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Glucose Transporters

Neelam Maurya

GLUCOSE TRANSPORTERS

Q. 1 The transport protein responsible for entry of glucose into the intestinal enterocyte is called:
 A Glut-2                         
 B Glut-5
 C SGLT1
 D SGLT2
Q. 1 The transport protein responsible for entry of glucose into the intestinal enterocyte is called:
 A Glut-2                         
 B Glut-5
 C SGLT1
 D SGLT2
Ans. C
Explanation:

The transport protein responsible for the sodium-dependent glucose transport in the small intestine is termed the SGLT1. The absorption of glucose occurs through the coordinated action of transport proteins located in the brush border and basolateral membranes of the enterocyte. Glucose uptake into the enterocyte occurs primarily via the sodium-dependent SGLT1 secondary active trans port mechanism. Exit from the enterocyte occurs by facilitated diffusion and is mediated by the membrane transporter, Glut-2. Glut-5 is the membrane transporter located on the apical portion of the enterocyte responsible for the facilitated entry of fructose into the cell.

Q. 2

Insulin stimulated glucose uptake is by 

 A

S G LT-1
 B GLUT-1 
 C

GLUT-2
 D

GLUT 4
Q. 2

Insulin stimulated glucose uptake is by 

 A

S G LT-1
 B GLUT-1 
 C

GLUT-2
 D

GLUT 4
Ans.
D
Explanation:

 GLUT 4 REF: Harper’s biochemistry 27th e p. 170-173, Lippincot 3rd e p. 95,310

Transporter

Function

Site

GLUT1

Basal glucose uptake

RBC, kidney , placenta , BBB

GLUT2

Beta cell glucose sensor,

transporter out of renal and

intestinal epithelial cells

Beta cell , small intestine , kidney

GLUT3

Basal glucose uptake

Brain , placenta , kidney

GLUT4

Insulin stimulated glucose

uptake

Skeletol and cardiac muscle and adipose

tissue

GLUTS

Fructose transporter

Jejunum , sperm

GLUT6

None

pseudogene

GLUT?

Glucose -6PO4 transporter in

ER

Liver

SGLT1

Active uptake of glucose against

conc. gradient

Small intestine , renal tubule

SGLT2

Renal tubule
Q. 3

Which among the following glucose transporter present in myocyte which is stimulated by insulin?

 A

GLUT 1
 B

GLUT 2
 C

GLUT 3
 D

GLUT 4
Q. 3

Which among the following glucose transporter present in myocyte which is stimulated by insulin?

 A

GLUT 1
 B

GLUT 2
 C

GLUT 3
 D

GLUT 4
Ans.
D
Explanation:

Glucose transporter 4 (GLUT 4) is found in two major insulin target tissues: skeletal muscle and adipose tissue. It is sequestered mainly within an intracellular compartment of these cells and thus does not function as a glucose transporter until insulin signaling causes translocation of GLUT 4 to the cell membrane, where it facilitates glucose entry into these tissues after a meal. In muscle, exercise also drives GLUT 4 translocation to the cell surface by activating AMPK.

GLUT 1 is present in all human tissues. GLUT 2 is a major transporter of glucose in hepatic, intestinal, and renal tubular cells. GLUT 3 is found in all tissues, and it is the major glucose transporter on neurons.
 
Ref: German M.S. (2011). Chapter 17. Pancreatic Hormones and Diabetes Mellitus. In D.G. Gardner, D. Shoback (Eds), Greenspan’s Basic & Clinical Endocrinology, 9e.
Q. 4

Facilitative glucose transporters (GLUTs) comprise a large family. Which of the following is a glucose transporter in myocytes?

 A

GLUT 1
 B

GLUT 2
 C

GLUT 3
 D

GLUT 4
Q. 4

Facilitative glucose transporters (GLUTs) comprise a large family. Which of the following is a glucose transporter in myocytes?

 A

GLUT 1
 B

GLUT 2
 C

GLUT 3
 D

GLUT 4
Ans.
D
Explanation:

Major Glucose Transporters and its locations:

 GLUT 1 Brain, kidney, colon, placenta, erythrocytes
 GLUT 2 Liver, pancreatic beta cell, small intestine, kidney
 GLUT 3 Brain, kidney, placenta
 GLUT 4 Heart and skeletal muscle, adipose tissue
 GLUT 5
Small intestine
 
Ref: Harper’s Illustrated Biochemistry, 29e > Chapter 20. Gluconeogenesis & the Control of Blood Glucose > Blood Glucose Is Derived from the Diet, Gluconeogenesis, & Glycogenolysis > Metabolic & Hormonal Mechanisms Regulate the Concentration of Blood Glucose > Table 20–2.
Q. 5

After overnight fasting, levels of Glucose transporters are reduced in

 A

Brain cells
 B

Hepatocytes
 C

Adipocytes
 D

RBCs
Q. 5

After overnight fasting, levels of Glucose transporters are reduced in

 A

Brain cells
 B

Hepatocytes
 C

Adipocytes
 D

RBCs
Ans.
C
Explanation:

C i.e. Adipocytes

Insulin sensitive (dependent) glucose transporter, GLUT- 4 that are found in adipose tissueQ and skeletal muscles are reduced in fasting state, when the insulin levels are low.

Q. 6

Insulin acts on glucose metabolism by:

 A

T permeability of glucose across cell membrane
 B

permeability across cell membrane against glucose gradient
 C

T permeability of renal cells
 D

T glucose transport to brain
Q. 6

Insulin acts on glucose metabolism by:

 A

T permeability of glucose across cell membrane
 B

permeability across cell membrane against glucose gradient
 C

T permeability of renal cells
 D

T glucose transport to brain
Ans.
B
Explanation:

B i.e. T permeability across cell membrane against glucose gradient

Insulin increases glucose uptake by increasing the number of glucose transporter in cell membrane. Direct insulin stimulated glucose uptake is mediated by Glut 4 and is seen only in:

  1. Muscle: Skeletal muscleQ and cardiac muscleQ
  2. Adipose tissueQ

Glucose Transporters In Mammals

Facilitated

Bidirection

Diffusion

Function

Major Sites of

Expression

Km

GLUT 1

Basal glucose uptake

–  Placenta, blood –

brain barrier, Red

cells, kidneys

1-2

GLUT 2

B cell glucose sensor;

transport out of

intestinal & renal

epithelial cells.

–  B cells of islets,

Liver, Small

intestine, Kidney

12-20

GLUT 3

Basal glucose uptake

–  Brain, placenta,

kidney

<1

GLUT 4

Insulin stimulated

glucose uptakeQ

– Skeletal & cardiac

muscleQ

– Adipose tissueQ

5

GLUT 5

Fructose transport

– Jejunum, Sperm

1-2

GLUT 6

None

– Pseudogene

‑

GLUT 7

Glucose 6-PO4

transporter in

endoplasmic

reticulum

–   Liver

‑

Secondary Active Transport Na+ glucose cotransport

(unidirectional -transporter)

SGLT-1

Active uptake of

glucose against

Small intestine, renal

tubule

0.1 – 1.0

SGLT-2

concentration

gradient

Renal tubule

1.6
Q. 7

Na dependent glucose transport is /are inhibited by:

 A

Oubain
 B

Na azide
 C

Phlorhizine
 D

Phloretin
Q. 7

Na dependent glucose transport is /are inhibited by:

 A

Oubain
 B

Na azide
 C

Phlorhizine
 D

Phloretin
Ans.
C
Explanation:

C i.e. Phlorhizine

Q. 8

Insulin dependent glucose uptake is not seen in ‑

 A

Skeletal muscles
 B

Heart
 C

Adipose tissue
 D

Kidney
Q. 8

Insulin dependent glucose uptake is not seen in ‑

 A

Skeletal muscles
 B

Heart
 C

Adipose tissue
 D

Kidney
Ans.
D
Explanation:

 

Insulin dependent glucose uptake is through GLUT-4 and is seen in :‑

1) Skeletal muscles

2) Cardiac muscles (heart)

3) Adipose tissue

Q. 9

Glucose diffusion in RBC by ‑

 A

GLUT I
 B

GLUT 2
 C

GLUT 3
 D

GLUT 4
Q. 9

Glucose diffusion in RBC by ‑

 A

GLUT I
 B

GLUT 2
 C

GLUT 3
 D

GLUT 4
Ans.
A
Explanation:

Ans. is ‘a’ i.e., GLUT 1

Q. 10

Glucose is transported in pancreas through whichreceptor ‑

 A

GLUT 1
 B

GLUT 2
 C

GLUT 3
 D

GLUT 4
Q. 10

Glucose is transported in pancreas through whichreceptor ‑

 A

GLUT 1
 B

GLUT 2
 C

GLUT 3
 D

GLUT 4
Ans.
B
Explanation:

Ans. is ‘b’ i.e., GLUT 2 

  • Glucose enters the B cells of pancreatic islets via GLUT2 transporter and this stimulate the release of insulin.
Q. 11

GLUT 2 receptors ‑

 A

Insulin dependent
 B

Insulin independent
 C

Found in cardiac muscle
 D

Found in brain
Q. 11

GLUT 2 receptors ‑

 A

Insulin dependent
 B

Insulin independent
 C

Found in cardiac muscle
 D

Found in brain
Ans.
B
Explanation:

Ans. is ‘b’ i.e., Insulin independent 

  • GLUT – 2 is insulin independent (insulin dependent GLUT is GLUT-4).
  • It is found in B-cells of islets of pancreas, liver, epithelial cells of small intestine and kidney.
  • Also see explanation-4 of session-2.


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