CSIR- A short note on Energy and Enzymes

A short note on Energy and Enzymes

The force that through the green fuse drives the flower

Drives my green age; that blasts the roots of trees

Is my destroyer.

And I am dumb to tell the crooked rose

My youth is bent by the same wintry fever.

The force that drives the water through the rocks

Drives my red blood; that dries the mouthing streams

Turns mine to wax.

And I am dumb to mouth unto my veins

How at the mountain spring the same mouth sucks.

Dylan Thomas, Collected Poems (1952)

In these opening stanzas from Dylan Thomas’s famous poem, the poet proclaims the essential unity of the forces that propel animate and inanimate objects alike, from their beginnings to their ultimate decay. Scientists call this force energy. Energy transformations play a key role in all the physical and chemical processes that occur in living systems. But energy alone is insufficient to drive the growth and development of organisms. Protein catalysts called enzymes are required to ensure that the rates of biochemical reactions are rapid enough to support life. In this chapter we will examine basic concepts about energy, the way in which cells transform energy to perform useful work (bioenergetics), and the structure and function of enzymes. Living organisms, including green plants, are governed by the same physical laws of energy flow that apply everywhere in the universe. These laws of energy flow have been encapsulated in the laws of thermodynamics.

Energy is defined as the capacity to do work, which may be mechanical, electrical, osmotic, or chemical work. The first law of thermodynamics states the principle of energy conservation: Energy can be converted from one form to another, but the total energy of the universe remains the same. The second law of thermodynamics describes the direction of spontaneous processes: A spontaneous process is one that results in a net increase in the total entropy (ΔS), or randomness, of the system plus its surroundings. Processes involving heat transfer, such as the cooling due to water evaporation from leaves, are best described in terms of the change in heat content, or enthalpy (ΔH), defined as the amount of energy absorbed or evolved as heat under constant pressure. The free-energy change, ΔG, is a convenient parameter for determining the direction of spontaneous processes in chemical or biological systems without reference to their surroundings. The value of ΔG is negative for all spontaneous processes at constant temperature and pressure. The ΔG of a reaction is a function of its displacement from equilibrium. The greater the displacement from equilibrium, the more work the reaction can do.

Living systems have evolved to maintain their biochemical reactions as far from equilibrium as possible. The redox potential represents the free-energy change of an oxidation–reduction reaction expressed in electrochemical units. As with changes in free energy, the redox potential of a system depends on the concentrations of the oxidized and reduced species. The establishment of ion gradients across membranes is an important aspect of the work carried out by living systems. The membrane potential is a measure of the work required to transport an ion across a membrane. The electrochemical-potential difference includes both concentration and electric potentials. The laws of thermodynamics predict whether and in which direction a reaction can occur, but they say nothing about the speed of a reaction. Life depends on highly specific protein catalysts called enzymes to speed up the rates of reactions. All proteins are composed of amino acids linked together by peptide bonds. Protein structure is hierarchical; it can be classified into primary, secondary, tertiary, and quaternary levels. The forces responsible for the shape of a protein molecule are non covalent and are easily disrupted by heat, chemicals, or pH, leading to loss of conformation, or denaturation. Enzymes function by lowering the free-energy barrier between the substrates and products of a reaction. You are reading crest science academy blog for more blog you can subscribe and see our more blog .

Catalysis occurs at the active site of the enzyme. Enzyme-mediated reactions exhibit saturation kinetics and can be described by the Michaelis–Menten equation, which relates the velocity of an enzyme-catalyzed reaction to the substrate concentration. The substrate concentration is inversely related to the affinity of an enzyme for its substrate. Since reaction velocity is relatively insensitive to small changes in substrate concentration, many enzymes exhibit cooperativity. Typically, such enzymes are allosteric, containing two or more active sites that interact with each other and that may be located on different subunits.

Enzymes are subject to reversible and irreversible inhibition. Irreversible inhibitors typically form covalent bonds with the enzyme; reversible inhibitors form noncovalent bonds with the enzyme and may have competitive, noncompetitive, or mixed effects. Enzyme activity is often regulated in cells. Regulation may be accomplished by compartmentalization of enzymes and/or substrates; covalent modification; feedback inhibition, in which the end products of metabolic pathways inhibit the enzymes involved in earlier steps; and control of the enzyme concentration in the cell by gene expression and protein degradation.