Cellular respiration: Difference between revisions

Latest revision as of 19:21, 22 March 2025

Process by which cells convert glucose into energy

Cellular respiration is a set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products. These reactions are crucial for the survival of most organisms, as they provide the energy necessary for cellular functions.

Overview[edit]

Cellular respiration can be divided into three main stages: glycolysis, the citric acid cycle (also known as the Krebs cycle), and oxidative phosphorylation. Each of these stages plays a critical role in the conversion of glucose into ATP.

Glycolysis[edit]

Glycolysis is the first step in the breakdown of glucose to extract energy for cellular metabolism. It occurs in the cytoplasm of the cell and does not require oxygen, making it an anaerobic process. During glycolysis, one molecule of glucose is converted into two molecules of pyruvate, with a net gain of two molecules of ATP and two molecules of NADH.

Citric Acid Cycle[edit]

The citric acid cycle, also known as the Krebs cycle, takes place in the mitochondria of the cell. It is an aerobic process, meaning it requires oxygen. In this cycle, the pyruvate produced in glycolysis is further broken down, releasing carbon dioxide and transferring energy to carrier molecules such as NADH and FADH2. The cycle results in the production of two ATP molecules per glucose molecule.

Oxidative Phosphorylation[edit]

Oxidative phosphorylation is the final stage of cellular respiration and occurs in the inner mitochondrial membrane. It involves the electron transport chain and chemiosmosis. Electrons from NADH and FADH2 are transferred through a series of proteins, releasing energy that is used to pump protons across the mitochondrial membrane. This creates a proton gradient that drives the synthesis of ATP by ATP synthase. This stage produces the majority of ATP during cellular respiration, approximately 34 ATP molecules per glucose molecule.

Anaerobic Respiration[edit]

In the absence of oxygen, cells can undergo anaerobic respiration or fermentation. This process allows for the continuation of ATP production through glycolysis alone, with pyruvate being converted into lactic acid or ethanol and carbon dioxide, depending on the organism. Anaerobic respiration is less efficient than aerobic respiration, yielding only 2 ATP molecules per glucose molecule.

Importance of Cellular Respiration[edit]

Cellular respiration is essential for the production of ATP, which is the primary energy currency of the cell. ATP is used to power various cellular processes, including muscle contraction, nerve impulse propagation, and biosynthesis. Without cellular respiration, cells would not be able to maintain their functions and life would not be sustainable.

Related pages[edit]

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-'''Cellular respiration''' is the process of breaking sugar into a form that the cell can use as energy. This happens in all forms of life. Cellular respiration takes in food and uses it to create [[ATP]], a [[Chemicals|chemical]] which the cell uses for energy.
+{{Short description|Process by which cells convert glucose into energy}}
+{{Use dmy dates|date=October 2023}}
-Usually, this process uses [[oxygen]], and is called '''aerobic respiration'''. It has four stages known as [[glycolysis]], [[Link reaction]], the [[Krebs cycle]], and the [[electron transport chain]]. This produces [[ATP]] which supplies the energy that cells need to do work.
+'''Cellular respiration''' is a set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products. These reactions are crucial for the survival of most organisms, as they provide the energy necessary for cellular functions.
-When they don't get enough oxygen, the cells use [[anaerobic respiration]], which doesn’t require oxygen.  However, this process produces [[lactic acid]], and is not as efficient as when oxygen is used.
+==Overview==
+Cellular respiration can be divided into three main stages: [[glycolysis]], the [[citric acid cycle]] (also known as the Krebs cycle), and [[oxidative phosphorylation]]. Each of these stages plays a critical role in the conversion of glucose into ATP.
-Aerobic respiration, the process that does use oxygen, produces much more energy and doesn’t produce lactic acid.  It also produces carbon dioxide as a waste product, which then enters the [[circulatory system]].  The carbon dioxide is taken to the lungs, where it is exchanged for oxygen.
+==Glycolysis==
+Glycolysis is the first step in the breakdown of glucose to extract energy for cellular metabolism. It occurs in the [[cytoplasm]] of the cell and does not require [[oxygen]], making it an anaerobic process. During glycolysis, one molecule of glucose is converted into two molecules of [[pyruvate]], with a net gain of two molecules of ATP and two molecules of [[NADH]].
-The simplified formula for aerobic cellular respiration is:
+==Citric Acid Cycle==
+The citric acid cycle, also known as the Krebs cycle, takes place in the [[mitochondria]] of the cell. It is an aerobic process, meaning it requires oxygen. In this cycle, the pyruvate produced in glycolysis is further broken down, releasing carbon dioxide and transferring energy to carrier molecules such as NADH and [[FADH2]]. The cycle results in the production of two ATP molecules per glucose molecule.
-<center>[[Glucose|C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>]] + 6[[Oxygen|O<sub>2</sub>]] → 6[[Carbon dioxide|CO<SUB>2</SUB>]] + 6[[Water|H<sub>2</sub>O]] + Energy (as [[ATP]])</center>
+==Oxidative Phosphorylation==
-The word equation for this is:<center>[[Glucose]] (sugar) + [[Oxygen]] → [[Carbon dioxide]] + [[Water]] + Energy (as [[ATP]])</center>
+Oxidative phosphorylation is the final stage of cellular respiration and occurs in the inner mitochondrial membrane. It involves the [[electron transport chain]] and [[chemiosmosis]]. Electrons from NADH and FADH2 are transferred through a series of proteins, releasing energy that is used to pump protons across the mitochondrial membrane. This creates a [[proton gradient]] that drives the synthesis of ATP by [[ATP synthase]]. This stage produces the majority of ATP during cellular respiration, approximately 34 ATP molecules per glucose molecule.
-Aerobic cellular respiration has four stages. Each is important, and could not happen without the one before it. The steps of aerobic cellular respiration are:
+==Anaerobic Respiration==
-* [[Glycolysis]] (the break down of [[glucose]])
+In the absence of oxygen, cells can undergo anaerobic respiration or [[fermentation]]. This process allows for the continuation of ATP production through glycolysis alone, with pyruvate being converted into lactic acid or ethanol and carbon dioxide, depending on the organism. Anaerobic respiration is less efficient than aerobic respiration, yielding only 2 ATP molecules per glucose molecule.
-* [[Link reaction]]
-* [[Krebs cycle]]
-* [[Electron transport chain]], or ETC
-[[File:Cellularrespiration.JPG|center|border|300px]]
+==Importance of Cellular Respiration==
+Cellular respiration is essential for the production of ATP, which is the primary energy currency of the cell. ATP is used to power various cellular processes, including [[muscle contraction]], [[nerve impulse propagation]], and [[biosynthesis]]. Without cellular respiration, cells would not be able to maintain their functions and life would not be sustainable.
-== Glycolysis ==
+==Related pages==
-{{main|Glycolysis}}
+* [[Photosynthesis]]
-In glycolysis, glucose in the cytoplasm is broken into two [[molecule]]s of [[pyruvate]]. Ten [[enzyme]]s are needed for the ten intermediate compounds in this process.
+* [[Metabolism]]
-# Two energy-rich [[ATP]] kick-start the process.
+* [[Mitochondrion]]
-# At the end are two pyruvate molecules, plus
+* [[ATP synthase]]
-# Substrate level - Four molecules of ATP are made in reaction number 7 & 10
+* [[Electron transport chain]]
- But in reaction number 1 & 3 two molecules of ATP are consumed. Hence the direct gain is 4-2=2ATP
-  Oxidative phosphorylation - Two [[NADP|NADH]] molecules.
-  one[[NADP|NADH]] = 3 molecules of ATP.Hence the indirect gain is
-×3=6ATP
-  TOTAL GAIN OF ATP = 2+6= 8ATP .
-# In cells which use [[oxygen]], the pyruvate is used in a second process, the [[Krebs cycle]], which produces more ATP molecules.
-=== Productivity of the cycle ===
-Biology textbooks often state that 38 ATP molecules can be made per oxidised glucose molecule during cellular respiration (two from glycolysis, two from the Krebs cycle, and about 34 from the electron transport chain).<ref name=Rich/> However, the process actually makes less energy (ATP) because of losses through leaky [[membrane]]s. Estimates are 29 to 30 ATP per glucose.<ref name=Rich/>
-Aerobic metabolism is about (see sentence above) 15 times more efficient than anaerobic metabolism. Anaerobic metabolism yields 2&nbsp;mol ATP per 1&nbsp;mol glucose. They share the initial pathway of [[glycolysis]] but aerobic metabolism continues with the Krebs cycle and oxidative phosphorylation. The post glycolytic reactions take place in the mitochondria in [[eukaryote|eukaryotic cell]]s, and in the [[cytoplasm]] in [[prokaryote|prokaryotic cell]]s.
-== Link reaction ==
-{{main|Link reaction}}
-Pyruvate from glycolysis is actively pumped  into [[mitochondria]]. One carbon dioxide molecule and one hydrogen molecule are removed from the pyruvate (called oxidative decarboxylation) to produce an [[acetyl]] group, which joins to an enzyme called [[CoA]] to form acetyl CoA. This is essential for the Krebs cycle.
-== Krebs cycle ==
-{{main|Krebs cycle}}
-Acetyl CoA joins with oxaloacetate to form a compound with six [[carbon]] atoms. This is the first step in the ever-repeating Krebs cycle. Because two acetyl-CoA molecules are produced from each glucose molecule, ''two cycles are required per glucose molecule''. Therefore, at the end of two cycles, the products are: two ATP, six NADH, two FADH, and four CO2. The ATP is a molecule which carries energy in chemical form to be used in other cell processes.
-== Electron transport chain (ETC) ==
-{{main|Electron transport chain}}
-This is where most of the ATP is made. All of the hydrogen molecules which have been removed in the  steps before (Krebs cycle, Link reaction) are pumped inside the mitochondria using energy that electrons release. Eventually, the electrons powering the pumping of hydrogen into the mitochondria mix with some hydrogen and oxygen to form water and the hydrogen molecules stop being pumped.
-Eventually, the hydrogen flows back into the cytoplasm of the mitochondria through [[protein channels]]. As the hydrogen flows, ATP is made from [[ADP]] and phosphate ions.<ref name=Rich>Rich P.R. 2003. The molecular machinery of Keilin's respiratory chain. ''Biochemical Society Transactions'' '''31''' (pt 6): 1095–1105. doi:10.1042/BST0311095 PMID 14641005</ref>
-== References ==
-{{Reflist}}
+[[Category:Cellular respiration]]
 [[Category:Metabolism]]
-[[Category:Cellular respiration| ]]
+[[Category:Biochemistry]]