METABOLIC
PATHWAYS
CATABOLIC PATHWAYS
Are involved in oxidative
breakdown of larger
complexes.
They are usually
exergonic in nature
ANABOLIC PATHWAYS
Are involved in the
synthesis of
compounds.
They are usually
endergonic in nature.
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METABOLIC PATHWAYS CATABOLIC PATHWAYS Are involved in oxidative breakdown of larger complexes. They are usually exergonic in nature ANABOLIC PATHWAYS Are involved in the synthesis of compounds. They are usually endergonic in nature.
CHARACTERISTICS OF METABOLISM
- Metabolic pathways are mostly irreversible
- Every metabolic pathway has a committed first step.
- All metabolic pathways are regulated.
- Metabolic pathways in eukaryotic cells occur in specific cellular locations.
GLYCOLYSIS
Glycolysis comes from a merger of two Greek words: Glykys = sweet Lysis = breakdown/ splitting It is also known as Embden-Meyerhof-Parnas pathway or EMP pathway.
INTRODUCTION
- GLYCOLYSIS is the sequence of 10 enzyme-catalyzed reactions that converts glucose into pyruvate with simultaneous production on of ATP.
- In this oxidative process, 1mol of glucose is partially oxidised to 2 moles of pyruvate.
- This major pathway of glucose metabolism occurs in the cytosol of all cell.
- This unique pathway occurs aerobically as well as anaerobically & doesn’t involve molecular oxygen.
Glucose Extracellular matrix & cell wall polysachharide. Glycogen, Starch, Sucrose Pyruvate Ribose- 5 - phosphat e Oxidation via pentose phosphate pathway Synthesis of structural polymers storage Oxidation via glycolysis Major pathways of glucose utilization.
PREPARATORY PHASE
- It consists of the 1 st 5 steps of glycolysis in which the glucose is enzymatically phosphorylated by ATP to yield Fructose-1,6-biphosphate.
- This fructuse-1,6-biphosphate is then split in half to yield 2 molecules of 3-carbon containing Glyceraldehyde- 3 - phosphate/ dihyroxyacteone phosphate.
- Thus the first phase results in cleavage of the hexose chain.
- This cleavage requires an investment of 2 ATP molecules to activate the glucose mole and prepare it for its cleavage into 3-carbon compound.
PAYOFF PHASE
- This phase constitutes the last 5 reactions of Glycolysis.
- This phase marks the release of ATP molecules during conversion of Glyceraldehyde- 3 - phosphtae to 2 moles of Pyruvate.
- Here 4 moles of ADP are phosphorylated to ATP. Although 4 moles of ATP are formed, the net result is only 2 moles of ATP per mole of Glucose oxidized, since 2 moles of ATP are utilized in Phase 1.
STEP 1: PHOSPHORYLATION
- Glucose is phosphorylated by ATP to form sugar phosphate.
- This is an irreversible reaction & is catalyzed by hexokinase.
- Thus the reaction can be represented as follows: Glucose Glucose- 6 - phosphate Hexokinase ATP ADP
STEP 2: ISOMERIZATION
- It is a reversible rearrangement of chemical structure of carbonyl oxygen from C1 to C2, forming a Ketose from the Aldose.
- Thus, isomerization of the aldose Glucose6-phosphate gives the ketose, Fructose- 6 - phoshphate. Glucose- 6 - phosphate Fructose- 6 - phosphate Phosphoglucoisomerase
STEP 4: BREAKDOWN
- This six carbon sugar is cleaved to produce two 3-C molecules: glyceradldehyde- 3 - phosphate (GAP) & dihydroxyacetone phosphate(DHAP).
- This reaction is catalyzed by Aldolase. Fructose-1,6- bisphosphate Glyceraldehyde- 3 - phosphate Dihydroxyacetone Triose phosphate^ phosphate isomerase Aldolase
STEP 5: ISOMERIZATION
- Dihydroxyacetone phosphate is oxidized to form Glyceraldehyde- 3 - phosphate.
- This reaction is catalyzed by triose phosphate isomerase enzyme. Glyceraldehyde- 3 - phosphate Dihydroxyacetone phosphate Triose phosphate isomerase