Carbohydrates Flashcards
Insulin independent Glucose transport proteins
GLUT 1,2,3
GLUT 1
*in erythrocytes, blood brain barrier
-found throughout body in low concentration
-high affinity for glucose
-does not require high concentration of glucose
GLUT 2
*in small intestine, pancreas, liver
-low affinity for glucose
-require high concentrations of glucose in order for glucose to be transported across cell membrane
GLUT 3
*in neurons
-high affinity for glucose
insulin dependent glucose transport proteins
*in muscle adipose
-insulin binds to receptor on the cell, this results in GLUT 4 expression on cell membrane
-when GLUT 4 is expressed on cell membrane, glucose can be transported into cell
Fed state
when high blood glucose, GLUT 2 transports glucose into the pancreas
-pancreas will then secrete insulin
-insulin will lower blood glucose by GLUT 4 expression
(the stimulation of storage and usage of glucose)
Fasted State
when blood glucose is normal/low, GLUT 2 does not transport glucose into pancreas
-pancreas will secrete glucagon
-maintains blood glucose by stimulating synthesis of glucose & release of stored glucose
Glycolysis step one
glucose into glucose-6-phosphate
*uses hexokinase or glucokinase in the liver
-ATP turned into ADP
Glycolysis step two
glucose-6-phosphate into fructose-6-phosphate
*uses phosphoglucose isomerase
Glycolysis step three
fructose-6-phosphate into fructose 1,6-Biphosphate
*uses phosphofructokinase-1
-ATP turned into ADP
Glycolysis step four
fructose 1,6- Biphosphate into dihydroxyacetonephosphate and glyceraldehyde -3-phosphate
*uses aldolase
Glycolysis step 5
dihydroxyacetonephosphate into glyceraldehyde -3-phosphate
*uses triose phosphate isomerase
Glycolysis step 6
glyceraldehyde-3-phosphate into 1,3-biphosphoglycerate
*uses glyceraldehyde-3-phosphate dehydrogenase
-NAD+ into NADH, H+
-Pi is released
Glycolysis step 7
1,3- biphosphoglycerate into 3-phosphoglycerate
*uses phosphoglycerate kinase
-ADP into ATP
Glycolysis step 8
3-phosphoglycerate into 2-phoshphoglycerate
*uses phosphoglycerate mutase
Glycolysis step 9
2-phosphoglycerate into phosphoenol pyruvate
*uses enolase
-H2O released
Glycolysis step 10
phosphoenol pyruvate into pyruvate
*uses pyruvate kinase
-ADP into ATP
from a single glucose
net ATP of 7
1 NADH, H+
2.5 ATP
Regulation of glycolysis
- glucose transport
- glucokinase
- phosphofructokinase-1
- pyruvate kinase
Glucose transport
if glucose cant get into the cell glycolysis cant happen
GLUT 4
only transports glucose when insulin is present, glycolysis will only happen when insulin is present
GLUT 2
only transports glucose into cells when high blood glucose, glycolysis will only happen when high blood glucose
Glucokinase
has low affinity for glucose
-requires high cellular concentration of glucose to be active
Phosphofructokinase-1
1st committed step of glycolysis
-inhibited by high cellular concentration of ATP
Insulin signals for production of
fructose 2,6 -biphosphate which activates phosphofructokinase-1
What is pyruvate kinase activated by?
fructose 1,6 -biphosphate
What is Pyruvate kinase inhibited by?
glucagon
Glycogen is
-a complex polymer of glucose molecules
-glucose chain attached to glycogenin
-storage form of glucose in liver and muscle
What does liver glycogen do?
stores of glucose to maintain blood glucose
What does muscle glycogen do?
stores of glucose to store energy for muscle contraction
Glycogen structure
1,4 - linkages are found b/w glucoses on straight chains
1,6 - linkages are found at branching points
Glycogenesis step 1
glucose into glucose- 6-phosphate
*uses hexokinase in muscle and glucokinase in liver
-turns ATP into ADP
Glycogenesis step 2
glucose-6-phosphate into glucose-1-phosphate
*uses phosphoglucomutase
Glycogenesis step 3
glucose-1-phosphate into UDP-glucose
*uses UDP-glucose phyrophosphorylase
-turns UTP into PPi
Glycogenesis step 4
UDP-glucose into (Glucose)n+1
*uses glucose synthase
-(glucose)n goes into this and UDP comes out
-only 1,4 linkages are created
How does a branching enzyme work?
once an existing glycogen is at least 11 glucoses long, 7 are removed and added at an 1,6- linkage to an existing chain at least 4 glucoses away from another branch
What is GLUT 2’s role in glucose transport which can regulate glycogenesis?
GLUT 2 has a low affinity for glucose so glucose can only be transported into liver when there are high blood glucose concentrations
-glycogenesis will only happen when GLUT 2 is able to transport glucose into cell
What is GLUT 4’s role in glucose transport which can regulate glycogenesis?
will only transport glucose to muscle when insulin is present
-glycogenesis will only happen when glucose is able to get into the cell
Glycogenesis can only happen at?
high blood glucose levels
Glycogen synthase: synthesizing glycogen
inactive glycogen synthase to active glycogen synthase
*uses protein phosphate-1 which is activated by insulin
Glycogen synthase: breaking down glycogen
active to inactive
*uses protein kinase A which is activated by glucagon
What is glycogenolysis?
breakdown of glycogen
-cytosolic
-liver: glucose
-muscle: glucose-6-phosphate
What is glycogenesis regulated by?
glucose transport and
glycogen synthase
What is glycogenesis regulated by?
glucose transport and
glycogen synthase
What is glycogenolysis regulated by?
glycogen phosphorylase
Step 1 of glycogenolysis
(glucose)n turns into glucose-1-phosphate
*uses glycogen phosphorylase
-Pi goes into this, (glucose)n goes out of it
-breaks down 1,4 linkages
Step 2 of glycogenolysis
glucose-1-phosphate turns into glucose-6-phosphate
*uses phosphoglucomutase
STOPS FOR GLYCOLYSIS IN MUSCLES
Step 3 of glycogenolysis
glucose -6-phosphate tuns into glucose
*uses glucose-6-phosphate
-H2o is put into this and Pi is released
BLOODSTREAM FROM LIVER
How does Debranching occur?
when 4 glucoses remain on branch 3 are removed and added to another chain at an 1,4 linkage
the remaining glucose is released as a free group
Where does the breakdown of glycogen occur?
-cytosolic
-liver: glucose
-muscle: glucose-6-phosphate
Whats the process that causes glycogenolysis?
inactive glycogen phosphorylate becomes an active glycogen phosphorylate (phosphorylated)
-uses protein kinase A (pka)
What activates pka?
glucagon or epinephrine
Whats the process that stops glycogenesis?
active glycogen synthase becomes inactive glycogen synthase (phosphorylated)
-uses pka
Whats the process that stops glycogenolysis?
active glycogen phosphorylase (phosphorylated) becomes glycogen phosphorylase
-uses protein-phosphorylase-1 (pp-1)
What activates PP-1?
insulin
Whats the process that causes glycogenesis?
inactive glycogen synthase (phosphorylated) becomes active glycogen synthase
Whats gluconeogenesis?
synthesis of glucose
-occurs in liver, kidney, cytosolic
-maintenance of blood glucose
What are the precursors for gluconeogenesis?
lactate, glycerol, amino acids
Lactate
produced during anaerobic metabolism
-pyruvate into lactate
-sources: red blood cells, muscle contraction
Amino Acids
come from the breakdown of protein during starvation
Glycerol
comes from the breakdown of fat during fasted states
Where does gluconeogenesis start?
mitochondria then it goes to the cytosol
What step of gluconeogenesis in the mitochondria?
pyruvate turns into oxaloacetate
*uses pyruvate carboxylase
-ATP put into this ADP + Pi comes out
-HCO3 goes into
Where does that pyruvate come from?
precursors
Step 2 of gluconeogenesis
oxaloacetate turns into phosphoenolpyruvate
*uses phosphoenolpyruvate carboxykinase
-GTP goes into GDP goes out
-CO2 released
Step 3 of gluconeogenesis
phosphoenolpyruvate turns into 2-phosphoglycerate
*uses enolase
-H20 goes into
Step 4 of gluconeogenesis
2-phosphoglycerate turns into 3-phosphoglycerate
*uses phosphoglycerate mutase
Step 5 of gluconeogenesis
3-phosphoglycerate turns into 1,3-bisphosphoglycerate
*uses phosphoglycerate kinase
-ATP goes in ADP comes out
Step 6 of gluconeogenesis
1,3-bisphosphoglycerate turns into glyceraldehyde-3-phosphate
*uses glyceraldehyde 3 -phosphate dehydrogenase
-NADH, H+ goes in and NAD+ comes out
-Pi goes out
Step 7 of gluconeogenesis
glyceraldehyde-3-phosphate turns into dihydroxyacetone phosphate
*uses triose phosphate isomerase
Step 8 of gluconeogenesis
glyceraldehyde-3-phosphate + dihydroxyacetone phosphate turns into fructose 1,6-biphosphate
*uses aldolase
Step 9 of gluconeogenesis
fructose 1,6- biphosphate turns into fructose-6-phosphate
*uses fructose 1,6-biphosphatase
-H2O goes into this
-Pi realesed
Step 9 of gluconeogenesis
fructose 1,6- biphosphate turns into fructose-6-phosphate
*uses fructose 1,6-biphosphatase
-H2O goes into this
-Pi released
Step 10 of gluconeogensis
fructose-6-phosphate turns into glucose-6-phosphate
*uses phosphoglucose isomerase
Step 11 of gluconeogenesis
glucose-6-phosphate turns into glucose
*uses glucose-6-phosphate
-H20 goes into this
-Pi goes out
What regulates gluconeogenesis?
-pyruvate carboxylase (step 1)
-phosphoenolpyruvate carboxykinase (step 2 )
-fuctose1,6-biphosphate (step 9)
-glucose-6-phosphate (last step/11)
What is pyruvate carboxylase activated by?
the breakdown of fat
What is phosphoenolpyruvate activated by?
glucagon and glucocorticoids (cortisol)
What is phosphoenolpyruvate deactivated by?
insulin
What is fructose 1,6- biohsphatase activated by?
fructose 2,6-biphosphate
What is glucose-6-phosphate deactivated by?
insulin
What are normal levels of blood glucose?
4.5-5.5 mmol/L
What average blood glucose levels after a meal?
6.5-7.2 mmol/L
What are average blood glucose levels during starvation?
3.3-3.9 mmol/L
Where does blood glucose come from?
-dietary carbohydrates
-liver glycogen
-gluconeogenesis
Whats the lactate cycle?
lactate from the muscle/red blood cells
-leaves to enter the blood
-then the lactate goes to the liver
-then it is made into glucose through gluconeogenesis
-then it goes back to the beginning to repeat
What happens with glycerol during the fasted state?
-glycerol in the adipose fat turns into
-fatty acids and glycerol
-then it goes into the blood
-then the liver
-then it is made into glucose and it goes back into the blood
What happens with Amino acids typically during the starved sate?
-amino acids in the muscle
-go to the blood
-then the liver
-become glucose then enter the blood
How is blood glucose regulated?
-transport
-glucokinase
GLUT 2 role in regulation of blood glucose
only removes glucose from bloodstream when blood glucose is high
-will decrease BG
GLUT 4 role in regulation of blood glucose
only removes glucose from the bloodstream when insulin is present (high BG)
-will decrease BG
How does Glucokinase play a role in the regulation of blood glucose?
will convert glucose to glucose-6-phosphate when there are high cellular concentrations of glucose
-high cellular concentrations of glucose in the cell when GLUT 2 is transporting glucose into the cell
*keeps glucose out of bloodstream to help decrease BG
What cant go into the bloodstream?
glucose-6-phosphate
What is insulin secreted by?
pancreatic b cells
-GLUT 2 transports glucose into these cells when there are high BG concentrations
-pancreatic b cells secrete insulin in order to lower BG
How do pancreatic b cells parallel blood glucose concentrations?
-GLUT 4 expression
-activates glycogenesis & glycolysis (keeps it out of bloodstream bc both are using glucose)
-inhibits glycogenolysis & gluconeogenesis
What is glucagon secreted by?
pancreatic a-cells
-anytime insulin is not present
How does glucagon work to maintain BG levels?
-activates glycogenolysis & gluconeogenesis
-inhibits glycolysis(liver) & glycogenesis
What are the anterior pituitary gland hormones?
-growth hormone
-ACTH
What does growth hormone do?
mobilizes energy sources to provide energy for growth
-breaks down fat
-activates gluconeogenesis
What does ACTH do?
stimulates adrenal cortex to secrete glucocorticoids
What is the adrenal cortex hormone?
glucocorticoids
-stimulate gluconeogenesis
What is the adrenal medulla hormone?
epinephrine
-activates glycogenolysis
