Membrane Proteins Flashcards
Integral membrane proteins
Interact extensively with the hydrophobic region of membrane phospholipids, some are transmembrane proteins.
Peripheral membrane proteins
Have hydrophilic r groups on their surface and are bound to the surface of membranes, mainly by ionic and hydrogen band interactions. Many interact with the surfaces of integral membrane proteins
What holds integral membrane proteins within the phospholipid bilayer?
Regions of hydrophobic r groups allow strong hydrophobic interactions that hold integral membrane proteins within the phospholipid bilayer..
What is the phospholipid bilayer a barrier to?
lons and most uncharged polar molecules
What can pass through the bilayer by simple diffusion?
Some small molecules, like oxygen and carbon dioxide
Facilitated diffusion
The passive transport of substances across the membrane through specific transmembrane proteins
How do cells use channel and transporter proteins to perform specialised functions?
Different cell types have different channel and transporter proteins.
Channels
Multi-subunit proteins with the subunits arranged to form water-filled parts that extend across the membrane
How do gated channel proteins work?
They change conformation to allow or prevent diffusion
Ligand-gated channels
Controlled by the binding of signal molecules
Voltage - gated channels
Controlled by changes in i on concentration
How do transporter proteins work?
Transporters alternate between two conformations so that the binding site for a solute is sequentially exposed on one side of the bilayer then the other. Transporter proteins bind to the specific substance to be transported and undergo a conformational change to transfer the solute across the membrane.
Active transport
Uses pump proteins that transfer substances across the membrane against their concentration gradient. Pumps that mediate active transport are transporter proteins coupled to an energy source.
How is the energy ter active transport produced?
Some active transport proteins hydrolyse ATP directly to provide the energy needed for the conformational change required to more substances across Te membrane, ATPases hydrolyse ATP.
What forms the electrochemical gradient?
For a solute carrying a net charge, the concentration gradient and the electrical potential difference combine to form the electrochemical gradient that determines the transport of the solute,
How is a membrane potential (an electrical potential difference) created?
When there is a difference in electrical charge on the two sides of the membrane
What do Ian pumps do?
Ion pumps, such as the sodium potassium pump, use energy from ty hydrolysis of ATP to establish and maintain i on gradients
What does the sodium potassium pump do?
Transports ions against a steep concentration gradient using energy directly from ATP hydrolysis, it actively transports sodium ions out of the cell and potassium ions into the cell.
How does the sodium potassium pump work?
The pump has a high affinity for sodium inside the cell, binding occurs, phosphorylation by ATP, conformation changes, affinity for sodium decreases, sodium ions released outside the cell, potassium ions bind outside the cell, dephosphorylation, conformation changes, potassium ions taken into cell, affinity returns to start.
What is the ratio of sodium to potassium for each ATP hydrolysed?
Three sodium ions are transported outside the cell and two potassium ions are transported into the cell, this establishes both concentration gradients and an electrical gradient.
Where is the sodium-potassium pump found?
In most animal cells, accounting for a high proportion of the basal metabolic rate in many organisms.
How does the sodium potassium pump work in the small intestine?
The sodium gradient created by the pump drives the active transport of glucose, in intestinal epithelial cells the pump creates a sodium ion gradient across the plasma membrane.
Glucose transporter
The glucose transporter responsible for this glucose symport transports sodium ions and glucose at the same time and direction. Sodium ions enter the cell down their concentration gradient, the simultaneous transport of glucose pumps glucose into the cell against its concentration gradient.
