Membrane transport Flashcards
What is the primary function of cells within an organism regarding metabolites?
Cells exchange compounds with their environment by passing them across biological membranes.
What are some examples of compounds commonly exchanged across membranes?
- Glucose
- Ions
- Amino acids
What is the permeability of the lipid bilayer to uncharged molecules?
Fairly permeable to a few uncharged molecules such as oxygen and CO2.
Why does the lipid bilayer retard diffusion of hydrophilic compounds?
It is very hydrophobic.
What types of components are incorporated in the membrane of a living cell?
- Lipids (cholesterol/steroid)
- Peripheral and integral proteins
- Glycoproteins
What is facilitated transport?
Transport of ions and small molecules that don’t pass readily by passive diffusion.
What are the two types of transport across membranes?
- Passive
- Active
What is the major difference between passive and active transport?
Active transport requires an input of free energy to function.
What is passive transport also referred to as?
Accelerated diffusion.
What does passive transport do regarding concentration gradients?
Can only dissipate the gradient.
What is the energy requirement for passive transport?
No energy requirement.
What does active transport involve?
Moving a solute across a membrane against concentration gradient.
What is the source of energy for active transport within the cell?
Adenosine triphosphate (ATP).
What process do many active transport proteins utilize?
Hydrolysis of ATP.
Fill in the blank: The process of reaching equilibrium in passive transport is energetically _______.
favoured
What is passive transport?
Transport across the membrane facilitated by transporters that provide passageways for specific compounds.
What are pores and channels?
Transporters that provide passageways across the membrane for specific compounds.
What do porins do?
Form aqueous channels that accelerate passive diffusion of small hydrophilic molecules.
What determines the solute selectivity of a porin?
Characteristics of the amino acid side chains and the size of the opening.
How do positively charged regions affect porins?
They make the pore specific for small anions.
What are ion channels?
More complex transporters that generally require multiple subunits to form a membrane passageway.
What are gated channels?
Channel-like transporters that open only when stimulated.
What can stimulate gated channels to open?
- Ligand binding * Changes in membrane potential * Changes in pH * Covalent modification by a cellular enzyme.
What happens after stimulation of a gated channel?
The blocked gate opens through conformational changes or rotation of helices.
