Name: glycolysis: how cells break down glucose
Uploaded: 2019-03-11T09:21:10.000Z
Duration: 56 s
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What is Glycolysis?

Glikoliza to proces metaboliczny, który rozkłada cukry w celu wytworzenia energii. Proces ten zachodzi w dwóch głównych fazach – fazie wymagającej energii i fazie uwalniania energii.
Po pierwsze, glukoza najpierw dostaje się do cytoplazmy komórki. Następnie, w wyniku szeregu reakcji enzymatycznych, które wymagają energii w postaci ATP, glukoza jest modyfikowana do dwóch cząsteczek trójwęglowego 3-fosforanu aldehydu glicerynowego.
W drugiej fazie, poprzez wiele etapów enzymatycznych, dwie cząsteczki 3-fosforanu aldehydu glicerynowego są przekształcane w 2 cząsteczki pirogronianu, 2 cząsteczki NADH i 4 cząsteczki ATP.
Obie te cząsteczki pirogronianu są następnie transportowane do mitochondriów w celu wejścia w cykl kwasu cytrynowego.

co to jest glikoliza?

<h4>Przegląd</h4>

Komórki wytwarzają energię poprzez rozkład makrocząsteczek. Oddychanie komórkowe to proces biochemiczny, który przekształca "energię pożywienia" (z wiązań chemicznych makrocząsteczek) w energię chemiczną w postaci trifosforanu adenozyny (ATP). Pierwszym etapem tego ściśle regulowanego i skomplikowanego procesu jest glikoliza. Słowo glikoliza pochodzi od łacińskiego słowa glyco (cukier) i lysis (rozkład). Glikoliza pełni dwie główne funkcje wewnątrzkomórkowe: wytwarzanie ATP i wytwarzanie metabolitów pośrednich, które trafiają do innych szlaków. Szlak glikolityczny przekształca jedną heksozę (sześciowęglowy węglowodan, taki jak glukoza) w dwie cząsteczki triozy (trójwęglowy węglowodan), takie jak pirogronian, w celu wytworzenia w sumie dwóch cząsteczek ATP (cztery wyprodukowane, dwie zużyte) i dwie cząsteczki dinukleotydu nikotynamidoadeninowego (NADH).

<h4>Wyjaśnienie glikolizy</h4>

W połowie XIX wieku Louis Pasteur ustalił, że mikroorganizmy powodują rozkład glukozy pod nieobecność tlenu (fermentacja). W 1897 roku Eduard Buchner odkrył, że w bezkomórkowych ekstraktach drożdżowych nadal można prowadzić reakcje fermentacji poprzez rozbicie komórki i zebranie cytoplazmy zawierającej rozpuszczalne cząsteczki i organelle. Wkrótce potem, w 1905 roku, Arthur Harden i William Young odkryli, że szybkość fermentacji spada bez dodatku nieorganicznego fosforanu (Pi) i że fermentacja wymaga obecności zarówno składnika wrażliwego na ciepło (później zidentyfikowanego jako zawierającego pewną liczbę enzymów). oraz frakcję o niskiej masie cząsteczkowej, termostabilną (jony nieorganiczne, ATP, ADP i koenzymy, takie jak NAD). Do roku 1940 wysiłkiem wielu osób Gustav Embden, Otto Meyerhof, Jakub Karol Parnas i inni ustalili kompletny szlak glikolizy. Obecnie glikoliza jest znana jako szlak EMP.

<h4>Przeznaczenie glukozy</h4>

Glukoza może przedostać się do komórki na dwa sposoby. Grupa integralnych białek GLUT (transporterów glukozy) transportuje glukozę do cytozolu poprzez ułatwioną dyfuzję. Członkowie rodziny białek GLUT są obecni w określonych tkankach w całym organizmie człowieka. Alternatywnie, przezbłonowe białka symporterowe przemieszczają glukozę wbrew gradientowi stężeń poprzez wtórny transport aktywny. Symporter wykorzystuje energię elektrochemiczną z pompowania jonów. Przykładami są transportery związane z sodem i glukozą w jelicie cienkim, sercu, mózgu i nerkach.

W warunkach tlenowych (bogatych w O2) i beztlenowych (z niedoborem O2) glikoliza może rozpocząć się, gdy glukoza dostanie się do cytozolu komórki. Istnieją dwie główne fazy glikolizy. Pierwsza faza to wymagający energii etap przygotowawczy, który zatrzymuje glukozę w komórce i restrukturyzuje sześciowęglowy szkielet tak, aby można go było skutecznie rozszczepić. Druga faza uwalnia energię i wytwarza pirogronian.

<h4>Losy pirogronianu</h4>

W zależności od poziomu tlenu i obecności mitochondriów pirogronian może mieć jeden z dwóch możliwych losów. W warunkach tlenowych, w obecności mitochondriów, pirogronian przedostaje się do mitochondriów, gdzie przechodzi cykl kwasu cytrynowego i łańcuch transportu elektronów (ETC), gdzie zostaje utleniony do CO2, H2O, i jeszcze więcej ATP. Natomiast w warunkach beztlenowych (tj. pracujących mięśni) lub bez mitochondriów (tj. prokariotów) pirogronian ulega fermentacji mleczanowej (tj. w warunkach beztlenowych ulega redukcji do mleczanu). Co ciekawe, drożdże i niektóre bakterie w warunkach beztlenowych mogą przekształcać pirogronian w etanol w procesie znanym jako fermentacja alkoholowa.

<h4>Regulacja glikolizy</h4>

Ścisła kontrola i regulacja szlaków metabolicznych, w których pośredniczą enzymy, takich jak glikoliza, ma kluczowe znaczenie dla prawidłowego funkcjonowania organizmu. Kontrola odbywa się poprzez ograniczenie substratu lub regulację związaną z enzymem. Ograniczenie substratu występuje, gdy stężenie substratów i produktów w komórce jest bliskie równowagi. W konsekwencji dostępność substratu determinuje szybkość reakcji. W regulacji enzymatycznej stężenie substratów i produktów jest dalekie od równowagi. Aktywność trzech enzymów (heksokinazy, fosfofruktokinazy i kinazy pirogronianowej) determinuje szybkość reakcji, która kontroluje przepływ całego szlaku.

Co to jest glikoliza?

Przegląd
Komórki wytwarzają energię poprzez rozkład makrocząsteczek. Oddychanie komórkowe to proces biochemiczny, który przekształca "energię pokarmową" (z ...

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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 are used. It also generates two molecules of NADH, a carrier used in later energy reactions.

The history of glycolysis began with studies of fermentation. In the mid-1800s, Louis Pasteur showed that microorganisms break down glucose without oxygen. In 1897, Eduard Buchner found that fermentation could still happen in cell-free yeast extracts, which showed that the cytoplasm contains the needed soluble components.

Later, Arthur Harden and William Young found that fermentation slows without inorganic phosphate. They also showed that the process needs both a heat-sensitive part, later linked to enzymes, and a heat-stable part with small molecules such as inorganic ions, ATP, ADP, and coenzymes like NAD. By 1940, Gustav Embden, Otto Meyerhof, Jakub Karol Parnas, and others had established the full pathway, which is now also called the EMP pathway.

Glucose can enter cells in two main ways before glycolysis begins. GLUT proteins move glucose into the cytosol by facilitated diffusion. Transmembrane symporter proteins can also bring glucose in against its concentration gradient by secondary active transport, using energy from ion pumping. Sodium-glucose-linked transporters are examples found in the small intestine, heart, brain, and kidneys.

Glycolysis can begin after glucose enters the cytosol under both aerobic and anaerobic conditions. The pathway has two main phases. The first is an energy-requiring preparatory phase that traps glucose in the cell and rearranges its six-carbon backbone so it can be split efficiently. The second phase releases energy and forms pyruvate.

Pyruvate can follow different paths depending on oxygen and mitochondria. Under aerobic conditions with mitochondria, pyruvate enters the mitochondria and continues through the citric acid cycle and the electron transport chain, where it is oxidized to carbon dioxide, water, and more ATP. Under anaerobic conditions, such as in working muscles, or in cells without mitochondria, such as prokaryotes, pyruvate undergoes lactate fermentation. Yeast and some bacteria can instead convert pyruvate to ethanol through alcohol fermentation.

Glycolysis is tightly regulated because metabolic pathways must be controlled for proper cell function. Regulation can depend on substrate limitation, which occurs when substrate and product levels are near equilibrium and the available substrate sets the reaction rate. It can also depend on enzyme-linked regulation, where the pathway is controlled by key enzymes. Hexokinase, phosphofructokinase, and pyruvate kinase are three enzymes that help determine the overall flux of glycolysis.

Glycolysis: How Cells Break Down Glucose

what is glycolysis?

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...

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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 glycolysis breaks down glucose, produces ATP and NADH, and connects to pyruvate fate, fermentation, and pathway regulation in cells.

Glycolysis: How Cells Break Down Glucose | JoVE K12

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Glycolysis: How Cells Break Down Glucose

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