9.2: The Process of Cellular Respiration

Glycolysis is a word that literally means

"sugar-breaking."

What are the advantages of glycolysis?

- speed - does not require oxygen

Every time ____ high-energy electrons pass down the electron transport chain, their energy is used to

1st: 2 2nd: transport hydrogen ions across the membrane

The acetyl part of acetyl-CoA is made up of

1st: 2 carbon atoms 2nd: 1 oxygen atom 3rd: 3 hydrogen atoms

Glycolysis produces ____ ATP molecules. This gives the cell a net gain of ____ ATP molecules for each molecule of glucose that enters glycolysis.

1st: 4 2nd: 2

One of the reactions of glycolysis removes ____ electrons, now in a high-energy state, and passes them to an electron carrier called ____.

1st: 4 2nd: NAD+

electron carriers present in the Krebs cycle

1st: NAD+ or NADH 2nd: FAD or FADH₂

What happens to the inputs of the Krebs cycle?

1st: Once inside the matrix, 1 carbon atom from pyruvic acid becomes part of a molecule of carbon dioxide, which is eventually released into the air. 2nd: The other 2 carbon atoms from pyrvuic acid rearrange and form acetic acid, which is joined to a compound called coenzyme A.

The products of the Krebs cycle are

1st: carbon dioxide 2nd: ATP 3rd: electron carriers

What happens to each of the Krebs cycle products?

1st: carbon dioxide expelled into the air (as it is no longer useful) 2nd: ATP molecules become immediately available to power cellular activities 3rd: carrier molecules (NADH/FADH₂) are used to generate ATP in the presence of oxygen

With each rotation, the ATP synthase

1st: grabs an ADP molecule 2nd: attaches it to a phosphate group 3rd: produces ATP in the process

wastes of cellular respiration

1st: low-energy electrons 2nd: low-energy hydrogen ions

Each starting molecule of glucose results in

1st: two complete turns of the Krebs cycle. 2nd: 2 ATP molecules.

At the beginning of glycolysis

2 ATP molecules are used up.

On average, each pair of high energy electrons that moves down the full length of the electron transport chain provides enough energy to produce ____ molecules of ATP.

3

For each turn of the Krebs cycle, what happens to ADP?

A molecule of ADP is converted to a molecule of ATP.

The inner mitochondrial membrane contains enzymes known as

ATP synthases.

What happens to the acetyl-CoA produced in the Krebs cycle?

Acetyl-CoA adds the 2-carbon acetyl group to a 4-carbon molecule already present in the cycle.

What is at the end of the electron transport chain?

An enzyme that combines the electrons with hydrogen ions and oxygen to form water.

Why is the Krebs cycle also known as the citric acid cycle?

Citric acid is the first compound formed in this series of reactions.

What happens during the process of glycolysis?

During glycolysis, 1 molecule of glucose, a 6-carbon compound, is transformed into 2 molecules of pyruvic acid, a 3-carbon compound.

What happens during the Krebs cycle?

During the Krebs cycle, pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions.

True or False Glycolysis is an energy-absorbing reaction.

False Glycolysis is an energy-releasing reaction. However the cell needs to put in a little energy to get things going.

True or False The strongest characteristic of glycolysis is its ability to yield large amounts of energy.

False However, the process is so fast that cells can produce thousands of ATP molecules in just a few milliseconds.

What does it mean that glycolysis does not require oxygen?

Glycolysis can quickly supply chemical energy to cells when oxygen is not available.

The Krebs cycle is named after

Hans Krebs (British biochemist who demonstrated its existence in 1937).

What role does NADH play in glycolysis?

NADH holds electrons until they can be transferred to other molecules.

How efficient is cellular respiration?

The 36 ATP molecules generated represent about *36 percent* of the total energy of glucose.

Why is the Krebs cycle a "cycle"?

The 4-carbon molecule produced in the last step is the same as the molecule that accepts the acetyl-CoA in the first step.

How does the electron transport chain use high-energy electrons from glycolysis and the Krebs cycle?

The electron transport chain uses the high-energy electrons from gylcolysis and the Krebs cycle to convert ADP into ATP.

When oxygen is available, what happens to the outputs of glycolysis?

The pyruvic acid and NAD+ "outputs" generated during glycolysis become the "inputs" for the other processes of cellular respiration.

What might happen to the NADH formed in glycolysis?

Those NADH molecules can enter the mitochondrion, where they join the NADH and FADH₂ generated by the Krebs cycle.

How much ATP does cellular respiration generate?

Together, glycolysis, the Krebs cycle, and the electron transport chain release about 36 molecules of ATP per molecule of glucose.

During the stage of energy extraction (in the Krebs cycle), citric acid is broken down into

a 4-carbon molecule.

In glycolysis, each NAD+ molecule accepts

a pair of high-energy electrons.

The electron transport chain is composed of

a series of electron carriers.

What do acetic acid and coenzyme A produce?

acetyl-CoA

The 2 ATP molecules used at the onset of glycolysis can be compared to

an investment that pays back interest.

During the stage of energy extraction (in the Krebs cycle), ____ is released.

carbon dioxide

In prokaryotes, the electron transport chain is located in the

cell membrane

The cell uses a process known as ____ to produce ATP.

chemiosmosis

What do the 2-carbon acetyl group of acetyl-CoA and the 4-carbon molecule present in the cycle produce?

citric acid (6-carbon compound)

From where does the electron transport chain get electrons?

electron carriers (NADH/FADH₂)

As the bonds in glucose are broken and rearranged

energy is released.

In the electron transport chain, oxygen is essential for

getting rid of low-energy electrons and hydrogen ions, the wastes of cellular respiration.

What prompts the change of NAD+ to NADH in glycolysis?

high-energy electrons

During electron transport, where do H+ ions build up?

intermembrane space

What happens to the acetic acid produced in the Krebs cycle?

joined to coenzyme A

In eukaryotes, the electron transport chain is located in the

mitochondrial inner membrane

Where does the Krebs cycle occur?

mitochondrial matrix

The buildup of H+ ions in the intermembrane space makes it

positively charged relative to the matrix.

The Krebs cycle begins when

pyruvic acid produced by glycolysis passes through the two membranes of the mitochondrion and into the matrix.

The end result of glycolysis is

pyruvic acid.

What happens to the remaining 64% of the energy stored in glucose?

released as heat

What happens to the carbon dioxide produced in the Krebs cycle?

released into the air

The electron transport chain couples

the *movement of high-energy electrons* with the *production of ATP*.

In the electron transport chain, oxygen serves as

the final electron acceptor.

During the stage of energy extraction (in the Krebs cycle), eletrons are

transferred to energy carriers.

Under areobic conditions, ____ times as much energy is generated than by glycolysis alone.

two (roughly 36 ATP molecules per glucose molecule versus just 2 ATP molecules in glycosis)