Cellular Respiration
This molecule is the final electron acceptor in the electron transport chain. Without it, oxidative phosphorylation would stop.
What is oxygen?
Unlike the citric acid cycle and oxidative phosphorylation, glycolysis occurs in this cellular compartment.
What is the cytosol?
This cellular compartment is where the citric acid cycle occurs
What is the mitochondrial matrix?
Note:All enzymes of the citric acid cycle are located in the mitochondrial matrix. This allows direct interaction with NAD⁺, FAD, and the electron transport chain
This part of the mitochondria is where the electron transport chain and ATP synthase are located.
What is the inner mitochondrial membrane?
Note: The electron transport chain (ETC) complexes and ATP synthase are embedded in the inner membrane. The matrix is where the citric acid cycle happens, but ATP generation occurs at the inner membrane.
How many carbons are in acetyl Co-A?
Glycolysis can produce ATP without oxygen. However, cells still rely on the later stages of respiration because this/these molecule(s) produced in glycolysis carries high energy electrons to the mitochondria.
NADH and FADH2
Though 4 ATP molecules get produced in glycolysis, net yield of ATP is only 2 because this many ATP are invested in early steps.
What is 2 ATP?
What is NADH?
Explanation: Three NADH are produced per acetyl-CoA through oxidation steps, which feed electrons into the electron transport chain for ATP production.
The main purpose of the electron transport chain is to do this, which creates a gradient used to make ATP.
What is pump protons across the inner mitochondrial membrane?
Explanation: lectrons from NADH and FADH₂ pass through complexes I–IV (proteins in the chain). Energy from electrons pumps H⁺ into the intermembrane space, creating an electrochemical gradient that drives ATP synthase.
This is the name for the oxidized form of FADH2.
What is FAD?
Explanation: FADH₂ → FAD + 2 electrons + 2 protons
If the inner mitochondrial membrane suddenly became permeable to protons, ATP production by ATP synthase would substantially decrease due to the loss of this driving force.
This enzyme catalyzes the "committed" (aka irreversible) step of glycolysis and is a major regulatory target.
What is phosphofructokinase-1? (PFK)
Note: this enzyme contains the word "kinase."
The citric acid cycle begins when acetyl-CoA combines with this 4-carbon molecule to form citrate?
What is oxaloacetate?
Note: Acetyl-CoA (2C) + oxaloacetate (4C) → citrate (6C). This regenerates oxaloacetate each cycle
Electrons in the electron transport chain move “downhill” from one carrier to the next, releasing energy that pumps protons. This happens because each carrier holds electrons more tightly than the previous one, meaning electrons naturally flow in this direction.
What is from lower to higher electron affinity (or from weaker to stronger electron acceptor?
Explanation: Each complex in the ETC increases in its affinity for electrons, which makes it easier for them to be donated down the chain. This property is also what makes the electron flow directional and drives proton pumping as energy is released through electron movement.
A cell oxidizes glucose completely, but not all of the energy is captured in the form of ATP. What form does this energy take on?
What is heat?
Explanation:
A scientist adds cyanide to a respiring cell culture, which blocks electron transfer to the final acceptor of the ETC. The citric acid cycle slows dramatically because this molecule is no longer generated in sufficient amounts.
What is NAD+?
Explanation: electrons from NADH are moving through the ETC and reduce oxygen to water. During this process, NADH is oxidized back into NAD+. If electrons are no longer flowing down the ETC, NADH is not being oxidized back into NAD+ and the pool of NAD+ is depleted. Without enough NAD+, the reactions of the citric acid cycle cannot efficiently proceed, slowing down the cycle.
Follow up: Would glycolysis also eventually slow down? Why?
In glycolysis, ATP is produced without the electron transport chain when a phosphate group is transferred from a metabolic intermediate to a molecule of ADP. This process is known as
What is substrate level phosphorylation?
Note: 4 total ATP are made because glycolysis splits glucose into two 3 acrbon molecules. Each reaction happens twice per molecule of glucose. However, since 2 molecules of ATP are also invested in glycolysis, the net yield is only 2.
Glucose is not the only fuel for the citric acid cycle. What other compounds can enter the citric acid cycle? *Hint: What are the 4 major biological macromolecules?
What is/are amino acids/glycerol/fatty acids/etc.
Note: The subunits of fats and proteins can enter the TCA at different points in the cycle. It is a central hub for energy production from multiple sources.
A toxin lets electrons flow through the electron transport chain but prevents the mitochondria from making ATP. What is blocked?
What is ATP synthase?
Note: Electrons still move, but no ATP is produced. The energy from the proton gradient MUST go through ATP synthase to make ATP
Pyruvate enters mitochondria through a specialized protein in the inner membrane. What type of molecule is needed to carry pyruvate inside? *Hint: we learned about this before lesson 9!
What is a transporter?
A researcher observes glycolysis continuing in muscle cells even after a dramatic drop in oxygen levels. This is possible because pyruvate acts as an electron acceptor in this metabolic process.
What is lactic acid fermentation?
Explanation: Pyruvate is reduced to lactate by NADH, which forms NAD+. Regeneration of NAD+ allows for glycolysis to continue running in the absence of oxygen.
When a cell's ATP levels drop, the level of this molecule rises and binds to PFK-1, speeding up glycolysis to restore the energy balance.
What is AMP?
Note: AMP naturally rises as ATP falls, then binds to PFK-1 and acts as a signal to speed up glycolysis.
Follow Up: What would negatively regulate PFK-1 and inhibit or slow down glycolysis? Why?
In a lab experiment, scientists supply mitochondria with a fuel source derived from glucose, fats, or proteins. They notice that the citric acid cycle can run as long as this molecule is produced, acting as the entry point into the cycle.
What is acetyl-CoA?
Explanation: Acetyl-CoA is the common entry point to the TCA for carbohydrates (via pyruvate), fats (via fatty acids), or proteins (via amino acids).
During intense exercise, a muscle runs out of oxygen. The electron transport chain stops, and NADH accumulates. What is missing?
What is oxygen?
Note: Oxygen is the final electron acceptor. Without it, electrons get "backed up" since they can't continue flowing down the electron transport chain. Without it, ATP production will stop.
A researcher removes phosphate from ADP in a mitochondria preparation. No ATP is made even though the proton gradient is intact. What is missing?
What is inorganic phosphate?
Explanation: ATP synthase requires ADP + Pi.