Carbohydrate Metabolism Pt. 2 Flashcards
How many grams of glucose does our body need in one day?
160 grams
How many grams of glucose does our brain need in one day?
120
How much glucose is present in our body fluids?
20
How much glucose is readily present in our glycogen?
190
Can our glycogen reserves provide glucose for long periods of time?
No. Our glycogen reserves only can give us about 190 g of glucose. Our body as a whole needs about 160g. Thus, we glycogen only gives us enough for about a day.
When is gluconeogenesis useful?
During longer periods of fasting, gluconeogenesis is v important.
What is gluconeogenesis
gluconeogenesis is the creation of glucose from carbs and non-carb precursors
When does gluconeogenesis occur?
Gluconeogenesis will occur when our glucose and glycogen stores have been depleted. That is, when we are starving, on a low carb diet (ketogenic diet) or during exercise.
Where does gluconeogenesis occur?
- liver* (main site)
- small intestine
- kidney
Overall summary of gluconeogenesis?
Converts pyruvate–> glucose
What are the major precursors of gluconeogenesis?
- lactate
- AA
- glycerol
Gluconeogenesis must bypass the irreversible steps of glycolysis. What enzymes do this?
- Pyruvate carboxylase
- PEP carboxykinase
- F16Bisphophotase
- Glucose-6-phosphotase
When is gluconeogenesis favored?
Glucose and glycogen are low
Tissue location of gluconeogenesis
- liver- mostly
- SI
- kidney
Where does gluconeogenesis occur?
Gluconeogenesis occurs in two areas:
- Mitochondria
- Cytosol
Positive regulators of gluconeogenesis
- glucagon
- citrate
- acetyl co-A
- thyroxine
- cortisol
Negative regulators of gluconeogenesis
- ADP-
- AMP
- Fructose-2,6-BP
What is the net yield of gluconeogenesis? 0
Uses: 4 ATP and 2 GTP
Makes: 6 ATP equilvalents
so 0 net yield
What is the net yield of gluconeogenesis? 0
Uses: 4 ATP and 2 GTP
Makes: 6 ATP equilvalents
so 0 net yield
Pyruvate carboxylase in the gluconeogenesis
In gluconeogenesis, pyruvate carboxylase is the ONLY gluconeogenesis enzyme found in the MT. Here, it will convert [pyruvate–>OAA] though carboxylation.
Pyruvate carboxylase has a BIOTIN COFACTOR and is activated by [acetyl-coA] and [cortisol]
What type of co-factor does pyruvate carboxylase have?
Biotin cofactor
What activates the biotin co-factor on pyruvate carboxylase?
- acetyl co-A
2. cortisol
How can we prevent gluconeogenesis from occuring all of the time?
As we have mentioned, pyruvate carboxylase converts [pyruvate–> OAA] in the MT. OAA cannot pass the MT membrane to go outside into the cytosol.
SOOO. OAA must be converted into [malate] by [malate dehydrogenase]. Malate can readily cross the MT membrane into the cytosol. It is then [REOXIDIZED] into OAA.
Pyruvate carboxylase is an enzyme located in the ______, that converts ______ to ______
MT
Pyruvate
OAA
Can OAA readily pass the MT membrane–> cytosol?
No. It must be converted to malate via malate DH in the MT and re-converted to OAA once outside.
This ensures that specificity of gluconeogenesis.
PEP Carboxykinase in gluconeogenesis
[OAA]–> [PEP] through phosphorylation & decarboxylation. A GTP is used.
Activators of PEP carboxykinase
Glucagon,
Cortisol
Thyroxine
What two processes are occur when PEP carboxykinase [OAA–> PEP]?
- Phosphorylation
2. De-carboxylation
Fructose-1,6-Bisphosphotase in gluconeogenesis
Fructose-1,6-bisphosphotase converts [F16P–>F6P].
IT IS THE RATE LIMITING STEP
F16BPase activators
Cortisol
Citrate
F16BPase inhibitors
AMP
F26BP
[those two are both activators for glycolysis]
What is the rate limiting step in gluconeogenesis?
F16BPase.
Glucose-6-Phosphotase in Gluconeogenesis
[G6P–> glucose] via [G6Pase] via a dephosphorylation.
What activates G6Pase?
CORTISOL
What substance is a activator for all regulatory enzymes in gluconeogenesis?
CORTISOL. It is a activator of the biotin cofactor on Pyruvate kinase.
Where is G6Pase found?
SI, liver, kidneys and pancreas
G6P–> glucose via _____________, which is located in ______________
G6Pase
lumen of the ER
G6Pase has what kind of transporter?
GLUT7 transporter
Transportation of G6P and Glucose
- G6P is transported into the lumen of the ER using a G6P transporter.
- Here, G6Pase will convert G6P to glucose
- Glucose is then moved to the cytoplasm using GLUT7 transporter
What is the relevance of the Cori Cycle?
As we have previously said, anaerobic glycolysis occurs in 1. exercising muscle and 2. RBC. It converts pyruvate–> [lactate]. However, we do not want a buildup of lactate in these cells. So, the Cori Cycle prevents this by moving lactate out of these cells, into the blood, into the liver where the lactate can undergo gluconeogenesis. Glucose is made and then sent back to [exercising muscle] and [RBC].
What are the two disorders that can occur in gluconeogenesis?
- F-1,6-BP deficiency
2. Von Gierke Dz
What are the order of things broken down for gluconeogenesis?
- Glycogen
- Fat
- Proteins
What happens where there is a F-1,6-BP deficiency in gluconeogenesis?
A F-1,6-BP deficiency in gluconeogenesis is similar to Tarui disease in glycolysis.
We are unable to make glucose from our sources.
Von Gierke Disease
Von Gierke disease occurs when there is a problem with glucose-6-phosphotase (G6Pase).
In this disease, glucose is essentially stuck inside of the cell and cannot be transported into the blood from the liver in [gluconeogenesis and glycogenolysis].
What cycles can Von Gierke Dz appear in?
- Gluconeogenesis
2. Glycogenolysis
_________ can be cleaved by sucrase to make
__________ & _________.
Sucrose can be cleaved by sucrase to make
fructose & glucose
_________ can be cleaved by lactase to make
_________ & _______
Lactose can be cleaved by lactase to make
galactose & glucose
How does the cell take up fructose?
GLUT5 transporters
How does the cell take up [galactose] and [glucose], made from sucrose and lactose?
SGLT-1 Transporters
GLUT5 Transporters do what?
Move fructose into the cell
SGLT-1 Transporters do what?
Move galactose and glucose into the cell.
GLUT2 Transporters do what?
GLUT2 transporters move cells from [fructose, galactose and glucose] from the [CELL–> BLOOD].
So these work once these items are already inside the cell.
Fanconi-Bickel Syndrome
Fanconi Bickel Syndrome occurs when the GLUT2 receptors are fucked up. Fructose, glucose and galactose inside of the cell cannot be taken out into the bloodstream.
What are the genetics of Fanconi Bickel Syndrome?
Autosomal recessive
What transporter is affected in Fanconi Bickel Syndrome?
GLUT2- which moves fructose, galactose and glucose out of the cell into the bloodstream.
Polyol Pathway (basic)
Polyol pathway is the conversion of [glucose] into [fructose]
Why would we want to convert glucose to fructose in the polyol pathway?
We want to do this because fructose metabolism is FASTER. We can bypass the rate limiting step.
Describe the polyol pathway
[Glucose–> sorbitol] via aldose reductase
[Sorbital–> fructose] via sorbital DH