What is the common name given to the second step of cellular respiration?

five.9: Cellular Respiration

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Bring on the S'mores!

This inviting campfire tin exist used for both rut and light. Oestrus and light are two forms of energy that are released when a fuel like forest is burned. The cells of living things also go energy by "burning." They "fire" glucose in the process chosen cellular respiration.

Figure \(\PageIndex{1}\): Burning logs that convert carbon in wood into carbon dioxide and a meaning amount of thermal energy.

Inside every cell of all living things, free energy is needed to carry out life processes. Energy is required to break downwardly and build up molecules and to transport many molecules across plasma membranes. All of life'south work needs free energy. A lot of energy is likewise but lost to the environment as heat. The story of life is a story of energy period — its capture, its alter of class, its use for work, and its loss as heat. Energy, unlike affair, cannot be recycled, so organisms require a constant input of energy. Life runs on chemical energy. Where do living organisms get this chemical energy?

Where do organisms get energy from?

The chemical energy that organisms need comes from food. Food consists of organic molecules that store energy in their chemical bonds. Glucose is a simple carbohydrate with the chemical formula \(\mathrm{C_6H_{12}O_6}\). It stores chemical free energy in a concentrated, stable course. In your trunk, glucose is the course of energy that is carried in your claret and taken up by each of your trillions of cells. Cells do cellular respiration to extract energy from the bonds of glucose and other food molecules. Cells can store the extracted energy in the form of ATP (adenosine triphosphate).

What is ATP?

Permit'southward take a closer look at a molecule of ATP, shown in the figure \(\PageIndex{two}\). Although it carries less energy than glucose, its structure is more complex. "A" in ATP refers to the majority of the molecule – adenosine – a combination of a nitrogenous base and a five-carbon carbohydrate. "T" and "P" signal the three phosphates, linked past bonds that agree the energy actually used by cells. Usually, just the outermost bail breaks to release or spend free energy for cellular piece of work.

An ATP molecule is like a rechargeable bombardment: its free energy can exist used by the cell when it breaks apart into ADP (adenosine diphosphate) and phosphate, and then the "worn-out battery" ADP can exist recharged using new energy to adhere a new phosphate and rebuild ATP. The materials are recyclable, just think that energy is not! ADP can be further reduced to AMP (adenosine monophosphate and phosphate, releasing additional energy. As with ADT "recharged" to ATP, AMP can be recharged to ADP.

How much free energy does it toll to do your torso'south work? A single cell uses nigh ten one thousand thousand ATP molecules per second and recycles all of its ATP molecules about every 20-xxx seconds.

Figure \(\PageIndex{ii}\): Chemical structure of ATP consists of a 5-carbon saccharide (ribose) attached to a nitrogenous base of operations (adenine) and three phosphates. When the covalent bail between the last phosphate group and the eye phosphate group breaks, free energy is released which is used by the cells to do work.

What Is Cellular Respiration?

Some organisms can make their ain food, whereas others cannot. An autotroph is an organism that can produce its ain food. The Greek roots of the give-and-take autotroph hateful "cocky" (auto) "feeder" (troph). Plants are the best-known autotrophs, only others exist, including sure types of bacteria and algae. Oceanic algae contribute enormous quantities of food and oxygen to global nutrient chains. Plants are also photoautotrophs, a blazon of autotroph that uses sunlight and carbon from carbon dioxide to synthesize chemic energy in the form of carbohydrates. Heterotrophs are organisms incapable of photosynthesis that must therefore obtain energy and carbon from food by consuming other organisms. The Greek roots of the word heterotroph mean "other" (hetero) "feeder" (troph), meaning that their food comes from other organisms. Even if the food organism is another animal, this nutrient traces its origins back to autotrophs and the process of photosynthesis. Humans are heterotrophs, as are all animals. Heterotrophs depend on autotrophs, either direct or indirectly.

Cellular respiration is the process by which individual cells break down nutrient molecules, such every bit glucose and release energy. The process is like to called-for, although it doesn't produce light or intense heat equally a campfire does. This is because cellular respiration releases the energy in glucose slowly, in many small steps. It uses the energy that is released to form molecules of ATP, the free energy-carrying molecules that cells use to power biochemical processes. Cellular respiration involves many chemical reactions, but they tin can all be summed up with this chemical equation:

\[\ce{C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy} \nonumber\]

where the free energy that is released is in chemical energy in ATP (vs. thermal free energy as heat). The equation in a higher place shows that glucose (\(\ce{C6H12O6}\)) and oxygen (\(\ce{O_2}\)) react to form carbon dioxide (\(\ce{CO_2}\)) and h2o \(\ce{H_2O}\), releasing energy in the process. Because oxygen is required for cellular respiration, information technology is an aerobic process.

Cellular respiration occurs in the cells of all living things, both autotrophs and heterotrophs. All of them catabolize glucose to form ATP. The reactions of cellular respiration can be grouped into three main stages and an intermediate stage: glycolysis, Transformation of pyruvate, the Krebs cycle (besides chosen the citric acrid cycle), and Oxidative Phosphorylation. Figure \(\PageIndex{3}\) gives an overview of these iii stages, which are also described in item below.

Figure \(\PageIndex{3}\): Cellular respiration takes identify in the stages shown here. The procedure begins with Glycolysis. In this first pace, a molecule of glucose, which has six carbon atoms, is split into 2 iii-carbon molecules. The three-carbon molecule is chosen pyruvate. Pyruvate is oxidized and converted into Acetyl CoA. These 2 steps occur in the cytoplasm of the cell. Acetyl CoA enters into the matrix of mitochondria, where information technology is fully oxidized into Carbon Dioxide via the Krebs cycle. Finally, During the process of oxidative phosphorylation, the electrons extracted from food move downwardly the electron send concatenation in the inner membrane of the mitochondrion. As the electrons move down the ETC and finally to oxygen, they lose energy. This energy is used to phosphorylate AMP to make ATP.

Glycolysis

The first phase of cellular respiration is glycolysis. This process is shown in the top box in Effigy \(\PageIndex{3}\) showing a 6-carbon molecule existence cleaved down into two 3-carbon pyruvate molecules. ATP is produced in this process which takes place in the cytosol of the cytoplasm.

Splitting Glucose

The word glycolysis means "glucose splitting," which is exactly what happens in this stage. Enzymes split a molecule of glucose into ii molecules of pyruvate (as well known as pyruvic acrid). This occurs in several steps, as shown in effigy \(\PageIndex{iv}\). Glucose is first split into glyceraldehyde iii-phosphate (a molecule containing 3 carbons and a phosphate grouping). This process uses 2 ATP. Next, each glyceraldehyde iii-phosphate is converted into pyruvate (a 3-carbon molecule). this produces two 4 ATP and 2 NADH.

Figure \(\PageIndex{4}\): In glycolysis, a glucose molecule is converted into two pyruvate molecules.

Results of Glycolysis

Energy is needed at the start of glycolysis to split the glucose molecule into ii pyruvate molecules. These two molecules continue to stage II of cellular respiration. The free energy to split glucose is provided past two molecules of ATP. Every bit glycolysis gain, energy is released, and the energy is used to brand four molecules of ATP. As a result, there is a net gain of two ATP molecules during glycolysis. high-energy electrons are also transferred to energy-carrying molecules called electron carriers through the process
known as reduction. The electron carrier of glycolysis is NAD+(nicotinamide adenine diphosphate). Electrons are transferred to 2 NAD+ to produce two molecules of NADH. The energy stored in NADH is used in stage Iii of cellular respiration to make more ATP. At the end of glycolysis, the post-obit has been produced:
• 2 molecules of NADH
• 2 cyberspace molecules of ATP

Transformation of Pyruvate into Acetyl-CoA

In eukaryotic cells, the pyruvate molecules produced at the end of glycolysis are transported into mitochondria, which are sites of cellular respiration. If oxygen is bachelor, aerobic respiration will go forrard. In mitochondria, pyruvate will be transformed into a ii-carbon acetyl group (by removing a molecule of carbon dioxide) that will be picked up by a carrier compound called coenzyme A (CoA), which is made from vitamin B_v. The resulting compound is called acetyl CoA and its product is frequently called the oxidation or the Transformation of Pyruvate (see Figure \(\PageIndex{5}\). Acetyl CoA can exist used in a multifariousness of ways by the prison cell, merely its major role is to deliver the acetyl group derived from pyruvate to the adjacent pathway step, the Citric Acid Cycle.

Figure \(\PageIndex{5}\): Pyruvate is converted into acetyl-CoA earlier inbound the Citric Acid Bicycle (Krebs cycle)

Citric Acid Cycle

Earlier you read about the concluding two stages of cellular respiration, you demand to review the structure of the mitochondrion, where these two stages take place. Every bit you can see from Effigy \(\PageIndex{six}\), a mitochondrion has an inner and outer membrane. The space between the inner and outer membrane is chosen the intermembrane space. The space enclosed past the inner membrane is called the matrix. The second phase of cellular respiration, the Krebs bicycle, takes identify in the matrix. The 3rd stage, electron ship, takes identify on the inner membrane.

Figure \(\PageIndex{six}\): The structure of a mitochondrion is defined by an inner and outer membrane. The infinite inside the inner membrane is full of fluid, enzymes, ribosomes, and mitochondrial DNA. This space is chosen a matrix. The inner membrane has a larger surface area as compared to the outer membrane. Therefore, it creases. The extensions of the creases are chosen cristae. The infinite between the outer and inner membrane is called intermembrane space.

Recall that glycolysis produces two molecules of pyruvate (pyruvic acid). Pyruvate, which has three carbon atoms, is carve up autonomously and combined with CoA, which stands for coenzyme A. The product of this reaction is acetyl-CoA. These molecules enter the matrix of a mitochondrion, where they start the Citric Acid Bicycle. The third carbon from pyruvate combines with oxygen to class carbon dioxide, which is released as a waste product. High-energy electrons are also released and captured in NADH. The reactions that occur side by side are shown in Figure \(\PageIndex{7}\).

Steps of the Citric Acid (Krebs) Cycle

The Citric Acid Cycle begins when acetyl-CoA combines with a 4-carbon molecule called OAA (oxaloacetate; see the lower console of Figure \(\PageIndex{7}\)). This produces citric acid, which has six carbon atoms. This is why the Krebs cycle is also called the citric acid wheel. After citric acid forms, it goes through a series of reactions that release free energy. This energy is captured in molecules of ATP and electron carriers. The Krebs cycle has 2 types of energy-conveying electron carriers: NAD+ and FAD. The transfer of electrons to FAD during the Kreb's Cycle produces a molecule of FADH₂. Carbon dioxide is also released as a waste material of these reactions. The final pace of the Krebs cycle regenerates OAA, the molecule that began the Krebs cycle. This molecule is needed for the next plow through the bike. Two turns are needed because glycolysis produces ii pyruvate molecules when it splits glucose.

Figure \(\PageIndex{7}\): In the Citric Acrid Cycle, the acetyl group from acetyl CoA is attached to a four-carbon oxaloacetate molecule to form a six-carbon citrate molecule. Through a series of steps, citrate is oxidized, releasing two carbon dioxide molecules for each acetyl group fed into the cycle. In the process, iii NAD⁺ molecules are reduced to NADH, ane FAD molecule is reduced to FADH_two, and one ATP or GTP (depending on the prison cell type) is produced (by substrate-level phosphorylation). Because the final production of the citric acid bike is also the first reactant, the bicycle runs continuously in the presence of sufficient reactants.

Results of the Citric Acid Cycle

After the second turn through the Citric Acid Cycle, the original glucose molecule has been broken down completely. All half-dozen of its carbon atoms take combined with oxygen to form carbon dioxide. The energy from its chemical bonds has been stored in a total of xvi energy-carrier molecules. These molecules are:

• ii ATP
• 8 NADH
• ii FADH\(_2\)
• 6 CO\(_2\): 2 CO\(_2\) from Transformation of Acetyl CoA and 4 CO\(_2\) from Citric Acid Bicycle.

Oxidative phosphorylation

Oxidative phosphorylation is the final stage of aerobic cellular respiration. In that location are two substages of oxidative phosphorylation, Electron transport concatenation and Chemiosmosis. In these stages, energy from NADH and FADH₂, which result from the previous stages of cellular respiration, is used to create ATP.

Figure \(\PageIndex{8}\): Oxidative Phosphorylation: Electron Transport concatenation and Chemiosmosis.

Electron Transport Chain (ETC)

During this stage, high-energy electrons are released from NADH and FADH_two, and they move along electron-ship bondage found in the inner membrane of the mitochondrion. An electron-transport chain is a serial of molecules that transfer electrons from molecule to molecule by chemical reactions. These molecules are establish making upward the iii complexes of the electron ship chain (red structures in the inner membrane in Figure \(\PageIndex{8}\)). Equally electrons flow through these molecules, some of the energy from the electrons is used to pump hydrogen ions (H+) beyond the inner membrane, from the matrix into the intermembrane space. This ion transfer creates an electrochemical gradient that drives the synthesis of ATP. The electrons from the final protein of the ETC are gained by the oxygen molecule, and information technology is reduced to water in the matrix of the mitochondrion.

Chemiosmosis

The pumping of hydrogen ions across the inner membrane creates a greater concentration of these ions in the intermembrane space than in the matrix – producing an electrochemical gradient. This gradient causes the ions to flow back across the membrane into the matrix, where their concentration is lower. The catamenia of these ions occurs through a protein complex, known every bit the ATP synthase complex (see blueish structure in the inner membrane in Effigy \(\PageIndex{8}\). The ATP synthase acts as a channel protein, helping the hydrogen ions across the membrane. The flow of protons through ATP synthase is considered chemiosmosis. ATP synthase also acts as an enzyme, forming ATP from ADP and inorganic phosphate. Information technology is the catamenia of hydrogen ions through ATP synthase that gives the energy for ATP synthesis. After passing through the electron-transport concatenation, the depression-energy electrons combine with oxygen to class water.

How Much ATP?

You lot accept seen how the 3 stages of aerobic respiration apply the free energy in glucose to make ATP. How much ATP is produced in all three stages combined? Glycolysis produces two ATP molecules, and the Krebs cycle produces 2 more. Electron transport from the molecules of NADH and FADH₂ fabricated from glycolysis, the transformation of pyruvate, and the Krebs wheel creates as many as 32 more than ATP molecules. Therefore, a total of up to 36 molecules of ATP can be made from just one molecule of glucose in the process of cellular respiration.

Review

1. What is the purpose of cellular respiration? Provide a concise summary of the process.
2. Draw and explicate the structure of ATP (Adenosine Tri-Phosphate).
3. State what happens during glycolysis.
4. Describe the structure of a mitochondrion.
5. Outline the steps of the Krebs cycle.
6. What happens during the electron transport stage of cellular respiration?
7. How many molecules of ATP can be produced from ane molecule of glucose during all three stages of cellular respiration combined?
8. Do plants undergo cellular respiration? Why or why non?
9. Explain why the process of cellular respiration described in this section is considered aerobic.
10. Name three energy-carrying molecules involved in cellular respiration.
11. Free energy is stored inside chemic _________ inside a glucose molecule.
12. Truthful or Imitation . During cellular respiration, NADH and ATP are used to brand glucose.
13. Truthful or Simulated . ATP synthase acts as both an enzyme and a aqueduct protein.
14. True or False . The carbons from glucose cease up in ATP molecules at the cease of cellular respiration.
15. Which stage of aerobic cellular respiration produces the most ATP?

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Source: https://bio.libretexts.org/Bookshelves/Human_Biology/Book:_Human_Biology_%28Wakim_and_Grewal%29/05:_Cells/5.09:_Cellular_Respiration

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