Download Lecture 2 Glycolysis

Lecture 2 Glycolysis
Reactions & mechanism of glycolysis
• In this lecture, we focus on the reactions of glycolysis
Reference material
Biochemistry 4th edition, Mathews, Van Holde, Appling, Anthony‐Cahill. Pearson ISBN:978‐0‐13‐800464‐4
Lehninger Principles of Biochemistry 4th edition, David L. Nelson, Michael M. Cox. W. H. Freeman ISBN:978‐0716743392
Storage polysaccharides
Starch: composed of mainly amylose and amylopectin
amylose
amylopectin
Sugar (Sucrose): disaccharide of glucose and fructose
Sucrose
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Plant biomass composed of cellulose, hemicellose, and lignin
Cellulose: polymers of glucose
Hemicellulose: Copolymers of various sugars including, glucose
xylose
arabinose
glucuronic acid
etc..
Lignin: polymers of aromatic alcohols which provides structure strength for the cellulose and hemicellulose fibers
Enzymes that liberate monosaccharides from (hemi)cellulose
Endo(hemi)cellulases: randomly cleave the β1,4 bond to break the polymer
Exo(hemi)cellulases: cleaves 2 to 4 sugar units from the ends
Subsequently, short oligosaccharides can be further broken down into monomeric sugars
β‐glucosidase
Disaccharides such as cellubiose
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glucose
glucose
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Now that we have glucose… How does glucose get used?
Glycolysis converts Glucose to pyruvate in 10 enzymatic steps!
Glycolysis or the Embden–Meyerhof–Parnas (EMP) Pathway
Can be split into 2 phases
1. Preparatory or activation
(Investment) phase
2. Payoff phase
Net reaction:
Glucose  2 Pyruvate + 2 ATP + 2 NADH
Reaction 1: Hexokinase
“Activates” glucose
1 ATP used
+ H+
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Phosphotransferase system (PTS) used by many bacteria
In many bacteria, glucose is simultaneously transported and activated by the PTS.
PTS uses PEP as the phosphate donor, which in a series of reactions, phosphorylates glucose
Reaction 2: Phosphoglucose isomerase
phosphoglucose
isomerase
Moving the carbonyl to C2 prepares the molecule for cleavage in step 4
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Reaction 3: Phosphofructokinase
Further “activates” the sugar
1 ATP used
+ H+
• This step “commits” the hexose to being broken down
• Phosphorylations become even: at both ends of the molecule
Reaction 4: Aldolase
Aldolase performs an reversible Aldol reaction (recall from lec.1)
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Reaction 5: Triose isomerase
• Glycolysis continues using Glyceraldehyde‐3‐phosphate (G3P)
Summary of the investment phase
Net reaction for investment phase:
Glucose + 2 ATP  2 G3P + 2 ADP + 2 H+
isomerization
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Reaction 6: Glyceraldehyde‐3‐Phosphate dehydrogenase
Recall that oxidation of aldehyde can be used to make high energy ester bond!
Wouldn’t want to waste that energy!!
Reaction 7: Phosphoglycerate kinase
Mg2+
Phosphoglycerate
kinase
• Recall that the hydrolysis of 1,3BPG has a higher phosphoryl transfer potential
• Transfer phosphoester energy in 1,3‐BPG to ADP, forming ATP
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Reaction 8: Phosphoglycerate mutase
Reaction 9: Enolase
RECALL that Phosphoenolpyruvate (PEP) is used for PTS system!!
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Reaction 10: Pyruvate kinase
• Pyruvate can be considered as the end product
of glycolysis.
• Pyruvate is used for biosynthesis of many amino
acids
• Can also be turned into other metabolites which
enter other biosynthetic pathways
• Pyruvate can undergo oxidative decarboxylation
to make acetyl‐CoA, which is also widely used
for both energy generation and for biosynthesis
Summary of the glycolysis
In the payoff phase:
2 G3P + 4 ADP + 2 Pi + 2 NAD+
2 Pyruvate + 4 ATP + 2 H2O + 2 NADH
Net reactions:
Glucose  2 Pyruvate + 2 ATP + 2 NADH
carbon
energy
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electrons
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