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CELLULAR RESPIRATION
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CONCEPT
GLYCOLYSIS
LINK REACTION
KREB’S CYCLE
ELECTRON TRANSPORT CHAIN
CHEMIOSMOSIS
ALTERNATIVE PATHWAYS
ANAEROBIC REACTION
AEROBIC REACTION
GLYCOLYSIS
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Location – cytosol
•
Biochemical pathway
1 Glucose (6C)  2 Pyruvates (3C)
•
Names and structures of enzymes involved not
required except hexokinase and
phosphofructokinase)
•
Net production of 2 ATP and 2 NADH
•
Glyco= sweet, sugar;
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Catalysed by specific enzymes dissolves in
cytosol
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Occurs whether or not O2 is present
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2 phase:
lysis = split
– Energy Investment Phase (2 ATP used)
– Energy Yielding Phase (4 ATP and 2 NADH are
produced)
How many net ATP produced?
Phosphorylation
• ATP is used to phosphorylate other substrate
ATP
Substrate
ADP
Substrate
P
• Phosphorylation – adding of phosphate group
into a molecule making them chemically
active
GLYCOLYSIS
ENERGY INVESTMENT PHASE
STEP 4~splitting
STEP
STEP
1~
2~
phosphorylation
isomerization
STEP
3~ phosphorylation
STEP
5~isomerization
•Fructose-1,6•C6
of glucose ~is an is
•Isomerization
•C1 of fructose-6-phosphate
diphosphate
is splitcatalyses
phosphorylated
•Isomerase
isomerasethe
catalyses the
phosphorylated
into tworeversible
isomeris
3C
•catalysed
by hexokinase
conversion
rearrangement
of glucose-6•requires
anotherproducing
ATP
sugar produces:
an
two G3P’s
phosphate
to ATP
its isomer,
•produce•requires
fructose-1,6-diphosphate
dihydroxyacetoneph
•makes
glucose chemically
fructose-6-phosphate
osphate (DHAP) & reactive
glyceraldehydes-3- •produces glucose-6phosphate (G3P) phosphate
GLYCOLYSIS
ENERGY PAYOFF PHASE/
ENERGY YEILDING PHASE
Step
6: 7
STEP
STEP 10
8
STEP
& phosphorylation
Phoshate
Substrate-level
group oxidation
Substrate-level
phosphorylation
translocation •Glyceraldehyde-3-phosphate
phosphorylation
(G3P) is oxidized & NAD+ is
•A phosphate
•ATP
is produced
group
byreduced
•ATP is
produced
by
+
to NADH + H
on C3 is transferred
substrate
level
substrate-level
•For
each glucose molecule, 2
Step 9:
to C2
phosphorylation
phosphorylation
NADH
are produced
Removal of
water
•Produce
•A
phosphate
group
•For each glucose
•Glyceraldehyde-3-phosphate
molecule
is then 2
phosphorylated
2-phosphoglycerate
is
transferred
from (G3P)
molecule,
ATP are
onproduced
C1
•Creates
a double bond
PEP to ADP
•The
phospate
source
is
between
C1
&
C2
of
the
•For each glucose
•Produce
inorganic phosphate (not ATP!),
substrate
molecule, 2 ATP are which
3-phosphoglycerate
present in the cytosol
•Produce
produced
•Produce
phosphoenolpyruvate
•Produce pyruvate 1,3-diphosphoglycerate
(PEP)
(3C)
Oxidative Decarboxylation
LINK REACTION
(FORMATION OF ACETYL COA)
1. Decarboxylation – Pyruvate (3C) is converted into 2C molecule
by removing one CO2
2. Reduction – pyruvate is reduced producing 2 H+, NAD+ accept
H+ and becomes NADH + H+
3. The 2C compound called acetyl attaches to coenzyme A and
form acetyl CoA
KREB CYCLE
REDOX
• Oxidation and reduction at the same time
• AH + B  A + BH
• A is oxidized
• B is reduced
STEP
STEP4:5:OXIDATIVE
SUBSTRATE
DECARBOXYLATION
LEVEL
PHOSPHORYLATION
• -Ketoglutarate removes CO2 =
• Succinyl
decarboxylation
CoA is converted to
4C 7: HYDRATION
STEP
Succinate
NAD+ is reduced to NADH + H+ =
Water is added to Fumarate which
•
ATP
dehydrogenation/oxidation
produces
=
Substrate level
STEP 3: OXIDATIVE DECARBOXYLATION
rearranges the chemical bondsSTEP
to form
6: 4C
phosphorylation
Malate
DEHYDROGENATION/OXIDATION
•
Attachment
of
CoA
to
form
4C
Succinyl
2 major events:
• Breakdown
CoA (high energy
of Succinyl
bond).
CoA is
STEP 8:
•
Succinate
is oxidized to 4C
coupled
to
the
phosphorylation
of
DEHYDROGENATION/OXIDATION
• Isocitrate loses CO2 leaving a 5C
Fumarate and FAD is reduced.
GDP
to
GTP.
STEP
2:
ISOMERIZATION
compound = decarboxylation.
STEP 1: ENTRY OF ACETYL
GROUP
Malate
is oxidized and NAD+ is
•to
2H are transferred to FAD to form
•
GTP
then
transfers
its
phosphate
•
Citrate
is
rearranged
by
two
reactions.
reduced
to
NADH
+ H+
• 5C compound is oxidized and NAD+ is
FADH2
• Unstable
bond attaching the Acetyl group to CoA breaks.
ADP
to+ form
reduced to NADH
H+ toATP.
produce 5C •The first reaction,
is removed.
4C water
Oxaloacetate
is regenerated.
ketoglutarate = dehydrogenation/oxidation.
• 2C Acetyl CoA becomes attached to a 4C Oxaloacetate,
•Then water is added.
• Forming 6C Citrate.
•Through these two reactions Citrate is
• CoA is free
to combine
another
2C Acetyl group.
converted
to itswith
isomer,
6C Isocitrate
• The process is repeated.
STEP 1
•The unstable bond
attaching the acetyl
group to CoA breaks.
•The 2C Acetyl CoA
becomes attached to a
4C oxaloacetate
molecule,
•Forming citrate, a 6C
molecule with 3
carboxyl groups.
•CoA is free to combine
with another 2C group.
•The process is
repeated
STEP 2
•The citrate is
rearranged by two
preparation reactions.
•The first reaction,
water is removed.
•Then water is added.
•Through these two
reactions citrate is
converted to its isomer,
isocitrate
STEP 3
•Isocitrate loses CO2
leaving a 5C compound
(decarboxylation).
•The 5C compound is
oxidized and NAD+ is
reduced to NADH + H+
to produce ketoglutarate
(dehydrogenation)
STEP 4
•-Ketoglutarate
undergoes
decarboxylation
(removal of CO2)
•and dehydrogenation
(NAD+ is reduced to
NADH + H+)
•Attachment of CoA to
form 4C compound,
succinyl CoA (high
energy bond).
STEP 5
•Succinyl CoA is
converted to succinate
•Substrate level
phosphorylation takes
place (ATP produced).
•The breakdown of
succinyl CoA is coupled
to the phosphorylation
of GDP to GTP.
•GTP then transfers its
phosphate to ADP to
form ATP
STEP 6
•Succinate is oxidized to
fumarate and FAD is
reduced.
•2H are transferred to
FAD to form FADH2
STEP 7
•Water is added to
fumarate which
rearranges the chemical
bonds to form malate
STEP 8
•Malate is oxidized and
NAD+ is reduced to
NADH + H+
•Oxaloacetate is
regenerated
SUBSTRATE LEVEL PHOSPHORYLATION
Only few ATPs are directly produced by this
Phosphorylation.
2 net ATP per glucose from Glycolisis
2 ATP per glucose in Krebs cycle
1. At the end of Krebs cycle, most energy
extracted from glucose is in molecules of
6 NADH + H+ and 2 FADH2
2. These reduced compounds link glycolisis and
Krebs Cycle to ETC by passing those
electrons down to ETC to O2.
3. The transfer of electrons to O2 is exergonic
leads to the formation of ATP
• NAD+ + H+ + 2e-  NADH
(NAD is reduced, substrate is oxidized)
• NADH  NAD+ + H+ + 2e(NAD is oxidized, substrate is reduced)
FOR 1 GLUCOSE....
GLYCOLYSIS
• 2 net ATP produced
• 2 NADH  enter mitochondria as NADH/FADH
(depend on the type of shuttles)
• Malate-aspetate shuttle: NADH
• Glycerol-phosphate shuttle: FADH2
Malate-aspertate shuttle
Glycerol-phosphate shuttle
FOR 1 GLUCOSE....
GLYCOLYSIS
• 2 net ATP produced
• 2 NADH  enter mitochondria as NADH/FADH
KREB CYCLE
• 6 NADH (3X2 , 2 pyruvate)
• 2 FADH (1X2, 2 pyruvate)
• 2 ATP (1X2, 2 pyruvate)
In Electron Transport Chain,
• 1 molecule of NADH will generate 3 ATP
• And 1 molecule of FADH2 will generate 2 ATP.
PROCESS
GLYCOLYSIS
LINK REACTION
KREB CYCLE
TOTAL
PRODUCT
ATP
2 ATP
2 ATP
2 NADH /FADH
6 ATP
2 NADH
6 ATP
6 NADH
18 ATP
2 FADH
4 ATP
2 ATP
2 ATP
38 ATP
/ 4 ATP
/ 36 ATP
Intermembrane
space
ATP
Synthase
FADH2
Complex I
CoQ
Complex II
Complex III
Cyt C
Complex IV
FAD
: NADH Dehydrogenase
: Coenzyme Q
: Succinate Dehydrogenase
: Cytochrome bc1
: Cytochrome C
: Cytochrome c Oxidase
Intermembrane
space
ATP
Synthase
FADH2
FAD
1. NADH + H+ oxidizes, transfer H+ and 2e to complex I
Intermembrane
space
ATP
Synthase
FADH2
FAD
2. The transfer of electron cause complex I to pump H+ to
intermembrane space
Intermembrane
space
ATP
Synthase
FADH2
FAD
3. Complex I then transfer e to CoQ, a lipid soluble mobile electron
carrier
Intermembrane
space
ATP
Synthase
FADH2
FAD
4. CoQ transfer e to complex III
Intermembrane
space
ATP
Synthase
FADH2
FAD
5. This transfer of e cause complex III to pump H+ to
intermembrane space
Intermembrane
space
ATP
Synthase
FADH2
FAD
6. Complex III then transfer e to cyt c, another mobile e carrier
Intermembrane
space
ATP
Synthase
FADH2
FAD
7. Cyt c transfer e to complex IV, again H+ is pumped to
intermembrane space
Intermembrane
space
ATP
Synthase
FADH2
FAD
8. Complex IV lastly transfer e to O2 (last e acceptor)
Intermembrane
space
ATP
Synthase
FADH2
FAD
9. O2 acccept 4e with 4H+ and becomes 2 water molecules
O2 + 4e- + 4H+  2H2O
Intermembrane
space
ATP
Synthase
FADH2
FAD
REMEMBER: complex I, III and IV has been pumping H+ to the
intermembrane space!
This create a H+ gradient: H+ concentration in intermembrane
space higher than in matrix.
Intermembrane
space
ATP
Synthase
FADH2
FAD
This concentration gradient switch on the ATP synthase for
CHEMIOSMOSIS.
H+ will be pumped back to matrix. This pumping generate ATP
ATP synthase add inorganic phosphate (Pi) to ADP  ATP
Intermembrane
space
ATP
Synthase
FADH2
FAD
How about complex II?
Complex II undergo the same process but only accepts H+ from
FADH2,
Complex II is a peripheral proteins, it cant pump H+
Intermembrane
space
ATP
Synthase
FADH2
FAD
Complex II except e from FADH2, pass it to CoQ and then to
complex III
FADH2 will not encounter complex I, thus, for FADH2, H+ will be
pumped twice.
Cellular respiration
ANAEROBIC AND ALTERNATIVE
PATHWAY
ANAEROBIC RESPIRATION & OTHER
MACROMOLECULES METABOLIC PATHWAYS
OBJECTIVES:
1. DEFINITION OF ANAEROBIC RESPIRATION.
2. DIFFERENCES BETWEEN AEROBIC AND ANAEROBIC
RESPIRATION.
3. PRODUCTS OF GLYCOLISIS.
4. FERMENTATION – LACTIC ACID & ETHANOL
FORMATION.
5. IMPORTANCE OF FERMENTATION IN INDUSTRY
6. OTHER MACROMOLECULES METABOLIC PATHWAYS.
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Overview of Glucose Catabolism
1. Anaerobic Respiration
– In the absence of
oxygen, some
organisms can still
respire anaerobically,
using inorganic
molecules to accept
electrons.
• Methanogens
• Sulfur Bacteria
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Fig. 9.9
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RELATED METABOLIC PROCESSES
1. FERMENTATION
● enables some cells to produce ATP without
the presence of O2.
● anaerobic catabolism of organic nutrients.
► Oxidizing agent : NAD+ , not O2.
► Involves glycolisis followed by
pyruvate
reduction by NADH.
► Result: 2 ATPs.
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Anaerobic Routes of ATP Formation
• Fermentation pathways
– Bacteria, yeasts and
protistans
– Intensive Exercising
• Glycolysis - first step
• Net yield of two ATP
• Final product is lactate or
ethanol
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LACTIC ACID FERMENTATION
1. Intensive exercising, O2 is scarce, human
muscle cells switch from aerobic respiration
to lactic acid fermentation.
● Lactate accumulates.
● Gradually it is carried to liver, to be
converted back to pyruvate when O2
is available. (O2 Debt)
2. Commercial Importance: cheese production,
yoghurt.
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Lactate Fermentation
• Muscle cells in
animals
• Quick ATP
production
• Some bacteria
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ALCOHOL FERMENTATION
1.
2.
3.
4.
5.
Pyruvate loses CO2.
Pyruvate is converted to 2C Acetaldehyde.
NADH is oxidized to NAD+.
Acetaldehyde is reduced to ethanol.
Examples: Yeast, Bacteria
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Alcohol Fermentation
• Acetaldehyde
is intermediate
product
• Yeasts
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FERMENTATION & RESPIRATION: COMPARISON
1. Similarity:
● Both use glycolisis to oxidize glucose and
other substrates to pyruvate.
● Produce 2 ATPs by substrate-levelphosphorylation.
● Use NAD+ as oxidizing agent in
glycolisis.
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2. Differences:
● Fermentation produce NAD+ during the
reduction of pyruvate to form lactate or
ethanol and CO2.
● Aerobic respiration produce NADH during
the oxidation of intermediates.
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3. Final electron acceptor:
● Fermentation: pyruvate acts as the final
electron acceptor.
● Cell respiration: O2 is the final electron
acceptor.
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4. Amount of energy harvested:
● Fermentation yields net 2 ATPs by
substrate- level phosphorylation.
● Cell respiration: 18 times more by
substrate-level phosphorylation and
oxidative phosphorylation.
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5. Requirement of O2:
● Fermentation does not require O2.
● Cell respiration occurs only in the
presence of O2.
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6. Occurrence:
● Fermentation happens in cytosol.
● Cell Respiration occurs in cytosol and
mitochondria.
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OTHER METABOLIC PATHWAYS
1. Glycolisis and Krebs
Cycle can connect to
many other metabolic
pathways.
2. Cell respiration can
oxidize organic
molecules other than
glucose to make ATP.
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Fig. 9.21
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1. PROTEINS
- hydrolyzed to amino acids.
2. Excess Amino Acids
- enzymatically converted to intermediates
of
glycolisis & Krebs Cycle. (Pyruvate,
Acetyl CoA, -ketoglutarate).
3. This conversion
deaminates amino acids, nitrogenous
waste are excreted & carbon skeleton can
be oxidized.
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1. FATS
- rich in hydrogens. (high energy electrons)
2. Oxidation of 1 g of fat
produces 2 times more ATP than 1 g of
Carbohydrate.
3. Fats- digested into glycerol and fatty acids.
4. Glycerol can be converted into
glyceraldehydes
phosphate (intermediate of glycolisis).
5. Fatty acids – converted into Acetyl CoA by βoxidation.
The 2C compounds enter Krebs Cycle.
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Review
• Chemical Energy Drives Metabolism
• Glucose Catabolism
– Glycolysis
– Pyruvate Oxidation
– Krebs Cycle
– Electron Transport Chain
• Aerobic Respiration Summary
• Energy Storage
• Fermentation
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Raven - Johnson - Biology: 6thFig. 9.11
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• The conversion of
pyruvate and the
Krebs cycle
produces large
quantities of
electron carriers.
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Fig. 9.15
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2002 Pearson Education, Inc., publishing as Benjamin Cummings
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