Test 2 Ch 13 and 14 pt.1 Flashcards
Why glucose oxidation occurs in many steps
Burning Glucose All at Once (Diagram A - Left Side)
If glucose were oxidized in a single step (like burning sugar in a fire), a large activation energy would need to be overcome.
The result: All the free energy would be released as heat, meaning no energy would be stored for later use.
This is inefficient for biological systems, as cells need to store energy rather than lose it all as heat.
Stepwise Oxidation in Cells (Diagram B - Right Side)
In cells, glucose oxidation happens gradually through a series of small steps.
Each step has a lower activation energy, which enzymes at body temperature can overcome.
Instead of releasing all energy as heat, some free energy is captured and stored in activated carriers (e.g., ATP, NADH).
This allows cells to use the energy efficiently for biological processes.
formula
Stages of catabolic breakdown of sugars fats and proteins
Stage 1: Breakdown of large food molecules to simple subunits
Stage 2: Breakdown of simple subunits to Acetyl coA; Limited amounts of ATP and NADH produced
Stage 3: Complete oxidation of the Acetyl group in Acetyl CoA to H20 and C02; Large amounts of ATP produced on the inner mitochondrial membrane
Glucose oxidation overrall formula
C6H12O6 + 6O2 –> 6 CO2 + 6 H20+ ~ 32-36 ATP
Glycolysis: splitting of glucose
- Occurs in cytosol
- Doesn’t require oxygen
Products from one
molecule of glucose (6C):
* 2 pyruvates (3C)
* 2 NADH
* 2 ATP (net)
* Pyruvate moves into the
mitochondria only if oxygen
is present
* If no oxygen, pyruvate
undergoes fermentation in
the cytosol
Glyoclysis
Energy investment phase: Two ATP are utilized to split glucose 6C into two molecules of glyceraldehyde-3-phosphate (G3P, 3C)
Energy Generation phase:: G3P is oxidized to pyruvate (3C, 2 per glucose)
- 2 NAD+ are reduced to NADH
- 4 ATP are made from ADP +P, by substrate-level phosphorylation, since 2 ATP were utilized in energy investment phase, net ATP=2
Products per glucose molecule in glycolysis
2 ATP (net), 2 NADH, 2 pyruvate 3C
Oxidation of pyruvate to Acetyl CoA
In mitochondria
*For each pyruvate: (occurs 2X per glucose molecule)-have to multiply everything by two
*Oxidation/reduction reaction:
* Pyruvate is oxidized, NAD+ is reduced.
*Decarboxylation reaction:
* Produces acetyl (2C) and CO2 is released
*Acetyl group linked to Coenzyme A:
* Produces acetyl-CoA (2C)
*All three reactions occur on the pyruvate dehydrogenase
complex
Oxidation of pyruvate to acetly CoA on hw
a. If oxygen is present, pyruvate moves to matrix of mitochondria
b. One carbon is removed from pyruvate to form CO2 and acetate (2C)
c.One NAD+ is reduced to NADH
d. Coenzyme-A is linked to acetate to form acetyl Co-A (2C)
e. These reactions occur on the pyruvate dehydrogenase complex
f. Reaction runs 2x per molecule
Oxidation of pyruvate to acetyl Co-A products per glucose molecule:
2 NADH, 2 acetyl Co-A, and 2 CO2 as waste
Acetyl Co-A enters citric acid cycle
-aka: Krebs Cycle or Tricarboxylic acid cycle (TCA)
* Fed by acetyl-CoA
* For each acetyl-CoA products are
* 2 CO2
* 3 NADH
*1 FADH2
* 1 GTP/ATP
* 1 oxaloacetate
* Occurs 2X per glucose molecule (means multiply everything by two so):
4 Co2
6 NADH
2 FADH2
2 GTP/ATP
2 oxoalcetate
By end of citric cycle all CO2 is gone and oxygen is not used yet
Stages and products of glucose oxidation
Citric Acid cycle (Hw)
a. Occurs in mitochondrial matrix
b. Acetyl-CoA linked to oxoacetate to form citric acid
c. Decarboxylation occurs twice to remove the last two CO2 of Acetyl Co-A
d. 4 redox reactions occur forming 3 NADH and 1 FADH2 per aetyl-coA that enters the cell
e. One ATP is formed by substrate level phosphorylation, which it can pass its terminal phosphate to ADP to for ATP
f. One oxoacetate is regenerated to keep the cycle going
g. Cycle must be completed 2x for each molecule of glucose
Citric acid cycle products per glucose molecule
6 NADH, 2 FADH2, 2 ATP, in addition 4 CO2 is released to atmosphere and 2 oxoalcetate regenerated
Mitochondria structure
Functions of Mitochondria
*Production of ATP
*Regeneration of NAD+
*Make precursors for biosynthesis of nucleotides, amino acids
and fatty acids during citric acid cycle
*Synthesis of heme and iron sulfur clusters for electron
transport
*Cell signaling: buffer Ca2+ concentrations and generation of
some signaling molecules
*Regulation of apoptosis
NADH and FADH2 are oxidized by electron transport
NADH and FADH2 are
activated carriers that
power ATP production
using both an electron
transport chain in which
oxygen acts as the final
electron acceptor and
chemiosmosis =
oxidative
phosphorylation.
Electron Transport Chain
NADH is oxidized to NAD+ (or FADH2 to FAD)
Electron transport is carried out by a series of protein complexes in the inner mitochondrial membrane (Respiratory Enzyme Complexes)
Oxygen is the final electron acceptor.
A proton gradient is established between the intermembrane space and the matrix
This is the only part of glucose oxidation that uses O2 directly
Electrons move by redox reactions
For electrons to move spontaneously must move from better electron donor to better electron acceptor.
Redox pairs are compounds capable of undergoing
oxidation/reduction
NAD+ and NADH
½ O2 and H2O
NADP+ and NADPH
H2C-CH3 and H3C-CH3
Fe3+ and Fe2+
Measuring redox potential half-cell reaction
Electrons move from H2
positive redox
potential, strong
electron acceptor
- Electron move to H+,
negative redox
potential, strong
electron donor - Electrons flow
spontaneously from
materials with more
negative redox potentials to those with more positive redox
potentials.
Standard Free energy in Electron Transport
What is the overall formula for cellular respiration?
C6H12O6 + 6O2 –> 6 CO2 + H20 + ATP
What is the overall formula for photosynthesis?
6 CO2 + 6H20 + light energy __> C6H12O6 + 6O2
How do cellular respiration and photosynthesis compare?
They are reverse processes—photosynthesis stores energy in glucose, while respiration releases it.
What structures do both mitochondria and chloroplasts share?
Both have a double membrane, their own DNA, and internal membrane structures (cristae in mitochondria, thylakoids in chloroplasts).
How do chloroplasts and mitochondria differ in function?
Chloroplasts capture light energy for photosynthesis; mitochondria break down glucose for ATP production.
What is redox potential?
The tendency of a molecule to gain or lose electrons.
How is redox potential measured?
In volts (V) using a reference electrode to compare electron affinity.
How do you calculate
ΔG^o from redox potential?
DeltaG^o = -nFdeltaeE^o,
where 𝑛 is the number of electrons, 𝐹 is Faraday’s constant, and E is the difference in redox potential.
What does a negative deltaG indicate about electron flow?
Electrons flow spontaneously along the electron transport chain, releasing energy.
How does oxidative phosphorylation produce ATP?
The electron transport chain pumps protons across the membrane, and ATP synthase uses this gradient to generate ATP.
How is a proton gradient formed during electron transport?
Electrons move through the ETC, pumping protons into the intermembrane space, creating an electrochemical gradient.
What is the function of the proton gradient?
It stores potential energy used to drive ATP synthesis.
What is the structure and function of ATP synthase?
ATP synthase is an enzyme complex that allows protons to flow down their gradient, using the energy to convert ADP to ATP.
How are sealed vesicles used to study ATP synthesis?
Artificial vesicles with embedded ATP synthase can show ATP production when a proton gradient is created.
What are the three ways ATP is produced?
Substrate-level phosphorylation, oxidative phosphorylation, and photophosphorylation.
How does substrate-level phosphorylation differ from oxidative phosphorylation?
Substrate-level phosphorylation directly transfers a phosphate group to ADP; oxidative phosphorylation relies on a proton gradient and the ETC.
What is photophosphorylation?
ATP production in chloroplasts using light energy to drive a proton gradient
Electrons move to more positive redox potential spontaneously
- As electrons move through
respiratory enzyme complexes they are moving spontaneously from more negative to more positive redox potential (from a
stronger electron donor to a
stronger electron acceptor) - Each redox reaction results
in a loss of free energy and is
thus spontaneous.
electron transport chain (ETC) in the inner mitochondrial membrane, which is part of cellular respiration.
NADH Dehydrogenase Complex (Complex I):
NADH donates electrons (2e⁻) to this complex.
These electrons are transferred to ubiquinone (Q), a small molecule that carries electrons to the next complex.
As electrons pass through the complex, protons (H⁺) are pumped into the intermembrane space, creating a proton gradient.
Cytochrome c Reductase Complex (Complex III):
Ubiquinone transfers electrons to this complex.
Electrons are passed to cytochrome c (an electron carrier protein).
More H⁺ ions are pumped into the intermembrane space.
Cytochrome c Oxidase Complex (Complex IV):
Cytochrome c transfers electrons to this complex.
Oxygen (O₂) acts as the final electron acceptor, combining with electrons and protons to form water (H₂O).
More protons are pumped across the membrane.
Purpose of Proton Gradient
The proton gradient created by pumping H⁺ ions into the intermembrane space is used by ATP synthase to generate ATP through chemiosmosis.
iron in a heme group in cytochromes serves as an
electron acceptor
Electon transport is coupled to proton pumping
Electron Transport Provides Energy
As electrons are passed through a series of protein complexes in the inner mitochondrial membrane, they release energy.
This energy is used to pump protons (H⁺) from the mitochondrial matrix into the intermembrane space, creating a proton gradient.
Proton Pumping and Affinity Changes
The proteins in the ETC have high affinity for protons on one side of the membrane.
As electrons move through the chain, conformational changes in the proteins lower their H⁺ affinity, causing them to release protons into the intermembrane space.
Establishing a Proton Gradient
The pumping of protons creates a high concentration of H⁺ in the intermembrane space and a low concentration in the matrix.
This difference in proton concentration (electrochemical gradient) is essential for ATP production in the final step of oxidative phosphorylation.
Next Step: ATP Synthesis
The proton gradient drives ATP synthase, which uses the flow of H⁺ back into the matrix to synthesize ATP from ADP and Pi (chemiosmosis).
Proton motive force
Result of protons
pumped across
inner membrane
is a steep electrochemical
gradient of protons =proton
motive force
Chemiosmosis (also occurs in chloroplasts)
Utilizes energy of a H+
electrochemical gradient
generated by ETC to produce
ATP
*Driven by the proton motive
force: the combination of the
membrane potential and the H+
concentration gradient
*Drives the synthesis of ATP
from ADP and inorganic
phosphate (Pi)
Stage 1: energy of electron transport is used to pump protons across the membrane
Stage 2: energy in the proton gradient is harnessed by Atp Synthase to make ATP
ATP Synthase uses energy of H+ gradient to make ATP
1Electron Transport Chain (ETC) Pumps Protons (H⁺)
The ETC, located in the inner mitochondrial membrane, transports electrons and releases energy.
This energy is used to pump protons (H⁺) from the mitochondrial matrix into the intermembrane space, creating a proton gradient.
- pH Difference Across the Membrane
The intermembrane space has a lower pH (pH = 7) due to the high concentration of H⁺.
The matrix has a higher pH (pH = 8) because protons are removed.
This proton gradient represents stored potential energy.
- ATP Synthase Uses Proton Gradient to Make ATP
ATP synthase, a large enzyme, is embedded in the inner membrane.
As H⁺ ions flow back into the matrix (down their gradient) through ATP synthase, the enzyme harnesses the energy to convert ADP + Pi (inorganic phosphate) into ATP.
This process is called chemiosmosis.
- Final Electron Acceptor: Oxygen (O₂)
At the end of the ETC, oxygen (O₂) acts as the final electron acceptor, combining with electrons and H⁺ ions to form water (H₂O).
- Significance
This process is crucial for aerobic respiration, producing ATP—the main energy currency of cells.
Without oxygen, the ETC cannot function, leading to anaerobic respiration or fermentation.
ATP synthase
The left panel (A) provides a simplified schematic of ATP synthase, showing:
- H+ (protons) flowing through the enzyme from the intermembrane space into the matrix.
-This movement powers the rotor (F₀ subunit), which in turn drives conformational changes in the F₁ ATPase head.
-ADP and inorganic phosphate (Pᵢ) are combined to produce ATP.
-The right panel (B) presents a detailed molecular structure of ATP synthase, labeling key components like:
-The rotor ring (which allows proton flow)
-The central stalk (which connects the rotor to the ATP-producing head)
-The F₁ ATPase head, where ATP synthesis occurs
ATP synthase is reversible
- ATP synthase is a reversible enzyme, meaning it can function in two ways:
ATP Synthesis (left panel)
When a proton gradient exists, protons move down their concentration gradient from the intermembrane space to the matrix, driving ATP formation. - ATP Hydrolysis (right panel)
If ATP is abundant but the proton gradient is weak, ATP synthase can work in reverse, using ATP hydrolysis to pump protons back into the intermembrane space, restoring the proton gradient.
Key Takeaways of ATP Synthase
- ATP synthase couples proton movement with ATP production in oxidative phosphorylation.
-The enzyme can function bidirectionally, either producing ATP or using ATP hydrolysis to move protons.
It plays a crucial role in cellular energy metabolism within the mitochondria.
Uncouplers
Uncouplers are H+
carriers that insert
in the membrane.
- Shows that H+
gradient necessary
for ATP synthesis
-Uncouplers make intermembrane permeable to protons so no proton gradient is made and ATP will no longer be made
Sealed vesicles
Sealed vesicles show
that artificially created
proton gradient is
necessary and
sufficient for ATP
synthesis
experiment using sealed vesicles (liposomes) to demonstrate the proton gradient is necessary and sufficient for ATP synthesis
- Panel (A) – No ATP Generated
The vesicle contains bacteriorhodopsin, a light-driven proton pump.
Light causes bacteriorhodopsin to pump H⁺ (protons) into the vesicle, creating a proton gradient.
However, since ATP synthase is absent, no ATP is generated.
- Panel (B) – ATP Generated
Both bacteriorhodopsin and ATP synthase are present.
Light activates bacteriorhodopsin, pumping protons into the vesicle, creating a proton gradient.
ATP synthase uses this gradient to drive ATP synthesis from ADP and phosphate.
Conclusion: A proton gradient is sufficient for ATP synthesis if ATP synthase is present.
- Panel (C) – No ATP Generated
The vesicle contains ATP synthase, but no bacteriorhodopsin to generate a proton gradient.
Since there is no proton movement, ATP synthesis does not occur.
Conclusion: A proton gradient is necessary for ATP synthesis.
- Panel (D) – No ATP Generated (Uncoupling Agent Present)
Both bacteriorhodopsin and ATP synthase are present.
However, an uncoupling agent allows protons to leak across the membrane, preventing a gradient from forming.
Without a proton gradient, ATP synthase cannot produce ATP.
Conclusion: The proton gradient must be maintained for ATP synthesis.
Key takeaways:
A proton gradient is essential for ATP synthesis.
ATP synthase can only function when a proton gradient exists.
Uncoupling agents disrupt ATP synthesis by dissipating the gradient.
This experiment mimics how mitochondria generate ATP using proton gradients established by the electron transport chain.
Protons and voltage gradients used to transport molecules in and out of mitochondria
How proton gradient (H+) and voltage gradient across the inner mitochondrial membrane facilitate the movement of molecules
- ADP/ATP Exchange:
The voltage gradient (difference in charge) drives the exchange of ADP (3⁻) for ATP (4⁻) across the inner membrane.
ATP (more negative) moves out into the cytosol, while ADP enters the mitochondria.
-Pyruvate Import:
The pH gradient (H⁺ concentration difference) helps import pyruvate (from glycolysis) into the mitochondrial matrix.
-Phosphate Import:
Similarly, the pH gradient drives the import of phosphate (Pᵢ), which is needed for ATP synthesis.
1.Glycolysis (not shown in detail here):
Pyruvate is produced from glucose in the cytoplasm and transported into the mitochondria.
Citric Acid Cycle (Krebs Cycle):
Pyruvate is converted into Acetyl-CoA, which enters the cycle.
This process generates NADH and FADH₂ (electron carriers) and releases CO₂.
- Electron Transport Chain (ETC) and Oxidative Phosphorylation:
NADH donates electrons (e⁻) to the ETC in the inner membrane.
Electrons move through protein complexes, pumping protons (H⁺) into the intermembrane space, creating a proton gradient.
Oxygen (O₂) acts as the final electron acceptor, forming H₂O.
4.ATP Synthesis:
The accumulated protons flow back into the matrix through ATP synthase, driving ATP production from ADP and Pᵢ.
Key Takeaways
The proton gradient is crucial for ATP generation.
ADP/ATP exchange, pyruvate import, and phosphate import rely on electrochemical gradients.
The oxidation of glucose leads to the production of NADH, which powers the ETC, ultimately producing ATP through oxidative phosphorylation.
Total ATP yields from
Glucose oxidation as most ATP from NADH to FADH2 being oxidized
Electron transport summary
Oxidizes NADH, FADH2 from glycolysis, pyruvate oxidation
and CAC
*Utilizes O2 as final electron acceptor
*electrons move by stepwise oxidation/reduction reactions (going from better electron donor and electron acceptor)
*Three reaction centers embedded in inner membrane of mitochondria
*Electrons flow from neg to pos redox potential compounds -
spontaneous
*H+ gradient is established - IMS to Matrix
Oxidative Phosphorylation
making ATP via electron transport chain + chemiosmosis
ATP is synthesized from ADP and Pi by ATP Synthase
pH (H+) gradient developed in electron transport provides the
energy
Oxygen consumed during the ETC
The pH gradient is both necessary and sufficient as an energy source for ATP synthesis (IMPORTANT)
-Make majority of ATP
Substrate Level Phosphorylation
-Occurs when enzyme breaks phosphate and adds it to make ADP into ATP
- ATP is made during
glycolysis and the CAC by
substrate level
phosphorylation - An enzyme breaks a
phosphate bond off a
substrate and adds it to
ADP
- Substrate-Level Phosphorylation Definition:
Unlike oxidative phosphorylation (which uses the electron transport chain and ATP synthase), substrate-level phosphorylation directly transfers a phosphate group from a high-energy molecule to ADP, forming ATP. - Reaction Shown (Step 7 of Glycolysis):
-The enzyme phosphoglycerate kinase catalyzes the conversion of 1,3-bisphosphoglycerate (1,3-BPG) to 3-phosphoglycerate (3-PG).
-A phosphate (P) is transferred from 1,3-BPG to ADP, producing ATP.
-This reaction is an example of substrate-level phosphorylation because ATP is made directly without the need for an electron transport chain.
3.Energy Considerations (Right Side of the Image):
The red arrow represents the free energy (ΔG) of hydrolysis of different phosphate bonds.
1,3-bisphosphoglycerate (-49.0 kJ/mol) has a high-energy phosphate bond.
ATP formation from ADP has a ΔG of -30.6 kJ/mol, meaning that energy from 1,3-BPG hydrolysis is sufficient to drive ATP synthesis.
Other high-energy molecules like phosphoenolpyruvate (PEP, -61.9 kJ/mol) are even more energetic and can also drive ATP production in later glycolysis steps.
Importance of This Step:
This is the first ATP-generating step in glycolysis.
Since two molecules of 1,3-BPG are produced per glucose, this step yields two ATP molecules per glucose.
It contributes to the net energy gain of glycolysis.
Oxidative Phosphorylation vs substrate level phosphorylation
Both are means to make ATP
Stage of Glucose oxidation (where they occur):
Substrate level – glycolysis and CAC
Oxidative phosphorylation- ETC + Chemisosmosis
Source of phosphate (comes from):
Substrate level - organic molecule
Oxidative phosphorylation- inorganic phosphate
Source of energy:
Substrate level- hydrolysis of high energy bond
Oxidative phosphorylation – dissipation of proton gradient
Mitochondrial Structure and Function Summary
Outer membrane is porous due to porin, lets small molecules pass. Inner membrane selectively permeable.
Matrix contains enzymes for oxidation of pyruvate and fatty acids to acetyl coA and the citric acid cycle
Inner membrane contains both respiratory enzyme complexes and ATP synthase
Proton gradient formed during electron transport between
intermembrane space and matrix fuels ATP synthesis
