14 terms

Glycolysis steps

Step One
Glucose enters cell, phosphorylated by hexokinase - phosphate group transfers from ATP to sugar, makes glucose more chemically reactive
Step Two
Glucose-6-phosphate converted to its isomer, fructose-6-phosphate
Step Three
Phosphofructokinase transfers another phosphate group from ATP, sugar not has 2 phosphate groups and is ready to be split in half
Step Four
Aldolase cleaves the sugar molecule into two different 3-carbon sugars: 1) Dihydroxyacetone phosphate, 2) Glyceraldehyde-3-phosphate (isomers of each other)
Step Five
Isomerase catalyzes the reversible reaction b/w the two 3-carbon sugars - never reaches an equilibrium because step six only uses gyceraldehyde-3-phosphate
Step Six
Triose phosphate dehydrogenase catalyzes 2 sequential reactions while it holds glyceraldehyde-3-phosphate in its active site: First, sugar is oxidized by the transfer of electrons and H+ to NAD+ --> NADH - this is a very exergonic reaction, phosphate group is then attached to the oxidized substrate so it has very high potential energy
Step Seven
Some ATP produced by substrate-level phosphorylation - phosphate group added in step six transferred to ADP to make ATP, produces 2 total (every product after step 4 is doubled). We now have 2 molecules of phosphoglycerate- no longer a sugar.
Step Eight
Phosphoglyceromutase relocates remaining phosphate group to prepare substrate for next reaction, creating 2-phosphoglycerate
Step Nine
Enolase causes a double bond to form in the substrate by extracting a water molecule, yielding phosphoenolpyruvate (PEP). Electrons are rearranged so resulting compound has very high potential energy - allows step 10 to occur.
Step Ten
The last reaction of glycolysis produces more ATP, phosphate group transferred from PEP to ADP - second instance of substrate-level phosphorylation. 2 ATP produced total
Net results of glycolysis
2 ATP invested, 4 produced, meaning a net gain of 2 ATP. Additional energy stored in form of NADH in step 6 - can be used to make ATP w/ oxidative phosphorylation if oxygen is present. Glucose has been broken down and oxidized into two molecules of pyruvate.
Two Phases of Glycolysis
1) Energy investment phase
2) Energy payoff phase
Location of Glycolysis
Occurs in the cytosol of a cell
Substrate-level Phosphorylation
A mode of ATP synthesis when an enzyme transfers a phosphate group from a substrate molecule to ADP rather than adding an inorganic phosphate to ADP as in oxidative phosphorylation.