Biochemical Pathways and Energy Coupling Quiz

Spontaneous work

Building up

To remove complex molecules no longer useful to the cell

Metabolism

Decreases it

Anabolism

Non-spontaneous work

To produce complex molecules

Catabolism

Basic building blocks

To provide energy for cellular work and minimize heat loss

It acts as a barrier to the reaction taking place

By lowering the energy activation and allowing the reactants to achieve the transition state

Enzymes are central to controlling metabolism

Catalysts decrease the EA, allowing spontaneous reactions to occur

Cells control metabolism by controlling the amount of enzymes and their regulatory properties

To regulate metabolic pathways by inhibiting the first dedicated enzyme of a pathway

To show specificity and control metabolism

Because catalysts decrease the EA, allowing spontaneous reactions to occur

To have a high G and act as a barrier to the reaction

Gibbs free energy (G)

Free energy change (ΔG)

Adenosine triphosphate (ATP)

ATP hydrolysis

A spontaneous reaction

Energy coupling

Biochemical pathways

Entropy (S)

Hexokinase

Calvin cycle

Biochemical pathways are governed by the laws of thermodynamics, which state that energy is conserved and every energy transformation increases the entropy of the universe. The second law of thermodynamics implies that all energy is eventually converted into heat, which cannot be used by cells to perform work.

Adenosine triphosphate (ATP) is the energy currency of a cell and is consumed during various types of cellular work. ATP hydrolysis is a common coupling reaction used to drive forward nonspontaneous reactions in cells.

At the cellular level, energy coupling can be analogized to water at the top of a dam, electricity, and making toast. Just as the potential energy of water at the top of a dam can be harnessed to perform work, cells use energy coupling to drive energy-requiring processes.

Enzymes speed up biochemical reactions by lowering the activation energy, allowing reactants to achieve the transition state more easily. They are essential for cellular metabolism because most biochemical reactions have a high activation energy, and without enzymes, these reactions would not occur at an appreciable rate.

Catalysts lower the activation energy of spontaneous reactions, allowing them to occur at a faster rate. Catalysts are needed because spontaneous reactions may not occur at an appreciable rate if the activation energy is large, and catalysts decrease the activation energy, making the reactions more likely to happen.

Cells control metabolism by using enzymes to catalyze biochemical reactions. Regulatory enzymes are important in metabolic pathways because they can be up-regulated or down-regulated, allowing cells to control the rate of specific reactions and overall metabolic processes.

Feedback inhibition is a regulatory mode in which the end-product of a metabolic pathway inhibits an earlier enzyme in the pathway, slowing down the production of more product. It is common in metabolic pathways because it helps maintain homeostasis by preventing the overproduction of certain substances.

Metabolism is the sum of anabolism and catabolism. Anabolism involves building complex molecules from simpler ones, while catabolism breaks down complex molecules into simpler ones. Together, they represent the biochemical reactions of an organism or cell, with catabolism making energy available for cellular work.

Spontaneous work is a process that can happen on its own, without the input of external energy, while non-spontaneous work requires external energy input for the process to occur. An example of spontaneous work is water flowing down a dam, while non-spontaneous work includes water moving back up the dam.

A cell engages in catabolism to remove complex molecules that are no longer useful, releasing monomers for recycling; to provide basic building blocks for producing monomers; and to make existing potential energy available for cellular work.