What is Protein Good For

What is Protein

Protein is one of the very important macronutrient, which forms the main basic unit for dv cells. In other words, it is a body building nutrient. Body building is primary function of protein. But in absence of carbohydrates and fat it acts as source of energy.


The protein chemically can be defined as highly complex organic compound made up of carbon, hydrogen, oxygen and nitrogen. Some protein may contain sulphur and phosphorous in their structure. The basic unit of protein is amino acid. Several amino acid combines together to form protein. Hence, protein can also be defined as compound of high molecular weight, in which number of amino acid join through peptide bond to form polypeptide chain called protein.

What is Amino Acids | Non Essential Amino Acids

The smallest unit of protein is called amino acid. It is nitrogenous compound having – oil group -COOH and amino -NH2 group. Its structure has one hydrogen atom e carbon ring attached to it.

Basically twenty different amino acid are found in protein.

What are Essential Amino Acids | 20 Amino Acids

List of twenty amino acid

  1. Alanine
  2. Glutamine
  3. Leucine
  4. Serine
  5. Arginine
  6. Glutamic acid
  7. Lysine
  8. Threonine
  9. Asparagine
  10. Glycine
  11. Methionine
  12. Tryptophan
  13. Aspartic acid
  14. Histidine
  15. Phenyl alanine
  16. Tyrosine
  17. Cysteine
  18. Isoleucine
  19. Proline
  20. Valine

Essential and Non Essential Amino Acids

Essential amino acid for man


Classification on Basis of Shape

1. Globular protein: These proteins are spherical in shape and play role in varie biological function, e.g., blood protein like serum albumin, glycoprotein, antibo haemoglobin, hormones, enzymes, etc.

2. Fibrous protein: The fibrous protein have long ribbons of fibre like structure. I mainly found in animal body. It is fully or partially resistant to action of enzym Example: protein of skin, hair, nails, etc.

Classification on Basis of Composition

On basis of chemical composition, protein is categorized into three types:

1. Simple or holoprotein: It possesses only amino acid in their structure, e.g., albs globulins, glutelins, prolamine, scleroprotein or animal skeleton protein.

a. Wheat protein is glutenin and gliadin

b. Corn protein is glutelin and zein

c. Oryzenin is rice protein

Conjugated or complex protein: These protein possess non protein component called prosthetic group along with amino acid in their structure. Prosthetic group can be metal or compound.

Examples of proteins:

Haemoglobin: It has prosthetic group heme i.e., iron attached.

Glycoprotein: Carbohydrate acts as prosthetic group.

Nucleoprotein: Proteins are attached with nucleic acid.

Derived protein: It is defined as those protein which are obtained as a result of treatment of simple or conjugated protein with heat, enzymes or chemical e.g., peptones and polypeptides.

Classification on Basis of Origin

It is the category which is obtained on basis of source:

Animal protein: Protein which is obtained from animals is called animal protein. Exampl: milk and milk products, poultry, meat and meat products.

Plant protein: Protein which is obtained from plants, e.g., pulses, nuts and oilseeds.

Classification of Amino Acid

(On Basis of Nutritional Essentiality or Qualtity)

Quality of protein depends on types of amino acid in their structure and their composition. On basis of nutritional importance of particular type of protein for human amino acid can be categorisied into five types:

Essential or complete amino acid: Essential amino acid are those amino acid that cannot be synthesized by body itself. So, they are important to be consumed in diet by mans.

Partially complete or conditionally essential amino acid: There are some amino acid, which are not sythesised in infants while adults can synthesise it. So, such amino become essential for one particular group. Hence are called conditionally – essential amino acid. As arginine become conditionally essential amino acid in -estinal metabolic dysfunction.

Incomplete or non-essential amino acid: Non-essential amino acids are group of those amino acid which body can synthesize itself. So are not necessary to be present in diet.

High biological value protein or complete protein: It is defined as that protein which contains nearly all the essential amino acid in their structure. It is mainly obtained from animal sources.

Low biological value protein: It is a type of protein which is usually obtained from plants sources and is deficient in one or more of the essential amino acid.

Example: Tryptophan is limiting amino acid in maize. Lysine is absent in wheat.

List of Three Types of Amino acid

Essential Amino Acids List

Essential Amino acid  Conditionally Essential Amino acid  Non-Essential Amino acid  
Aspartic acid
Glutamic acid  
Glutamine Serine  


Quality of protein depends on the composition of protein, i.e. type of amino acid in their structure. If a protein contains all amino acid required for tissue building, it is called high quality protein, e.g., animal protein.


It is defined as amount of energy produced when lg of protein is completely oxidised Primary function of a protein is tissue building. But it is also used for energy purpose when diet has inadequate carbohydrates and fats. Protein can provide 4 kcal of energy per gram.


Recommended daily allowances for protein depends on the type of protein being consumed in diet. If high biological value protein i.e. protein of animal origin is used then requirement is lesser. While requirement increases if our diet includes more proteins of plant origin. In general more protein requirement for adults is 1gm per kg body weight. Requirement changes with the age and physiological condition. During infancy childhood, adolescent, pregnancy and lactation requirements are high. Below the table shows RDA of protein for various age groups:

Table – 10.3 RDAs of Protein by ICMR

Group  Protein g/day  
Pregnant woman50+15
0-6 month
6-12 month

0-6 month
6-12 month

1-3 years
4-6 years
7-9 years

10-12 years
13-15 years
16-18 years
10-12 years
13-15 years
16-18 years

Dietary Sources

The sources from which we get from protein can be categorisied in two groups:

1. Animal sources: Milk and milk products, Meat, fish, chicken and poultry product

2. Plant sources: Pulses, cereals also contribute good amount of protein in Indian diet, they are cheap and consumed in larger amount. While fruit, vegetable are poor source of protein.

Protein Content of Food

SourceProtein g/100g
Skimmed milk powder (cow’s milk)38
Egg, Hen13
Green gram dhal29
Peas dry20
Bengal gram whole17
Wheat whole12
Milk Buffalo’s4

What is the Function of Protein

1. Growth and development: Protein is a basic cell building material. New cells formation, repair of damage tissues occurs by protein. So, protein plays vital role in body building and body repair.

Example: Collagen is most abundant protein of animal.

2. Enzymes and co-enzymes: All enzymes and coenzymes which catalyse metabolism reaction are proteinous in nature.

Example: Urease, amylase, catalase, cytochrome.

3. Hormones formation: Hormones play regulatory role in several metabolic function of cells. These hormones are formed from protein.

Example: Epinephrine derived from amino acid tyrosine.

4. Transport or carrier protein: Several protein acts as carrier of essential biological factors to various part of organism.

Example: Globin- a protein acts as carrier of heme i.e. Iron in body and two together form haemoglobin which acts as transporter of oxygen in the body.

5. Visual pigments: The visual pigment which enables us to see are protein in nature Rhodopsin of rod cell and iodopsin of cone cells of retina are protein.

6. Contractile protein: Ability to move and contract in animal is also provided by certain specific protein.

Example: muscle protein actin and myosin make muscle fibre contractile.

7. Defense protein: There are certain special protein which increases our immunity. They defend human body against foreign material.

Example: Anti bodies, interferon which are antiviral in nature.

8. Toxin: Some proteins are toxic in nature and proves to be vunerable on entering the human body.

Example: Snake venom.

9. Regulatory protein: Protein plays role in regulating physiological activity. Example: Insulin regulates sugar metabolism.

10. Fuel: Protein can also provide energy, when carbohydrate or fats are deficient in diet.

11. Biological buffers: Protein helps in maintaining acidity and alkalinity of cell. So, act as biological buffers.

12. Storage protein: Some protein acts as storage protein. Example: albumen of egg and gluten of grain.

Digestion of Proteins

The hydrolysis of complex protein takes place in several steps to ultimately get converted to simple absorbable form is called digestion.

Steps of Digestion

The process of digestion of protein starts in mouth and completes in small intestine.

In Mouth or Buccal Cavity

Mouth contains no protein digesting enzyme. So, no protein digestion starts in mouth. It – lubricates food to help in swallowing.

Gastric Phase of Digestion

In this phase of digestion, protein undergoes both mechanical and chemical changes. As stomach contain gastric juice. Gastric juice contain hydrochloric acid (HC1), two protein digesting proenzymes pepsinogen or propepsin and prorenin. Pepsinogen and prorenin converted to active forms of pepsin and Renin respectively by HC1.

Now rest of inactivated pepsinogen is activated to pepsin by pepsin itself. This process ed autocatalytic reaction.

The pepsin is now ready to carryout protein digestion. It acts on protein to convert in proteoses, which is partial hydrolysed product.

While Renin acts on milk protein casein to form paracasein and whey protein.

Paracasein formed reacts with calcium to form calcium paracaseinate in precipated form.  

The calcium paracaseinate is now acted upon by pepsin to form peptones.

Intestinal Phase

Pancreatic juice in intestine contain various inactivated protein digesting enzyme. These are Chymotrypsinogen, procarboxy peptidases and trypsinogen. Various protein splitting enzyme are secreted in inactive forms to protect protein of cells. Enzyme trypsinogen is converted to trypsin in presence of non digestive enzyme enterokinase.

This trypsin then act as autocatalyst and convert rest of inactivated trypsinogen into trypsin.

Trypsin acts upon protein and other proenzymes to form protein and active protein digesting enzymes.


The absorption of protein occurs in form of amino acid. It occurs by active process, IN requires energy. It occurs in small intestine.


Amino acid after absorption has various fate. It firstly reaches vein into hepatic portal vein the liver. In liver protein is released by liver to body cell to participate in particular cell or body material formation. While other surplus amino acid combines with carbondioxide to form urea CO (NH2)2. This urea is excreted out through urine. Some amino acid is converted to sugar or fat to give energy. Especially in fasting condition.


Extra protein is converted into fats and carbohydrates. So, there is no specific protein storage site and storage form of protein.


Protein is the basic body building nutrient, required for growth and repair of tissues. The term malnutrition in context with protein energy malnutrition is very wide. It covers wide spectrum of diseases, ranging from Kwashiorkor and Marasmus, which are very severe conditions and growth retardation is comparatively milder. All these proteins deficiency disorder is due to undernutrition, while disorder due to excess of protein consumption are rarely there. Protein deficiency occurs usually due to lesser consumption, improper digestion and absorption. The major reasons behind this is poverty, illiteracy and unsanitary living condition.

Kwashiorkor (Signs and Symptoms)

The disorder is mainly seen in the children of the age group 1-3 years. It is usually seen in people with low socio-economic status, where child after prolonged period of breast is weaned with low protein food for a long time. The main deficient nutrient is protein. But calories are also less in the diet of child.

Signs and Symptoms

  1. The child is usually below his normal weight.
  2. Muscle wasting is also there.
  3. Mental growth of child is affected.
  4. Skin is affected and skin shows pigmentation and ulceration.
  5. Hair are also affected.
  6. Digestive system is affected and becomes weak.Because of diarrhoea and vomiting.
  7. One of the most important symptom of this disease is oedema.
Marasmus (Signs and Symptoms)

This disorder is mainly seen in infants i.e. under the age of one year. It is also due to ill consumption of diet lacking in calories and protein both or it occurs if early is started.

Signs and Symptoms

1. The child is very much underweight.

2. As child weight is quite below normal weight. So, wasting of muscle is very high.

3. Mental growth is comparatively less affected as compared to that in kwashiorkor.

4. As muscle wasting is high. So, skin becomes more wrinkled.

5. Hair are not affected.

6. Digestive system disorders are also less common.

7. Oedema is absent in marasmus.

Sometimes child shows mixed signs of kwashiorkor and marasmus. Such a disorder called Marasmic Kwashiorkor.


1. The quality or condition of being deficient; incompleteness or inadequacy.

2. A lack or shortage especially of something essential to health; an insufficiency: a nutritional deficiency.

Classification, Causes and Symptoms 

Protein energy malnutrition (PEM) is the term given group of clinical conditions which occur due to inadequate protein and calorie intake, especially in children.  It is a grave problem in developing countries as mothers do not get enough nutrition and healthy food, which puts the baby at a disadvantage even before he/she is born.

Classification of Protein Energy Malnutrition

Protein energy malnutrition has been classified in many ways, two of the important types rationed below:

Classical classification

  1. Kwashiorkar
  2. Marasmus
  3. Marasmic Kwashiorkar

Gomez classification :

Grade 1- 90-75% of expected weight

Grade 2 – 75-60% of expected weight

Grade 3 – <60% of expected weight

Causes of Protein Energy Malnutrition

1. Dietary deficiency: When PEM is purely due to dietary deficiency, it is termed as the primary type. Nearly 25% of the paediatric hospital beds in India are occupied by children suffering from malnutrition and around 80% of hospitalised children are malnourished to some extent. Secondary malnutrition arises due to a serious illne like tuberculosis, cancer or inability of the body to absorb nutrients for e.g. in bow disease like ulcerative colitis, metabolic syndromes and long-standing gastro-enteritis

 2. Inadequate nutrition of a mother: Dietary factors contributing to PEM are inadequate breast feeding by the mother due to inability of mother’s body to make milk due to inadequate nutrition, stopping breastfeeding early in case of working mothers and inadequate supplementation of other foods, ignorance of weaning and weaning foods, inverted or cracked nipples in mother causing difficulty in breastfeeding. Another important reason is nipple confusion when the baby is switched from breast to t artificial nipple and bottle. Formula milk may not be well tolerated leading to diarrhea.  

3. Maternal problems: Problems in the mother such as mental or psychiatric illness post-natal depression (severe cases), poor maternal health like anaemia and have too many children in quick succession or having twins may lead to the mot producing not enough milk to meet the demand of the infants.

4. Traditional methods which are harmful to the baby may be practised in villages rural areas such as not offering colostrum (the fluid that comes out of the nipple in first few hours after delivery) which is very healthy and boosts the baby’s immune system and withholding breast milk when the baby has diarrhoea. Even in remote areas, health professions should conduct antenatal classes for mothers to be educated them.

5. Infections in baby: All kinds of infections in the baby such as oral ulcers, gas enteritis, food poisoning, diarrhoea and serious conditions such as congenital heart kidney disease may cause inability to suckle which causes malnutrition. Th infection and malnutrition is a vicious cycle as one contributes to the other.

6. Low socioeconomic status: People coupled with the desire to have more children (especially boys) is a social malady that many uneducated people suffer from it.

Prevention of PEM

Research studies shows that malnutrition is not due to lack of food but rather due to of knowledge on when to wean children. Breast milk contains insufficient iron, calcium and protein for a growing child after age of 6 months of the more at risk the children can become particulary, if mother also have borderlive nutrition. Mothers often believe that children should be fed breast milk alone until they heart walking.

Malnutritioncan also be prevented by giving health education on hygiene, im-munization, nutrition as well as weaning.

Who has outlive five main prioritus that should be set to prevent PEM. The WHO priotity programme for prevention of PEM cells for GOBIF.

  1. Growth monitoring (Simple growth chart kept by mother)
  2. Oral rehydration (speciallyfor diarrhoea diseases)
  3. Breast feeding supplements by food after 6 months
  4. Immunization against measles. tetanus, putusis, diptheria, polio and Tb

Effects of Excess Protein Intake

Popular high protein diets affect your body in many ways. Many high protein animal foods contain high amounts of saturated fats, which can raise your blood cholesterol levels. High protein break-down products may cause your kidneys to work hard, while -acting your blood glucose levels. This raises concerns, if you have chronic kidney disease or diabetes. Also, ketosis, a secondary effect of high protein intake, can become threatening. As your body’s nutritional balance is upset by high protein intake, it becomes chemically unbalanced, as well.

High Protein Defined

Protein is needed for your body to grow and repair tissues. The National Institutes of health recommends 10 percent to 35 percent of total calories as dietary protein. Children need to consume more protein per kilogram of body weight than adults because they grow issues faster than adults. Americans consume twice as much protein than what is required, an amount that hasn’t changed since 1909. High-protein diets contain much more protein than the 0.36 g per pound per day as your body requires.

Cardiovascular Effects

Diets in protein tend to be high in saturated fats. Some high-protein diets provide 20 percent to 25 percent of calories from saturated fat, while the American Diabetes on recommends less than 10 percent of calories from this type of fat. According to the 2005 “American Journal of Epidemiology,” coronary heart disease was statistically associated with red meats and dairy products. Also, as higher amounts of protein replace dietary fiber, fiber’s innate ability to lower blood cholesterol levels becomes deficient. These high-protein intake factors likely increase your risk of heart disease.

Renal Effects

High-protein diets accelerate renal decline in people with mild renal insufficiency. It increases urinary output, thus putting additional strain on already compromised kidneys. If you have chronic renal disease, dietary protein is usually restricted. As of 2011, there was no proof that high protein intake causes kidney damage in healthy individuals. Protein-induced high urine output commonly leaves less time for dietary blood calcium to be absorbed into your body and causes you to lose the calcium in your urine. This results in your body using calcium from your bones for its needs, thus predisposing you to osteoporosis. Also, high calcium in urine may cause increased kidney stone formation.

Insulin Effects

Insulin is responsible for lowering your blood glucose. When your blood glucose levels rise, insulin stimulates uptake of excess glucose by your liver and muscle cells. The cells store the glucose for later energy needs. High protein diets increase the amount of insulin circulating in your blood. This continuous effect promotes insulin resistance, which impairs your body’s response to use the insulin it produces. Such an impaired response upsets your body’s glucose equilibrium, especially in certain types of diabetics.


High-protein diets promote abnormal fat metabolism, which produces ketones. Ketosis is Energy Require a term for high amounts of ketones in your blood, urine and other tissues. Excessive Measurements ketone accumulation is known as ketoacidosis. Ketoacidosis causes acidic blood and very Body Mass Ind high levels of blood glucose. Untreated, ketosis causes dehydration and possible death. In high-protein diets, this diuretic effect often produces quick weight loss and nausea. Many dieters enjoy the immediate weight decrease and the nausea deters further eating, although the harmful effects of ketosis may outweigh the benefits.


Q-1 What are non canonical amino acids?

Ans: Non canonical amino acids (ncAAs) can be genetically encoded to produce potent methods for modifying the characteristics of viruses, proteins, and cells. Additionally, to their rapidly growing use in fundamental research, non-canonical amino acids (ncAAs), also known as unnatural amino acids (uAAs), non-natural amino acids (nAAs), and non-standard amino acids (nsAAs) also show significant promise in therapeutic applications.

Q-2 What is Azidohomoalanine?

Ans: An analogue of methionine called azidohomoalanine (AHA) can be incorporated into freshly generated proteins by the translational machinery of cells (NSPs). CuAAC-mediated click chemistry can be used to bind AHA-NSPs to biotin, and avidin-based affinity purification can be used to enrich them. As a result, it is possible to efficiently enrich and segregate AHA-containing proteins and peptides from the entire proteome. In this review, we cover the evolution of AHA techniques based on mass spectrometry (MS) and their potential for measuring proteins associated in immune response, gut microbiota, secretome, and proteostasis, as well as their potential for therapeutic applications.

Q-3 What are unnatural amino acid?

Ans: Modern drug discovery research is increasingly relying on synthetic or naturally occurring non-proteinogenic amino acids, known as “unnatural amino acids,” as a tool. They are frequently employed as chiral building blocks and molecular scaffolds in the construction of combinatorial libraries due to their infinite structural diversity and functional adaptability. If they are incorporated into therapeutic peptidomimetics and peptide analogues, they constitute a potent tool in drug development. They can be used as molecular probes to learn more about how biological systems work.

Q-4 What is selenocysteine?

Ans: The 21st proteogenic amino acid is selenocysteine (Sec), and it is now generally acknowledged that Sec participates in redox biochemistry when incorporated into proteins. Many of the molecular mechanisms behind Sec bioactivity are still unclear, though.

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