Lecture 17 Flashcards
Hexokinase
The first step in glycolysis is the conversion of D-glucose into glucose-6-phosphate. The enzyme that catalyzes this reaction is hexokinase.
Phosphoglucose isomerase
2nd step in Glycolysis
Glucose-6-P to Fructose-6-P : setting up for phosphorylation
why important?
Third step
(phosphorylation at C-1) would be tough for hemiacetal – OH
Phosphoglucose Isomerase – Reaction 2
Glucose-6-P to Fructose-6-P : setting up for 3 carbon cleavage
Why is this reaction important?
Isomerization activates C-3 for cleavage in aldolase reaction.
Phosphofructokinase
3rd step in Glycolysis
Fructose-6-P to Fructose-1,6-Bis : phosphorylation round 2
Why is this reaction important?
When cleavage splits to 3 carbon molecules in step 4,
each will have a phosphate
PFK-I and PFK-II play a central role in glycolysis regulation
difference between “bis” phosphate vs. “di” phosphate.
Aldolase
4th step in Glycolysis
Fructose-1,6-Bis to DHAP and GAP : Split bond between carbons 3 and 4.
Cleavage of molecule doubles the substrate (i.e, doubles ATP generation in later steps).
10 steps two phases
first 5 are energy investment
last 5 are energy generation
TIM
Triose phosphate isomerase
Driving force for the TIM reaction is the “siphoning off” of Glyceraldehyde 3 P into the final stages of glycolysis.
Aldolase and Triose Phosphate
4th and 5th steps in Glycolysis
Triose phosphate isomerase (TIM)
GAPDH and phosphoglycerate kinase
6th and 7th steps in Glycolysis The first ATP is made!
GAPDH:
Glyceraldehyde 3-phosphate dehydrogenase
step 6
NAD+ —> NADH H+
PGK:
Phosphoglycerate kinase
step 7
ADP —> ATP
This type of ATP production is called “SUBSTRATE-LEVEL PHOSPHORYLATION”
How does this reaction help “pull” Glyceraldehyde-3-P into the later stages of glycolysis instead of conversion to DHAP?
Transfer of phosphate from #1 position of 1,3- Bisphosphoglycerate to ATP = lower energy.
The GAPDH and PGK reactions are coupled
to drive production of both NADH and ATP.
GAP + Pi + NAD—-> + 1,3-Bisphosphoglycerate + NADH ΔGo’ = +6.7 kJ/mol
1,3-BPG + ADP —-> 3-Phosphoglycerate + ATP ΔGo’= -18.8kJ/mol
Exergonic net reaction drives GAP enter later stages of glycolysis.
Phosphoglycerate mutase
8th step in Glycolysis 3 phosphoglycerate to 2-phosphoglylcerate: phosphate transfer
Why is this reaction important?
Creates the favorability for phosphate to leave molecule and transfer to ATP in Step 10.
Phosphoglycerate mutase (phosphoryl shift)
Mutases cause intramolecular shift of a chemical group.
For phosphoglycerate mutase, this is mediated by a histidine.
The process involves a 2,3-bisphosphate intermediate.
How an intermediate in glycolysis influences the affinity of hemoglobin for O2.
(top)There’s less oxygen in the atmosphere, I’m so glad for 2,3 BPG!
More 2,3 BPG in red blood cells is way of compensating for the lower O2 that is in the air at high
Hyperventilation
(at low atmospheric O2) raises the pH of blood.
Le Chatelier’s principle
“Respiratory Alkalosis”
What happens when the pH of the blood goes up?
The affinity of hemoglobin for O2 goes up with increasing pH, holding onto the O2 and keeping it from entering muscles, brain, and all other O2 consuming tissues.
Synthesis of 2,3 bisphosphoglycerate in ERYTRHOCYTES
The amount of 2,3 BPG in erythrocytes increases when the pH of blood
increases
Bisphosphoglycerate mutase is primarily found in erythrocytes.
Inherited diseases involving 2,3 BPG
Higher affinity of O2 for hemoglobin. Less gets into
muscles.
Glycolysis blocked at final step, much more O2 getting
into muscles.
Enolase and Pyruvate Kinase
9th and 10th steps in Glycolysis.
Second phase of making ATP!
Two more (for a total of 4) ATP are made for a net gain of 2 ATP in glycolysis.
Substrate level phosphorylation again…
phosphoenolpyruvate
Very favorable transfer of phosphate from “super-charged” phosphoenolpyruvate to ADP to make ATP
1,3 Bisphosphoglycerate
Transfer of phosphate from #1 position of 1,3- Bisphosphoglycerate to ATP = lower energy.
The Investment Phase
Driving force for the TIM reaction is the “siphoning off” of Glyceraldehyde 3 P into the final stages of glycolysis.
How to regenerate NAD+?
• One pathway is through the mitochondria, making more ATP via the TCA cycle (aerobic).
• Another is anaerobic, without O2 or mitochondria.
30
1. How our muscles regenerate NAD+.
2. How NAD+ regenerates in yeast (the beer making phase!)
- Anaerobic fate of pyruvate
muscle
• This reaction is referred to as “homolactic fermentation”
– no net change in oxidation state of the carbons.
• Glycolysis to lactate is referred to as “anaerobic glycolysis”.
- Anaerobic fate of pyruvate
yeast
This reaction is referred to as “alcoholic fermentation”.
*We also will encounter TPP in pyruvate dehydrogenase (PDH) reaction.
Structure & Function of Thiamine Pyrophosphate
The cofactor, TPP is used as a coenzyme for de-carboxylations of α-keto acids. It is derived from thiamine (Vitamin B1) by transfer of a pyrophosphate group from ATP to thiamine, yielding TPP and AMP.
Aldehyde dehydrogenase
2 forms of aldehyde dehydrogenase:
mitochondrial and cytoplasmic
NOTE: Some people (particularly in Asian populations) have a less active form of the mitochondrial form of aldehyde dehydrogenase. Acetaldehyde accumulates in blood.
step 2
Phosphoglucose Isomerase
The second reaction of glycolysis is the rearrangement of glucose 6-phosphate (G6P) into fructose 6-phosphate (F6P) by glucose phosphate isomerase (Phosphoglucose Isomerase).
step 3
Phosphofructokinase
Phosphofructokinase, with magnesium as a cofactor, changes fructose 6-phosphate into fructose 1,6-bisphosphate.
step 4
Aldolase
The enzyme Aldolase splits fructose 1, 6-bisphosphate into two sugars that are isomers of each other. These two sugars are dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (GAP).
Step 5
Triphosphate isomerase
The enzyme triophosphate isomerase rapidly inter- converts the molecules dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (GAP). Glyceraldehyde phosphate is removed / used in next step of Glycolysis.
Step 6
Glyceraldehyde-3-phosphate Dehydrogenase
Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) dehydrogenates and adds an inorganic phosphate to glyceraldehyde 3-phosphate, producing 1,3-bisphosphoglycerate.
Step 7
Phosphoglycerate Kinase
Phosphoglycerate kinase transfers a phosphate group from 1,3-bisphosphoglycerate to ADP to form ATP and 3-phosphoglycerate.
Step 8
Phosphoglycerate Mutase
The enzyme phosphoglycero mutase relocates the P from 3- phosphoglycerate from the 3rd carbon to the 2nd carbon to form 2-phosphoglycerate.
Step 9
Enolase
The enzyme enolase removes a molecule of water from 2-phosphoglycerate to form phosphoenolpyruvic acid (PEP).
Step 10
Pyruvate Kinase
The enzyme pyruvate kinase transfers a P from phosphoenolpyruvate (PEP) to ADP to form pyruvic acid and ATP Result in step 10.
Steps 1 and 3
-2 ATP
Steps 7 and 10
+4 ATP
Net ATP produced
2
