Biological membranes 2 Flashcards
What is the main function of cell membranes?
Lipids provide the physical characteristics of membranes and form a permeability barrier
How do ions and polar molecules cross biological membranes?
They cannot easily diffuse across membranes due to their charge and size.
What is the exception to the rule that ions and polar molecules cannot easily diffuse across membranes?
Water can diffuse slowly across membranes due to its low molecular weight and high concentration.
What technique is used to study the permeability of lipid bilayers?
Patch-clamping
What are the two main types of membrane proteins?
Integral proteins and peripheral proteins.
Describe integral membrane proteins.
They are embedded in and span the bilayer, interacting with lipid hydrocarbon chains.
What are peripheral membrane proteins?
Proteins bound to the membrane by electrostatic and hydrogen-bond interactions.
What technique provides evidence for the ‘mosaic’ nature of membranes?
Freeze fracture and electron microscopy.
What is the fluid mosaic model of membranes?
It describes membranes as dynamic structures with phospholipids forming a bilayer and proteins embedded within.
What distinguishes passive transport from active transport?
Passive transport does not require energy, while active transport requires energy to move substances against their concentration gradient.
What is primary active transport?
Transport that works against a concentration gradient and requires hydrolysis of ATP
Define secondary active transport
Transport that uses the energy from the electrochemical gradient of one molecule to move another molecule against its gradient.
What is osmosis?
The net movement of water from a solution of low solute concentration to one of high concentration
What are aquaporins?
Water-channel proteins that facilitate the rapid movement of water across cell membranes.
How do ion channels function?
They allow specific ions to move down their concentration gradients, introducing specificity for ion transport.
What is the resting membrane potential?
The electrical potential difference across a cell membrane when the cell is at rest, typically ranging from -30 to -100 mV.
What causes the resting membrane potential?
The semi-permeable nature of the cell membrane leading to unequal ion distribution and the presence of ion pumps and channels.
What are the three types of secondary transporters?
Antiporters
Symporters
Uniporters
Describe a symporter
A transporter that moves two molecules in the same direction across the membrane
What is an antiporter?
A transporter that moves one molecule into the cell while moving another molecule out.
What is the function of ATP-powered pumps?
They transport ions or molecules across membranes using the energy from ATP hydrolysis
Name the four classes of ATP-powered pumps
P-class pumps, V-class pumps, F-class pumps, and ABC transporters
What is the function of P-class pumps?
They transport ions and form a phosphorylated intermediate during the pumping process.
What do V-class pumps primarily transport?
Protons, which can alter pH levels in various cellular compartments.
