One of the most important biological processes for all life on Earth is cellular respiration. This process takes place in an organelle known as the mitochondria, colloquially referred to as the "powerhouse of the cell." Three stages encompass cellular respiration: glycolysis, the Krebs cycle, and oxidative phosphorylation. The final stage is aerobic and generates the most ATP for the energy put in. Glycolysis is an anaerobic process that uses two ATP molecules and produces 4, resulting in a net gain of two ATP molecules. By breaking down glucose, the cell is able to tap into a bit of the energy stores located in the molecule. Glycolysis takes place outside the mitochondria in the cell's cytoplasm.
A molecule known as Acetyl CoA helps take the pyruvate, the ending molecule of glycolysis, into the matrix of the mitochondria. Here, the Krebs cycle occurs and many electrons are stripped from molecules and their intermediates to eventually be utilized in generating ATP. These electrons are picked up by electron carriers, such as NAD+ and FADH, which transport these electrons to the electron transport chain in oxidative phosphorylation. At the electron transport chain, electrons are pulled through a series of proteins by electronegative oxygen. Along the way, proton pumps establish a gradient in the intermembrane space of the mitochondria. The electrons eventually join with oxygen and are released as water, and the protons in the intermembrane space flow down their concentration gradient through ATP synthase. When ATP synthase spins, it generates ATP.
Mojawapo ya michakato muhimu zaidi ya kibiolojia kwa uhai wote duniani ni upumuaji wa chembe. Utaratibu huo hufanywa katika chembe inayoitwa mitochondria, ambayo kwa kawaida huitwa "kiwanda cha nguvu cha chembe". Hatua tatu hutia ndani kupumua kwa chembe: glycolysis, mzunguko wa Krebs, na phosphorylation ya oxidative. Hatua ya mwisho ni aerobic na inazalisha ATP zaidi kwa nishati iliyowekwa. Glycolysis ni mchakato wa anaerobic ambao hutumia molekuli mbili za ATP na hutengeneza 4, na kusababisha faida ya jumla ya molekuli mbili za ATP. Kwa kuvunja glukosi, chembe huweza kutumia sehemu ya akiba ya nishati iliyoko katika molekuli hiyo. Glycolysis hufanyika nje ya mitochondria katika cytoplasm ya chembe. Acetyl CoA (ACOA) ni molekuli ya pyruvate ambayo huchangia kuondolewa kwa glycolysis na kuingiza katika mitochondria. Katika mzunguko wa Krebs, elektroni nyingi hutolewa kutoka kwa molekuli na vitu vya kati ili hatimaye kutumiwa kutengeneza ATP. Electrons hizi huchukuliwa na waendeshaji wa elektroni, kama vile NAD + na FADH, ambao husafirisha elektroni hizi kwenye mlolongo wa usafirishaji wa elektroni katika phosphorylation ya oxidative. Katika mlolongo wa usafirishaji wa elektroni, elektroni huvutwa kupitia mfululizo wa protini na oksijeni ya elektronegative. Njiani, pampu za protoni huanzisha mwinuko katika nafasi ya kati ya utando wa mitochondria. Baada ya muda, protoni hujiunga na oksijeni na kutolewa kama maji, na protoni katika nafasi ya intermembrane hutiririka chini ya gradient yao ya mkusanyiko kupitia ATP synthase. Wakati ATP synthase inazunguka, inazalisha ATP.