Andrea: Glycolysis Biochem Exam 4

Final Exam

How many steps does cellular respiration have?

It has three steps: glycolysis, citric acid cycle, and electron transport chain.

What is Acetyl-CoA production?

glycolysis and amino acid/fatty acid catabolism

What is Acetyl-CoA oxidation?

It’s the citric acid cycle (TCA cycle/Krebs cycle)

What are the four major ways that glucose is used?

the making of polysaccharides, its oxidized into pyruvate (to provide ATP), its also oxidized into ribose-5-phosphate and NADPH for nucleic acid synthesis and reductive biosynthetic processes

So what is glycolysis?

almost the universal pathway for the breaking down of glucose (catabolism)

What is glycolysis governed by?

it’s governed by thermodynamic principles and common mechanisms shared by all pathways of cell metabolism=model of principles

How many steps and phases does glycolysis have?

10 steps, and two phases (predatory and payoff phases)

What is Phase 1 also referred to?

the preparatory phase

What is the 1st step of glycolysis?

glucose if phosphorylated into glucose-6-phosphate, by enzyme hexokinase

What is the 2nd step of glycolysis?

glucose-6-phosphate is converted into fructose-6-phosphate

What is the 3rd step of glycolysis?

fructose-6-phosphate is phosphorylated to fructose-1,6-bisphosphate by phosphofructokinase.

What is the 4th step of glycolysis?

it splits into two molecules: dihydroxyacetone phosphate and glyceraldehyde-3-phosphate.

What is the 5th step of glycolysis?

Isomerization of dihydroxyacetone to glyceraldehyde 3-phosphate

What is the phase 1 (preparatory phase) overview?

-after the first five steps of glycolysis, two molecules of ATP are invested to raise the free energy content.

-carbon chains are also converted to the product= glyceraldehyde-3-phosphate

Why is glucose 6-phosphate converted to fructose 6-phosphate in step 2?

To convert an aldose to a ketose, allowing symmetric cleavage in a later step

What is phase two also referred as?

the payoff phase of glycolysis

What is step 6 of glycolysis?

Oxidation of glyceraldehyde-3-phosphate and phosphorylation to form 1,3-bisphosphoglycerate happens

What is step 7 of glycolysis?

it gets dephosphorylated to form 3-phosphoglycerate

What is step 8 of glycolysis?

the molecule is then isomerize to form 2-phosphoglycerate

What is step 9 of glycolysis?

goes through elimination to produce phosphoenolpyruvate

What is step 10 of glycolysis?

molecule is dephosphorylated to produce two pyruvate molecules

What do the dephosphorylation steps do?

They were put in place to add phosphate to ADP to produce ATP

Why does glucose remain in the cell?

because of initial phosphorylation (only on carbon 6, can’t happen on carbon 1)

Why does the carbonyl have to be moved to carbon two?

so the rest of the reactions can occur

What can happen now that the carbonyl has moved?

now carbon 1 can be phosphorylated, and that ensures that both products after cleavage are phosphorylated.

What does the carbonyl at carbon two also ensure?

carbon-carbon bond cleavage (which gives us two three-carbon products) necessary for glycolysis.

What do we want specifically to happen during step 5?

We want both products to be the same (DHAP to G3P) to get through the rest of the pathway.

What is required for ATP production?

oxidation and phosphorylation (also NADH will be made)

What happens during step 8?

The phosphoryl group moves from carbon 3 to carbon 2, which sets up the final steps of the pathway.

What happens during step 9?

dehydration activates the phosphoric group for transfer to ADP

Step 10?

ATP production

Why does triose phosphate isomerase in step 5 convert dihydroxyacetone phosphate (DHAP) into glyceraldehyde-3-phosphate (G3P)?

Only G3P can continue through the subsequent oxidation and ATP-generating steps of glycolysis.

Why can’t phosphorylated glycolytic intermediates leave the cell?

there is a lack of transporters for phosphorylated sugars, and their negative charge prevents diffusion across the membrane.

Why are phosphoryl groups essential components in the enzymatic conservation of metabolic energy?

because there’s potential chemical energy stored in their phosphate ester bonds, and group transfer converts high energy phosphoryl to ATP.

What does the binding of phosphate groups to an enzyme’s active site do?

It lowers activation energy and increases specificity of the enzymatic reaction.

What allows hexokinase to favor glc over h20?

Induced fit (conformational change)

What happens in the absence of GLC?

inactive conformation, and active site residues are out of position for the reaction.

Phosphohexose Isomerization is?

a reversible reaction from aldose to ketose (step 2)

What is Phosphohexose Isomerization catalyzed by?

phosphohexose isomerase (requires Mg2+)

What does the mechanism of Phosphohexose Isomerase involve?

this mechanism involves an acid-base catalysis with an enediol intermediate.

How does the ring opening occur during phosphohexose isomerase?

by catalytic His

How is the proton abstraction possible?

by active site Glu in the cis-enediol formation

What amino acid is responsible for the general acid catalysis by the same Glu?

Glu

How does the ring close during Phosphohexose Isomerase?

also closes by catalytic His

How does the phosphorylation of fructose-6-phosphate happen?

phosphoryl group transfer from ATP, which is catalyzed by PFK-1.

Is the phosphorylation of fructose-6-phosphate reversible or irreversible?

Irreversible in cellular conditions

Glucose 6-phosphate and fructose 6-phosphate:

have other possible fates outside of glycolysis

Fructose 1,6-bisphosphate (FBP)

is only in glycolysis

How is PFK-1 regulated?

it’s regulated allosterically, meaning it’s activity is controlled by molecules that bind to sites other than its active site (allosteric sites).

When is PFK-1 activated?

it’s activated when ATP is running lower than normal, when ADP and AMP builds up, and when ribulose-5-phosphate increases.

When is PFK-1 inhibited?

when a lot of ATP is present, and when a lot of other fuels (like fatty acids) are present as well.

What triggers the aldol cleavage of fructose 1,6-biphosphate (FBP?)

reverse aldol condensation, which is a carbon-carbon bond breakage.

What does the carbon carbon bond breaking during aldol condensation result to?

this forms two different triose phosphates.

What is the aldol cleavage of Fructose 1,6-biphosphate catalyzed by?

aldolase

What happens during the trios phosphate interconversion step?

This step changes dihydroxyacetone phosphate (DHAP) into glyceraldehyde-3-phosphate (G3P) so it can continue through the rest of glycolysis.

What happens after triose phosphate interconversion?

After this step, both halves of the original glucose molecule become G3P.

What monosaccharide is responsible for both halves of the original glucose molecule becoming G3P?

triose isomerase

During step 6 of glycolysis, what is the aldehyde group oxidized to?

a carboxylic acid anhydride with phosphoric acid

What is an acyl phosphate bond a representation of?

very high standard free energy of hydrolysis

What is the oxidation of GAP to 1,3-BPG catalyzed by?

glyceraldehyde 1-phosphate dehydrogenase (GAPDH)

What does glyceraldehyde 1-phosphate dehydrogenase (GAPDH) require?

it requires NAD+

Mechanism of GAPDH: What happens when the ES-complex is formed?

the pka of Cys is reduced when NAD+ is bound, making it more reactive

Mechanism of GAPDH: What is the second mechanism of GAPDH?

thiohemiacetal is formed

Mechanism of GAPDH:What is the third mechanism of GAPDH?

Mechanism of GAPDH:What is the fourth mechanism of GAPDH?

Mechanism of GAPDH: What is the fifth mechanism of GAPDH?

Phosphorolysis by P_i

What is step 7 of glycolysis?

it’s the 1st production of ATP, and it consists of a transfer

Which step of glycolysis is considered the first committed step of the pathway?

PFK-1 phosphorylation of fructose 6-phosphate

Why must glucose be converted from glucose 6-phosphate to fructose 6-phosphate before cleavage?

To allow symmetric cleavage into two 3-carbon products

Which enzyme uses an induced-fit mechanism to prevent ATP hydrolysis when glucose is absent?

Hexokinase

Which glycolytic step produces the first molecule of ATP?

Step 7

Which glycolytic intermediate contains a high-energy acyl phosphate bond?

1,3-bisphosphoglycerate

Which molecule must accumulate in order to allosterically activate PFK-1?

AMP

Which cofactor is required by enolase to stabilize the enolate intermediate during dehydration?

Mg²⁺

Which enzyme catalyzes the only redox reaction in glycolysis?

GAPDH

Why must dihydroxyacetone phosphate (DHAP) be converted to glyceraldehyde 3-phosphate (G3P)?

Only G3P continues through glycolysis

Which step of glycolysis requires both K⁺ and either Mg²⁺ or Mn²⁺?

Pyruvate kinase

Which statement best explains why glycolytic intermediates remain inside the cell?

They lack dedicated transporters across the membrane

Which metabolic condition increases flux through glycolysis in tumor cells?

Increased glucose transporter expression

Which enzyme deficiency leads to the most severe form of galactosemia?

Uridyltransferase

In liver fructose metabolism, which enzyme converts fructose 1-phosphate into dihydroxyacetone phosphate and glyceraldehyde?

Fructose 1-phosphate aldolase

Which coenzyme is required by pyruvate decarboxylase during ethanol fermentation?

TPP