Chapter 18 (Glycolysis) Flashcards
Glycolysis is ten reactions that are (different/the same) in all cells but have (different/the same) rates of reaction
the same different
The products of glycolysis are
2 NADH 2 ATP (net) 2 pyruvate
Three possible fates for pyruvate
Aerobic oxidation (TCA cycle) Anaerobic glycolysis (2 lactate) Anaerobic fermentation (2 ethanol + 2 CO2)
Two stages of glycolysis
First stage - the conversion of a 6C sugar to 2 3C sugars (requires 2 ATP) Second stage - the energy products (produces 2 NADH + 4 ATP)
The first reaction of glycolysis (Stage 1) Hexokinase
The phosphorylation of glucose Irreversible Priming reaction Requires 1 ATP
Reaction 1 of glycolysis is important because (Stage 1)
Glucose readily diffuses through the cell via facilitated diffusion (which goes from high to low concentrations) so the conversion of glucose to glucose-6-P allows it to stay inside the cell (cannot diffuse across)
Why is the first reaction in glycolysis not the most important? (Stage 1)
Because glucose-6-P can go into several different metabolic pathways
Why is H2O excluded from a kinase active site
Because the -OH of H2O would hydrolyze the ATP (instead of the gamma phosphate going to the -OH on the C#6 in glucose)
The second reaction of glycolysis (Stage 1) Phosphoglucose Isomerase (PGI)
It is the isomerization of glucose-6-P into fructose-6-P Changes an aldehyde into a ketone
Why is the second reaction of glycolysis important? (Stage 1)
Because it makes the C#1 in fructose-6-P easier to be phosphorylated (primary -OH) Activates C#3 for cleavage in the aldolase reaction (breaking of bond between C#3 and C#4)
An isomerase reaction will always have a ___ intermediate
endiolate intermediate (HO-C=C-OH)
The third reaction of glycolysis (Stage 1) Phosphofructokinase (PFK)
It is the phosphorylation of the C#1 of fructose-6-P which produces fructose-1,6-BP The first committed step of glycolysis The second priming reaction Highly regulated Requires 1 ATP
When energy is low the enzyme phosphofructokinase activity (increases/decreases) and vis versa
increases
The bis- in bisphosphate means
That there are 2 phosphate groups but they are not attached to one another
The fourth reaction of glycolysis (Stage 1) Aldolase
The cleavage of fructose-1,6-BP in between C#3 and #4 into 2 3C sugars: DHAP and GAP
For an aldol cleavage to occur between the C#3 and C#4 in fructose-1,6-BP, there must be
a carbonyl at C#2 (C=O) and a hydroxyl group at C#4 (C-OH) This is one of the reasons why the isomerization of glucose-6-P to fructose-6-P is so important
Class I Aldolase
Animal aldolases that form a covalent Schiff base intermediate between a substrate and the active site on lysine (Fru-C=N-lys)
The reason why we make a Schiff base
Because the carbon in the Schiff base is more electrophilic
Class II Aldolase
Occurs in bacteria and fungi A metal ion (usually Zn) is used as the active site No Schiff base is formed
The fifth reaction of glycolysis (Stage 1) Triosphosphate Isomerase (TIM)
The isomerization of DHAP into GAP A ketone to aldehyde isomerization
In the cell which concentration is usually higher - DHAP or GAP?
DHAP because it helps with regulation
Carbon labeling of GAP
Aldehyde = C#3 or C#4 Alcohol = C#2 or C#5 Phosphate group = C#1 or C#6
The sixth reaction of glycolysis (First of Stage 2) GAP Dehydrogenase (GAPDH)
The oxidation (of the aldehyde) and the phosphorylation of GAP by NAD and Pi which produces 1,3-Bisphophoglycerate Since the aldehyde is oxidize that means the NAD+ is reduced
Is 1,3-Bisphosphoglycerate (BPG) considered a high energy or low energy compound?
High energy
Using the enzyme GAPDH involves a ___ transfer and a ___ intermediate
hydride transfer (from GAP to NAD) acylthioester intermediate (E-S-C=O)
The seventh reaction of glycolysis (Second of Stage 2) Phosphoglycerate Kinase (PGK)
The transfer of a phosphate group from 1,3-BPG to ADP which yields 3-Phosphoglycerate Produces the first ATP of glycolysis Considered substrate level phosphorylation because it takes the “high energy” phosphate from 1,3-BPG
The eighth reaction of glycolysis (Third of Stage 2) Phosphoglycerate Mutase (PGM)
The transfer of a phosphate group from C#1/6 to C#2/5 to yield 2-Phosphoglycerate Has unique phosphorylated Histidine in its active site Important step in creating the next high energy compound
Mutase
catalyzes the transfer of a function group from one position to another on a molecule
Using the enzyme PGM forms a ___ intermediate
2,3-BPG intermediate required in trace amounts to regenerate PGM when it is inactive
The ninth reaction of glycolysis (Fourth of Stage 2) Enolase
The dehydration of 2-PG (-OH on C#1/6) into Phosphoenolpyruvate Creates a compound (PEP) that is capable of synthesizing ATP via its high energy phosphate
The last reaction of glycolysis (Fifth of Stage 2) Pyruvate Kinase
The transfer of a phosphate group from C#2/5 on PEP to ADP to generate ATP Irreversible Involves a tautomerization
Tautomerization
Going from the enol form (O-C=C-R) to the more stable keto form (O=C-C-R)
The tautormerization produced when using Pyruvate Kinase is very
exergonic and represent the majority of the phosphoryl group transfer potential of PEP (where all the energy in the reaction comes from)
What are the three irreversible steps of glycolysis and why are they irreversible
Hexokinase Phosphofructokinase Pyruvate kinase They are irreversible because they have a large delta G
What is the overall reaction of glycolysis
Glucose + 2 NAD + 2 ATP + 2 Pi goes to 2 Pyruvate + 2 NADH + 2 ATP + 2 H2O + 4 H
For glycolysis to continue ___ must be recycled to ___
NADH NAD+
Through glycolysis there is a net ATP gain of ___ per molecule of Glucose
2
