Carbohydrate Metabolism Flashcards
What is the starting molecule of glycolysis, and what are the end products?
- 1 molecule of glucose
- 2 molecules of pyruvate and 2 molecules of ATP
What kind of cells are powered solely by glycolysis?
- Red Blood Cells
Why can’t glucose enter the cell on its own?
- Polarity of glucose
What kind of transporters move glucose into the cell?
- GLUT transporters
What are the 4 types of GLUT transporters, and where are they located?
- GLUT1: ubiquitous. High in RBCs and brain.
- GLUT2: Main transporter in liver.
- GLUT3: main transporter in neurons
- GLUT4: present in skeletal muscle, heart, and adipose tissue
Which GLUT receptor is insulin dependent?
GLUT4
Where does Glycolysis occur?
Cytoplasm
What are the three phases of glycolysis?
What is consumed/generated in each step?
- Investment: requires 2 ATP
- Splitting: Generates 2 3-carbon molecules
- Recoup: 4 ATP molecules are generated
What are the enzymes that initiate glycolysis? Where are they found?
- Hexokinase: All Cells
- Glucokinase: Liver Cells
What is the rate limiting step of glycolysis?
Conversion of Fructose 6-P to Fructose 1,6-BP
What is the rate limiting enzyme for glycolysis?
Phosphofructokinase-1
What are the 3 steps of the investment phase of glycolysis?
- Phosphorylation of Glucose to G6P (traps glucose in cell)
- Isomerization of G6P to F6P
- Phosphorylation of F6P to F-1,6-BP (rate limiting)
What are the two steps of the splitting phase of glycolysis? What enzymes are used?
- Cleavage of F-1,6-BP to DHAP and G3P via ALDOSE A
2. Isomerization of these two products via triose phosphate isomerase.
What are the 3 steps of the payoff phase of glycolysis? What enzymes are used, and where are products formed?
- Phosphorylation of G3P to 1,3-BPG
- uses GADPH, makes 2 NADH - Conversion of 1,3-BPG to 3-PG
- Uses phosphoglycerate kinase, makes 2 ATP - Formation of pyruvate
- uses Pyruvate Kinase, makes 2 ATP
What enzyme catalyzes the step where the first ATP is made in glycolysis?
Phosphoglycerate kinase
What are the enzymes used in the three irreversible phosphorylation steps in glycolysis?
- Hexokinase/glucokinase
- Phosphofructokinase-1
- Pyruvate Kinase
What are the two main differences between hexokinase and glucokinase?
- Hexokinase is in all cells, glucokinase is only in the liver
- Hexokinase can use other sugars as its substrate
Hexokinase is inhibited by______
G6P (product)
The rate limiting enzyme in glycolysis is ______
PFK-1
PFK-1 is activated by (1) and is inhibited by (2)
- AMP, Fructose-2,6-BP
2. ATP, Citrate
____ is the hormone that stimulates PFK-1, and ____ is the hormone that inhibits PFK-1.
- Insulin
2. Glucagon
What is tarui disease? What is it a deficiency of?
- Deficiency of PFK-1
- symptoms can be mild, induced muscle cramps and soreness.
Pyruvate Kinase catalyzes the reaction of ____ into ____
Phosphoenol Pyruvate (PEP) into Pyruvate and ATP
Pyruvate Kinase is activated by (1) and inactivated by (2)
- F-1,6-BP & insulin
2. ATP, Alanine, Glucagon
Which Glycolysis intermediate is used as the precursor for the pentose-5-phosphate pathway?
- Glucose-6-phosphate
Which cells are affected the most by defects in glycolysis?
- RBCs
What is the result of pyruvate kinase deficiency
- hemolytic anemia, caused by erythrocyte mutation
In the ____ state glucose is abundant, there is inceased uptake, increased rates of glycolyis, production of glycogen, and decreased gluconeogenesis.
Fed state
In the _____ state there is low glucose, decreased uptake, less storage, increase in gluconeogenesis, and glycogenolysis.
Fasting state.
What is the difference between type 1 and type 2 diabetes?
Type 1 = loss of pancreatic beta cells
Type 2 = insulin resistance leads to loss of Beta cell function
What is fanconi bickel syndrome? What is its pattern of inheritance?
- Mutation in GLUT2 transporter
- Unable to take up glucose, fructose, and galactose
- Treat with vitamin D and phosphate
- Autosomal recessive disorder
How much daily glucose does your brain, and body need to function?
- brain = 120g a day
- body = 160g a day
What is gluconeogenesis?
- synthesis of glucose from carbohydrate and non-carbohydrate precursors.
What gluconeogenesis enzymes are equivalent (comparable) to those used in glycolysis ( Hexo/glucokinase, PFK-1, and Pyruvate Kinase).
- Hexo/glucokinase = Glucose-6-phosphatase
- PFK-1 = fructose-1,6-bisphosphatase
- Pyruvate Kinase = PEP Carboxykinase + pyruvate carboxylase
What are the major 6 rxns of gluconeogenesis and what are their enzymes?
- Pyruvate to OAA via pyruvate carboxylase
- OAA to PEP via PEP carboxykinase
- PEP to Fructose-1,6-bisphosphate
- F1,6BP to F6P via Fructose-1,6-bisphosphatase
- F6P to G6P
- G6P to Glucose via Glucose 6 phosphatase
What is the rate limiting enzyme of gluconeogenesis?
Fructose-1,6-bisphosphatase
What is the first enzyme in Gluconeogenesis?
Pyruvate carboxylase
What does pyruvate carboxylase catalyze?
Conversion of pyruvate to OAA
What is pyruvate carboxylases cofactor?
Biotin (B7)
Oxaloacetate has to leave mitochondria to participate in Gluconeogenesis, how does this occur?
OAA is converted to malate by Mitochondrial Malate Dehydrogenase, moved out of mitochondria via Malate Shuttle, and is converted back to OAA by Cytosolic malate dehydrogenase.
What regulates the conversion of OAA to PEP?
PEPCK (phosphoenolpyruvate carboxykinase)
What breaks down Fructose-1,6-bisphosphate to F6P?
Fructose-1,6-bisphosphatase
—> this is the rate limiting enzyme/ step
Where is glucose 6 phosphatase found? What does it do?
Liver, kidneys, small intestine. It converts G6P to Glucose
What is the Cori cycle?
- Takes lactate produced by anaerobic glycolysis in RBC and exercising muscle to liver to regenerate glucose.
Before entering gluconeogenesis, galactose and glycogen must convert to (1) before entering gluconeogenesis as (2)
- Glucose-1-phosphate
2. Glucose-6-phosphate
What intermediate form does glycerol have to take before entering gluconeogenesis?
Glycerol-3-phosphate to DHAP
What intermediate form do lactate and alanine have to take before entering gluconeogenesis?
Pyruvate
What is Fructose-1,6-bisphosphatase deficiency, what are its symptoms.
- similar to tarui disease
- leads to chronic hypoglycemia and lactic acidosis
What is Von Gierke Disease(called GSD1 also)?
Deficiency in glucose-6-phosphatase. Ineficient release of free glucose into the blood stream by the liver. Dietary management is treatment.
Conversion of Glucose into Fructose -
Glucose is reduced to (1) by (2)
- Sorbitol
2. Aldose reductase
Conversion of glucose to fructose -
Sorbitol is oxidized to (1) by (2)
- Fructose
2. Sorbitol dehydrogenase
Describe Sorbitol accumulation
Cells that lack sorbitol dehydrogenase can accumulate sorbitol. This can manifest as cataracts or retinopathy.
Describe Fructose Metabolism
- Fructose can enter glycolysis as Fructose 6-P VIA hexokinase
- Fructose can enter glycolysis as glyceraldehyde-3-P after conversion to glyceraldehyde via aldose B and conversion of glyceraldehyde to glyceraldehyde-3-P VIA triose kinase.
Fructose metabolism is (1) than glycolysis because it bypasses the (2) and there is no (3).
- Faster
- Rate limiting steps
- PFK-1 or 2 regulation
Galactose can enter glycolysis as glucose-6-P. What are the steps and enzymes used.
- Galactose to Galactose-1-P via galactokinase.
- Galactose-1-P to UDP-galactose
- UDP-galactose to UDP-glucose
- UDP glucose to Glucose-1-P via GALT
- Glucose-1-P to glucose-6-P
What is the rate limiting enzyme in Galactose metabolism?
GALT
What is Galactosemia, and deficiency in what enzyme causes it?
- Disrupted galactose metabolism
- leads to cataracts, lethargy, and retardation
- deficiency in galactose-1-phosphate uridyl transferase (GALT)
What causes an accumulation of galactose and galactitol in blood and urine?
- deficiency in galactokinase
What is the Pentose Phosphate Pathway?
- another oxidative pathway for glucose metabolism
- produces no energy
- produces the sugar for DNA and RNA formation
- Produces NADPH
Where does the Pentose Phosphate Pathway Take Place?
Cytosol
What is the rate limiting step of the pentose phosphate pathway?
G6PD
Glucose-6-phosphate dehydrogenase
What are the major steps of the PPP?
- Conversion of G6P to 6-p-lactone via G6PD.
2. Reduction of NADP+ to NADPH
Study PPP from notes
It is too complicated to make note cards on lol