biology - 1.3 Flashcards
What hold integral membrane proteins within the phospholipid bilayer?
Regions of hydrophobic R groups allow strong hydrophobic interactions.
What do integral membrane proteins interact extensively with?
The hydrophobic region of
membrane phospholipids.
What are some integral proteins?
Transmembrane proteins.
What do peripheral membrane proteins have?
Hydrophilic R groups on their surface and are bound to the surface of membranes, mainly
by ionic and hydrogen bond interactions.
What do many peripheral membrane proteins interact with?
The surfaces of integral membrane .
What is the phospholipid bilayer?
A barrier to ions and most uncharged polar molecules.
What pass through the bilayer by simple diffusion?
Some small molecules, such as oxygen and carbon dioxide.
What is facilitated diffusion?
The passive transport of substances across the membrane through specific transmembrane proteins.
To perform specialised functions, what do different cell types have?
Different channel and transporter proteins.
What are most channel proteins in animal and plant cells?
Highly selective.
What are channels?
Multi-subunit proteins with the
subunits arranged to form water-filled pores that extend across the membrane.
What are some channel proteins?
Gated and change conformation to allow or prevent diffusion.
What are ligand-gated channels controlled by?
The binding of signal molecules.
What are voltage-gated channels controlled by?
Changes in ion concentration.
What do transporter proteins do?
They bind to the specific
substance to be transported and undergo a conformational change to transfer the solute
across the membrane.
Why do 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.
What does active transport use?
Pump proteins that transfer substances across the membrane against their concentration gradient.
What are pumps that mediate active transport?
Transporter proteins coupled to an energy source.
What is required for active transport?
A source of metabolic energy.
What do some active transport proteins hydrolyse?
ATP directly to provide the energy for the conformational change required to move substances across the membrane.
What hydrolyse ATP?
ATPases.
For a solute carrying a net charge, what do the concentration gradient and the electrical potential gradient do?
They combine to form the electrochemical gradient that determines the transport of the solute.
When is a membrane potential, or an electrical potential difference, created?
When there is a difference in electrical charge on the two sides of the membrane.
What do ion pumps, such as the sodium-potassium pump, use?
Energy from the hydrolysis of ATP to establish and maintain ion gradients.
How does the sodium-potassium pump transport ions across a steep concentration gradient?
Using energy directly from ATP hydrolysis.
What does the sodium-potassium pump actively transport?
Sodium ions out of the cell and potassium ions into the cell.
For each ATP hydrolysed, what is transported?
Three sodium ions are transported out of the cell and two potassium ions are transported into the cell.
In the sodium-potassium pump, what does the transport of ions establish?
Both concentration gradients and an electrical gradient.
Sodium-potassium pump: Step 1
The pump has high affinity for sodium ions inside the cell; binding occurs;
Sodium-potassium pump: Step 2
Phosphorylation by ATP; conformation changes;
Sodium-potassium pump: Step 3
Affinity for sodium ions decreases; sodium ions released outside of the cell;
Sodium-potassium pump: Step 4
Potassium ions bind outside the cell;
Sodium-potassium pump: Step 5
Dephosphorylation; conformation changes;
Sodium-potassium pump: Step 6
Potassium ions taken into cell; affinity returns to the start.
Where is the sodium-potassium pump found?
In most animal cells, accounting for a high proportion of the basal metabolic rate in many organisms.
In the small intestine, what does the sodium gradient created by the sodium-potassium pump drive?
The active transport of glucose.
In intestinal epithelial cells, what does the sodium-potassium pump generate?
A sodium ion gradient across the plasma membrane.
What does the glucose transporter responsible for this glucose support transport?
Sodium ions and glucose at the same time and in the same direction.
How do sodium ions and glucose enter the cell?
Sodium ions enter the cell down their concentration gradient; the simultaneous transport of glucose pumps glucose into the cell against its concentration gradient.
