GLYCOLYSIS1 375KB Nov 04 2011 08:36:35 AM

The first step of cellular respiration
What the [email protected] is Glycolysis?
 The word glycolysis is constructed from glycose,
an older term for glucose, and –lysis, which means
breakdown. (Greek for “sugar splitting”)
 The metabolic pathway that converts glucose,
C6H12O6 into pyruvate, CH3COCOO− + H+.
 The products formed are adenosine
triphosphate (ATP), and nicotinamide adenine
dinucleotide (NADH)
The 10 Steps of Glycolysis
 Glycolysis is split up into 10 different steps.
 In the first 3 steps, energy in the form of ATP is
invested to be reused later.
 In the next 2 steps, the energy allows glucose to be
split into 2 smaller molecules.
 In the last 5 steps, energy is released as ATP and
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Step 1: ATP phosphorylates glucose
 Hexokinase is an enzyme that uses ATP to
phosphorylate glucose.
This investment of energy prepares glucose for
releasing energy later on.
Results in Glucose 6-phosphate.
ADP is released.
Step 2: G6P rearranged to F6P
 The enzyme phosphoglucose isomerase catalyzes the
opening of the ring form of G6P into the open ring
 Carbonyl group of G6P changes position from the 1st to
the 2nd carbon on the chain.
 Fructose 6-phosphate is formed by this reaction.
 Phosphoglucose isomerase catalyzes F6P into its ring
G6P to
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Step 3: ATP phosphorylates F6P to
F 1, 6-BP
 Enzyme phosphofructokinase uses ATP to
phosphorylate F6P.
 ADP is released, and the molecule fructose 1, 6bisphosphate is formed.
 Steps 1-3 all include an investment of energy in the
form of ATP that will be repaid in the later steps of
F6P to
Step 4: Splitting up F 1, 6-BP
 Begins with the opening of the ring for of F 1, 6-BP into
the open chain form.
 The enzyme aldolase cleaves F 1, 6-BP into 2
 One molecule formed is glyceraldehyde 3phosphate.
 The other molecule formed is dihydroxyacetone
Cleaving the Hexose Ring
Step 5: DHAP converted to G3P
 The enzyme triophosphate isomerase catalyzes the
isomerization of dihydroxyacetone phosphate (DHAP)
into G3P.
 This reaction is similar to step 2.
 Result is 2 molecules of G3P.
 These 2 steps break down the molecules formed in the
first 3 steps into smaller molecules.
Step 6: BPG and NADH
 Steps 6-10 are the energy generating steps of
 NAD+ is used to oxidize G3P
 An inorganic phosphorus bond is connected to the
molecule to form 1,3 biphosphoglycerate.
 Hydrogen atoms reduce NAD+ to NADH
G3P to BPG
Step 7: BPG to 3PG
 The high energy phosphate group in BPG is
 The phosphate group is transferred to ADP, which
becomes ATP
 The 3 carbon molecule is now 3-phosphoglycerate.
 Reaction occurs twice, 2 ATP molecules generated.
The energy usage has been paid back.
BGP to 3GP
Step 8: 3PG rearranged to 2PG
 3-phosphoglycerate is transformed by an enzyme into
3GP to 2PG
Step 9: 2PG converted into PEP
 Enzyme removes a water molecule from 2-
phosphoglycerate, creating phosphoenolpyruvate.
 The loss of the water molecule redistributes the energy
within the molecule.
 Creates phosphate group with high free energy of
2PG to PEP
Step 10: PEP converted to pyruvate
 Enzyme transfers the phosphate group from PEP into
ADP, creating ATP and pyruvate.
PEP to Pyruvate
 In the first part of glycolysis, ATP is invested to be used
 In the second part, the bigger molecules are split up
into smaller ones.
 In the third part, many of the reactions release energy
in the form of ATP and NADH.
 Net energy: 2 ATP molecules and 2 NADH molecules.
 Mitochondria (singular: mitochondrion) sausage
shaped organelles that are usually scattered
through a cell’s cytoplasm.
 Glycolysis takes place in the cytoplasm.
 Pyruvate oxidation, the Krebs cycle, and electron
transport and chemiosmosis take place in the
 Only eukaryotic cells contain mitochondria
 Mitochondria possess a double membrane; a
smooth outer membrane and a folded inner
 Folds of inner membrane called cristae
 Mitochondrial matrix is a protein-rich liquid
filling the innermost space of a mitochondrion.
 Mitochondrion possess their own DNA, called
mtDNA, RNA, and ribosomes.

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