Biochemistry

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Biochemistry
Lec 2
Dr. Munaf S. Daoud
Regulatory Enzymes
HK = Hexokinase
PFK = Phosphofructokinase
PK = Pyruvate Kinase
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 The phosphorylation that occurs at the expense of inorganic phosphate (Pi) of a
compound is known as substrate-level phosphorylation.
e.g.
Glycrald. 3-P
1,3 bis PG
1,3 bis PG
3 PG
PEP
Pyruvate
Bis is of two parts; Bi =‫ثنائي‬, while s = “separated” (i.e. on different locations)
 Glycerald. 3-P converts into 2,3 bis PG or 2,3 BPG or 1,3 DPG and is present in
most cells at low concentrations, but in the RBCs (erythrocytes) it is at high
concentration (4 mM) which is equal to hemoglobin.
It acts as a regulator of oxygen transport, stabilizing the deoxygenated form of
hemoglobin.
Glycrald. 3-P
1,3 bis PG
Mutase
2,3 bis PG
Phosphatase
3PG
Glycolysis and RBC Metabolism:
1- Mature RBCs or Erythrocytes contain NO mitochondria, so they are totally
dependent on glycolysis for ATP production.
2- ATP is required for the ATPase-ion transport system which is necessary to
maintain the proper biconcave shape of the erythrocyte membrane.
Energy or ATP production:
1- Anaerobic Glycolysis
2 moles ATP used Glc
Frc 6P
Glc 6P
Frc 1,6 bis P
2 moles ATP produced ( 1,3 bis PG
3 PG)
2 moles ATP produced (PEP
Pyruvate)
2ATP
4ATP
 net ATP produced is 4-2= 2ATP
Produced by substrate-level phosphorylation
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2- Aerobic Glycolysis
2 moles ATP used
Glc
Frc 6P
Glc 6P
Frc 1,6 bis P
2ATP
2 moles ATP produced ( 1,3 bis PG
3 PG)
2 moles ATP produced (PEP
Pyruvate)
4ATP
 net ATP produced is 4-2= 2ATP
Produced by substrate-level phosphorylation
Plus 2 NADH that give 4 moles ATP through the Glycerol 3-Phosphate
shuttle
(NADH
Glycerol 3-P
 Net ATP produced is 2+4 =
FADH2
4 ATP)
ETC
6ATP
Glycerol 3-Phosphate shuttle
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Malate Shuttle:
NADH produced in glycolysis is extra-mitochondrial (cytosol), whereas ETC is
mitochondrial. NADH is impermeable into mitochondrial membrane  it transfers
reducing equivalents via substrate pairs linked by suitable dehydrogenases by
Shuttle Systems.
These dehydrogenases should be present on both sides of the membrane
1- Glycerol phosphate shuttle
2 ATP are yielded of 1 NADH
FADH2
Oxidized
2- Malate shuttle
3 ATP are yielded of 1 mole NADH (cytosol)
1
mole NADH (Mitochondria).
Diseases associated with impaired glycolysis:
1- Pyruvate kinase deficiency
A genetic defect that leads to low ATP production, decreased RBCs
stability and swelling and lysis that results in Hemolytic anemia
2- Hexokinase deficiency
A genetic defect in RBCs that lead to low 1,3 bis PG and 2,3 bis PG.
2,3 bis PG binds hemoglobin (Hb) and lowers its affinity to oxygen and
normally allows Hb to release O2 in tissue capillaries. But in these
patients Hb has high O2 affinity, leading to Hemolytic Anemia
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Fate of pyruvate or pyruvic acid, the end product of Aerobic
glycolysis:1- Conversion to lactate (lactic acid) by Lactate dehydrogenase (LDH) and
NADH in anaerobic glycolysis.
2- Conversion to alanine (Ala)
This occurs in reversible transamination reactions of amino acids
metabolism
3- Conversion to acetyl CoA
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Pyruvate DeHydrogenase Complex (PDC or PDH):123456-
Provide a link between Glycolysis and citric acid cycle.
Oxidizes pyruvate to give CO2 and Acetyl CoA.
Acetyl CoA is the substrate for citric acid cycle.
The reaction is irreversible.
Located within the matrix of mitochondria.
PDC is of 4 distinct enzymatic activities and require 5 coenzymes (TPP, CoA,
NAD, FAD, and lipoic acid).
7- PDC is inhibited by Dietary Deficiency of thiamine (vitamin B1) and arsenite or
mercuric ions.
Regulation of Glycolsis:
1) Allosteric activation or inhibition of GK, HK, PFK & Pk. e.g. phosphorylation
and dephosphorylation. This is short term influence (minutes-hours).
2) Hormonal influence on the amount of enzyme synthesized. This is long term
influence by increasing 10-20 fold the enzyme activity and takes hours-days.
3) Well-fed state (after a meal of CHO) or high insulin
High enzyme
activity.
4) Starvation or diabetes
low enzyme activity.
5) PFK-activated by cAMP, AMP, Frc 6P, Pi and frc 2,6 bisP (in liver).
-inhibited by Citrate & ATP.
6) PK-activated by Frc 1,6 bisP
-Inhibited by ATP, glucagon, epinephrine.
The enzyme Pyruvate dehydrogenase complex (PDC)
-Activated by CoA, NAD+, Insulin, ADP and Pyruvate.
-Stimulated in the well-fed state. And it’s inhibited in starvation and DM.
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Abbreviations of Biochemical compounds and Enzymes and their
full names:ATP = Adenosine Triphosphate
ADP =Adenosine Diphosphate
Glc = Glucose
G6P= Glucose 6 Phosphate
CTP = Cytidine Triphosphate
GTP = Guanosine Triphosphate
UTP = Uridine Triphosphate
PEP = Phosphate Enol Pyruvate
Frc 6P = Fructose 6 Phosphate
Frc 1,6 bis P = Frc 1,6 Bis Phosphate
ATPase = Adenosine Triphosphatase
Gly3P = Glycerol 3 phosphate
NAD+, FAD, NADH & FADH2 – coenzymes
GK = Glucokinase
HK= Hexokinase
ETC = Electron Transport Chain
Glycerald. 3P = Glyceraldehyde 3 Phosphate
DHAP = Dihydroxy Acetone Phosphate
1,3 Bis PG = 1,3 Bis PhosphoGlycerate
3PG = 3 Phosphoglycerate
2PG = 2 Phosphoglycerate
2,3 bis PG = 2,3 bis phosphoglycerate
LDH = Lactate Dehydrogenase
PFK = PhosphoFrcutokinase
ALT = alanine amino transferase
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