i want 30 multiple choice questions with their model answer below each question that covers different aspects of all of the following information: Regulation of glycolysis
 Three regulatory irriversible enzymes: 1. Hexokinase & glucokinase 2. Phosphofructokinase 3. Pyruvate kinase ➢ The reaction catalyzed by these enzymes are irreversible {i.e., step 1,3,10}. ➢ Regulatory Mechanisms: ➢ Rapid, short-term: Allosteric, Covalent modifications ➢ Slow, long-term: Induction/repression (Hormonal)Regulation of glycolysis
1. Hexokinase (Allosteric)
 Hexokinase is inhibited by glucose 6- phosphate. (Allosteric)
 This enzyme prevents the accumulation of glucose 6-phosphate due to product inhibition.
 Glucokinase, which specifically phosphorylates glucose, is an inducible enzyme.
 The substrate glucose, probably through the involvement of insulin, induces glucokinase.

HEXOKINASERegulation of Glycolysis
2. phosphofructokinase-1 (Allosteric)
 PFK 1 is Allosteric enzyme.
 Negative allosteric effectors are Citrate, ATP.
 Positive allosteric effectors are ADP,
fructose2,6-bisphosphate, AMP.
 Phosphofructo kinase 1 (PFK 1) is the most important
regulatory enzyme in glycolysis.3. Pyruvate kinase
Allosteric & covalent
 PK Inhibited by ATP. (Allosteric).
 Other positive effectors are AMP and ADP while ATP is a negative effector
 Pyruvate kinase is active (a) in dephosphorylated state & inactive (b) in phosphorylated state
(covalent modification).
 Inactivation of hepatic isoenzyme pyruvate kinase is brought about by cAMP-dependent
protein kinase. So PEP won’t continue glycolysis & be available for gluconeogenesis. The
hormone glucagon inhibits hepatic glycolysis & stimulate gluconeogenesis by this mechanism.
 PK deficiency is the second most common cause of hemolytic anemia.Pyruvate kinase deficiency
 Deficiency of one or more glycolytic enzymes cause lysis of RBCs and hemolytic anemia
 Glycolysis is the only source of energy in RBCs. RBCs need ATP to fuel the ion pumps necessary
for the maintenance of flexible, biconcave shape that allows them to squeeze through narrow
capillaries. Deficiency of glycolytic enzymes results in reduced glycolysis and decreased ATP
production, leading to alternations in the RBCs membrane and phagocytosis of RBCS by cells
of reticuloendothelial system (particularly the spleen). The premature death of RBS leads to
hemolytic anemia.
 The majority of patients has pyruvate kinase (PK) deficiency. The effects range from mild to
severe.
 Hepatic PK is encoded by the same gene as the RBC isozyme. The tissue specific expression of
PK in RBCs and liver is due to different promotor utilization in transcription.ALLOSTERIC EFFECTORS
Net reaction: Glucose +2NAD+ + 2ADP + 2 Pi
2Pyruvate + 2NADH + 2ATP +2H2OHORMONAL REGULATION
1- Short term regulation:
 Hormone can shortly control rate of glycolysis (in time of minutes and hours) by covalent modification.
 In well feed state, where insulin/glucagon ratio is high, this favor dephosphorylation and activation of
pyruvate kinse and increased rate of glycolysis.
 In fasting state: typically the reverse.
 Another important control is the inhibition of pyruvate kinase by phosphorylation during starvation
(increase Glucagon).
2- Long term regulation:
 Hormones can also control rate of glycolysis over long period of time (hours or days), by inducing
(increase amount) of enzymes of glycolysis.
 In well feed state, key regulatory enzymes of glycolysis (glucokinase, PFK-1 and PK) will be induced
under influence of high insulin level and this will increase rate of glycolysis.HORMONAL LONG TERM
REGULATION
 Insulin: Induction, Glucagon: Repression. (regulation of gene expression & enzyme
production)
 Hormonal regulation, is slow and more profound.
 Regulation by Insulin, Glucokinase activity is increased.
 Increase blood glucose→ insulin release → increase transcription of glucokinase
 Increase levels of insulin, activate PFK1, increase levels of Glucagon inhibit it.
 cAMP dependent protein kinase leads to phosphorylation of pyruvate kinase, which becomes
inactive.
 Elevated levels of glucagon are responsible for the phosphorylation of pyruvate kinase.Biological importance of
GLYCOLYSIS
1) Energy production.
2) Formation of 2,3 BPG.
3) Glycolysis in RBCS (Rapaport-Leubering Cycle).
4) Synthetic function.
glycolysis can be used for synthesis of other compounds, such as :
❑ DHAP → Glycerol 3 P (for TAG synthesis in adipose tissue)
❑ Non-essential amino acid as serine and alanine from pyruvate.1. Energy production from
glycolysis2. Significance of 2,3-BPG
 The 2,3-BPG combines with hemoglobin & reduces the affinity towards oxygen.
1. In presence of 2,3-BPG, oxyhemoglobin will unload oxygen more easily in tissues.
2. Under hypoxic conditions the 2,3-BPG concentration in the RBC increases, thus favoring the
release of oxygen to the tissues even when PO2 is low.
3. The compensatory increase in 2,3-BPG in high altitudes favors oxygen dissociation.
4. BPG is increased in fetal circulation.3. Rapaport-Leubering Cycle
 It is a supplementary pathway to glycolysis. (Importance of glycolysis to RBCs).
 Rapaport-Leubering cycle is mainly concerned with the synthesis of 2,3- bisphosphoglycerate
(2,3-BPG) in the RBC.
 1,3 Bisphosphoglycerate (1,3-BPG) produced in glycolysis is converted to 2,3-BPG by the
enzyme 2,3-bisphosphoglycerate mutase
 2,3-BPG is hydrolysed to 3-phosphoglycerate by bisphosphoglycerate phosphatase.Inhibitors of Glycolytic
pathways
1. Iodoacetate inhibit Glyceraldehyde 3-P dehydrogenase involved in glyceraldehyde 3 P to 1,3-
bisphosphoglycerate
2. Arsenate inhibit sysnthesis of ATP by inhibiting G3P Dehydrogenase.
3. Fluoride inhibit enolase in conversion of 2- Phosphoglycerate to phosphoenolpyruvate.
▪ Fluoride in the tooth paste inhibit the activity of Enolase Enzyme So it can inhibit glycolysis in
bacteria & lactic acid formation So tooth past can prevent the teeth decay!!Fate of end product of glycolysis (Fate of
end product of anaerobic glycolysis)
A- Fate of NADH+H+:
➢ As the cell has a limited amount of NAD, so NADH+H+ must be reoxdized to resynthesize NAD.
➢ In absence of mitochondria and/or oxygen NADH+H is reoxdized by converting pyruvate to
lactate
B- Fate of lactate:
➢ Diffuse out of anaerobic tissue with H+ to blood, then pass to liver where it will converted to
glucose and go back to muscle. This cycle of lactate to glucose is known as Cori cycle.
➢ First, in the direction of lactate formation the LDH reaction requires NADH and yields NAD+
which is then available for use by the glyceraldehyde-3-phosphate dehydrogenase reaction of
glycolysis. These two reactions are, therefore, intimately coupled during anaerobic glycolysis.2- Fate of end products of
aerobic glycolysis
A- Fate of NADH+H+:
➢ As the cell has a limited amount of NAD, so NADH+H+ must be reoxdized to resynthesize NAD.
➢ Reoxidation of NAD occur in mitochondria in ETC.
➢ But the mitochondrial membrane impermeable to NADH+H+
➢ NADH+H+ enter to mitochondria through one of shuttles (Malate-Asparatate shuttle or
Glycerol 3 P substrate shuttle) across the mitochondrial membrane.
B- Fate of pyruvate:
➢ Converted to acetyl CoA by pyruvate dehydrogenase complex enzyme to be completely
oxdized to CO2, H2O with production of more energy in TCA cycle.Conversion of pyruvate to
lactate
 In anaerobic condition, pyruvate is reduced to lactate by lactate dehydrogenase (LDH).
 In the cells lacking mitochondria and under anaerobic conditions, the NADH⁺ formed in the
oxidation of glyceraldehyde 3- phosphate is consumed in the hydrogenation of pyruvate.
 The regeneration of NAD + in the hydrogenation of pyruvate to lactate sustains the continued
operation of glycolysis under anaerobic conditions.Significance of Lactate
Production
 The NADH is obtained from the reaction catalysed by glyceraldehyde 3-phosphate
dehydrogenase & also from Kreb’s cycle. The formation of lactate allows the regeneration of
NAD+ which can be reused by glyceraldehyde 3-phosphate dehydrogenase.
 So Glycolysis proceeds even in the absence of oxygen to supply ATP.
 Glycolysis is very essential in skeletal muscle during strenous exercise where oxygen supply is
very limited. Accumulated lactic acid will decrease PH & cause muscle cramps.
 In RBCs, there are no mitochondria. Glycolysis in the erythrocytes leads to lactate production
RBCs derive energy only through glycolysis, where the end product is lactic acid.CORI CYCLE
 The cycle involving the synthesis of glucose in liver from the skeletal muscle lactate and the
reuse of glucose thus synthesized by the muscle for energy purpose is known as Cori cycle.
 It is a process in which glucose is converted to Lactate in the muscle and in the liver this
lactate is re-converted to glucose.
 Lactate produced by active skeletal muscle is a major precursor for gluconeogenesis.
 Importance of cori cycle:
 preventing lactic acidosis during anaerobic conditions in the muscle.
 This cycle is, important in ATP production during muscle exertion.
 The Cori cycle is an important source of substrate for gluconeogenesis.ACORI CYCLE (cont.)
Mechanism of Cori Cycle:
 Under anaerobic conditions, pyruvate is reduced to lactate by lactate dehydrogenase (LDH)
 In an actively contracting muscle, pyruvate is reduced to lactic acid which may tend to accumulate in
the muscle.
 Lactate is a dead end in glycolysis, since it must be reconverted to pyruvate for its further metabolism.
 The very purpose of lactate production is to regenerate NADH so that glycolysis proceeds
uninterrupted in skeletal muscle.
 Lactate or pyruvate produced in the muscle cannot be utilized for the synthesis of glucose due to the
absence of the key enzymes of gluconeogenesis (glucose 6-phosphatase and fructose 1,6-
bisphosphatase).
 To prevent lactate accumulation, body utilizes cori cycle.CORI CYCLE (cont.)
 The plasma membrane is freely permeable to lactate. So lactic acid from muscle diffuses into
the blood.
 Lactate is carried from the skeletal muscle through blood and handed over to liver, where it is
oxidized to pyruvate.
 Pyruvate, so produced, is converted to glucose by gluconeogenesis, Regenerated glucose can
enter into blood and then transported to the skeletal muscle.
 The cycle involving the synthesis of glucose in liver from the skeletal muscle lactate and the
 reuse of glucose thus synthesized by the muscle for energy purpose is known as Cori cycle
 From a biochemical point of view, the Cori cycle links gluconeogenesis with anaerobic
glycolysisTake Home Messages
 Glycolysis is the major oxidative pathway for glucose
 Glycolysis is employed by all tissues
 Glycolysis is a tightly-regulated pathway
 PFK-1 is the rate-limiting regulatory enzyme
 Glycolysis is mainly a catabolic pathway for ATP production, But it has some anabolic features
(amphibolic)
 Pyruvate kinase deficiency in RBCs results in hemolytic anemia
 Net energy produced in:
 Aerobic glycolysis:
8 ATP
 Anaerobic glycolysis:
2 ATPTake Home Messages
 When? It is an emergency cycle occurring All the time depending on:
1- Availability of substrates
2- Energy state of the cell
 So it could be inhibited In:
1- The high energy state i.e. (High ATP ) .
2-Presence of alternative source of energy (as indicated by high level of citrate)
3- Absence of substrate (Starvation)Take Home Messages
❑ Tissues Dependent On Glycolysis 1. Brain: ▪ Dependent on glucose as primary source of fuel (rapid source of ATP) 2. RBC: ▪ Dependent on glucose for energy production. ▪ Lack mitochondria ▪ (No FA oxidation, No TCA, No ETC) (So It depends on glycolysis) 3. Exercising Muscles (sever exrcise): 4. Anaerobic condition (No O2)…..(No ETC)