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Chapter 13: Problem 1

Identify which of the ten reactions of glycolysis are a. phosphorylations; b. isomerizations; c. oxidation-reductions; d. dehydrations; e. carbon-carbon bond cleavages.

Short Answer

Expert verified
Phosphorylations: Steps 1, 3, 7, 10; Isomerizations: Steps 2, 5, 8; Oxidation-Reduction: Step 6; Dehydration: Step 9; Carbon-Carbon bond cleavages: Step 4.

Step by step solution

01

Understand the concept

Glycolysis is a metabolic pathway with 10 reactions that convert glucose into pyruvate, generating ATP. Each reaction involves different types of biochemical processes such as phosphorylations, isomerizations, oxidation-reductions, dehydrations, and carbon-carbon bond cleavages.
02

Identify phosphorylation reactions

Mark any reactions in which a phosphate group is added. These occur in steps 1 (glucose to glucose-6-phosphate), 3 (fructose-6-phosphate to fructose-1,6-bisphosphate), 7 (1,3-bisphosphoglycerate to 3-phosphoglycerate), and 10 (phosphoenolpyruvate to pyruvate).
03

Identify isomerization reactions

Isomerizations involve the rearrangement of atoms within a molecule. Identify reactions in steps 2 (glucose-6-phosphate to fructose-6-phosphate), 5 (dihydroxyacetone phosphate to glyceraldehyde-3-phosphate), and 8 (3-phosphoglycerate to 2-phosphoglycerate).
04

Identify oxidation-reduction reactions

Oxidation-reduction reactions involve the transfer of electrons. In glycolysis, this occurs in step 6 (glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate).
05

Identify dehydration reactions

Dehydration involves the removal of a molecule of water. Locate this in step 9 (2-phosphoglycerate to phosphoenolpyruvate).
06

Identify carbon-carbon bond cleavage

Carbon-carbon bond cleavage happens when a carbon-carbon bond is broken. This occurs in step 4 (fructose-1,6-bisphosphate to glyceraldehyde-3-phosphate and dihydroxyacetone phosphate).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Phosphorylation in Glycolysis
Phosphorylation plays a crucial role in glycolysis as it helps to activate molecules, allowing them to participate in subsequent reactions that are essential for energy production. This process involves the addition of a phosphate group into a molecule. Let's break down the key phosphorylation events in glycolysis:
  • Step 1: The first phosphorylation event occurs when glucose is converted into glucose-6-phosphate. This is an important regulatory step, often referred to as the 'commitment step,' because it keeps glucose within the cell for processing.
  • Step 3: The conversion of fructose-6-phosphate to fructose-1,6-bisphosphate is another phosphorylation step. This reaction is catalyzed by phosphofructokinase, a major regulatory enzyme.
  • Step 7: This involves the generation of ATP through the transfer of a phosphate group from 1,3-bisphosphoglycerate to ADP to form 3-phosphoglycerate.
  • Step 10: Phosphoenolpyruvate donates a phosphate to ADP to form pyruvate and ATP, marking the final phosphorylation in glycolysis.
These phosphorylation events facilitate the transfer and storage of energy, allowing glycolysis to proceed efficiently.
Isomerization in Glycolysis
Isomerization in glycolysis involves the rearrangement of atoms within a molecule, transforming it into a different isomeric form without adding or removing atoms. Understanding these conversions is vital, as they prepare molecules for subsequent reactions by forming structures suitable for further processing.
  • Step 2: This step converts glucose-6-phosphate into fructose-6-phosphate. This transformation is crucial because it structures the molecule for further phosphorylation and cleavage later on.
  • Step 5: Dihydroxyacetone phosphate is isomerized to glyceraldehyde-3-phosphate. Both molecules are in equilibrium, but only glyceraldehyde-3-phosphate continues in glycolysis, making this step vital.
  • Step 8: Here, 3-phosphoglycerate is converted to 2-phosphoglycerate. This prepares the molecule for the subsequent dehydration step.
Each isomerization step ensures the molecules are primed for the next stages of glycolysis, maintaining efficiency and continuity in the pathway.
Oxidation-Reduction in Glycolysis
The oxidation-reduction reaction in glycolysis is fundamental for ATP production. It involves the transfer of electrons, leading to the oxidation of one molecule and the reduction of another.
  • Step 6: This is the only oxidation-reduction reaction in glycolysis, where glyceraldehyde-3-phosphate undergoes oxidation to form 1,3-bisphosphoglycerate. NAD+ is reduced to NADH during this process.
This step is pivotal as it links glycolysis with aerobic metabolism by producing NADH, which can be used in the electron transport chain to generate additional ATP.
Dehydration in Glycolysis
Dehydration in glycolysis involves the removal of a water molecule from a substrate. It alters the structural form of the substrate, preparing it for the final steps of glycolysis.
  • Step 9: This step involves the conversion of 2-phosphoglycerate to phosphoenolpyruvate (PEP). The dehydration process increases the energy potential of the molecule, setting the stage for the production of more ATP in the next step.
By removing water, the substrate's energy state becomes more favorable for subsequent reactions, contributing to the energy yield at the end of the glycolytic process.
Carbon-Carbon Bond Cleavage in Glycolysis
Carbon-carbon bond cleavage in glycolysis signifies a crucial transformation where a six-carbon sugar is split into two three-carbon molecules.
  • Step 4: In this step, fructose-1,6-bisphosphate is cleaved into two three-carbon molecules: glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. This fragmentation is facilitated by the enzyme aldolase.
The cleavage of carbon-carbon bonds is essential as it divides the glucose-derived molecule into smaller units, enabling them to undergo further energy-extracting transformations.

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Most popular questions from this chapter

Arsenate, \(\mathrm{AsO}_{4}^{3-}\), acts as a phosphate analog and can replace phosphate in the GAPDH reaction. The product of this reaction is 1-arseno-3-phosphoglycerate, which is unstable and spontaneously hydrolyzes to form 3-phosphoglycerate, as shown. What is the effect of arsenate on cells undergoing glycolysis?

Biochemists use transition state analogs to determine the structure of a short-lived intermediate in an enzyme-catalyzed reaction. Because an enzyme binds tightly to the transition state, a compound that resembles the transition state should be a potent competitive inhibitor. Phosphoglycohydroxamate binds 150 times more tightly than dihydroxyacetone phosphate to triose phosphate isomerase. Based on this information, propose a structure for the intermediate of the triose phosphate isomerase reaction.

ADP stimulates the activity of phosphofructokinase (PFK), yet it is a product of the reaction and not a reactant. Explain this apparently contradictory regulatory strategy.

There are four isozymes of hexokinase termed hexokinases I, II, and III (which have \(K_{\mathrm{M}}\) values of \(\sim 0.02 \mathrm{mM}\) ) and hexokinase IV (which has a \(K_{\mathrm{M}}\) value of \(\sim 5 \mathrm{mM}\) ). Normal hepatocytes (liver cells) express very little of hexokinases I and II, but upon transformation to cancer cells, the expression of hexokinase II (and to some extent hexokinase I) increases while hexokinase IV expression is silenced. How does this strategy promote the survival of the cancer cell?

Except during starvation, the brain burns glucose as its sole metabolic fuel and consumes up to \(40 \%\) of the body's circulating glucose. Brain hexokinase has a \(K_{\mathrm{M}}\) for glucose that is 100 times lower than the concentration of circulating glucose \((5 \mathrm{mM})\). What is the advantage of this low \(K_{\mathrm{M}}\) ?
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