Name: fermentation pathways without oxygen
Uploaded: 2019-03-11T09:21:11.000Z
Duration: 1 min 29 s
Channel: JoVE

K12 Standards

Tennessee Academic Standards

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Biology

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

BIO1.LS1.9

Fermentation

La fermentation est un processus anaérobie,c'est le fait d'utiliser du sucre sans oxygène. 
Par exemple, pendant la fermentation lactique,lorsque les muscles sont à court d'oxygène,le glucose est décomposé en deux moléculesde pyruvate pendant la glycolyse,produisant de deux ATPet réduisant deux molécules de NAD en NADH. 
Ensuite, le NADH réagit avec le pyruvatepour former du lactate,sans émission de dioxyde de carboneet plus de production d'ATP. 
En fait, pour produire la même quantitéd'ATP sous forme de respiration aérobie,la cellule doit consommer des quantitésbeaucoup plus importantes de sucre. 
Après l'oxydation du NADH,le NAD+ est réinjecté dans la glycolyse,où l'ATP est récolté par décomposition du glucose. 
Chez l'homme, quand l'oxygène est rareles cellules musculaires peuvent produire de l'ATPpar ce processus pendant un exercice intense. 
L'excès de lactate qui s'accumuleest ensuite transporté au foie par le sangoù il sera reconverti en pyruvate.

fermentation

La plupart des organismes eucaryotes ont besoin d’oxygène pour survivre et fonctionner adéquatement. Ces organismes produisent de grandes quantités d’énergie pendant la respiration aérobie en métabolisant le glucose et l’oxygène en dioxyde de carbone et en eau. Cependant, la plupart des eucaryotes peuvent générer un peu d’énergie en l’absence d’oxygène par le métabolisme anaérobie.
 
 La respiration aérobie se déroule par le biais d’une série de réactions d’oxydation-réduction qui se terminent lorsque l’oxygène — l’accepteur d’électrons final — est réduit en eau. En l’absence d’oxygène, cette réaction ne peut pas se poursuivre. Au lieu de cela, les cellules régénèrent le NADH produit pendant la glycolyse en utilisant une molécule organique, telle que le pyruvate, comme accepteur d’électrons final. Le processus qui utilise une molécule organique pour régénérer NAD+ à partir de NADH s’appelle la fermentation.
 
 Il existe deux types de fermentation basés sur les produits finaux de la réaction : 1) la fermentation en acide lactique et 2) la fermentation en alcool. Chez les mammifères, la fermentation en acide lactique a lieu dans les globules rouges qui ne peuvent pas respirer de façon aérobie en raison du manque de mitochondries, ainsi que dans les muscles squelettiques pendant l’exercice intense. Elle se produit également dans certaines bactéries, comme celles qu’on trouve dans le yogourt. Dans cette réaction, le pyruvate et le NADH sont transformés en acide lactique et en NAD+.
 
 La fermentation en alcool est un processus en deux étapes. Dans la première étape, le pyruvate est transformé en dioxyde de carbone et en acétaldéhyde. Dans la seconde étape, l’acétaldéhyde agit comme un accepteur d’électrons et il est réduit en éthanol avec la transformation concomitante de NADH en NAD+. Dans l’ensemble, la fermentation alcoolique transforme le pyruvate et le NADH en éthanol, en dioxyde de carbone et en NAD+. Les levures utilisent la fermentation alcoolique pour transformer les sucres en dioxyde de carbone et en éthanol. Ce procédé est exploité pour produire des boissons alcoolisées telles que la bière et le vin.

La plupart des organismes eucaryotes ont besoin d’oxygène pour survivre et fonctionner correctement. Ces organismes produisent de grandes quantités d’énergie pendant la respiration aérobie en ...

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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.

During glycolysis, NAD+ becomes NADH. Fermentation transfers electrons from NADH to an organic molecule, such as pyruvate. This reaction produces a new organic molecule and restores NAD+.

The two main fermentation types are lactic acid fermentation and alcohol fermentation. Lactic acid fermentation occurs in red blood cells, which lack mitochondria, and in skeletal muscles during strenuous exercise. It also happens in certain bacteria, including those found in yogurt. In this pathway, pyruvate and NADH are converted to lactic acid and NAD+.

Alcohol fermentation happens in two steps. First, pyruvate is changed into carbon dioxide and acetaldehyde. Then acetaldehyde accepts electrons and is reduced to ethanol, while NADH becomes NAD+. Overall, alcohol fermentation turns pyruvate and NADH into ethanol, carbon dioxide, and NAD+.

Yeasts use alcohol fermentation to convert sugars into carbon dioxide and ethanol. People harness this process to produce alcoholic beverages such as beer and wine. Fermentation shows how cells can keep making energy when oxygen is limited.

Fermentation Pathways Without Oxygen

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

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...

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 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

Explore how fermentation helps cells make energy without oxygen, regenerate NAD+, and produce lactic acid or ethanol in high school biology.

Fermentation Pathways Without Oxygen | JoVE K12

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BIO1.LS1.3

Fermentation Pathways Without Oxygen

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