Anatomy

1. 1
Regulation of Metabolic
Pathways
• Limited number of regulatory enzymes
• Negative feedback
Inhibition
Substrate
1
Substrate
2
Enzyme B Substrate
3
Enzyme C Substrate
4
Enzyme D
Product
Rate-limiting
Enzyme A
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2. 2
4.4: Energy for Metabolic
Reactions
• Energy is the capacity to change something; it is the
ability to do work
• Common forms of energy:
• Heat
• Light
• Sound
• Electrical energy
• Mechanical energy
• Chemical energy

3. 3
ATP Molecules
• Each ATP molecule has three parts:
• An adenine molecule
• A ribose molecule
• Three phosphate molecules in a chain
• Third phosphate attached by high-energy bond
• When the bond is broken, energy is transferred
• When the bond is broken, ATP becomes ADP
• ADP becomes ATP through phosphorylation
• Phosphorylation requires energy release from cellular respiration
Energy transferred
and utilized by
metabolic
reactions when
phosphate bond
is broken
Energy transferred
from cellular
respiration used
to reattach
phosphate
P
P P
P
P P P
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4. 4
Release of Chemical Energy
• Chemical bonds are broken to release energy
• We burn glucose in a process called oxidation

5. 5
4.5: Cellular Respiration
• Occurs in a series of reactions:
1. Glycolysis
2. Citric acid cycle (aka TCA or Kreb’s Cycle)
3. Electron transport system

6. 6
Cellular Respiration
• Produces:
• Carbon dioxide
• Water
• ATP (chemical energy)
• Heat
• Includes:
• Anaerobic reactions (without O2) - produce little ATP
• Aerobic reactions (requires O2) - produce most ATP

7. 7
Glycolysis
• Series of ten reactions
• Breaks down glucose into 2 pyruvic acid molecules
• Occurs in cytosol
• Anaerobic phase of cellular respiration
• Yields two ATP molecules per glucose molecule
Summarized by three main phases or events:
1. Phosphorylation
2. Splitting
3. Production of NADH and ATP

8. 8
Glycolysis
Event 1 - Phosphorylation
• Two phosphates
added to glucose
• Requires ATP
Event 2 – Splitting (cleavage)
• 6-carbon glucose split
into two 3-carbon
molecules
Phase 1
priming
Phase 2
cleavage
Phase 3
oxidation and
formation of
ATP and release
of high energy
electrons
2 ADP
2 NADH + H+
2 NAD+
2 NADH + H+
2 NAD+
P
ATP
P
P
P
Glyceraldehyde
phosphate
Glucose
Dihydroxyacetone
phosphate
2
4 ADP
ATP
4
Fructose-1,6-diphosphate
O2
2 Pyruvic acid
2 Lactic acid
To citric acid cycle
and electron transport
chain (aerobic pathway)
Carbon atom
Phosphate
P
P
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O2

9. 9
Glycolysis
Event 3 – Production of NADH and
ATP
• Hydrogen atoms are released
• Hydrogen atoms bind to NAD+
to produce NADH
• NADH delivers hydrogen atoms
to electron transport system if
oxygen is available
• ADP is phosphorylated to
become ATP
• Two molecules of pyruvic acid
are produced
• Two molecules of ATP are
generated
Phase 1
priming
Phase 2
cleavage
Phase 3
oxidation and
formation of
ATP and release
of high energy
electrons
2 ADP
2 NADH + H+
2 NAD+
2 NADH + H+
2 NAD+
P
ATP
P
P
P
Glyceraldehyde
phosphate
Glucose
Dihydroxyacetone
phosphate
2
4 ADP
ATP
4
Fructose-1,6-diphosphate
O2
2 Pyruvic acid
2 Lactic acid
To citric acid cycle
and electron transport
chain (aerobic pathway)
Carbon atom
Phosphate
P
P
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O2

10. 10
Anaerobic Reactions
• If oxygen is not available:
• Electron transport
system cannot accept
new electrons from
NADH
• Pyruvic acid is
converted to lactic acid
• Glycolysis is inhibited
• ATP production is less
than in aerobic reactions
Phase 1
priming
Phase 2
cleavage
Phase 3
oxidation and
formation of
ATP and release
of high energy
electrons
2 ADP
2 NADH + H+
2 NAD+
2 NADH + H+
2 NAD+
P
ATP
P
P
P
Glyceraldehyde
phosphate
Glucose
Dihydroxyacetone
phosphate
2
4 ADP
ATP
4
Fructose-1,6-diphosphate
O2
2 Pyruvic acid
2 Lactic acid
To citric acid cycle
and electron transport
chain (aerobic pathway)
Carbon atom
Phosphate
P
P
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O2

11. 11
Aerobic Reactions
• If oxygen is available:
• Pyruvic acid is used
to produce acetyl CoA
• Citric acid cycle
begins
• Electron transport
system functions
• Carbon dioxide and
water are formed
• 34 molecules of ATP
are produced per each
glucose molecule
ATP
2
ATP
2
Glucose
Pyruvic acid Pyruvic acid
Acetyl CoA
CO2
2 CO2
Citric acid
O2
H2O
2e–
+ 2H+
Electron transport chain
ATP
32-34
Cytosol
Mitochondrion
High energy
electrons (e–) and
hydrogen ions (H+)
High energy
electrons (e–) and
hydrogen ions (h+)
Oxaloacetic
acid
High energy
electrons (e–) and
hydrogen ions (H+)
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12. 12
Citric Acid Cycle
• Begins when acetyl CoA
combines with oxaloacetic
acid to produce citric acid
• Citric acid is changed into
oxaloacetic acid through a
series of reactions
• Cycle repeats as long as
pyruvic acid and oxygen are
available
• For each citric acid molecule:
• One ATP is produced
• Eight hydrogen atoms are
transferred to NAD+ and
FAD
• Two CO2 produced
Citric acid cycle
ADP +
ATP
Pyruvic acid from glycolysis
Citric acid
(start molecule)
Acetyl CoA
(replenish molecule)
Acetic acid
Oxaloacetic acid
(finish molecule)
Isocitric acid
CO2
CO2
CO2
Succinyl-CoA
Succinic acid
FAD
FADH2
Fumaric acid
Malic acid
Cytosol
Mitochondrion
NADH + H+
NAD+
NADH + H+
NAD+
NADH + H+
NAD+
CoA
CoA
CoA
CoA
P
NADH + H+
NAD+
P
CoA
Carbon atom
Phosphate
Coenzyme A
-Ketoglutaric acid
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