Glycolysis Steps Flashcards
(19 cards)
Which steps of glycolysis are assigned to each phase?
Energy investment => steps 1-3
Cleavage => steps 4-5
Energy payoff/liberation => steps 6-10
Glycolysis step 1 (energy investment)
Glucose is phosphorylated by ATP to make glucose-6-phosphate (G6P)
Enzyme: Hexokinase
What is the importance of glucose-6-phosphate (G6P)?
Glucose can participate in both passive and active transport (mostly passive), but attaching a phosphate ion prevents backflow of glucose because ions are not permeable across the cell membrane
What is hexokinase?
An enzyme that adds a phosphate group from ATP to the 6th carbon of glucose; it is a rate-limiting step (one of the slowest enzymes of glycolysis)
Glycolysis step 2 (energy investment)
The structure of G6P is rearranged to Fructose-6-phosphate (F6P)
Enzyme: Phosphoglucose isomerase (PGI)
Glycolysis step 3 (energy investment)
Fructose-6-phosphate is phosphorylated by ATP to make fructose-1,6-bisphosphate (FBP) => achieving symmetrical molecule
Enzyme: Phosphofructokinase (PFK)
What is phosphofructokinase?
An enzyme that adds a phosphate group from ATP to the first carbon of F6P; SLOWEST glycolysis enzyme => another rate limiting step
Relationship between ATP and phosphofructokinase?
ATP is an allosteric regulator of phosphofructokinase, specifically a non competitive inhibitor; when ATP binds to phosphofructokinase at a regulatory site, the reaction rate slows dramatically
What is feedback inhibition? (textbook; lecture info)
When an enzyme in a pathway is inhibited by the product of the reaction sequence, feedback inhibition occurs; how your cell knows when to stop
Glycolysis step 4 (cleavage)
Fructose-1,6-bisphosphate (FBP) is cleaved into dihydroxyacetone phosphate (DAP) and glyceraldehyde-3-phosphate (G3P)
Enzyme: Aldolase
Glycolysis step 5 (cleavage)
Dihydroxyacetone phosphate (DAP) is isomerized to glyceraldehyde-3-phosphate (G3P) because only G3P proceeds through glycolysis => 2 G3Ps
No enzyme; enediol intermediate
Glycolysis step 6 (energy payoff/liberation)
-The two G3Ps are phosphorylated and oxidized into two 1,3-bisphosphoglycerate (1,3-BPG), a high energy compound (this is an exergonic reaction)
-electrons/protons from the two G3P (oxidation) reduce 2 NAD+ to 2 NADH (this is an endergonic reaction)
Enzyme: Glyceraldehyde-3-phosphate dehydrogenase (GAPDH)
-OVERALL ENDERGONIC reaction => must be coupled w/ reaction 7
Is G3P phosphorylated from an ATP?
No; it is through a dehydration synthesis from a free inorganic phosphate, and the energy for this process comes from oxidation energy i.e. high energy electrons (from redox reaction between G3P and NAD+)
Glycolysis step 7
-A phosphate is removed from each 1,3-BPG to form two 3-phosphoglycerate (3PG)
Enzyme: Phosphoglycerate Kinase (PGK)
-The removed phosphates are transferred to 2 ADPs to make 2 ATPs via SUBSTRATE-LEVEL PHOSPHORYLATION
What is reaction coupling? How are steps 6 and 7 of glycolysis coupled?
An energetically favorable reaction (exergonic) is directly linked with an energetically unfavorable (endergonic) reaction
Reaction 6 is endergonic and reaction 7 is highly exergonic
Glycolysis step 8
The phosphate groups in both 3-phosphoglycerate is moved to a new location creating two 2-phosphoglycerate
Enzyme: Phosphoglycerate mutase (PGM)
Glycolysis step 9
A water molecule is removed from each 2PG (not dehydration synthesis) to form two phosphoenol-pyruvate (PEP; second high energy phosphate compound), the phosphate group is destabilized => bond will break in a highly exergonic reaction (drives next step i think)
Enzyme: Enolase
Glycolysis step 10
-Each PEP transfers its phosphate to 2 ADPs, turning it into 2 pyruvates
-TWO more molecules of ATP are made
-The second substrate level phosphorylation
Enzyme: Pyruvate Kinase (PK)
What is the final outcome of glycolysis?
Make 2 pyruvate (and 2 NADH and 2 ATP)
