Lecture 6 (Part 1)

Question 1

Can Glucose, galactose, and fructose freely cross the enterocyte membrane

Answer 1

Glucose, galactose, and fructose are monosaccharides that cannot cross the enterocyte membrane freely through simple diffusion

Question 2

what facilitates the transport of these sugars into the enterocytes hydrophobic lipid bilayer

Answer 2

3 different transporters:

1. SGLT1 (Sodium dependent glucose transporter 1)
   2 . GLUT2
2. GLUT5

Question 3

SGLT1 (Sodium-glucose linked transporter 1) function/how it works:

exit strategy of monosaccharides:

Answer 3

primary transporter for glucose and galactose

presence of sodium activates this transporter(SGLT1) which allows glucose and galactose to enter the cytoplasm of the enterocyte

Once inside the enterocyte, glucose and galactose can exit into the bloodstream through facilitated diffusion via glucose transporters (GLUT2) on the basolateral side of the cell.

Question 4

GLUT2 Function:

Location:

affinity for glucose and galactose:

Answer 4

helps to transport glucose and galactose into the enterocyte

in the apical membrane

Has high affinity for glucose and galactose

Question 5

GLUT5 function:

Location:

Exit strategy of monosaccharide:

Answer 5

Transport fructose into enterocyte

apical membrane

fructose exits into the bloodstream through GLUT2 transporters on the basolateral membrane

Question 6

where does glucose, galactose, and fructose exit from the blood

Answer 6

*from the blood, these molecules enter the portal vein to the liver

blood stream –> portal vein –> liver

Question 7

In the bloodstream Glucose is in its final state, however what is the issue with galactose and fructose

Answer 7

galactose and fructose still have to be converted
into glucose

Question 8

*The liver holds some glucose and uses it for its own energy, but some glucose escapes the liver (liver released a controlled amount), which goes to the brain, as well as the pancreas. True or False

Answer 8

true

Question 9

How does glucose enter the pancreas after escaping from the liver

Answer 9

Has GLUT2 transporters to allow glucose molecules to enter the organ

Question 10

what reaction/negative feedbackloop occurs when glucose enters the pancreas

Answer 10

The pancreatic beta cells sense this rise in glucose, and in turn produces insulin

Insulin goes into the portal vein and drains towards the liver (the liver is the first area to see insulin)

The insulin binds to the receptors on the surface of the liver cells and tells the liver to store a large amount of glucose as glycogen which reduces the
amount of glucose circulating

↑ glucose in pancreas → insulin release by pancreas → insulin through portal vein →attaches to liver receptors → tells liver to store glucose as glycogen → reduce glucose circulation

Question 11

How does glucose enter skeletal muscle as a result of insulin?

Answer 11

↑ blood glucose levels rise –>
pancreas releases insulin –>
insulin bind to receptor on skeletal muscle –>
translocation of GLUT4 to cell membrane–>
glucose enter cell

Question 12

role of glucose in skeletal muscle

Answer 12

energy
storage as glycogen

Question 13

the role of insulin in adipocytes (adipose tissue) :

Answer 13

↑ blood glucose levels rise –>
pancreas releases insulin –>
Insulin also goes to adipocytes in the subcutaneous area –>
insulin bind to receptor on adipose tissue –>
translocation of GLUT4 to cell membrane–>
glucose enter cell

Question 14

difference between adipocytes (adipose tissue) and skeletal muscle in terms of glycogen

Answer 14

stores very little glycogen, unlike skeletal muscle.

takes glucose and converts it into Gly-3P

Gly-3P merges with 3FA to form triglycerides

Question 15

How is glucose transported inside the brain

Answer 15

via GLUT1 and GLUT3.

Question 16

where is GLUT1 located

Answer 16

GLUT1 (located in the blood-brain barrier)

Question 17

where is GLUT3 located

Answer 17

GLUT3 (found in neurons)

Question 18

Function of GLUT1

Answer 18

GLUT1 ensures a continuous supply of glucose from the bloodstream to the brain

Question 19

Function of GLUT3

Answer 19

GLUT3 is highly efficient in transporting glucose into neurons

Question 20

is glucose uptake in the brain Insulin-Independent

Answer 20

Unlike peripheral tissues such as skeletal muscle and adipose tissue, the brain does not rely on insulin for glucose uptake

Question 21

Are GLUT1 and GLUT3 always present on the cell membrane

Answer 21

GLUT1 and GLUT3 always present on the cell membrane which allow constant flow of glucose into the cells;

Question 22

GLUT3 and GLUT1 are characterized by

Answer 22

GLUT3 and GLUT1 are characterized by high affinity for glucose, meaning they are saturated with substrate (glucose) even at normal blood glucose levels

Question 23

Do wide variations in blood glucose levels cause little or large change in the rate at which glucose is taken up by the brain

Answer 23

Wide variations in blood glucose levels cause little change in the rate at which glucose is taken up by the brain due to the high affinity of GLUT1 and GLUT3 for glucose

It’s only when blood glucose falls below a critical threshold (around 2 mmol/L) that mental function can be impaired

This emphasizes the brain’s reliance on a steady supply of glucose for optimal function.