10/1 Glucose Transport and Phosphorylation

Question 1

how do glucose/galactose get into the body

Answer 1

intestinal lumen —–[SGLT1]—-> enterocyte —-[GLUT2] —–> blood

Question 2

SGLT1

Answer 2

symporter, Na+ dependant, bring glucose into enterocytes from intestinal lumen

Question 3

GLUT transporter characteristics

Answer 3

12 membrane-spanning portions

all passive facilitated transport

Question 4

GLUT 1 (location, Km, notes)

Answer 4

all tissues
1mM
basal glucose uptake

Question 5

GLUT 3 (location, Km, notes)

Answer 5

all tissues
1mM
basal glucose uptake, esp brain

Question 6

GLUT 2 (location, Km, notes)

Answer 6

liver, pancreatic B cells, enterocytes
15-20mM
pan: regulates insulin
liv: removes excess glucose from blood
ent: exports glucose into the blood

Question 7

GLUT 4 (location, Km, notes)

Answer 7

muscles and fat cells
5mM
insulin dependant, # in PM increases with endurance training

Question 8

GLUT 5 (location, Km, notes)

Answer 8

fructose into enterocyte from intestinal lumen

Question 9

why is glucose phosphorylated

Answer 9

becomes G6P

1) to keep it from going back out of the cell, no transporter of G6P
2) must be phosphorylated to enter downstream metabolic pathways (glycolysis, glucogenesis, penthose phosphate)

Question 10

Hexokinase I-III (location, Km, regulation)

Answer 10

all cells
0.1mM
feedback inhibition by G6P

Question 11

Hexokinase IV (aka Glucokinase)
(location, Km, regulation)

Answer 11

liver cells, pancreatic B cells
10-20mM
induced by insulin

Question 12

Glucose-6-Phosphatase

Answer 12

dephosphorylated G6P, last step of gluconeogenesis and glucogenolysis

in membrane of ER in liver and kidneys ONLY
T1: G6P into ER
T2: Pi into cytosol
T3: Glucose into cytosol