Metabolism is referred to as biochemical reactions that contribute towards the survival of cells in different organisms. Metabolism plays an important role in channelising the energy cycle within human body. This article aims to discuss metabolism, the process and different types. Students must follow this article to understand the concepts associated with metabolism better.

What is Metabolism?

Metabolism is the sum of all life-sustaining chemical reactions within the cells of living organisms. Metabolism may also be defined as the series of chemical processes catalysed by enzymes, occurring within the body of living beings.

The term Metabolism originates from the Greek word “metabolē ” which means change.
These chemical reactions or metabolisms can be organised into pathways in which one compound is transformed into another compound with the help of enzymes.
Example- Cellular respiration, in which a series of metabolic processes takes place to generate ATP. This ATP is used for performing various cellular activities. Products of cellular respiration are carbon dioxide (excreted out of the body during respiration) and water.

Enzymes and Metabolism

1. Almost all chemical reactions in the cell need enzymes to occur at a rate faster enough to sustain life.
2. Enzymes are crucial for metabolism as they speed up chemical reactions.
3. The molecules upon which enzymes act are called substrates and the enzyme converts the substrate into a different molecule called products.

Fig: Enzymes- Substrate and Products

4. There are all over \(5000\) chemical reactions that occur in plants, animals, and microbes that are controlled by enzymes.
5. Most of the structures that make up animals, plants, and microbes are made from three basic classes of molecules – proteins, carbohydrates, and lipids.
6. Many chemical reactions focus on making these molecules during the construction of cells and tissue.
7. These molecules can be broken down and used as a source of energy during digestion and cellular respiration.

Fig: Metabolism

Metabolic Process

Metabolism can be classified into two processes:

1. Catabolism (Greek: kato “downward” and ballein “to throw”) or catabolic reactions – It refers to the reactions in which larger complex molecules are broken down into simpler molecules. Like-
   a. Protein is broken down into amino acids.
   Amino acids —–> Proteins
   b. Lipids are broken down into fatty acids and glycerol.
   Lipids —–> Fatty acids + glycerol
   c. Carbohydrate is broken down to glucose.
   Carbohydrate ——> Glucose  
   The glucose that is formed is completely oxidised inside our living cells to produce ATP.

2. Anabolism  (Greek: ana “upward” and ballein “to throw”) or anabolic reactions – It is opposite to catabolism. Here energy is consumed when small simple molecules are changed into large and complex molecules like enzymes, hormones, receptors, hair, nails, etc.
Photosynthesis is a typical anabolic process.
Metabolism is described as the sum of all the biochemical reactions occurring in a cell and these interconnecting networks of reactions are called metabolic pathways.

Metabolism of Protein

Metabolism of proteins refers to the breakdown and synthesis of proteins. Breakdown of protein into amino acids is called catabolism of protein, while synthesis of protein from amino acids is called anabolism of protein.
Inside the cell, amino acids are joined together to form polypeptide chains in the process called translation. This takes place in the cytoplasm mainly. Three types of RNAs, (mRNA, tRNA, rRNA)and amino acids are required for making a polypeptide chain.

Catabolism of protein helps in the formation of amino acids, which are re-used in our cells. Proteins that we ingest in our diet are catabolized under the influence of various proteolytic enzymes (pepsin, trypsin, chymotrypsin, etc.) in our alimentary canal.
Proteins can break down and lose their functionality under high temperature (denaturation), high or low \(pH\), high salt concentration, acid, or alkali. However, this is generally not a process of catabolism.

Metabolism of Carbohydrates

Metabolism of carbohydrates includes breakdown or catabolism of carbohydrates and synthesis or anabolism of carbohydrates.
Glycogen is broken down into glucose, and the process is called glycogenolysis. Glucose, being the most common source of energy in our cell, is completely oxidised to yield ATP molecules in a process called cellular respiration.
In our body, glucose can be formed from some non-carbohydrate sources, like lipids or amino acids. This process is called gluconeogenesis and the formation of glycogen occurs by the process glycogenesis when there is excess glucose in the body.

Metabolism of carbohydrate

Metabolism in Human Body

We eat different types of food to get energy. Calories present in the food are burned to get energy. Glucose reacts with oxygen to form ATP which liberates energy that our body needs for different functions.
During rest, like when we are sitting or sleeping, some of the calories are burned to carry out bodily functions like breathing, circulation of blood, maintenance of hormone level, and repair of cells. This is the BMR or Basal Metabolic Rate.
BMR can be defined as “the rate of energy expenditure per unit time by animals at rest.”

BMR is different in different bodies. Like:

1. If a body is larger with more muscle then it will have more BMR than the smaller body. So we can say our body size determines the BMR.
2. Generally, men have more BMR than women, i.e. they burn more calories than women. So, Sex also determines the BMR.
3. Age also affects the BMR of the body. Older people have less BMR than young ones.
4. Besides BMR, the following aspects also contribute to the burning of calories:
5. Food processing systems like digestion, absorption, assimilation, storage, etc.
6. Physical activities and exercise that we do each day play a very important role in burning the calories of the body.
7. The basal metabolic rate varies and depends upon the different body types.
   The three main body types are:-
   a. Endomorph– It refers to the large body with high body fat. These types of bodies can store fat easily. They are unable to use their stored fat as energy, so looks fatty and gets fatigued easily.
   b. Ectomorph– It refers to skinny, fit, tall bodies that can never get fatty or obese. They can eat whatever they want. They can burn their fat at a faster rate.
   c. Mesomorph– These types of bodies fall between the two discussed above. They are neither too fatty nor too skinny.

Summary

Sum of all the chemical reactions of the body that could be catabolic or anabolic, is called metabolism. Metabolism is one of the fundamental features of living organisms. Catabolism and anabolism are two types of metabolism. Catabolism refers to the breakdown while anabolism is the synthesis of complex compounds of the body. This is done either to liberate or store energy which we use to do various functions.

Frequently Asked Questions (FAQs) on Metabolism

Frequently asked questions related to metabolism is listed as follows:

Q.1. Does fast metabolism mean you poop a lot?
Ans: Digestion should not be misunderstood with metabolism. But pooping a lot may or may not be associated with a fast metabolism. Pooping a lot may give a sign of poor digestion, or it may also show that fast metabolism results in fast food processing leading to fast excretion or pooping.

Q.2. What are the symptoms of high metabolism?
Ans: Some of the symptoms of high metabolism are- weight loss, anaemia, feeling hot and sweaty every time, fatigue, increased heart rate, feeling hungry all the time, maybe pooping a lot, etc.

Q.3. What is metabolism in the body?
Ans: Metabolism is the sum of all life-sustaining chemical reactions within the cells of living organisms.

Q.4. How do you gain metabolism?
Ans: We can increase our metabolism by-
a. Intake of more proteinaceous food
b. Doing more physical work and exercise
c. Drinking more water
d. Good sleep
e. Reducing stress
f. Taking green tea

Q.5. What does high metabolism do to your body?
Ans: Metabolism is the sum of all life-sustaining chemical reactions within the cells of living organisms. If metabolism is high, then more calories of our body are burnt, and we remain energetic and fit as the burning of calories gives energy to the body.

Q.6. What are the \(2\) types of metabolism?
Ans: Metabolism can be classified into two, i.e. catabolism and anabolism. Catabolism refers to the breakdown of complex molecules into simpler ones stored in the body for the liberation of energy. Anabolism refers to the formation or synthesis of biomolecules that can be stored for future use.

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