Membrane Transport

Question 1

absorption/reabsorption

Answer 1

___ of molecules from the external milieu is generally mediated by active transport process

Question 2

redistribution

Answer 2

___ of molecules within the organism is generally mediated by facilitated transport process

Question 3

transport of glucose

Answer 3

can be active (SGLT1 and SGLT2) or passive transport (GLUT)

Question 4

SGLT1

Answer 4

active glucose transporter that has higher affinity for glucose, couples sodium for entry to cells, mostly found in the intestine external milieu

Question 5

SGLT2

Answer 5

active glucose transporter with lower affinity, couples sodium for entry to cells, unable to transport galactose, mostly found in kidneys external milieu

Question 6

GLUT1

Answer 6

facilitative glucose transporter that is ubiquitously expressed throughout the body, important for glucose crossing the BBB, has high affinity for glucose at normal physiological levels (not after feeding)

Question 7

GLUT2

Answer 7

facilitative glucose transporter found in the liver, beta islet cells, kidney and small intestine; only active when blood glucose levels are high after a feeding, plays a role in insulin secretion (increased glu in cell is oxidized, ADP->ATP, increased membrane potential from -70 to -20, Ca2+ channels open, influx Ca2+, Ca2+ helps vesicles of insulin to be secreted)

Question 8

GLUT3

Answer 8

facilitative glucose transporter found in brain and nerve cells, thought to function in neuronal transport of glucose

Question 9

GLUT4

Answer 9

facilitative glucose transporter found in muscle, heart, and adipose cells. Has high affinity for glucose at normal physiological levels (not after feeding); normally stored in vesicles in the cell until stimulated by insulin

Question 10

GLUT5

Answer 10

facilitative glucose transporter that does not actually transport glucose - transports fructose instead. Found in intestine, kidney, testis, sperm.

Question 11

FDG-PET

Answer 11

GLUT1 is often overexpressed in cancer cells, leading to much higher uptake of glucose in cancer tissues. Through administration of 2-deoxy-D-glucose, a form of glucose that cannot be metabolized/oxidized and thus gets trapped in cells, to a patient with suspected cancer, we can see the tumors as light spots on this type of imaging

Question 12

insulin secretion

Answer 12

requires GLUT2, stimulates increased expression of GLUT4 in muscle cells and adipose tissue.

Question 13

exercise, insulin

Answer 13

2 factors that stimulate increased expression of GLUT4 in muscle cells and adipose tissue, leading to increased glucose uptake in those tissues

Question 14

amino acid transporter

Answer 14

transporter that allows for absorption and reabsorption of amino acids in the mucosal cells and kidney cells. Mainly uses sodium-coupled active transporters for external milieu, and facilitated diffusion for internal milieu

Question 15

Hartnup disease

Answer 15

autosomal recessive disease due to defect in sodium-dependent neutral amino-acid transporter. Leads to decreased reabsorption of neutral amino acids primarily in the kidneys. Usually benign in industrialized nations but causes Pellagra-like symptoms and cerebellar ataxia in less developed countries due to diet. Treat with niacin and Trp

Question 16

cystinuria

Answer 16

autosomal recessive disease due to defect in cationic amino acid transporter, causes increased risk for kidney stones

Question 17

cystinosis

Answer 17

defective transport of cystine out of lysosomes, cystine crystallizes within lysosomes