Active transport
Describe how the sodium-potassium pump works.
1. The pump is open to the inside of the cell, 3 Na+ ions enter the pump, attaching to their binding sites. 2. ATP binds to the pump and transfers a phosphate group to the pump. 3. Phosphorylation (addition of the phosphate) causes a conformational change of the pump in which the interior of it closes and it opens outside, releasing the Na+ ions. 4. 2 extracellular K+ ions bind to the exposed sites, causing a dephosphorylation of the pump, leading to a change back to its original conformation, the pump opens once more to the inside of the cell. The cycle repeats. 5. Cellular respiration must then occur to add the phosphate back to the ADP and restore the ATP.
What is a uniport? Symport? Antiport?
A uniport transports one molecule in one direction. A symport transports two types of molecules in one direction. An antiport transports two types of molecules in two directions.
What kinds of proteins are ATPases?
ATPases are integral enzymes.
What does ATP stand for?
Adenosine triphosphate.
Describe the process of receptor mediated endocytosis.
After the binding of a ligand to plasma membrane-spanning receptors, a signal is sent, the membrane is coated, and a vesicle is formed. It is then marked for ingestion and uncoated so that it can fuse with other membranes. The molecule has been absorbed.
In phagocytosis, what do white blood cells take in?
Bacteria and viruses.
What is the difference between constitutive and regulated secretion?
Constitutive secretion is continuous. It does not need a specific signal. Regulated secretion requires a signal, such as a hormone, to start signal transduction in which a number of reactions occur and the material is then released.
Identify four different factors that affect the rate of diffusion across a membrane.
Distance, surface area, temperature, and concentration of solute.
What is endocytosis?
Endocytosis is the taking of an external material by the infolding of the plasma membrane and the formation of a vesicle. This reduces the size of the overall membrane so cells can take in fluid (pinocytosis) or solids (phagocytosis.)
What is exocytosis?
Exocytosis is the secretion of a substance from inside the cell to the outside using vesicles, which dock and fuse with the plasma membrane in order to release protein, which enlarges the size of the overall membrane.
True or false: Pinocytosis is used to take in water. Why or why not?
False, because it is used to take in the materials present inside the water.
In phagocytosis, what do unicellular organisms take in?
Food particles.
Give some example of osmotically active substances.
Glucose, sodium ions, potassium ions, chloride ions...
What are ion channels?
Ion channels are gated channels used to diffuse ions.
If a solution is hypertonic, what is the osmolarity with regards to the tissue present in the solution?
It has a higher osmolarity.
If a solution is hypotonic, what is the osmolarity with regards to the tissue present in the solution?
It has a lower osmolarity.
If a solution is isotonic, what is the osmolarity with regards to the tissue present in the solution?
It has the same osmolarity.
Give and explain three examples of primary active transport.
One example would be the sodium-potassium pump, an integral protein which binds and hydrolyzes ATP. Another would be the calcium pump, which transports calcium out of the sarcoplasmic reticulum of muscle cells after muscle contraction. Another would be proton pumps, which are in the stomach in order to secrete H+ and maintain the acidity of the stomach contents. They are also in lysosomes, pumping H+ from the cytoplasm into the lysosomes.
What substances can be transported by pumps that directly hydrolyze ATP?
Positively-charged ions, such as Na+, K+, Ca+, or H+.
What is secondary active transport?
Secondary active transport is a form of active transport across the plasma membrane in which a transporter protein couples the movement of an ion down its electrochemical gradient, to the movement of another molecule/ion against its concentration gradient.
What are aquaporins involved in?
The diffusion of water.
Where does the energy come from in secondary active transport?
The energy is provided by the concentration gradient of a substance/ion which moves back inside the cell, whilst the other molecule is transported against its concentration gradient.
How can the cell membrane form and break in order to conduct endocytosis and exocytosis?
The fluidity of the membrane allows it to change shape, break, and reform.
How does concentration affect the rate of diffusion across a membrane?
The higher the concentration, the longer the net movement will take.
How does temperature affect the rate of diffusion across a membrane?
The higher the temperature, the higher the kinetic energy, the more molecular movement, the more random collisions with the membrane.
How does surface area affect the rate of diffusion across a membrane?
The more surface area available to diffuse, the higher the rate of diffusion.
How is osmolarity measured (what units)?
The osmolarity, or the concentration of osmotically active solutes, is measured by osmoles or milliosmoles (mOsm).
Give four examples of exocytosis.
The secretion of proteins (enzymes, peptide hormones, antibodies etc), the release of neurotransmitters, the placement of membrane proteins, the recycling of receptors, the excretion of waste.
What is the difference between primary and secondary active transport? Explain.
The source of energy. In primary active transport, the carrier protein uses energy directly from ATP through hydrolysis. In secondary active transport, it uses energy stored in the concentration gradients of ions.
Describe glucose-sodium cotransport.
The two substances will move across the membrane in the same direction at the same time. The sodium ions will move down their concentration gradient, providing the energy to pull glucose into the cell against its concentration gradient. No direct ATP is needed for the glucose.
How are protein pumps specific?
They each only transport a particular substance.
How do carrier proteins diffuse substances across the plasma membrane?
They undergo a change in conformation.
What is the purpose of active transport?
To speed up movement across the plasma membrane by expending ATP and moving solutes against their electrochemical gradient.
What do we call a substance that can form bonds with water?
We call it "osmotically active."
