the concentration gradient
- Simple diffusion
Membrane Transport - Active (overview)
- Uses ATP
- Solute moves up concentration gradient
- Primary active transport
- Secondary active transport
Membrane Transport: Types
- Simple Diffusion
- Channel (facilitated diffusion - passive)
- Carrier (facilitated diffusion - passive)
- Active transport
- Gradient (through the membrane)
The Kinetics of Facilitated Transport
The saturation kinetics of facilitated transporters follows a hyperbolic relationship
Ex. Michaelis-Menton Kinetics
Types of Transporters (1. Uniporter)
- Glucose (RBC)
- Na+ Channel
Types of Transporters (2. Antiporter)
- Na+/K+ ATPase
- Cl-/HCO3 - Exchanger
Types of Transporters (3. Symporter)
- NKCC = Na+, K+, 2Cl- cotransporter
- Symporter = Co-transporter
Aquaporins:
A family of membrane proteins that form channels specifically for the transport of water and small molecules
Aquaporins Functions
- Water regulation
- Kidney functions
- Plant physiology
- Cell signaling
Aquaporins Functions - 1. Water Regulation
Facilitate water movements in and out of cells. Maintaining cell tugor and overall fluid balance
Aquaporins Functions - 2. Kidney Functions
Vital to concentration urine and regulate water reabsorption⁷
Aquaporins Functions - 3. Plant Physiology
Help manage water in and out of body/roots
Aquaporins Functions - 4. Cell Signaling
Participate in signaling pathways and can transport other small molecules, such as glycerol or urea
Facilitated Diffusion - 1. Voltage-Gated channels
Open/close in response to changes in membrane potential
Facilitated Diffusion - 2. Ligand-Gated Channels
Open/close in response to presence/absence in ligand
Facilitated Diffusion - 3. Mechanically-Gated Cahnnels:
Open/close in response to changes in cell shape
The Na+ - K Pump is Responsible for:
- Maintaining high {K+}in and {Na+}out
- Maintaining the transmembrane electrical potential
