GENBIO ☻ Cellular Respiration (Aerobic)
I.
Aerobic Respiration
METABOLIC PATHWAYS:
CATABOLIC PATHWAYS → release stored energy
by breaking down complex molecules.
→ oxygen is consumed as a reactant; it is considered
as the most effective and efficient.
ANABOLIC PATHWAYS → small molecules are
assembled into large ones. Energy is required.
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Release energy to create more energy
Three main processes of Aerobic Respiration:
1. GLYCOLYSIS
a. converts 1 glucose molecule →
2 pyruvate
molecules = releases a small amount of energy.
b. Pyruvate is passed along to a mitochondrion and
cytoplasm of the cell where the oxidation
continues.
AEROBIC RESPIRATION → uses oxygen as a
reactant.
→ considered the most effective and efficient in
producing energy in the form of ATP.
c.
Mitochondrion completes the enzymatic burning
of glucose by passing the compounds through the
Kreb cycle.
more efficient than anaerobic bc more ATP
produced, in anaerobic there is too much lactic
acid.
Reaction:
Organic compound + oxygen = CO2 + H2O + Energy
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Oxygen is something that would break the
organic compound.
→ occurs between both animals and plants.
→ for animals (respiration), glucose from food
molecules are turned into ATP in the cells Cytoplasm
and Mitochondria.
→ for plants (photosynthesis), the reaction requires
CO2 and sunlight to make food molecules in
chloroplasts and release oxygen as waste.
2. CITRIC ACID CYCLE (Kreb cycle)
a. Energy-enriched compounds are created,
then it passes these compounds to the
Electron transport chain (NADH and
FADH2) or Oxidative phosphorylation.
3. OXIDATIVE PHOSPHORYLATION
→ uses electronic gradients to produce ATP
Glycolysis → Citric Acid Cycle
→ requires enzyme and substrate reaction
→ the energy of the enzyme and substrate interaction
leads to production of ATP via substrate-level
phosphorylation.
11HA21_KIT ★
GENBIO ☻ Cellular Respiration (Aerobic)
Glycolysis
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Goal: breakdown glucose → two pyruvates.
Location: Cytosol (outside the mitochondria)
(goal1) Produced: 4 ATP, 2 Pyruvate, and 2
NADH; used: 2 ATP
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phosphate group can be found in the 6th carbon
of glucose). The charge in the phosphate
molecule traps the sugar in the cell.
“Magnesium” is the cofactor
STEP 2
Three phases of Glycolysis:
1. ENERGY INVESTMENT PHASE → the cell
spends (2) ATP.
2. CLEAVAGE → it is the splitting of sugar.
3. ENERGY PAYOFF PHASE
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→ when ATP is
Glucose-6-phosphate is converted to its
isomer (Fructose-6-phosphate) with the enzyme
Phosphoglucose-isomerase.
produced by substrate-level phosphorylation and
NADH+ is reduced to NADH (pays off the used 2
ATPS) by electrons released through the
oxidation of glucose.
ISOMER → are molecules with the same chemical
Net energy yield from Glycolysis per glucose
molecule = 2 ATP, 2 NADH molecules
STEP 3
formula but different structures.
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10 steps of Glycolysis:
A. INVESTMENT
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STEP 1
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Phosphofructokinase transfers a phosphate
group from ATP to the first carbon of Fructose
6-phosphate.
This is the second ATP invested.
Resulting product is Fructose 1,6
bisphosphate (it’s like this because you have
phosphate groups for carbon 1 and carbon 6 of
fructose molecules).
This reaction is a key step for the regulation of
glycolysis.
B. CLEAVAGE
STEP 4
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First, we have a glucose molecule.
Then, Hexokinase transfers the phosphate
group from ATP to the 6th carbon of glucose.
By doing that, it invests in the first ATP.
That whole reaction will produce Glucose-6phosphate (it is written like that, because the
11HA21_KIT ★
GENBIO ☻ Cellular Respiration (Aerobic)
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Aldolase splits Fructose 1,6-bisphosphate
into two different carbon sugars:
Dihydroxyacetone (DHAP) and
Glyceraldehyde 3-phosphate (G3P).
G3P immediately proceeds to step 6, DHAP
needs to be converted to G3P first in step 5.
STEP 5
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Conversion of DHAP to G3P with the enzyme
triose phosphate isomerase.
This reaction never reaches equilibrium.
Upon the reaction between the two, G3P is then
used in the next step.
STEP 7
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Two molecules are produced from 1,3
bisphosphoglycerate through substrate level,
phospho-relation and an exergonic reaction.
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The carbonelle group of G3P has been oxidized
via phosphoglycerate to the carboxyl group of
3-phosphoglycerate.
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Because of this, the two ATPs invested earlier
C. ENERGY HARVEST
STEP 6
● The two G3P molecules enter the pay-off phase,
all enzymes and products here will be doubled.
● Triose phosphate dehydrogenase catalyze
two reactions:
are already paid-off (+2 ATP) → net ATP = 0.
STEP 8 (walang-kwentang step)
a. Sugar (H) is oxidized by the transfer of electrons
to NAD + forming NADH ( +2 NADH)
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NAD+ → NADH (reduction - gaining electrons)
Phosphate group in 3-phosphateglycerate is
relocated to its second carbon by
phosphoglycerate mutase.
This transforms the molecule into two
phosphoglycerates.
STEP 9
b. A phosphate group is attached to the oxidized
substrate (of inorganic phosphate) making 1,3bisphosphoglycerate.
11HA21_KIT ★
GENBIO ☻ Cellular Respiration (Aerobic)
Why do we use ATP when we can use energy
stored in bonds?
When Glucose is converted to ATP it is better
because Phosphate bonds when broken gives more
energy and is less stable, allowing it to be easily
broken.
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Enolase causes a double bond to form in the
substrate by extraction of water.
Which yields Phosphoenolpyruvate (PEP), a
compound with a very high potential energy.
STEP 10
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The last phosphate group is transferred from
PEP to ADP.
PRE-CITRIC ACID CYCLE: PYRUVATE
OXIDATION
→ Follows Glycolysis
→ Pyruvate is carried from Cytosol to the
mitochondria via active transport.
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From the Cytosol to the Mitochondria, the
pyruvate should be converted to a Acetyl CoA.
In doing that, decarboxylation happens by
removing a molecule of carbon dioxide and
converting NAD+ to NADH which is helped by
Coenzyme A. After doing that we have our final
product = Acetyl CoA
This produces two more molecules of ATP (+2)
The release of the phosphate group transforms
the molecule into Pyruvate.
The enzyme that catalyzes this process would
be Pyruvate kinase.
IMPORTANT CONCEPTS
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Enzymes with “kinase” → have a relation to ATP.
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Enzymes with “isomerase” → have the same
formulas but different shapes
➔ Steps 1 & 3 - used ATP
➔ Steps 7 &10 - made ATP
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DAP & G3P - they are the same thing.
The body will ONLY use G3P.
To know if an isomerase is a triose phosphate
isomerase, you count the carbons and check if
the function is the same even if the shape is
different.
To know if a dehydrogenase was used, check if
there was any hydrogen removed.
Why do we need Acetyl CoA?
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Delivers the Acetyl group from the pyruvate
to the next stage → Citric Acid Cycle
CITRIC ACID CYCLE (“Kreb’s Cycle, “Tricarboxylic
Acid (TCA) Cycle”)
→ happens in the Mitochondrial Matrix
11HA21_KIT ★
GENBIO ☻ Cellular Respiration (Aerobic)
→ the sort of “heater” that oxidizes fuel (combines
oxygen) from pyruvate.
STEP 2
● Citrate will now be converted to Isocitrate by
the enzyme Aconitase.
● This whole reaction is called dehydration
reaction or Isomerization because Isocitrate is
the Isomer of Citrate.
Net Yield/Final Products :
1. 3 NADH
2. 1 FADH2
3. 1 ATP and/or GTP
STEP 1
● We start with the molecule Oxaloacetate. With
Citrate synthase, we will be able to create
Citrate.
● This
whole
reaction
is
called
Aldol
Condensation and Hydrolysis.
STEP 3
● The enzyme Isocitrate dehydrogenase will
undergo oxidative decarboxylation (redox)
where NAD+ is converted to NADH.
● With this NADH, we have our new product =
Alpha-Ketogluterate.
● In this step, we got our FIRST NADH
MOLECULE.
11HA21_KIT ★
GENBIO ☻ Cellular Respiration (Aerobic)
STEP 6
● Succinate will be helped by the enzyme
Succinate dehydrogenase. It will undergo
Redox reactions to convert FAD into FADH2
● By this reaction, Succinate is converted to
Fumarate.
STEP 4
● Alpha-Ketoglutarate, with the enzyme AlphaKetoglutarate dehydrogenase complex will go
through the oxidative decarboxylation again.
● With this we get our SECOND NADH
MOLECULE.
● With this reaction, Alpha-Ketoglutarate is now
converted to Succinyl-CoA
STEP 5
● Succinyl-CoA, with the enzyme Succinyl CoA
synthase, we can get our FIRST GTP.
● GTP will undergo Phosphorylation where it will
be converted to an ATP molecule.
● After these reactions, Succinyl CoA will be
converted to Succinate.
STEP 7
● Fumarate with the help of the enzyme
Fumarase will undergo hydration reactions,
which is why H2O is present, to convert it to
Malate.
STEP 8
● Malate with the help of the enzyme Malate
dehydrogenase will undergo redox reaction and
give us our LAST NADH.
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The main goal of this step is to convert Malate →
Oxaloacetate.
11HA21_KIT ★
GENBIO ☻ Cellular Respiration (Aerobic)
IMPORTANT CONCEPTS
Why do we need Acetyl CoA?
● Not a straight line, it is a series of molecules
● GTP - guanine triphosphate
● When GTP meets ADP, ADP steals a phosphate
to become ATP. When it does not encounter
GTP, it will just be ADP.
● Citrate is the starting substrate to start the
cycles.
● For this cycle, you can start anywhere.
● Alpha-ketoglutarate dehydrogenase complex
Phase 1: ELECTRON TRANSPORT CHAIN
→ No ATP is generated YET.
→ This phase involves:
1.
2.
3.
4.
NADH Dehydrogenase
Succinate Dehydrogenase
Cytochrome-C Oxidoreductase
Cytochrome Oxidase
Aided by another protein → Coenzyme Q or
→ add hydrogen, remove hydrogen. Then
Ubiquinone
remove carbon.
Cytochrome C - Cyto C
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Affinity of molecules - meaning mas fit siya
don.
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OXIDATIVE PHOSPHORYLATION
● Goal: ATP Generation
● Location: Inner membrane of Mitochondria
Net Yield = 10 NADH and 2 FADH2
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NADH and FADH2 releases Hydrogen Ions and
high-energy electrons.
Four proteins’ main goal is to release a
hydrogen Ion outside the intermembrane
space.
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Which is, based on the figure above, going up.
→ Phase 1: ELECTRON TRANSPORT CHAIN
→ Phase 2: CHEMIOSMOSIS
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Organization is maintained by using energy to
catalyze chemical reactions which are known as
metabolisms.
Electron transport chain (has 4 protein
complexes) and Chemiosmosis (has protein,
ATP Synthase)
1. NADH Dehydrogenase
● Start with an NADH molecule that will
undergo the reaction Dehydrogenation.
● By the end of the reaction, it will be able to
release four hydrogen Ions.
11HA21_KIT ★
GENBIO ☻ Cellular Respiration (Aerobic)
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The electrons will be carried out by
Coenzyme Q leading it to protein number 2.
2. Succinate Dehydrogenase
● does not pass through the cell membrane
● is the smallest of the four.
● it doesn’t effectively release a hydrogen Ion.
● With this, the Coenzyme Q will just move
the electron to the third enzyme.
3. Cytochrome-C Oxidoreductase
● A redox reaction will happen, where four
hydrogen Ions will be released.
● The cytochrome C will pass on the electron
to the last protein.
4. Cytochrome Oxidase
● Oxidation will happen and it will only give 2
hydrogen ions .
● Only 2 ions were released because we have
a byproduct of water, water is made of
H2O, so the other 2 ions were used for
that.
NOTES:
● Electrons were passed on from protein to
protein, this is why it is called Electron
Transport Chain
● No ATP is generated yet, but we get important
products such as hydrogen ions.
● We have a total of 10, 4 from protein 1 and 2,
then 2 from protein 2.
Phase 2: CHEMIOSMOSIS
→ When energy stored in the form of hydrogen ions
is used to deliver cellular work, like the making of
ATP.
→ Only 1 enzyme is involved: ATP Synthase whose
job is to make ATP from ADP
STEP 1: Hydrogen ions will flow down from the
intermembrane space entering the Stator.
STEP 2: The shape of the ions will change once it
enters the rotor.
STEP 3: The ions make one complete turn before
leaving the rotor. It transfers back into a second
channel in the rotor which serves as entry to the
mitochondrial matrix.
STEP 4: As it spins, the knob below it starts to spin
as well.
11HA21_KIT ★
GENBIO ☻ Cellular Respiration (Aerobic)
STEP 5: Which finally leads to ATP synthesis.
Net Yield: 28 ATP
^ This follows the formula in which 4 hydrogen
atoms will be converted to 1 ATP.
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Oxidative phosphorylation is not included
because it allows the conversion of hydrogen
ions NADH, FADH2 into ATP.
The total net yield is a range because it depends
on the shuttle that transports NADH into the
mitochondria.
IMPORTANT CONCEPTS
Osmosis - like diffusion
Oxidative - loss of electron
O2 - stable
O - unstable
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