Physiology of Finfish and Shellfish (2+1)

4.1.1. Introduction

Energy necessary for the varied activities of life is generated in a series of chemical reactions referred to as cellular metabolism or respiration catolism bess it +O₂ ® CO₂ . This term metabolism is universally used to describe the many chemical reactions which take place in the living organism, whether these are constructive (Anabolism) or destructive (Cattolism).

In respiration the chemical energy contained in carbohydrates fats and proteins is transfored into a more labile and directly usually form of energy. The glycerol of fatsjoin the glycolysis. The FAs and some of AAs join also form pyruvic acid and join the cycle other AAs join at other stages as shown in fig. This energy in trun is used for animal activities such as remove muscular movement biosynthesis, secretion, heat (and sometimes light and electricity) etc. the oxidation of foods takes place in a series of reactions and the energy contained in the foods is released gradually at every stage of reaction (and not at once).

For example, the phosphorylation of glucose is an exchange reaction (energy liberating) energy reaction phosphorylation is the process of combination of organic molecules like tas, lats and proteins with phosphate (mostly ATP) by enzyme action. Phosphate of glucose is an essential preliminary step before break down. The combination with phosphate produces compounds that are highly reactive in water with other organic molecules. When their phosphate is in turn is transferred, energy becomes available). Although glucose is a.

The reactions involved in tissue respiration are chemical in nature and can be represented as

A+B --->

<---- C+D

At equilibrium, in accordant with the law of mass action the product of the concentrations of the substances formed (C&D) divided by the product of the reactants (A&B) is a constant known as the equilibrium constant K.

[C] [D]

K = -------------

[A] [B]

If K=1 the product of reactants will be equal to that of substances formed and there will be no change in free energy.

If K>1 in forward reaction, the product of link, if substances formed will be greater. Such reaction will release energy and will be called an “exergonic” reaction.

If K<1 = reverse called consume energy – “endergomicr”.

Rich potential energy source, this energy cannot be released to the organism thro’ direction oxidation to CO₂ < H₂O. to perform useful animal work, it must first be changed into more reactive form and then form pass thin a series of reactions with gradual release of energy. The first step in the process is phosphorglation with ATP.

Glucose + ATP --->

<--- Glucose – 6 – Phosphate + ADP

K of this is 1600

[G-6-p] [ADP]

Glocose --------------------- = 1600 This reaction releases 4300 cal. of energy.

[Glucose] [ATP]

This energy is from stored ATP and not from the nutrient. In later reactions of entalolism, ADP is converted into ATP the energy for which comes from the nutrient.