1.8 KiB
1.8 KiB
Cell Structure and Function
Mechanisms of active transport.
Summary
- Active transport moves substances against their concentration gradient and requires energy, usually from ATP hydrolysis
- Membrane proteins (pumps) required for active transport. Bind to molecules and moves them.
- Na+/K+ pump (sodium potassium pump) moves 3 Na+ out and 2K+ in per ATP. Builds chemical and electric gradients.
- Unequal ion movement contribute to membrane potential, helping cell's separation of charges.
- Gradients store potential energy.
- Passive transport requires no energy and moves substances down the gradient.
Why ATP Is Required
Requires metabolic energy. Uses hydrolysis to break ATP (adenosine triphosphate) ADP and inorganic phosphate (Pi), which releases energy that membrane proteins require. When ATP runs out, active transport stops.
The Role of Membrane Proteins
Specialized membrane proteins:
- Act as pumps
- Undergo conformational changes using the ATP hydrolysis energy
- Selective for which molecules they bind to
- Moves substances across the membrane
The Sodium-Potassium Pump: The Key Example
Na+/K+-ATPase is a transmembrane protein that:
- Runs continuously to maintain ion concentrations, since ions tend to equalize
- Acts as an ATPase enzyme, catalyzing the ATP hydrolysis
- Transports 3 Na+ out and 2K+ in per ATP
- Uses released energy to pump ions against gradient Sodium potassium pumps use gradients that combine chemical and electric gradients.
Chemical Gradient:
- Keeps Na concentration higher outside cell
- Keeps K concentration higher inside cell
- Stores potential energy
Electrical Gradient:
- Because 3 positive ion leave for every 2 that enter, net loss of charge, making interior more negative
- Contributes to resting membrane potential
- Helps support nerve impulse transmission, muscle activity, nutrient uptake,