Glycolysis Flashcards
T or F: Glycolysis only occurs in Liver and Skeletal muscle cells
False
Glycolysis occurs in all cell types
What is the name of the process that transfers an inorganic phosphate from a high-energy intermediates to ADP?
Substrate-level Phosphorylation
In what cellular location does glycolysis take place?
Glycolytic enzymes are found in the Cytosol
What is the main function of glycolysis? Other functions?
Main Function: Produce ATP in cells
Other Functions: Produce metabolic intermediates used for other metabolic pathways
T or F: All cells exhibit the same glycolytic activity
False
The activity of glycolysis (Amount of Glucose oxidized per minute) Varies in different tissues
Example: RBC have low activity, while Skeletal Muscles have high activity
The phosphorylation of glucose to glucose 6-phosphate is catalyzed by what enzyme(s)?
Hexokinase or Glucokinase (In liver)
T or F: The conversion of glucose to glucose 6-phosphate is a irreversible reaction
True
Which enzyme has the lowest Km (Highest affinity) for glucose?
Hexokinase has a lower Km or Higher affinity for glucose
T or F: Hexokinase is non-specific, meaning it can phosphorylate other sugars such as fructose
True
Hexokinase can phosphorylate other sugars. However, it has a greater affinity (lower Km) for glucose
The enzyme phosphoglucose Isomerase catalyzes the conversion of glucose 6-phosphate to what product?
Phosphoglucose Isomerase catalyzes the conversion of glucose 6-phosphate to Fructose 6-phosphate
Isomerized from Aldehyde to Keto sugar
What is the first committed step of glycolysis?
The phosphorylation of Fructose 6-phosphate by Phosphofructokinase-1 (PFK-1) to Fructose 1,6-bisphosphate
- Rxn is irreversible
PFK-1 is rate limiting enzyme
Which two reactions of Glycolysis CONSUME ATP?
- Glucose + ATP –> Glucose 6-phosphate +ADP
(Hexokinase or glucokinase) - Fructose 6-P + ATP –> Fructose 1,6-BP
(PFK-1)
The cleavage of Fructose 1,6-BP by Aldoase produces what two triose phosphates?
- Glyceraldehyde 3-phosphate (G3P)
- Dihydroxyacetone Phosphate *
*Dihydroxyacetone Phosphate gets isomerized to G3P by triose phosphate isomerase
The oxidation and phosphorylation of Glyceraldehyde 3-phosphate (G3P) is catalyzed by what enzyme? and what are the products of this reaction?
Catalyzed by Glyceraldehyde 3-P dehydrogenase
Products: 1,3-bisphosphoglycerate, NADH , and H+
How many moles of:
1. NADH
2. ATP
are produced per 1 mole of glucose in the ATP-generation phase of Glycolysis?
For 1 mole of glucose oxidized:
2 NADH and 4 ATP* are produced
*ATP-generation phase produces 4 ATP but net production is 2 mol ATP because 2 moles of ATP were consumed in the ATP-utilization phase
What two reactions of glycolysis produce ATP?
- 1,3-Bisphosphoglycerate —> 3-phosphoglycerate
(via Phosphoglycerate Kinase) - Phosphoenol pyruvate —> Pyruvate
(via Pyruvate Kinase)
What determines the fate of pyruvate and NADH after glycolysis?
The availability of oxygen
How is NAD+ replenished during anaerobic conditions of glycolysis? Where does this occur?
Lactate Dehydrogenase (LDH) converts pyruvate to lactate, which oxidizes NADH back to NAD+
This occurs in the cytosol
NAD+ is needed as an electron acceptor for the conversion of G3P to 1,3-Biisphosphoglycerate
What is the fate of pyruvate in the presence of oxygen?
It is completely oxidized to CO2
this process produces about 12.5 mol ATP/ pyruvate
Under aerobic conditions, where does the oxidation of NADH back to NAD+ occur?
In the Mitochondria
T or F: NADH diffuses through the inner mitochondrial membrane to reach the electron transport chain
False
The inner mitochondrial membrane is impermeable to Cytosolic NADH
The transfer of electrons require the use of Shuttle Systems
What are the names of the two shuttle systems used to transfer reducing equivalents across the inner mitochondrial membrane?
- Glycerol 3-phosphate shuttle
2. Malate-Aspartate Shuttle
In the Glycerol 3-phosphate shuttle system, what enzyme transfers electrons from cytosolic NADH to Dihydroxyacetone-phosphate (DHAP)?
Glycerol 3-phosphate dehydrogenase
This transfer produces Glycerol 3-phosphate, which then diffuses through the outer mitochondrial membrane
After diffusing through the outer mitochondrial membrane, Glycerol 3-phosphate transfers electrons to what e- acceptor?
Glycerol 3-phosphate transfers electrons to (inner) membrane-bound Flavin Adenine Dinucleotide (FAD)
This produces a FAD(2H) which eventually donates electrons to Coenzyme Q (CoQ) resulting in the generation of ATP via oxidative phosphorylation
In the Malate- Apartate Shuttle System, what enzyme transfers electrons from NADH to cytosolic oxaloacetate?
Malate Dehydrogenase
NADH + oxaloacetate —–> Malate
How does Malate cross the inner mitochondrial membrane?
Malate is exchanged for alpha-ketoglutarate by a specific translocase
Once in the mitochondrial matrix, malate is oxidized back to oxaloactetate by mitochondrial Malate dehydrogenase to generate NADH
NADH donates electrons to ETC
Which shuttle system results in the production of more ATP?
The Malate-Aspartate shuttle (about 2.5 mole ATP)
glycerol 3-phosphate shuttle ~ 1.5 mole ATP
Oxaloacetate cannot pass back through the inner mitochondrial membrane. How does it get back to cytosol?
Via Aspartate
In the matrix, Transamination reactions transfer an amino group to ocaloacetate to form aspartate
Aspartate is transported out to cytosol via an aspartate-glutamate exchange translocase
What are the four major enzymes regulated in glycolysis?
- Hexokinase (or glucokinase)
- Phosphofructokinase-1 (PFK-1)
- Pyruvate Kinase
- Pyruvate Dehydrogenase*
*coverts pyruvate to Acetyl CoA (kinda after glycolysis)
What regulates the activity of Hexokinase?
Glucose 6-phosphate inhibits hexokinase
(negative feedback)
G6-P does NOT inhibit glucokinase
What regulates Glucokinase?
Insulin induces GK
What are the activators and inhibitors of Phosphofructokinase-1?
PFK-1 Activators: AMP and Fructose 2,6-bisphosphate
PFK-1 Inhibitors: ATP and Citrate
PFK-1 is an allosteric enzyme with how many binding sites?
6
2 for substrates ( Fructose 6-phosphate, and ATP)
4 for Allosteric regulators
How does AMP and F 2,6-BP work to activate PFK-1?
AMP binds to activator site and increase affinity of PFK-1 for Fructose 6-phosphate
F 2,6-BP binds to PFK-1 and removes the inhibitory affect of ATP
Fructose 2,6-Bisphosphate is not an intermediate of glycolysis. How is it made?
The bifunctional enzyme, Phosphofructokinase-2, converts Fructose 6-phosphate to Fructose 2,6-Bisphosphate
How is Pyruvate Kinase regulated in the Liver?
Activated by: Fructose 1,6-Bisphosphate
Inhibited by: ATP and Alanine
How is Pyruvate Kinase regulated in skeletal muscle?
Trick Question!
- Pyruvate kinase in not involved in regulation of glycolysis in skeletal muscle
- the isoenzyme in skeletal muscle does not have allosteric site
- same for isoenzymes in brain and heart
