Name: citric acid cycle energy and products
Uploaded: 2019-03-11T09:21:11.000Z
Duration: 2 min 36 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Life Science

LS.4

LS.4.b

The Citric Acid Cycle

The citric acid cycle is a closed loop of reactions that occur in the mitochondrial matrix, including redox, dehydration, hydration, and decarboxylation reactions.

It&#39;s name is derived from the intermediate compound citric acid as the steps were first described by Hans Krebs, this aerobic pathway is also known as the Krebs cycle, which over a series of eight enzymatic steps, is critical in glucose catabolism.

To begin, acetyl CoA, the resulting compound from pyruvate oxidation donates its acetal group to a four carbon molecule oxaloacetate forming a six carbon intermediate citrate. While it&#39;s CoA group is bound to a self hydro group and diffused away to eventually combine with another acetal group. A water molecule is then removed and replaced, transforming citrate into its isomer isocitrate. The molecule is then oxidized, reducing NAD+ to NADH and H+, and a carbon dioxide molecule, forming a five carbon alpha-ketoglutarate.

This product releases another carbon dioxide molecule and two electrons, reducing another NAD+ to NADH and a proton. Leaving the molecule with an unstable bond, where a coenzyme A attaches forming succinyl CoA. In the next step, the coenzyme is replaced by a ph

the citric acid cycle

The citric acid cycle, also known as the Krebs cycle or TCA cycle, consists of several energy-generating reactions that yield one ATP molecule, three NADH molecules, one FADH2 molecule, and two CO2 molecules.

Acetyl CoA is the point-of-entry into the citric acid cycle, which occurs in the inner membrane (i.e., matrix) of mitochondria in eukaryotic cells or the cytoplasm of prokaryotic cells. Prior to the citric acid cycle, pyruvate oxidation produced two acetyl CoA molecules per glucose molecule. Hence, the citric acid cycle runs twice per glucose molecule.

The citric acid cycle can be partitioned into eight steps, each yielding different molecules (italicized below).

With the help of catalyzing enzymes, one acetyl CoA (2-carbon) reacts with oxaloacetic acid (4-carbon), forming the 6-carbon molecule citrate.

Next, citrate is converted into one of its isomers, isocitrate, through a two-part process in which water is removed and added.

The third step yields &alpha;-ketoglutarate (5-carbon) from oxidized isocitrate. This process releases CO2 and reduces NAD+ to NADH.

The fourth step forms the unstable compound succinyl CoA from &alpha;-ketoglutarate, a process that also releases CO2 and reduces NAD+ to NADH.

The fifth step produces succinate (4-carbon) after a phosphate group replaces the CoA group of succinyl CoA. This phosphate group is passed on to ADP (or GDP) to form ATP (or GTP).

The sixth step forms fumarate (4-carbon) from the oxidation of succinate. This reaction reduces FAD to FADH2.

The seventh step, in which water is added to fumarate, generates malate (4-carbon).

The final step produces oxaloacetate, the compound that reacts with acetyl CoA in step one, from the oxidation of malate. In the process, NAD+ is reduced to NADH.

The NADH and FADH2 produced in the citric acid cycle provide electrons in the electron transport chain and, hence, aid the production of additional ATP.

The citric acid cycle, also known as the Krebs cycle or TCA cycle, consists of several energy-generating reactions that yield one ATP molecule, three NADH ...

Education

JoVE Core

Biology

Cellular Processes

Cellular Respiration

KEY TERMS AND CONCEPTS

citric acid cycle energy and products

The citric acid cycle is a key energy-making pathway in cells. It is also called the Krebs cycle or the TCA cycle. In eukaryotic cells, it takes place in the matrix of mitochondria. In prokaryotic cells, it occurs in the cytoplasm.

The cycle starts with acetyl CoA, which enters the pathway after pyruvate oxidation. That earlier step makes two acetyl CoA molecules per glucose molecule. For that reason, the citric acid cycle runs twice for each glucose molecule.

The pathway includes eight enzyme-catalyzed steps. In the first step, one 2-carbon acetyl CoA joins with 4-carbon oxaloacetic acid to form 6-carbon citrate. Citrate then changes into its isomer, isocitrate, in a two-part process that removes water and adds it back. Next, oxidized isocitrate becomes 5-carbon α-ketoglutarate, and CO2 is released as NAD+ is reduced to NADH.

The fourth step forms succinyl CoA from α-ketoglutarate. This step also releases CO2 and makes more NADH. In the fifth step, a phosphate group replaces the CoA group in succinyl CoA, and that phosphate helps form ATP or GTP from ADP or GDP. The sixth step converts succinate to fumarate by oxidation, and FAD is reduced to FADH2.

In the seventh step, water is added to fumarate to form malate. The final step oxidizes malate and regenerates oxaloacetate, the molecule needed to begin the cycle again. This last reaction also reduces NAD+ to NADH. Overall, one turn of the cycle produces one ATP, three NADH, one FADH2, and two CO2.

The NADH and FADH2 made in the citric acid cycle carry electrons to the electron transport chain. That electron flow helps drive the production of additional ATP.

Citric Acid Cycle Energy and Products

what is glycolysis?

Glycolysis: How Cells Break Down Glucose

Glycolysis is the first stage of cellular respiration and a key way cells break down glucose to make energy. Cellular respiration converts food energy from macromolecules into ATP, the cell’s main energy currency. Glycolysis also creates intermediate molecules that can feed into other pathways. In this pathway, one six-carbon sugar such as glucose is split into two three-carbon molecules, including pyruvate. The process produces a net gain of two ATP molecules, since four ATP are made and two...

energy-requiring steps of glycolysis

Glycolysis: Glucose Trapping and Splitting

Glycolysis begins in the cytosol, where glucose is prepared for use as energy. This process has two phases: an energy-requiring phase and an energy-releasing phase. The first phase changes glucose into a more reactive, unstable form before it can move into later steps. In the first step, glucose is phosphorylated, which means a phosphate group is added from ATP. This produces glucose 6-phosphate. The added phosphate is negatively charged, so it cannot cross the hydrophobic cell membrane. As a...

energy-releasing steps of glycolysis

Glycolysis: ATP and NADH Formation

Glycolysis produces ATP and NADH during its energy-releasing phase. These reactions are the last steps of glycolysis and convert glyceraldehyde-3-phosphate, or G3P, into pyruvate. The phase is often described as steps 6 to 10, and it happens twice because two 3-carbon sugars are made earlier in glycolysis. The sixth step begins with two linked events. G3P is oxidized, which means it loses hydrogen, and it is phosphorylated, which means a phosphate group is added. NAD+ acts as the electron...

pyruvate oxidation

How Pyruvate Becomes Acetyl CoA

Pyruvate is prepared for the next stage of cellular respiration inside the mitochondria. After glycolysis, the charged pyruvate molecules enter the mitochondria by active transport. There, they go through three enzymatic reactions so the energy stored in pyruvate can be used by the cell. First, pyruvate dehydrogenase removes the carboxyl group from pyruvate. This step releases carbon dioxide. Next, the stripped molecule is oxidized, and the electrons are picked up by NAD+ to make NADH. The...

The citric acid cycle is a key energy-making pathway in cells. It is also called the Krebs cycle or the TCA cycle. In eukaryotic cells, it takes place in the matrix of mitochondria. In prokaryotic cells, it occurs in the cytoplasm. The cycle starts with acetyl CoA, which enters the pathway after pyruvate oxidation. That earlier step makes two acetyl CoA molecules per glucose molecule. For that reason, the citric acid cycle runs twice for each glucose molecule. The pathway includes eight...

electron transport chains

ATP Production by the Electron Transport Chain

ATP production in the electron transport chain is the final stage of cellular respiration. This stage is part of oxidative phosphorylation, which has two steps: the electron transport chain and chemiosmosis. In eukaryotic cells, the electron transport chain sits in the inner mitochondrial membrane. Its main job is to build a proton gradient. That gradient is then used during chemiosmosis to make ATP. The process also regenerates the electron carriers NAD+ and FAD, which are needed again in...

chemiosmosis

ATP Production by Chemiosmosis

ATP production by chemiosmosis is part of oxidative phosphorylation, the efficient stage of cellular respiration that makes most of the cell’s ATP. Oxidative phosphorylation includes two linked processes: the electron transport chain and chemiosmosis. Together, they help generate adenosine triphosphate, or ATP, the main energy molecule used by cells. The electron transport chain is a series of protein complexes in the inner mitochondrial membrane. These complexes pass electrons through a set...

electron carriers

Electron Carriers in Cellular Respiration

Electron carriers help move electrons through cellular respiration. They act like shuttles that can accept electrons, which means they are reduced, or give electrons away, which means they are oxidized. This changing between oxidized and reduced forms is essential for energy production. As glucose breaks down into carbon dioxide and water, it loses electrons at several stages. Electron carriers pick up those electrons and store them temporarily. They then release the electrons into the...

fermentation

Fermentation Pathways Without Oxygen

Fermentation is a metabolic pathway that lets cells make energy without oxygen. It begins after glucose is split into two pyruvate molecules during glycolysis. Glycolysis is the same first step used in aerobic respiration. When oxygen is unavailable, pyruvate does not enter aerobic respiration. Instead, cells convert pyruvate into other organic molecules through pathways that depend on the organism. A key purpose of fermentation is to regenerate NAD+ from NADH so glycolysis can keep running. <br...

dietary connections

How Food Becomes ATP

Food becomes ATP through connected steps in cellular respiration. Carbohydrates, proteins, and lipids all feed into these pathways. The body can use foods such as apples, cheese, and guacamole as sources of energy. Carbohydrate digestion starts with enzymes that break complex carbohydrates into simple sugars. Glucose can enter glycolysis directly. Fructose and galactose must first be converted into sugars that are intermediates of the glycolytic pathway. Proteins are digested into amino acids.

introduction to cellular respiration

Cellular Respiration: ATP Production Steps

Cellular respiration is the process cells use to turn energy from food into ATP. ATP, or adenosine triphosphate, stores energy in chemical bonds that can be released quickly when cells need it. Much of the energy released during respiration becomes heat, but some of it is captured to make ATP. This process depends on oxidation-reduction, or redox, reactions. In these reactions, oxidation means electron loss and reduction means electron gain. The electron carriers NAD+ and FAD, along with their...

products of the citric acid cycle

Citric Acid Cycle Output in Cellular Respiration

The citric acid cycle is a key stage of aerobic respiration in cells. It is also called the Krebs cycle or the tricarboxylic acid (TCA) cycle. Plants and animals use this oxygen-requiring pathway as part of cellular respiration. This cycle happens after glycolysis and pyruvate oxidation. Glycolysis makes two pyruvate molecules from each glucose molecule. During pyruvate oxidation, each pyruvate becomes acetyl-CoA, which is the input for the citric acid cycle. That means one glucose molecule...

outcomes of glycolysis

Glycolysis Products in Cellular Respiration

Glycolysis is the first step of cellular respiration and breaks glucose into smaller molecules. Cells use this process to pull energy from glucose over a series of chemical reactions. Cellular respiration can happen with oxygen or without oxygen. In both aerobic and anaerobic cellular respiration, glycolysis makes a net gain of two pyruvate molecules, two NADH molecules, and two ATP molecules. Four ATP molecules are produced, but two ATP molecules are used earlier in the pathway. Glycolysis...

atp yield

How Cellular Respiration Makes ATP

Cellular respiration makes ATP from glucose in several stages. The process usually produces 30 to 32 ATP per glucose molecule. Most of that ATP comes from oxidative phosphorylation and the electron transport chain, while 4 ATP are made earlier, with 2 from glycolysis and 2 from the citric acid cycle. The electron transport chain, or ETC, sits in the inner mitochondrial membrane. It has four main protein complexes and ATP synthase, the enzyme that makes ATP. NADH and FADH2 deliver electrons to...

key terms and concepts

Learn how the citric acid cycle makes ATP, NADH, and FADH2, and follows acetyl CoA through eight enzyme steps in mitochondria.

Citric Acid Cycle Energy and Products | JoVE K12

JoVE Core series brings biology to life through over 300 concise and easy-to-understand animated video lessons that explain key concepts in biology, plus more than 150 scientist-in-action videos that show actual research experiments conducted in today’s laboratories.

biology

Florida Department of Education

High School

SC.912.L.18

SC.912.L.18.8

Texas Essential Knowledge and Skills

BIO.11

BIO.11.A

myJoVE Corporation

What is Photosynthesis?

Photosynthesis is a multipart, biochemical process that occurs in plants as well as in some bacteria. It captures carbon dioxide and solar energy to ...

Light as Energy

The energy required to carry out photosynthesis is light&#8212; typically electromagnetic radiation from the sun. The range of all possible wavelengths is ...

Anatomy of Chloroplasts

Green algae and plants, including green stems and unripe fruit, harbor chloroplasts&mdash;the vital organelles where photosynthesis takes place. In ...

Photosystem II

The multi-protein complex photosystem II (PS II) harvests photons and transfers their energy through its bound pigments to its reaction center, and ...

Photosystem I

Although structurally similar to photosystem II (PSII), photosystem I (PSI) is has a different electron supplier and electron acceptor.
Both these ...

The Calvin Cycle

Overview

Oxygenic photosynthesis converts approximately 200 billion tons of carbon dioxide (CO2) annually to organic compounds and produces approximately ...

C4 Pathway and CAM

Most plants use the C3 pathway for carbon fixation. However, some plants, such as sugar cane, corn, and cacti that grow in hot conditions, use alternative ...

Primary Production

The total amount of energy acquired by primary producers in an ecosystem is called gross primary production (GPP). However, of this energy, producers use ...

The student will investigate and understand that there are chemical processes of energy transfer which are important for life. Key ideas include photosynthesis is the foundation of virtually all food webs; and

LS.4.a

Introduction to Cellular Respiration

Organisms harvest energy from food, but this energy cannot be directly used by cells. Cells convert the energy stored in nutrients into a more usable ...

What is Glycolysis?

Overview
Cells make energy by breaking down macromolecules. Cellular respiration is the biochemical process that converts &#34;food energy&#34; (from the ...

Energy-requiring Steps of Glycolysis

Glucose is the source of nearly all energy used by organisms. The first step of converting glucose into usable energy is called glycolysis. Glycolysis ...

Energy-releasing Steps of Glycolysis

Glycolysis is divided into two phases based on whether energy is utilized or released. While the first phase consumes ATP, the second phase produces ...

Outcomes of Glycolysis

Nearly all the energy used by cells comes from the bonds that make up complex organic compounds. These organic compounds are broken down into simpler ...

Pyruvate Oxidation

After glycolysis, the charged pyruvate molecules enter the mitochondria via active transport and undergo three enzymatic reactions. These reactions ensure ...

Products of the Citric Acid Cycle

The cells of most organisms&#8212;including plants and animals&#8212;obtain usable energy through aerobic respiration, the oxygen-requiring version of ...

Electron Transport Chains

The final stage of cellular respiration is oxidative phosphorylation that consists of two steps: the electron transport chain and chemiosmosis. The ...

Chemiosmosis

Oxidative phosphorylation is a highly efficient process that generates large amounts of adenosine triphosphate (ATP), the basic unit of energy that drives ...

Electron Carriers

Electron carriers can be thought of as electron shuttles. These compounds can easily accept electrons (i.e., be reduced) or lose them (i.e., be oxidized). ...

ATP Yield

Cellular respiration produces 30 - 32 ATP per glucose molecule. Although most of the ATP results from oxidative phosphorylation and the electron transport ...

Fermentation

Most eukaryotic organisms require oxygen to survive and function adequately. Such organisms produce large amounts of energy during aerobic respiration by ...

What is Metabolism?

Overview

Metabolism represents all of the chemical activity in a cell, including reactions that build molecules (anabolism) and those that break ...

Free Energy

Free energy&mdash;abbreviated as G for the scientist Gibbs who discovered it&mdash;is a measurement of useful energy that can be extracted from a reaction ...

Hydrolysis of ATP

The bonds of adenosine triphosphate (ATP) can be broken through the addition of water, releasing one or two phosphate groups in an exergonic process ...

Phosphorylation

The addition or removal of phosphate groups from proteins is the most common chemical modification that regulates cellular processes. These modifications ...

The student will investigate and understand that there are chemical processes of energy transfer which are important for life. Key ideas include photosynthesis and cellular respiration support life processes.

Citric Acid Cycle Energy and Products

Description

Transcript

Tags

More videos by Standards