Biology 9.2- Ch. Cellular Respiration/ L. The Krebs Cycle and Electron Transport

Because the pathways of cellular respiration require oxygen, they are said to be _____.

aerobic

During the Krebs cycle, _____ is broken down into _____ in a series of energy-extracting reactions.

pyruvic acid; carbon dioxide

This means that _____ times as much ATP can be generated from glucose in the presence of oxygen

18

Glycolysis produces just _____ ATP molecules per glucose. In the absence of oxygen, that is all the energy that a cell can extract from each molecule of glucose.

2

As the figure below shows, the Krebs cycle and electron transport enable the cell to produce _____ more ATP molecules per glucose molecule, in addition to the 2 ATP molecules obtained from glycolysis.

34

What happens to each of these Krebs cycle products?

First, the carbon dioxide released is the source of all the carbon dioxide in your breath. Every time you exhale, you expel the carbon dioxide produced by the Krebs cycle. Next, the ATP produced directly in the Krebs cycle can be used for cellular activities.

What happens to the remaining 62 percent of the total energy of glucose?

It is released as heat, which is one of the reasons your body feels warmer after vigorous exercise.

In the presence of oxygen, pyruvic acid produced in glycolysis passes to the second stage of cellular respiration, the _____.

Krebs cycle

second stage of cellular respiration, in which pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions

Krebs cycle

How does the cell use the charge differences that build up as a result of electron transport?

The inner membranes of the mitochondria contain protein spheres called ATP synthases. As H+ ions escape through channels into these proteins, the ATP synthases spin. Each time it rotates, the enzyme grabs a low-energy ADP and attaches a phosphate, forming high-energy ATP.

The role of ATP synthase is to...

convert ADP into ATP

Photosynthesis is the process that "_____" energy. Cellular respiration is the process that "_____" energy.

deposits; withdraws

a series of proteins in which the high-energy electrons from the Krebs cycle are used to convert ADP into ATP

electron transport chain

The energy flows in photosynthesis and cellular respiration take place in _____ directions.

opposite

The only way to get rid of lactic acid is in a chemical pathway that requires extra _____.

oxygen

The electron transport chain uses the high-energy electrons from the Krebs cycle to convert _____ into _____.

ADP; ATP

To obtain energy, the body uses _____ already in muscles and new ATP made by _____ and _____.

ATP; lactic acid fermentation; cellular respiration

Every time a pair of high-energy electrons moves down the electron transport chain, the energy is used to move _____ ions across the membrane.

H+

process that requires oxygen

aerobic

Does fermentation or cellular respiration release energy slower?

cellular respiration

Fermentation produces _____ as a byproduct.

lactic acid

For that reason, you can think of a quick sprint building up an _____ that a runner has to repay after the race with plenty of heavy breathing.

oxygen debt

Photosynthesis _____ carbon dioxide from the atmosphere, and cellular respiration _____.

removes; puts it back

On average, each pair of high-energy electrons that moves down the electron transport chain provides enough energy to produce _____ molecules of ATP from ADP.

three

Runners breathe heavily after a race because their bodies need...

to use their lungs to expel lactic acid.

Describe the process of electron transport.

- High-energy electrons from NADH and FADH2 are passed along the electron transport chain - In eukaryotes, the electron transport chain is composed of a series of carrier proteins located in the inner membrane of the mitochondrion. In prokaryotes, the same chain is in the cell membrane. - High-energy electrons are passed from one carrier protein to the next. At the end of the electron transport chain is an enzyme that combines these electrons with hydrogen ions and oxygen to form water. - Oxygen serves as the final electron acceptor of the electron transport chain which is why it is essential for getting rid of low-energy electrons and hydrogen ions, the wastes of cellular respiration. - Every time 2 high-energy electrons transport down the electron transport chain, their energy is used to transport hydrogen ions (H+) across the membrane - The H+ ions build up in the intermembrane space, making it positively charged. The other side of the membrane, from which those H+ ions have been taken, is now negatively charged.

Describe the process of the Krebs cycle.

- The Krebs cycle begins when pyruvic acid produced by glycolysis enters the mitochondrion. - One carbon atom from pyruvic acid becomes part of a molecule of carbon dioxide, which is eventually released into the air. - The other two carbon atoms from pyruvic acid are joined to a compound called coenzyme A to form acetyl-CoA - Acetyl-CoA then adds the 2-carbon acetyl group to a 4-carbon molecule, producing a 6-carbon molecule called citric acid. - As the cycle continues, citric acid is broken down into a 4-carbon molecule, more carbon dioxide is released, and electrons are transferred to energy carriers. - One 6 carbon atom in citric acid is removed, and then another, releasing 2 molecules of carbon dioxide and leaving a 4-carbon molecule that is then ready to accept another 2-carbon acetyl group, which starts the cycle all over again. - For each turn of the cycle, a molecule similar to ADP is converted to a molecule that is similar to ATP - At five places in the cycle, a pair of high-energy electrons is accepted by electron carriers, changing NAD+ to NADH and FAD to FADH2. FAD (flavine adenine dinucleotide) and FADH2 are molecules similar to NAD+ and NADH, respectively

What percent of the total energy of glucose is made up if the 36 ATP molecules the cell makes per glucose?

38%

At the end of glycolysis, about _____ percent of the chemical energy that was available in glucose is still unused, locked in the high-energy electrons of pyruvic acid.

90

What does the cell do with all those high-energy electrons in carriers like NADH?

In the presence of oxygen, those high-energy electrons can be used to generate huge amounts of ATP.

How efficient is the process of cellular respiration?

The 36 ATP molecules the cell makes per glucose represent about 38 percent of the total energy of glucose. That might not seem like much, but it means that the cell is actually more efficient at using food than the engine of a typical automobile is at burning gasoline.

What happens to the H+ ions after they move across the membrane.

These ions then rush back across the membrane, producing enough force to spin the ATP synthase and generate enormous amounts of ATP.

For exercise longer than about 90 seconds, _____ is the only way to generate a continuing supply of ATP.

cellular respiration

The Krebs cycle is also known as the _____.

citric acid cycle

The Krebs cycle is also known as the citric acid cycle because...

citric acid is the first compound formed in the cycle

The electrons are then passed from those carriers to the _____.

electron transport chain

Your body stores energy in muscle and other tissues in the form of the carbohydrate _____.

glycogen

The Krebs cycle generates _____ that are passed to NADH and FADH2.

high-energy electrons

To extract the rest of that energy, the cell turns to one of the world's most powerful electron acceptors—_____.

oxygen

The final wastes of cellular respiration are _____ and _____.

water; carbon dioxide

Do cells contain ATP?

yes- cells normally contain small amounts of ATP produced during glycolysis and cellular respiration