Krebs Cycle

What is the Krebs cycle?

Also known as the citric acid cycle, this series of energy-extracting reactions breaks down pyruvic acid into carbon dioxide in the presence of oxygen.

Hint: Named after British biochemist Hans Krebs, who demonstrated its existence in 1937.

What is the mitochondrial matrix?

The innermost compartment of the mitochondrion, specifically the site where the Krebs cycle reactions take place.

Hint: Think of it as the 'inner room' of the power plant where the main chemical reactions occur.

What is Acetyl-CoA?

A 2-carbon molecule formed when pyruvic acid loses a carbon atom and combines with coenzyme A, which then enters the Krebs cycle.

Hint: It acts as the 'fuel' that starts the Krebs cycle.

What is the electron transport chain (ETC)?

The final stage of cellular respiration located in the inner mitochondrial membrane (or cell membrane in prokaryotes) where high-energy electrons are passed down to produce ATP.

Hint: It's the conveyor belt that moves electrons to generate energy.

What is chemiosmosis?

The process where ATP synthase enzymes use the energy from a proton gradient to synthesize ATP molecules.

Hint: A coupling process where the movement of ions powers the machine.

Why is the Krebs cycle called a 'cycle'?

Because the 4-carbon molecule produced at the end of the cycle is the exact same molecule that accepts the acetyl-CoA at the start, allowing the cycle to restart repeatedly.

Hint: It loops back on itself; the output becomes the input.

What is the role of oxygen in the electron transport chain?

Oxygen acts as the final electron acceptor at the end of the chain. Without it, the chain cannot function aerobically, as electrons cannot be passed down to form water.

Hint: It's the last stop on the bus; if no one gets off, the bus stops.

How does the electron transport chain create a 'biological battery'?

As high-energy electrons move through the chain, they pump hydrogen ions (H+) from the matrix into the intermembrane space, creating a high concentration of positive charge that generates electrochemical pressure.

Hint: It's like a dam holding back water; the concentration difference creates potential energy.

How does the location of the electron transport chain differ between prokaryotes and eukaryotes?

In eukaryotes, the chain is located in the inner mitochondrial membrane, whereas in prokaryotes, it is located in the cell membrane.

Hint: Think about which organelle houses the mitochondria in complex cells.

What happens to the ATP produced by the Krebs cycle versus the Electron Transport Chain?

ATP produced directly in the Krebs cycle is used immediately by the cell. In contrast, ATP produced by the electron transport chain (via chemiosmosis) is generated in huge amounts to power various cellular activities.

Hint: Krebs makes some fast cash, while the transport chain prints large bills.

Pyruvic acid from glycolysis reacts to form a molecule called acetyl-_____, which then enters the Krebs cycle.

Coenzyme A (Acetyl-CoA)

Hint: It combines with the 'carrier' molecule.

The Krebs cycle releases carbon dioxide as a byproduct, which eventually enters the bloodstream and is _____.

exhaled

Hint: The gas leaves the body.

The energy from high-energy electrons moving down the electron transport chain is used to create a gradient of hydrogen ions that drive ATP _____.

synthesis

Hint: The creation of the molecule.

At five places in each Krebs cycle turn, electron carriers like NAD+ accept high-energy electrons and a hydrogen ion to become _____.

NADH and FADH2

Hint: These molecules carry the electrons to the next stage.

In the electron transport chain, _____ is the final electron acceptor that combines with electrons to form water.

Oxygen

Hint: We need it to breathe for this stage.

A student is exercising intensely in a gym. They stop running and stand still, breathing heavily. Why does the electron transport chain stop working efficiently if oxygen levels drop?

The electron transport chain requires oxygen as the final electron acceptor. Without oxygen, the chain stops, leading to a lack of ATP production and potential reliance on anaerobic pathways.

Hint: Think about what 'accepts' the electrons at the end.

A scientist is observing the mitochondria under a microscope. They notice the intermembrane space is very crowded with hydrogen ions and the matrix is negative. What process are they watching?

The electron transport chain is actively pumping hydrogen ions (H+) into the intermembrane space to create an electrochemical gradient that will be used for ATP production.

Hint: Look for where ions are moving across a membrane.

If one molecule of glucose enters cellular respiration, how many turns of the Krebs cycle will occur?

Two turns of the Krebs cycle will occur, because glycolysis produces two molecules of pyruvic acid from one glucose molecule.

Hint: Trace the pathway from one glucose molecule.

During cellular respiration, a 2-carbon molecule derived from pyruvic acid must be joined to a specialized carrier molecule to enter the cycle. What molecule is this?

Coenzyme A (Acetyl-CoA)

Hint: Think of the 'acetyl' group as the passenger and this as the taxi driver.

You are a researcher studying how ATP is made. You introduce a drug that blocks the channel in the ATP synthase enzyme. What will happen to the H+ ions and ATP production?

The H+ ions will accumulate in the intermembrane space without flowing through the synthase, and ATP production will stop because the spinning mechanism is blocked.

Hint: If the gears are stuck, the water won't turn the turbine.