Sections Available: Brief Overview, Video, Process: Easy Step by Step, Process: Word for Word, & Pictures

Video: https://www.osmosis.org/learn/Glycolysis

Process: Easy step by step

+ = added

- = broken down into/took away

→ turned into, energy NOT required

= = end result from reaction

{ } = byproducts from reaction or resulting reactions

italicized - enzyme

1. Glucose + phosphate group from ATP by Hexokinase = Glucose 6-phosphate {ADP}

2. Glucose 6-phosphate → Fructose 6-phostphate by Phosphohexose isomerase

3. Fructose 6-phosphate + phosphate group from ATP by phophofructokinase-1 = Fructose 1, 6 bisphophate {ADP}

4. Fructose 6-phosphate split by aldolase = 2 three-carbon molecules glyceraldehyde 3-phosphate (G₃P) and dihydroxyacetone phosphate (DHAP)

5. DHAP → G₃P by triosephosphate isomerase

6. (2) G₃P - Hydrogen & + phosphate by glyceraldehyde 3-phosphate dehydrogenase = (2) 1,3-Bisphosphoglycerate (BPG) {NAD⁺ + Hydrogen = NADH}

7. (2) 1,3 BPG - phosphate by phosphoglycerate = (2) 3-Phosphoglycerate. {ADP + phosphate = ATP)

8. (2) 3-Phosphoglycerate → (2) 2-phosphoglycerate by phosphoglycerate mutase

9. (2) 2-phosphoglycerate - H_²O (Water) by enolase = Phosphoenolpyruvate (PEP)

10. (2) PEP - phosphate by pyruvate kinase = (2) Pyruvate {ADP + phosphate = ATP)

Process: Word for word

Cellular Respiration is a metabolic pathway that uses glucose to produce ATP, which the body can use for energy. One molecule of glucose can produce 30-32 ATP. ATP supports many different reactions in the body. The three main stages of cellular respiration are: Glycolysis, the Krebs cycle (or TCA, the citric acid cycle), and the electron transport chain (ETC). During the electron transport chain oxidative phosphorylation occurs, which requires oxygen, and so does the Kreb cycle. However, oxygen is not needed for glycolysis and can be performed under anaerobic conditions.

Cellular respiration occurs in 2 different parts of the cell, the cytoplasm and the mitochondria. Glycolysis takes place in the cytoplasm, both the Kreb cycle and the ETC chain occur in the mitochondria, but Krebs takes place in the matrix while the ETC takes place in the inner mitochondrial membrane. In order to power cellular respiration, glucose, ATP, NAD⁺, and FAD are needed. While each stage may not require all reactants, they are all essential to the process. The final end products of cellular respiration are ATP and H₂O. While other products may be created throughout the process like NADH, FADH₂, or CO₂, they can be used later on by the ETC.

The first stage of cellular respiration is glycolysis. During glycolysis, glucose (a 6 carbon sugar molecule) is split into two three carbon molecules known as pyruvate. As glucose is split during a series of enzymatic reactions ATP is produced. Glycolysis has 10 steps, which can be split into two different phases, an energy consuming phase and an energy producing phase. Glycolysis requires ATP in order to make ATP. 

To begin the reaction, a molecule of glucose is transported inside the cells by glucose transporters or GLUT. Through phosphorylation, the shape of glucose changes, preventing it from diffusing out the cell. This added phosphate comes from ATP, which breaks down into ADP and phosphate. Enzymes hexokinase and glucokinase both add a phosphate to glucose turning it into glucose 6- phosphate. Glucose 6-phosphate is then converted to fructose 6-phosphate, its isomer, by the enzyme phosphohexose isomerase; this step does not require ATP to occur. Through another breakdown of ATP, to result in ADP and phosphate, the enzyme phosphofructokinase-1 adds another phosphate to fructose 6-phosphate creating fructose 1,6 bisphosphate. While the input of energy to make energy is not the clearest, the idea is to create more energy than what was used.

Fructose is then split by the enzyme aldolase into 2 three-carbon molecules, glyceraldehyde 3-phosphate (G₃P) and dihydroxyacetone phosphate (DHAP). Because DHAP cannot continue glycolysis, it’s converted into G₃P by triosephosphate isomerase, resulting in 2 G₃P molecules. Each G₃P molecule is converted into 1,3 bisphosphoglycerate (BPG) by G₃P dehydrogenase. In this reaction, G₃P dehydrogenase removes a hydrogen from G₃P and gives it to NAD⁺ to form NADH. It also adds a phosphate group to G₃P to make 1,3 BPG. Enzyme phosphoglycerate kinase removes a phosphate from 1,3 BPG and gives it to ATP, forming 3-phosphoglycerate and ATP. Next, enzyme phosphoglycerate mutase moves the phosphate to carbon 2 to make 2-phosphoglycerate. After, an enzyme called enolase removes a water molecule from 2-phosphoglycerate to make phosphoenolpyruvate and ATP. Because there are 2 G₃P molecules, all products after G₃P was formed are doubled. The final results of glucose are, 4 ATP, 2 NADH, 2 H₂O, and 2 pyruvates. However, the net result of ATP is only 2 since 2 ATP were used in the first half of glycolysis. While 2 ATP may be sufficient enough for smaller organisms, it cannot support all life forms. The other stages of cellular respiration are there to create more energy.