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The Law

Belief - V

Our Cellular Biology - IV

A cell's daily operations are accomplished through the biochemical reactions that take place within the cell. Metabolism is a term that is used to describe all chemical reactions occurring within the cells and organisms. 

Note: Metabolism can be conveniently divided into two categories:

• Catabolism - the breakdown of molecules to obtain energy.
• Anabolism - the synthesis of all compounds needed by the cells.

Metabolism is closely linked to nutrition and the availability of nutrients.

Nutrition is the key to metabolism. The energy obtained out of catabolism is required by the body to synthesize new proteins, nucleic acids (DNA, RNA) etc.

Reactions are turned on and off or accelerated and decelerated according to the cell's immediate needs and overall functions. At any given time, the numerous pathways for breaking down and building up cellular components must be monitored and balanced in a coordinated fashion. To this end, they organise reactions into various enzyme-powered pathways.

Note: Enzymes are very efficient catalysts for biochemical reactions. They speed up reactions by providing an alternative reaction pathway of lower activation energy. Activation energy is the energy required for a reaction to commence.

Like all catalysts, enzymes take part in the reaction - that is how they provide an alternative reaction pathway. But they do not undergo permanent changes and so remain unchanged at the end of the reaction.

Most chemical catalysts catalyse a wide range of reactions. They are not usually very selective. In contrast enzymes are usually highly selective, catalysing specific reactions only. This specificity is due to the shapes of the enzyme molecules.

Cells are expert recyclers. They break down large molecules into simpler building blocks and then use those building blocks to create new components they require. The breaking down of large components happens via the catabolic pathways and this process releases energy. Through catabolic pathways, polymers such as proteins, nucleic acids and poly-saccharides are reduced their constituent parts : nucleotides, amino acids and sugars respectively. In contrast the anabolic pathways require energy.

Polymers

Note: A polymer is a large molecule, or macro molecule, composed of many repeated sub units.

Cells must balance their catabolic and anabolic pathways in order to control the levels of critical metabolites and to ensure that sufficient energy is available. For example is supply of glucose begins to wane, as might happen in case of starvation, cells will synthesize glucose from other materials. Conversely in times of plenty, extra glucose iss coverted into storages forms, such as glycogen, starches, fats.

Note: Metabolite is a substance formed in or necessary for metabolism.

Not only do cells need to balance catabolic and anabolic pathways, but they also must monitor the needs and surpluses of all their metabolic pathways. In order to bolster a particular pathway, cells can increase the amount os a necessary enzyme. Conversely to slow down or halt a pathway, cells can decrease the amount of an enzyme or use inhibitors to make the enzyme inactive. Such up and down regulation of metabolic pathways is often a response to changes in concentrations of key metabolites in the cell.

Namaste

শীঘ্রই আবার দেখা হবে

(Śīghra'i ābāra dēkhā habē)

Prabir