Interactions Between Cells and the Extracellular Environment Part 2

Question 1

What are three characteristics Carrier Proteins share with enzymes?

Answer 1

1- Specificity
2- Competition
3- Saturation

Question 2

The transport of glucose from the blood across plasma membrane occurs by what mechanism?

Answer 2

Facilitated Diffusion

Question 3

What antibiotic often has a competitor mixed in with it? And why?

Answer 3

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.

Question 4

Name the isoforms of the glucose carriers.

Answer 4

GLUT 1, 2, 3, and 4. They each do the same thing, facilitated diffusion of glucose, but in different areas of the body.

Question 5

What is the name of the major glucose transporter in neurons?

Answer 5

GLUT 3

Question 6

Which GLUT isoform is found in the CNS and is increased under certain conditions? As well as mainly found in red blood cell?

Answer 6

GLUT 1

Question 7

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?

Answer 7

GLUT 2, which allow an exceptionally high rate of glucose to be transported into those cells from the external environment.

Question 8

Pancreatic beta cells secrete what hormone?

Answer 8

Insulin

Question 9

GLUT 4 transporters are found where?

Answer 9

In adipose tissue and skeletal and cardiac muscles.

Question 10

The insertion of GLUT 4 carriers into the plasma membrane of adipocytes and skeletal muscle fibers is regulated by what?

Answer 10

Exercise and Insulin

Question 11

In unstimulated muscles where are GLUT 4 proteins located?

Answer 11

They are located within the membrane of cytoplasmic vesicles.

Question 12

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)

Answer 12

Exercise and Insulin stimulation.

Question 13

Fatty acid transportation is analogous to what carrier protein?

Answer 13

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.

Question 14

Name two cases where glucose is transported against its concentration gradient, and so is a form a of active transport?

Answer 14

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.

Question 15

Is there a higher concentration of Ca2+ intracellularly or extracellularly?

Answer 15

Higher Concentration Extracellularly. The intracellular concentration by comparison is 1000-10000 times times lower than the extracellular concentration.

Question 16

Cyanide inhibits what? and leads to what in cells?

Answer 16

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.

Question 17

What is primary active transport?

Answer 17

Primary active transport occurs when the hydrolysis of ATP is directly responsible for the function of the carriers.

Question 18

Name three ATPase enzymes/pumps that rely on primary active transport.

Answer 18

1- Ca2+ pump
2- the Proton (H+) pump
3- the Na+/K+ pump

Question 19

Describe the two methods fo membrane transport for calcium ions and why the body uses them in such a way.

Answer 19

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.

Question 20

Where are calcium ion pumps located in the body?

Answer 20

In the plasma membrane of ALL cells, as well as in the membrane of the endoplasmic reticulum of striated muscle cells and others.

Question 21

Go through the steps of the Ca2+ pump with ATP

Answer 21

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.

Question 22

Where are Na+/K+ pumps located?

Answer 22

In ALL body cell plasma membranes

Question 23

Go through the steps of the Na+/K+ Pump

Answer 23

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.

Question 24

The steep Na+ and K+ gradients that are maintained serve three functions, what are they?

Answer 24

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.

Question 25

Secondary Active Transport or Coupled Transport, what is it?

Answer 25

The energy needed for the uphill movement of a molecule or ion is obtained from the downhill transport of Na+ into the cell. So ATP hydrolysis is used indirectly.

Question 26

What is Symport?

Answer 26

Symport, also called Cotransport, is a type of secondary active transport where the molecule being moved uphill is moved into the cell with Na+. So both moving intracellularly.

Question 27

What is Counter-transport?

Answer 27

Counter-transport, also called Antiport, is when the molecule being moved with Na+ goes in the opposite direction. So Na+ moves in while the other molecules move out extracellularly.

Question 28

Cotransport of Na+ and glucose happens where in the body?

Answer 28

Cotransport of Na+ and glucose happens from the extracellular fluid in the lumen of the intestine and kidney tubules across the epithelial cell membrane. The downhill transport of Na+ into the cell allows the uphill transport of glucose into the cell as well. Some cotransports require a 1:1 ratio while others, like in the small intestine, require a 2:1 Na+ glucose ratio.

Question 29

Give an example of a counter-transport involving Na+and Ca2+.

Answer 29

Na+/Ca2+ Exchanger (NCX) Uphill extrusion of Ca2+ from a cell by a type of pump is coupled to the passive diffusion of Na+ into the cell, that is the normal FORWARD action. However, based on relative concentration gradients this could go the other way so this reaction is REVERSIBLE. (in this case Ca2+ is not moved out with ATP directly).

Question 30

Whats the name of a counter-transport system that is reversible? What drug causes the reversible function of the Na+/Ca2+ exchanger?

Answer 30

Sodium-Calcium Exchanger

Digitalis

Question 31

What drugs induces stronger contractions of the heart by inactivating Na+/K+ pumps?

Answer 31

Digitalis, a derivative from the foxglove plant.

Question 32

How does Digitalis produce stronger contractions of the heart?

Answer 32

It inactivates Na+/K+ pumps, which leads to the accumulation of Na+ inside the cell, this increases the action of the Na+/Ca2+ exchanger pumps in the plasma membrane and works in reverse direction to pump Na+ out by bringing in Ca2+. The increase in intracellular Ca2+ causes stronger contraction of the heart cells.

Question 33

What specifically causes the stronger contractions from the drug digitalis?

Answer 33

The build up of intracellular Calcium ions. (Ca2+)

Question 34

What process allows the release of hormones, neurotransmitter, some polypeptides and proteins that are too large to go through carriers?

Answer 34

Exocytosis

Question 35

How do the liver and walls of blood vessels remove cholesterol from the blood?

Answer 35

Endocytosis via receptor-mediated endocytosis. This can happen with many other molecules as a way of signaling.

Question 36

Two types of bulk transport into and out of the cell?

Answer 36

Exocytosis and Endocytosis