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The conversion of glucose to adenosine triphosphate (ATP), the source of energy for the body's cells, occurs in the process of cellular respiration.
The conversion of glucose to adenosine triphosphate (ATP), the source of energy for the body's cells, occurs in the process of cellular respiration.
FUN AND SIMPLE OVERVIEW:
From https://www.eonslearning.org/uploads/1/8/5/2/18521226/cell-respiration-2_orig.png
1 Glucose + 6 Oxygen --> ATP + 6 Carbon Dioxide + 6 Water
1 Glucose + 6 Oxygen --> ATP + 6 Carbon Dioxide + 6 Water
1. Glycolysis
1. Glycolysis
**Glyco lysis = sugar splitting**
The main purpose of glycolysis is to provide two 3-carbon molecules called pyruvate. These pyruvate molecules later enter the second phase of cellular respiration to continue the process of ATP production. Glycolysis has two phases: one that requires energy, and one that produces energy. At the end of the process, we're left with two pyruvate molecules, a net gain of two ATP molecules, and two NADH molecules.
The purpose of NAD+ is to oxidize other molecules by removing an electron (a diagram for how this electron exchange generally works can be found on this page), which is necessary for the ultimate conversion of glucose to pyruvate. The reduced NADH holds onto these electrons and uses them later in the electron transport chain to power the synthesis of ATP (see Step 3).
Glycolysis needs the oxidized form of NADH, NAD+, to keep the process going; without NAD+, glycolysis will halt. In the presence of oxygen, NADH can pass through the electron transport chain (see Step 3) and become oxidized back to NAD+ to be used in glycolysis once again.
[10]
VISUAL SUMMARY:
(Pyruvate Oxidation)
(Pyruvate Oxidation)
In order for the citric acid cycle to occur, pyruvate must be oxidized to acetyl coenzyme A (acetyl-CoA). Pyruvate oxidation occurs twice, once for each of the two pyruvate molecules that come out of glycolysis. This process also produces one molecule of NADH and one molecule of carbon dioxide [11].
VISUAL SUMMARY:
2. Citric Acid Cycle
2. Citric Acid Cycle
The citric acid cycle occurs once per pyruvate molecule, which means twice per molecule of glucose that enters glycolysis. Acetyl CoA enters the citric acid cycle and combines with oxaloacetate to become citrate, after which this cycle is named. It's also known as the Krebs cycle (named after founder Hans Adolf Krebs) or the tricarboxilic acid (TCA) cycle.
Citrate releases the other two carbon dioxide molecules (think of the equation for the overall process of cellular respiration: 1 glucose --> 6 CO2 ; 1 pyruvate --> 3 CO2) and 2 NADHs, gathering more electrons for the electron transport chain in Step 3.
The enzymes that catalyze these reactions can speed up or slow down the cycle depending on the energy demands of the cell. This is why you breathe more rapidly when you exercise -- you're exhaling CO2 more quickly, which demonstrates the rapidified citric acid cycle (because CO2 is a product).
In total, one turn of the citric acid cycle releases two carbon dioxide molecules, three NADH, one FADH2 (another electron carrier), and one ATP or GTP (similar to ATP).
[12]
VISUAL SUMMARY:
3. Oxidative Phosphorylation
3. Oxidative Phosphorylation
In this step, electrons from NADH and FADH2 are finally used, and these molcules are oxidized back to NAD+ and FAD, respectively. Their electrons are transferred through a series of electron carrier proteins that are embedded in the inner membrane of the mitochodria, where most of cellular respiration takes place.
A byproduct of these electron transfers is a proton (H+) gradient across the inner mitochondrial membrane, and these protons diffuse back across the membrane through an enzyme called ATP synthase, which synthesizes ATP. This process is called chemiosmosis.
Lastly, oxygen becomes reduced, forming water, as the final electron acceptor at the end of the carrier proteins.
[13]
VISUAL SUMMARY:
Oxidative: oxygen is the final electron receptor
Phosphorylation: ADP gets phosphorylated (gains a phosphate group) to become ATP (diphosphate --> triphosphate) by ATP synthase
Phosphorylation: ADP gets phosphorylated (gains a phosphate group) to become ATP (diphosphate --> triphosphate) by ATP synthase
NOW FOR A MORE COMPLEX SUMMARY (specific amounts of products, more specific visuals):
In other words, carbs <3.
In other words, carbs <3.
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