Interactions Between Cells and the Extracellular Environment Part 2 Flashcards
What are three characteristics Carrier Proteins share with enzymes?
1- Specificity
2- Competition
3- Saturation
The transport of glucose from the blood across plasma membrane occurs by what mechanism?
Facilitated Diffusion
What antibiotic often has a competitor mixed in with it? And why?
Penicillin is often mixed with Probenecid. This is because penicillin has a half life of 30 minutes. Without something to compete against for the carrier proteins in tubular secretion, the penicillin exits the body very quickly. When given with probenecid both molecules are in competition over the carrier protein to exit the body and therefore penicillin experiences a lower rate of transport and stay in the body longer.
Name the isoforms of the glucose carriers.
GLUT 1, 2, 3, and 4. They each do the same thing, facilitated diffusion of glucose, but in different areas of the body.
What is the name of the major glucose transporter in neurons?
GLUT 3
Which GLUT isoform is found in the CNS and is increased under certain conditions? As well as mainly found in red blood cell?
GLUT 1
The pancreatic beta cells and the hepatocytes of the liver produce which GLUT isoform that is also found in those cells as well as kidneys, and lateral border of small intestine?
GLUT 2, which allow an exceptionally high rate of glucose to be transported into those cells from the external environment.
Pancreatic beta cells secrete what hormone?
Insulin
GLUT 4 transporters are found where?
In adipose tissue and skeletal and cardiac muscles.
The insertion of GLUT 4 carriers into the plasma membrane of adipocytes and skeletal muscle fibers is regulated by what?
Exercise and Insulin
In unstimulated muscles where are GLUT 4 proteins located?
They are located within the membrane of cytoplasmic vesicles.
What causes GLUT 4 cytoplasmic vesicles to fuse with the plasma membrane in a process similar to exocytosis? (Only no cellular product is secrete, but rather it fuses)
Exercise and Insulin stimulation.
Fatty acid transportation is analogous to what carrier protein?
GLUT 4 carrier protein. The fatty acid carrier protein functions similarly to GLUT 4 proteins by facilitating diffusion of fatty acids out of adipocytes and into the blood, then from out of the blood and into organs. And the uptake of fatty acids into skeletal muscle fibers is increased by exercise and insulin.
Name two cases where glucose is transported against its concentration gradient, and so is a form a of active transport?
In the epithelial cells of the kidney tubules and in the small intestine. Glucose is transported against its concentration gradient by a different carrier (Not a GLUT carrier) that depends on the simultaneous transport of Na+. This is an example of active transport.
Is there a higher concentration of Ca2+ intracellularly or extracellularly?
Higher Concentration Extracellularly. The intracellular concentration by comparison is 1000-10000 times times lower than the extracellular concentration.
Cyanide inhibits what? and leads to what in cells?
cyanide prevents oxidative phosphorylation. So no processes in the cells that require ATP to utilize active transport could happen (primary and secondary would both stop). Cells would die.
What is primary active transport?
Primary active transport occurs when the hydrolysis of ATP is directly responsible for the function of the carriers.
Name three ATPase enzymes/pumps that rely on primary active transport.
1- Ca2+ pump
2- the Proton (H+) pump
3- the Na+/K+ pump
Describe the two methods fo membrane transport for calcium ions and why the body uses them in such a way.
A concentration of Calcium ions is maintained by the work of ca2+ pumps which works constantly to pump calcium ions out of the cell into extracellular fluid (or cisternae of ER). The second type of membrane transport for calcium ions is passive transport through gated channels. When those channels are allowed to open and the stream of ca2+ that enters the cytoplasm can serve as signals for many different things. This is why both methods are used so the body can use calcium ions as a signal. For example in axon terminals the increase in cytoplasmic ca2+ leads to release of neurotransmitters.
Where are calcium ion pumps located in the body?
In the plasma membrane of ALL cells, as well as in the membrane of the endoplasmic reticulum of striated muscle cells and others.
Go through the steps of the Ca2+ pump with ATP
1- Pump is open to the cytoplasm allowing a cytoplasmic Ca2+ to bind to the amino acid active site, this activates ATPase causing hydrolysis of ATP into ADP + Pi, which remain bound to the pump.
2- Both exits to the pump are now closed
3-ADP is released producing a shape change in the protein allowing the Ca2+ a pathway to the extracellular environment (or Cisternae if in the ER) Ca2+ is released.
4-The Pi group is now released from the pump causing the carrier to return to its original shape where cytoplasmic Ca2+ can once again bind.
Where are Na+/K+ pumps located?
In ALL body cell plasma membranes
Go through the steps of the Na+/K+ Pump
1- Three Na+ ions in the cytoplasm move partway into the pump and bind to three amino acid active binding sites.
2- This activates the hydrolysis of ATP, resulting in ADP and Pi, which temporarily causes both exits of the carrier to close.
3-ADP is released from the carrier allowing the extracellular end to open to open and Na+ can exit.
4-Two K+ ions in the extracellular environment can now bind to two K+ amino acid active binding sites.
5- This causes Pi to be released and the carrier changes shape to allow K+ to be released into the cytoplasm.
The steep Na+ and K+ gradients that are maintained serve three functions, what are they?
1- The steep Na+ gradient is used to provide energy for the coupled transport of other molecules.
2- The gradients for Na+ and K+ concentrations across the plasma membranes of nerve and muscle cells are used to produce electrochemical impulses needed for functions of nerve and muscles, including the heart muscle.
3- The active extrusion of Na+ is important for osmotic reasons, if the pumps stop, the increased Na+ inside the cell will cause water to flow into the cell and damage it.
