Glycolysis

Stage 1 of both anaerobic and aerobic cellular respiration

What is glycolysis?

• Breaks down C₆H₁₂O₆

• The first step in both anaerobic and C₆H₁₂O₆ cellular respiration

• No O₂ is required for this step (anaerobic process)

• Occurs in the cytoplasm of the cell

• Each step catalyzed by a specific enzyme

• 2 ATP is required to start this process and 4 ATP is produced

  • Net: 2 ATP and 2 NADH

• C₆H₁₂O₆ (6C) is broken down into 2 pyruvate (3C)

What happens step 1 of glycolysis?

• The enzyme hexokinase adds a phosphate from ATP to glucose

• Phosphorylating glucose, creating Glucose-6- Phosphate (C6P)

What happens step 2 of glycolysis?

• Glucose-6-Phosphate is unstable

• It is quickly rearranged with the help of an enzyme (phosphohexoseisomerase)

• Into Fructose-6 Phosphate (F6P) a more structurally stable isomer

What happens in step 3 of glycolysis?

• The enzyme Fructokinase adds a second P_i to the branched C, phosphorylating it

• Creating Fructose-1,6-Biphosphate

What happens in step 4 of glycolysis?

• Fructose-1,6-Biphosphate is unstable

• so with the assistance of an enzyme it splits in to:

  • Glyceraldehyde-3-Phosphate (G3P)

  • Dihydroxyacetone-Phosphate (DHAP)

What happens in step 5 of glycolysis?

• Dihydroxyacetone-Phosphate (DHAP) rearranges to form a more stable state with the assistance of an enzyme (isomerization)

• Creating Glyceraldehyde-3-Phosphate (G3P)

What happens in step 6 of glycolysis?

• The 2 G3P molecules are oxidized by 2 NAD⁺ coenzymes

• There is enough free energy phosphorylate G3P

• The reaction is catalyzed by an enzyme.

• The two molecules are now known as 1,3-diphosphoglycerate

What happens in step 7 of glycolysis?

• The newly added 2 P_i is immediately used to create 2 ATP molecules from 2 ADP (with an enzyme present to hold everything in place)

• Resulting in 3-Phosphoglycerate

What happens in step 8 of glycolysis?

• Each of the molecules isomerize into a more stable form with assistance of an enzyme

• This puts the P_i in the centre of the molecule

What happens in step 9 of glycolysis?

• With assistance of an enzyme the hydroxyl groups (OH) in both molecules fold onto themselves and water is produced by both molecules via dehydration reaction

• The resulting molecule is Phosphoenolpyruvate (PEP)

What happens in step 10 of glycolysis?

• The remaining phosphate group is removed through phosphorylation (assisted by an enzyme)

• Forming 2 ATP molecules and 2 pyruvate (3C molecule)

What happens in stage 1 of glycolysis?

• Investment/ Activation

• First 4 steps

• 2 phosphate groups are transferred to glucose via phosphorylation where ATP is converted in to ADP

• Resulting in Fructose 1, 6-bisphosphate

What happens in stage 2 of glycolysis?

• Sugar splitting

• Fructose 1, 6-bisphosphate gets split into 2 fragments, Dihydroxyacetone phosphate (DHAP), and Glyceraldehyde 3-phosphate (G3P)

• DHAP gets converted into another G3P

• Resulting in 2 G3P molecules

What happens in stage 3 of glycolysis?

• Oxidation

• Both molecules of G#P become oxidized using NAD⁺, which becomes NADH

• This process releases energy which is used to attach phosphates to sugars

• Resulting in 1, 3-biphosphoglycerate

What happens in stage 4 of glycolysis?

• Payoff

• Last 4 steps of glycolysis

• the phosphate groups of molecules are transferred to ADP, creating ATP

• THis is done via the process of Substrate level phosphorylation

What are the overall inputs of the system?

2 ATP, glucose, 2 NAD⁺, 2 P_i

What are the overall outputs of the system?

4 ATP, 2 Pyruvate, 2 H₂O*, 2 NADH

*water molecules produced by glycolysis are not considered overall products as they are consumed and recycled in other stages of CR (mainly during the citric acid cycle)