Glycolysis Dr.S.Chakravarty MD
A year and a half old Amish girl from Pennsylvania girl is being seen by the hematologist after her pediatrician found her to be severely anemic with splenomegaly and jaundice. Her mother gives a possible history of a “blood problem” in her family but doesn’t know for sure.
Her hemoglobin electrophoresis was normal, and the complete
blood count (CBC) revealed a normocytic anemia. The platelet and white blood cell counts are normal. On the peripheral smear, there are many bizarre erythrocytes including spiculated cells. Heinz bodies are absent.
Questions:-
What can be the diagnosis?
What is the biochemical basis of the clinical features?
Learning objectives:
Analyze the importance of Glycolytic pathway that it can produce ATPs in both aerobic and anaerobic environment
Differentiate between substrate level and oxidative phosphorylation
List the GLUT transporters and classify them based on insulin dependency
List the rate limiting and irreversible steps of Glycolysis and their regulation
Explain the Importance of Embden Meyerhof pathway
Describe the clinical features of pyruvate kinase deficiency
Calculate the Energy generated during aerobic and anaerobic Glycolysis
Metabolism: Defined as sum of all chemical changes that occur in
the body
Divided into two groups :
1. Anabolism : synthesis of complex molecules from simple molecules like glucose to glycogen.
2. Catabolism : breakdown of complex molecules like proteins, carbohydrates and lipids to simple molecules such as CO2, H2O and NH2
Three stages of catabolism : Carbohydrates Lipids Proteins
Monosaccharides Fatty acids Glycerol
Aminoacids
Acetyl Co-A
TCA cycle
CO2 + H2O + ATP
Glucose uptake by cells:Major Glucose transporters (GLUT):Receptor Tissues Km Function Facilitative bidirectional transporters GLUT – 1 Most tissues (Brain,
RBCs, Colon ,Placenta)1 mMLOW Km-High affinity Basal uptake
GLUT – 2 LiverPancreas Small intestineKidney
15 mMHIGH Km(Low affinity transporter)
• Uptake and release of glucose by liver( AFTER A MEAL )
• Glucose sensor GLUT-3 Brain
KidneyPlacenta
1 mMLow Km-High
AFFINITYBasal uptake
GLUT – 4 Skeletal muscle
Adipose tissue Heart
5 mM • Insulin stimulated glucose uptake
GLUT -5 Small Intestine •Absorption
Sodium dependent unidirectional transporter
SGLT1 Small Intestine and Kidney
•Active uptake of glucose against a concentration gradient
NORMAL BLOOD GLUCOSE CONCENTRATION 4-6 mM (70-110 mg/dl)Glut 1 and Glut 3 are at Vmax at Normal glucose concentrationRECALL :Km is inversely proportional to affinity
Salient features of Glycolysis:Occurs in the cytoplasm of all the cells in the body
Immediate /basal source of energy (ATP) is provided by this pathway.
It provides intermediates for other pathways like Pyruvate, glucose-6-PO4, and Dihydroxyacetone phosphate etc.
Hub of carbohydrate metabolism – all carbs are finally converted to glucose or intermediates of Glycolysis before being metabolized.
ALL CELLS CARRY OUT GLYCOLYSIS Glycolysis is the ONLY source of ATPs in:
Cornea and lens of the eyeRenal medullaRBCsSkin Cancerous cells.
Two types of Glycolysis:A. Aerobic Glycolysis : formation of Pyruvate as end
product with production of ATP and NADH when oxygen is available
B. Anaerobic Glycolysis : formation of lactate as end product with production of only ATP in the absence of oxygen .
Allows continuous production of ATPs in cells without mitochondria or cells deprived of oxygen
Glycolysis
Glucose
Glucose -6-PO4
Fructose -6-PO4
Fructose -1,6-bisphosphate
Glucokinase /Hexokinase
Phosphofructokinase-1
ATP
ADP
ATP
ADP
Energy consuming phase
Irreversible step -1
Irreversible step -2
Rate limiting step
Phosphohexose isomerase
Glycolysis, Gluconeogenesis, The HMP shunt ,GlycogenesisGlycogenolysis
Reversible but driven forward because of a low concentration of F6P, which is constantly consumed during the next step of glycolysis.
GlycolysisSplitting phase – into molecules of 3 carbons each
Fructose -1,6-bisphosphate
Glyceraldehyde-3-PO4 Dihydroxyacetone phosphate
Aldolase A
6C
3C 3CIsomerase
Glycerol -3-po4
Glycerol -3-po4 dehydrogenase
Fatty acid synthesis
Energy yielding phase
Glyceraldehyde-3-PO4
1,3 bis phosphoglycerate
NAD
NADH
Glyceraldehyde-3-PO4
dehydrogenase
3-phosphoglycerate
2-phosphoglycerate
Phosphoenolpyruvate
Pyruvate
ADP
ATPPyruvate Kinase Irreversible step
-3
Pathway repeats twice because of 2 molecules of Glyceraldehye 3-PO4 formed
ADP
ATPPhosphoglycera
te kinase
Enolase (-) Fluoride
Substrate level phosphorylation
Phosphoglycerate mutase
Energy yield from one molecule of glucose
ATPs consumed during Glycolysis
1 – Glucokinase 1 – Phosphofructokinase
ATPs produced during Glycolysis
2 – Phosphoglycerate kinase 2 – Pyruvate kinase
NADH produced Glycolysis (Aerobic pathway / or cells with mitochondria)
2 – Glyceraldehyde-3-PO4 dehydrogenase (NADH = 2.5 ATPs)
Net gain in ATPs during Aerobic glycolysis = (4 + 5 – 2 = 7 ATPs)
Regeneration of NAD+
Very little NAD in the cytosol.
NADH NAD+ + 2 electrons
In Aerobic tissues: by transferring the electrons to mitochondria to produce ATP by shuttle mechanisms.
In Anaerobic tissues or aerobic tissues devoid of oxygen: by producing lactic acid.
Anerobic glycolysis:
Pyruvate
Lactate
Lactate Dehydrogenase
NADH
NADH
NAD
NAD
• Net energy gain during anaerobic Glycolysis is only 2 ATPs• NADH produced during anaerobic Glycolysis is utilized during lactate dehydrogenase step
Glycolysis in Erythrocytes:
1,3 Bis phosphoglycerate
3-phosphoglycerate
2,3 Bis phosphoglycerate(2,3BPG)
Mutase
Phosphatase
Phosphoglycerate kinase
ADP
ATP
• Net ATP production during production of 2,3 BPG in RBCs = 0 ATPs• Increase in 2,3 BPG shifts the oxygen dissociation curve to the right
Regulation of Glycolysis:
Regulation at the level of Glucokinase/Hexokinase
Regulation at Phosphofructokinase
Regulation of Pyruvate kinase
Hormonal regulation (mainly liver): Insulin favors Glycolysis and Glucagon inhibits Glycolysis
Difference between Hexokinase and Glucokinase Hexokinase Glucokinase
Substrate specificity All hexoses Mainly Glucose
Km Low (high affinity)Works at normal glucose concentration
High (low affinity) works only when glucose levels are elevated
Location Universal Mainly liver and Beta cells of pancreas
Vmax (rate of reaction) Low High
Glucose-6-PO4 (Allosteric inhibition)
Inhibits the enzyme No inhibition
Insulin No regulation Positive regulation
Diabetes Mellitus :
Insulin dependent Diabetes Mellitus (IDDM) – def of insulin due to autoantibodies against Beta cells
Non insulin dependent Diabetes mellitus (NIDDM) – insulin receptor resistance
Maturity onset diabetes of the young – (MODY) – mutation in the Glucokinase gene.
Allosteric Regulation of PFK-1:
Situation of high energy levels in the cells indicated by:
1. High ATP:2. High citrate levels :
Situation of low energy in the cells indicated by:
1. High ADP /AMP level2. High fructose 2,6 bisphosphate
Allosteric inhibition of PFK-1
Allosteric activation
Fructose -6-po4
Fructose -1,6- Bisphosphate
Fructose -2,6- Bisphosphate
PFK-1
PFK-2
Insulin
Glucagon
Regulation of PFK -1 :
Covalent modification of Pyruvate kinase :
Pyruvate Kinase
Pyruvate Kinase
po4ATP ADP
Protein kinase A
Glucagon cAMP(+)
(+)
Inactive
Active
(+)
Protein phosphatase Insulin
(+)
Inhibition of Glycolysis in liver and increase blood glucose
Pyruvate kinase def : in RBCs
Second most common cause for enzyme deficiency related hemolytic anemia.
Def causes decreased ATP production in RBCs
Decreased energy to fuel the pumps required to maintain the biconcave, flexible shape of RBCs.
Red cell damage and phagocytosis – premature death and lysis – hemolytic anemia (chronic hemolysis)
Absence of Heinz bodies ( to differentiate G6PD def)
Under conditions of anaerobic glycolysis, the NAD+ required by glyceraldehyde-3-phosphate dehydrogenase is supplied by a reaction catalyzed by which of the following enzymes?
Glycerol-3-phosphate dehydrogenaseAlpha-ketoglutarate dehydrogenaseLactate dehydrogenaseMalate dehydrogenasePDH
After consumption of a carbohydrate-rich meal, the liver continues to convert glucose to glucose-6-phosphate. The liver’s ability to continue this processing of high levels of glucose is important in minimizing increases in blood glucose after eating. What is the best explanation for the liver’s ability to continue this conversion after eating a carbohydrate-rich meal?
The Hepatocyte cell membrane’s permeability for glucose-6-phosphate
The high maximum reaction rate (high Vmax) of Glucokinase
The inhibition of Glucokinase by high glucose-6-phosphate
The lack of Glucokinase level regulation by insulinThe low Michaelis-Menten (Km) constant of Glucokinase
Fates of Pyruvate:
Various fates of Pyruvate:
How many ATPs are produced from oxidation of 2 molecules of Glucose ?
A. 32B. 38C. 64D. 48E. 0
Which of the following best describes the effect of ATP on PFK 1 ?
Thank You
Top Related