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

K12 Standards

Tennessee Academic Standards

High School

Biology

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

From Molecules to Organisms: Structures and Processes

BIO1.LS1.9

Fermentation

Die Gärung ist ein anaerober Prozess mit der Verwendung von Zucker ohne Sauerstoff.
 So wird beispielsweise während der Milchsäuregärung, wenn die Muskeln keinen Sauerstoff mehr haben, die Glukose während der Glykolyse in zwei Pyruvatmoleküle zerlegt, was zwei ATP produziert und zwei NAD-Moleküle zu NADH reduziert.
 Dann reagiert das NADH mit Pyruvat zu Laktat, ohne Kohlendioxid-Freisetzung und ohne weiterer ATP-Produktion.
 Um die gleiche Menge an ATP wie die aerobe Atmung zu produzieren, muss die Zelle viel mehr Zucker aufnehmen.
 Nachdem NADH oxidiert wurde, wird NAD+ in die Glykolyse zurückgeführt, wo ATP durch den Abbau von Glukose gewonnen wird.
 Beim Menschen können die Muskelzellen bei Sauerstoffmangel durch diesen Prozess bei anstrengendem Training ATP produzieren.
 Das aufgebaute überschüssige Laktat wird dann vom Blut zur Leber transportiert, wo es wieder in Pyruvat umgewandelt wird.

fermentation

Die meisten eukaryotischen Organismen benötigen zum Überleben und zur Ausführung ihrer Funktionen Sauerstoff. Solche Organismen produzieren während der aeroben Atmung große Mengen an Energie, indem sie Glucose und Sauerstoff in Kohlendioxid und Wasser verstoffwechseln. Die meisten Eukaryoten können jedoch auch in Abwesenheit von Sauerstoff bedingt Energie erzeugen. Dies geschieht dann über den anaeroben Stoffwechselweg.
 
 Die aerobe Atmung verläuft durch eine Reihe von Oxidations-Reduktionsreaktionen, welche enden wenn Sauerstoff, der letzte Elektronenakzeptor, zu Wasser reduziert wird. In Abwesenheit von Sauerstoff kann diese Reaktion nicht mehr ablaufen. Stattdessen regenerieren die Zellen das während der Glykolyse erzeugte NADH, indem sie ein organisches Molekül, wie z.B. Pyruvat, als den letzten Elektronenakzeptor verwenden. Der Prozess der Verwendung eines organischen Moleküls zur Regenerierung von NAD+ aus NADH wird als Fermentation bezeichnet.
 
 Es gibt zwei Arten der Fermentation, die durch die Endprodukte der Reaktion bestimmt werden. Zum einen gibt es die Milchsäuregärung und zum anderen die alkoholische Gärung. Bei Säugetieren findet die Milchsäuregärung in den roten Blutkörperchen statt. Sie können aufgrund fehlender Mitochondrien nicht aerob atmen. Der gleiche Prozess findet ebenso in der Skelettmuskulatur bei anstrengender Bewegung statt. Die Milchsäuregärung wird auch von bestimmten Bakterien genutzt, wie sie z.B. im Joghurt vorkommen. Bei dieser Reaktion werden Pyruvat und NADH zu Milchsäure und NAD+ umgewandelt.
 
 Die alkoholische Gärung ist ein zweistufiger Prozess. In der ersten Stufe wird Pyruvat zu Kohlendioxid und Acetaldehyd umgesetzt. Im zweiten Schritt wirkt Acetaldehyd als Elektronenakzeptor und wird zu Ethanol reduziert. Dabei wird NADH gleichzeitig in NAD+ umgewandelt. Insgesamt werden Pyruvat und NADH in der alkoholischen Gärung zu Ethanol, Kohlendioxid und NAD+ umgewandelt. Hefen verwenden die alkoholische Gärung, um Zucker in Kohlendioxid und Ethanol umzuwandeln. Dieser Prozess wird zur Herstellung von alkoholischen Getränken wie Bier und Wein genutzt.

Die meisten eukaryotischen Organismen benötigen Sauerstoff, um zu überleben und angemessen zu funktionieren. Solche Organismen produzieren während der aeroben Atmung große Mengen an Energie, indem sie ...

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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.

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BIO1.LS1.3

Fermentation Pathways Without Oxygen

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