Cellular Respiration

Glycolysis

Glycolysis

• “sugar-splitting”, is the first stage of cellular respiration

• 10-step process that occurs in the cytoplasm• each of the reactions is catalyzed by a specific

enzyme• is anaerobic because it does not require any

oxygen.

Glycolysis

• At the end of glycolysis, one 6-carbon glucose molecule is split into two 3-carbon pyruvate molecules.

Glycolysis Overview

http://www.science.smith.edu/departments/Biology/Bio231/glycolysis.html

3 Phases of Glycolysis

• glucose mobilization/activation (reactions #1-3)

• cleavage (reactions #4-5)• oxidation & ATP generation (reactions #6-

10)

Glucose Activation (#1-3)

• Glucose undergoes:– a phosphorylation (glucose --> glucose 6-phosphate)– an isomerization to fructose (G6P --> fructose 6-phosphate)– a second phosphorylation (F6P --> fructose 1,6-biphosphate)

• 2 ATP are used to power these reactions

Cleavage (#4-5)

• The 6-carbon molecule is split into two 3-carbon molecules: glyceraldehyde 3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP).

• DHAP immediately isomerizes into G3P• the products of the cleavage are two G3P molecules

Cleavage (#4-5)

• DHAP isomerization (to G3P) catalyzed by enzyme triosephosphate isomerase

Oxidation & ATP generation (#6-10)

• 6. For each G3P molecule, one NAD+ molecule is reduced to NADH and G3P is phosphorylated to 1,3-biphosphoglycerate

• 7. 1,3-BPG phosphorylates ADP to ATP through substrate-level phosphorylation, resulting in 3-phosphoglycerate (3PG)

• 8. 3PG is isomerized to 2PG

Oxidation & ATP generation (#6-10)

• 9. 2PG is converted to phosphoenolpyruvate (PEP) through the removal of a water molecule

• 10. PEP phosphorylates ADP to ATP through substrate-level phosphorylation, resulting in pyruvate.

Glycolysis Animations

• Overview of Glycolysis (simplified):http://www.science.smith.edu/departments/Biology/

Bio231/glycolysis.html

• Glycolysis:http://highered.mcgraw-hill.com/sites/0072507470/

student_view0/chapter25/animation__how_glycolysis_works.html

Glycolysis Overall Reaction:

Glucose + 2 NAD+ + 2 ADP + 2 Pi

2 pyruvate + 2 NADH + 2 H+ + 2 ATP

ATP Yield:

• Glycolysis produces 4 molecules of ATP per molecule of glucose.

• 2 ATP molecules are used to activate glucose.

There is an overall net yield of 2 ATP per glucose molecule.

What happens to pyruvate?

• depends on whether oxygen is present (aerobic respiration) or not (anaerobic respiration).

• fermentation is the anaerobic reduction of pyruvate to ethanol or lactic acid.

Test yourself…

• Try this quiz: http://www.zerobio.com/biofax12.htm

Further exploration…

• If you want more detail, this animation shows the enzymes involved in glycolysis as well as chemical structure of the intermediates:

• http://programs.northlandcollege.edu/biology/Biology1111/animations/glycolysis.html