GLYCOLYSIS AND KREBS CYCLE FULL

1. COLLEGE OF NATURALAND APPLIED SCIENCES (CONAS)
DEPARTMENT OF MOLECULAR BIOLOGYAND BIOTECHNOLOGY
MC 231; MICROBIAL NUTRITION AND METABOLISM
GROUP 20 ,ORGANOTROPHS: AEROBIC RESPIRATION (GLYCOLYSIS AND CITRIC ACID CYCLE
UNIVERSITY OF DAR ES SALAAM
S/N NAMES REGISTRATION NUMBER
01 ANTONY CHARLES KIMARIO 2017-04-07021
02 NDOMBELE JACKLINE E 2017-04-01387
03 MANGULA JUSTINE 2017-04-01391
04 SHIJA RACHEL 2017-04-01372
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DEGREE PROGRAM
BSC GENERAL
BSC MICROBIOLOGY
BSC MICROBIOLOGY
BSC MICROBIOLOGY
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2. ORGANOTROPHS (GLYCOLYSIS AND CITRIC
ACID CYCLE)
Organotrophs can be defined as organisms that obtain their energy from the
oxidation of organic compound
AEROBIC RESPIRATION is the catabolic reaction which occur under presence of
oxygen as electron acceptor
Respiration of glucose is divided into three major steps namely
Glycolysis
Citric acid cycle
Electron transport system
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3. GLYCOLYSIS
Glycolysis is a series of reactions in which glucose is oxidized to
pyruvate with the production of ATP. This pathway was described
by EMBDEN ,MEYERHOF and PARNAS hence it is called
Embden–Meyerhof–Parnas pathway (EM pathway). Glycolysis spilt
one molecule of glucose into two smaller molecules of pyruvate.
During sequential reaction of glycolysis some of the free energy is
released from glucose is conserved in the form of ATP and NADH
Glycolysis is major pathway for ATP synthesis in tissue lacking
Mitochondria
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4. Glycolysis take place inside the cytoplasm (cytosol) of cell and it’s the first
stage of both anaerobic (absence of oxygen) and aerobic respiration (presence
of oxygen) .it doesn’t need Oxygen to take place. Lactate is the end product
under anaerobic condition, in aerobic condition pyruvate is formed which is
then oxidized to co2 and H2o.
Glycolysis is a central metabolic pathway with many of its intermediate
providing branch point to other pathway. The intermediate of glycolysis are
useful for synthesis of amino acids and fats
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5. • THE TWO STAGES OF GLYCOLYSIS
• Glycolysis can be divided into two stages, each consisting of one or
more enzymatic reactions.
 Stage I PREPARATORY PHASES/STAGE consists of
“preparatory” reactions; these are not redox reactions and do not
release energy but instead form a key intermediate of the pathway.
 In Stage II, PAY OFF PHASE/STAGE redox reactions occur, energy
is conserved, and two molecules of pyruvate are formed.
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6. Preparatory Phase :
• This phase is also called glucose activation phase. In the preparatory
phase of glycolysis, two molecules of ATP are invested and the hexose
chain is cleaved into two triose phosphates.
• During this, phosphorylation of glucose and it’s conversion to
glyceraldehyde-3-phosphate take place. The steps 1, 2, 3, 4 and 5
together are called as the preparatory phase.
Payoff Phase :
• This phase is also called energy extraction phase. During this phase,
conversion of glyceraldehyde-3-phophate to pyruvate and the coupled
formation of ATP take place.
• Because Glucose is split to yield two molecules of D-Glyceraldehyde-3-
phosphate, each step in the payoff phase occurs twice per molecule of
glucose. The steps after 5 constitute payoff phase.
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7. STAGE 1 PREPARATORY STAGE
STEP 1 Phosphorylation of glucose to glucose 6 phosphate
• The first step in glycolysis is the conversion of D-glucose into glucose-
6-phosphate. The enzyme that catalyzes this reaction is hexokinase.
• Here, the glucose ring is phosphorylated. Phosphorylation is the
process of adding a phosphate group to a molecule derived from ATP.
As a result, at this point in glycolysis, 1 molecule of ATP has been
consumed. Hexokinase, like many other kinases, requires Mg2+ for its
activity.
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8. Step 2 : Isomerization of Glucose-6-Phsphate to Fructose-6-Phosphate
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 Glucose-6-phosphate is isomerised to fructose-6-phosphate by phosphohexose
isomerase
The second reaction of glycolysis is the rearrangement of glucose 6-phosphate (G6P) into
fructose 6-phosphate (F6P) by glucose phosphate isomerase (Phosphoglucose Isomerase).
Details:
The second step of glycolysis involves the conversion of glucose-6-phosphate to fructose-
6-phosphate (F6P). This reaction occurs with the help of the enzyme Phosphoglucose
isomerase (PI). As the name of the enzyme suggests, this reaction involves an
isomerization reaction. GROUP NO 20

9. Step 3 : Phosphorylation of Fructose-6-Phosphate to Fructose 1,6-
Biphosphate
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 Fructose-6-phosphate is further phosphorylated to fructose 1,6-bisphosphate.
The enzyme is phosphofructokinase-1. It catalyses the transfer of a phosphate group from ATP to fructose-6-
phosphate
Details:
In the third step of glycolysis, fructose-6-phosphate is converted to fructose- 1,6-bisphosphate (FBP). Similar to
the reaction that occurs in step 1 of glycolysis, a second molecule of ATP provides the phosphate group that is
added on to the F6P molecule.
The enzyme that catalyses this reaction is phosphofructokinase (PFK). As in step 1, a magnesium atom is involved
to help shield negative charges. GROUP NO 20

10. Step 4 : Cleavage of Fructose 1,6-
Biphosphate
• The 6 carbon fructose-1,6-bisphosphate is cleaved into two 3 carbon
units; one glyceraldehyde-3-phosphate (GAP) and another molecule
of dihydroxy acetone phosphate (DHAP).
• The enzyme which catalyses the reaction is aldolase. Since the
backward reaction is an aldol condensation, the enzyme is called
aldolase
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11. Step 5 :Isomerisation of dihydroxyacetone phosphate
(DHAP) to glyceraldehyde 3-phosphate (GAP).
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 GAP is on the direct pathway of glycolysis, whereas DHAP is not.
Hence Triose-phosphate isomerase converts DHAP into GAP useful for
generating ATP. Thus net result
 glucose is now cleaved into 2 molecules of glyceraldehyde-3-phosphate.
This reaction is rapid and reversible.
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13. STAGE 2 PAY OFF STAGE
Step 6 :phosphorylation of GAP to 1,3-Bisphosphoglycerate
• The first step in the payoff phase is the oxidation of glyceraldehyde 3-
phosphate to 1,3-bisphosphoglycerate.
• This reaction is catalysed by glyceraldehyde 3-phosphate dehydrogenase.
• the molecule is phosphorylated by the addition of a free phosphate group
• During this reaction, NAD+ is reduced to NADH.
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14. Step 7 : Conversion of 1,3-Biphosphoglycerate to 3-Phosphoglycerate
Phosphoglycerate kinase transfers a phosphate group from 1,3bisphosphoglycerate to ADP to
form ATP and 3-phosphoglycerate.
• Details:
• In this step, 1,3 bisphoglycerate is converted to 3-phosphoglycerate by the enzyme
phosphoglycerate kinase (PGK). This reaction involves the loss of a phosphate group from the
starting material. The phosphate is transferred to a molecule of ADP that yields our first
molecule of ATP. Since we actually have two molecules of 1,3 bisphoglycerate (because there
were two 3-carbon products from stage 1 of glycolysis), we actually synthesize two molecules of
ATP at this step. With this synthesis of ATP, we have cancelled the first two molecules of ATP that
we used, leaving us with a net of 0 ATP molecules up to this stage of glycolysis.
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15. Step 8 : Conversion of 3-Phosphoglycerate to 2-Phosphoglycerate
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 3-phosphoglycerate is isomerized to 2-phospho glycerate by
shifting the phosphate group from 3rd to 2nd carbon atom.
 The enzyme is phosphoglyceratemutase.
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16. Step 9 : Dehydration of 2-Phosphoglycerate to
Phosphoenolpyruvate
• 2-phosphoglycerate is converted to phosphoenol pyruvate by the
enzyme enolase.
• One water molecule is removed.
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17. Step 10 : Conversion of Phosphoenol Pyruvate to Pyruvate
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Details:
The final step of glycolysis converts phosphoenolpyruvate into
pyruvate with the help of the enzyme pyruvate kinase. As the
enzyme’s name suggests, this reaction involves the transfer of a
phosphate group. The phosphate group attached to the 2′ carbon
of the PEP is transferred to a molecule of ADP, yielding ATP. Again,
since there are two molecules of PEP, here we actually generate 2
ATP molecules. GROUP NO 20

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20. CITRIC ACID CYCLE
• The pathway by which pyruvate is oxidized to CO2 is called the
citric acid cycle (CAC). In the CAC, pyruvate is first decarboxylated,
leading to the production of CO2, NADH, and the energy-rich substance
acetyl-CoA
• It is also known as Tricarboxylic Acid (TCA) cycle. In prokaryotic cells,
the citric acid cycle occurs in the cytoplasm; in eukaryotic cells, the
citric acid cycle takes place in the matrix of the mitochondria.
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21. STEPS IN CITRIC ACID CYCLE
1 FORMATION OF CITRATE
• The first reaction of the cycle is the condensation of acety Coa with
Oxaloacetate to form citrate the reaction is catalyzed by citrate
synthase
• Citrate is a tricarboxylic acid, and the Krebs cycle is also known as the
tricarboxylic acid (or TCA) cycle
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22. 2 Formation of Isocitrate via cis-Aconitate
• The enzyme aconitase catalyzes the reversible transformation
of citrate to isocitrate, through the intermediary formation of
the tricarboxylic acid cis-aconitate, which normally does not
dissociate from the active site. Aconitase can promote the
reversible addition of H2O to the double bond of enzyme-
bound cis-aconitate in two different ways, one leading to
citrate and the other to isocitrate
• Aconitase contain iron sulfur center which acts both binding
of the substrate at the active site in the catalytic or removal
of water
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23. Cont........
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24. 3 Oxidation of Isocitrate to ∝-Ketoglutarate and CO2
• isocitrate dehydrogenase catalyzes oxidative decarboxylation of
isocitrate to form 𝛼 –ketoglutarate
• Mn2 in the active site interacts with the carbonyl group of the
intermediate oxalosuccinate
• There are two different forms of isocitrate dehydrogenase in all cells, one
requiring NAD+ as electron acceptor and the other requiring NADP+. The
overall reactions are otherwise identical.
• In eukaryotic cells, the NAD-dependent enzyme occurs in the
mitochondrial matrix and serves in the citric acid cycle. The main
function of the NADP-dependent enzyme, found in both the
mitochondrial matrix and the cytosol, may be the generation of NADPH,
which is essential for reductive anabolic reactions
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25. Cont ……….
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26. 4 Oxidation of -Ketoglutarate to Succinyl-CoA and CO2
• oxidative decarboxylation, in which ∝-ketoglutarate is
converted to succinyl-CoA and CO2 by the action of the 𝛼-
ketoglutarate dehydrogenase complex;
• NAD+ serves as electron acceptor
• CoA as the carrier of the succinyl group
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27. Cont……..
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28. 5 Conversion of Succinyl-CoA to Succinate
• Its catalyzed by succinyl COA synthetase or succinic thiokinase
• GTP (guanosine triphosphate ) is formed from phosphoryl group with
higher group transfer potential GDP (guanosine diphosphate)
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29. 6 Oxidation of Succinate to Fumarate
• The succinate formed from succinyl-CoA is oxidized to fumarate by
the flavoprotein succinate dehydrogenase:
• In eukaryotes, succinate dehydrogenase is tightly bound to the inner
mitochondrial membrane;
• in prokaryotes, to the plasma membrane.
• Electrons pass from succinate through the FAD and iron-sulfur enters
before entering the chain of electron carriers in the mitochondrial
inner membrane (or the plasma membrane in bacteria)
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31. 07 HYDRATION OF FUMARATE TO MALATE
• The reaction is catalyzed by fumerase
• The transition state in their reaction is carbanion “meaning there are
intermediate until to malate”
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32. 8 Oxidation of Malate to Oxaloacetate
• the last reaction of the citric acid cycle, NAD-linked L-malate
dehydrogenase catalyzes the oxidation of L-malate to oxaloacetate
• Malate is oxidized to produce oxaloacetate, the starting compound of
the citric acid cycle by malate dehydrogenase. During this oxidation,
NAD+ is reduced to NADH + H+
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33. Citric acid cycle
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35. REFERENCE
• Brock Biology of Microorganisms 15th edition, Michael T. Madigan,
John M. Martinko, David A. Stahl, David P. Clark.
• Lehninger PRINCIPLES OF BIOCHEMISTRY Fourth Edition by David L.
Nelson (University of Wisconsin–Madison) and Michael M. Cox
(University of Wisconsin–Madison)
• https://microbiologyinfo.com/glycolysis-10-steps-explained-steps-by-
steps-with-diagram/
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