CH 16 Glycolysis Stage 1 Flashcards
What does glycolysis produce?
pyruvate
What are the fates of pyruvate?
- Fermentation - ethanol.
- Lactate
- Complete Oxidation - CO2 and H20
Pancreatic and Salivary α-amylase cleaves at the ____ of ____ and ____ to yield ____ and ____.
α-1,4-bonds
starch and glycogen
maltose and maltriose
α-glucosidase (maltase)
completes digestion of di and trisaccharides into glucose.
Which molecule remains after amylase digestion?
limit dextrin
limit dextrin
dextran-rich in α-1,6-bonds.
α-Dextrinase
degrades limit dextrin.
Sucrase
hydrolyzes sucrose.
Lactase
cleaves lactose.
Glucose is generated from?
dietary carbohydrates.
What is the only fuel that the brain uses under non-starvation cond’s?
glucose
RBCs can only use this as fuel?
glucose
Why is glucose a prominent fuel in all life forms?
- available for primitive biochemical systems - formed under prebiotic cond’s.
- most stable hexose.
- low tendency to non-enzymatically glycosylate proteins.
The glycolytic pathway is common to?
virtually all cells, prokaryotic and eukaryotic.
In eukaryotic cells glycolytic enzymes are organized in?
cytoplasmic supramolecular complexes.
Cytoplasmic supramolecular complexes are an efficient organization strategy of glycolytic enzymes because?
the substrate channeling btw active sites prevents the release of toxic intermediates.
Glycolysis converts one molecule glucose into?
2 molecules pyruvate
generates 2 molecules ATP
Glycolysis - Stage 1
traps glucose in cell, modifies it to be cleaved into a pair of phosphorylated 3C compounds.
Glycolysis - Stage 2
oxidizes 3C compounds to pyruvate.
generates 2 molecules ATP.
The 1st stage of gylcolysis begins with _____ and ends with _____.
Phosphorylation of glucose by hexokinase.
Isomerization of dihydroxyacetone phosphate to glyceraldehyde 3-phosphate.
Hexokinase req’s ____ as cofactors to catalyze the rxn?
Mg2+, Mn2+
Glucose must enter the cell via?
a specific transport protein
Glucose is phosphorylated into ____ at the expense of ____ to form ____.
phosphorylated
ATP
glucose-6-phosphate
Hexokinase begins glycolysis by?
trapping glucose in the cell.
Hexokinase employs ____ to exclude ____ and minimize the undesired ____.
substrate-binding induced fit
water
hydrolysis of ATP
Hexokinase - Induced Fit
two lobes sep’d when glucose is absent.
conf. change when glucose binds.
lobes come together to create necessary environment for catalysis.
Step 1 - Glycolysis
Glucose is converted to G6-P.
Phosphorylation via hexokinase.
Irreversible.
Step 2 - Glycolysis
G6-P is converted to F6-P.
Catalyzed by phosphoglucose isomerase.
Readily reversible.
Step 3 - Glycolysis
F6-P converted to F-1,6-BP.
Catalyzed by allosteric enzyme PFK.
Irreversible.
In step 3 of glycolysis the ____ is trapped in ____ form by the addition of a _____.
carbohydrate
fructose
2nd phosphate
Step 4 - Glycolysis
F-1,6-BP cleaved into (2) 3C DHAP and GAP.
Catalyzed by aldolase.
Readily reversible rxn.
GAP can be processed to ____ to yield ___, while DHAP cannot.
pyruvate.
ATP.
Step 5 - Glycolysis
DHAP interconverted to GAP.
Isomerization by enzyme triose phosphate isomerase (TPI / TIM)
Proceeds via enediol intermediate.
TPI / TIM is the only glycolytic enzyme for which ____ can be ____.
genetic deficiency in expression.
lethal.
Triose Phosphate Isomerase (TIM / TPI) - Structure
Central core of 8 parallel β strands surrounded by 8 parallel α strands.
αβ barrel
His-95 and Glu 165 essential components of active site.
Loop closes off active site upon substrate binding.
αβ barrels are found in which glycolytic enzymes?
TPI / TIM
Aldolase
Enolase
Pyruvate Kinase
Triose Phosphate Isomerase (TIM / TPI) converts a ____ into a ____ via ____.
Ketose (ketone group ROR’). Aldose (aldehyde group ROH).
Enediol intermediate.
Triose Phosphate Isomerase (TIM / TPI) - Mechanism
- Glu 165 acts as gen base catalyst, removes H+ from substrate’s C1 to form enediol intermediate.
- Glu 165 acts as gen acid catalyst, donates H+ to C2 while His 95 removes H+ from C1.
- Product formed, Glu 161 and His 95 return to initial states.
TIM / TPI is considered a kinetically perfect enzyme because its?
rate of catalysis is near the diffusion limit.
The enediol intermediate of TPI could decompose into?
Reactive methyl gloxal (undesired product).
Structural features in enzyme prevent this.
The ____ of an aldehyde to an acid powers formation of a compound with a high ____.
oxidation
phosphoryl-transfer potential
When does the second stage of glycolysis begin?
high-phosphoryl transfer potential 1,3-bisphosphoglycerate gen’d by oxidation of GAP in rxn catalyzed by glyceraldehyde 3-phosphate dehydrogenase.
