The Essential Role of Protein Molecules in Living Systems

Proteins are fundamental macromolecules that serve as major structural and functional components of living organisms. Composed of amino acids linked by peptide bonds, proteins exhibit immense diversity in structure and function, playing critical roles in virtually every biological process. Thousands of different proteins exist, each tailored to a specific function essential for maintaining life.

Classification of Proteins Based on Biological Functions
1. Enzymatic Proteins
Enzymes are specialized proteins that act as biological catalysts, dramatically increasing the rate of chemical reactions. Without enzymes, many vital biochemical processes, such as digestion and metabolism, would occur too slowly to sustain life. Enzymes such as amylase, lipase, and protease facilitate the breakdown of carbohydrates, fats, and proteins, respectively. Some enzymes accelerate reactions by more than a million times without being consumed in the process. Emerging research has also led to the development of artificial enzymes and enzyme-based therapies for metabolic disorders.

2. Transport Proteins
Transport proteins play a crucial role in moving essential molecules within the body. Hemoglobin, a protein in red blood cells, binds oxygen in the lungs and transports it to tissues. Similarly, albumin helps transport fatty acids, minerals, and hormones through the bloodstream. Another vital transport protein, transferrin, carries iron, which is essential for red blood cell production. Advanced research in nanotechnology is exploring synthetic transport proteins for targeted drug delivery.

3. Structural Proteins
Structural proteins provide mechanical support and strength to cells and tissues. Collagen, the most abundant protein in mammals, forms the structural framework of skin, bones, tendons, and ligaments. Keratin strengthens hair, nails, and the outer layer of the skin, while actin and tubulin support cellular shape and movement. The study of structural proteins has led to innovations in tissue engineering and regenerative medicine.

4. Hormonal Proteins
Hormonal proteins act as chemical messengers, regulating physiological processes to maintain homeostasis. Insulin, secreted by the pancreas, controls blood glucose levels, preventing diabetes. Other hormones, such as growth hormone and thyroid hormones, regulate metabolism, development, and reproduction. Advances in biotechnology have enabled the production of synthetic hormones to treat endocrine disorders.

5. Defensive Proteins
Defensive proteins play a pivotal role in the immune system. Antibodies, produced by white blood cells, recognize and neutralize pathogens such as bacteria and viruses. Complement proteins assist in immune responses by marking invaders for destruction. Recent developments in immunotherapy harness defensive proteins to combat cancer and autoimmune diseases.

6. Proteins as an Energy Source
Although carbohydrates and fats are the body’s primary energy sources, proteins can be utilized for energy in times of prolonged fasting or intense physical exertion. When necessary, proteins undergo catabolism to provide energy, though excessive protein breakdown can lead to muscle loss and metabolic imbalances.

7. Building and Maintenance of Body Tissues
Proteins are essential for tissue growth, repair, and maintenance. They contribute to muscle synthesis, wound healing, and cellular regeneration. Essential amino acids, obtained from dietary proteins, are crucial for producing new proteins required for these processes. Protein deficiencies can lead to weakened immunity, muscle wasting, and delayed recovery from injuries.

Conclusion
Proteins are indispensable molecules that perform diverse and vital functions in living organisms. From enzymatic catalysis to structural support, transport, defense, and hormonal regulation, proteins are involved in every aspect of biological activity. Ongoing research continues to uncover new protein functions and their applications in medicine, biotechnology, and health sciences. Ensuring an adequate protein intake through a balanced diet is crucial for overall health and well-being.
The Essential Role of Protein Molecules in Living Systems

Top High-Protein Cereals for a Nutritious Breakfast

Several cereal brands are recognized for their high protein content. Here are some of the most popular options:

• Post Premier Protein Cereal: With 20 grams of protein per serving, this cereal is one of the highest in protein available. Flavors include mixed berry almond and chocolate almond.
• Kellogg’s Special K Protein Cereal: A well-known brand, Special K Protein delivers about 15 grams of protein per serving and is offered in flavors like Original Multi-Grain and Touch of Cinnamon.
• Magic Spoon Cereal: Famous for its low-carb, high-protein content, Magic Spoon cereals provide around 12-14 grams of protein per serving. Flavors include cocoa, fruity, and cinnamon.
• Kashi GO: Featuring plant-based ingredients, Kashi GO cereals offer 10-12 grams of protein per serving, with flavors like Crunch and Lean.
• Nature Valley Protein Granola: This granola provides about 10 grams of protein per serving and is often enjoyed as a yogurt topping or on its own.
• RX Cereal: Produced by the same company that makes RX bars, this cereal contains 11-12 grams of protein per serving, made with simple, whole food ingredients.
• Catalina Crunch: A keto-friendly option, Catalina Crunch offers around 11 grams of protein per serving, available in flavors such as dark chocolate and cinnamon toast.

These cereals are not only high in protein but also come in a variety of flavors, making them a nutritious and tasty addition to your breakfast routine.
Top High-Protein Cereals for a Nutritious Breakfast

Fish - an important source of a variety of nutrients

Fish is a food source comparable to other animal protein foods in nutrient composition. There are dozens of varieties of fish, with a variety of flavors and cooking styles to suit any taste. Fish is filled with omega-3 fatty acids and vitamins such as D and B2 (riboflavin). Fish is rich in calcium and phosphorus and a great source of minerals, such as iron, zinc, iodine, magnesium, and potassium.

The vitamin B12 found in fish is crucial for the growth of healthy red blood cells, DNA reproduction, and nerve function. Consuming enough vitamin B12 is linked to a lower risk of dementia and heart disease.

Seafood is an important contributor of selenium to the American diet and is unique among animal protein foods as a rich source or omega-3 fatty acids EPA and DHA. Eating fish is an important source of omega-3 fatty acids.

These essential nutrients keep human heart and brain healthy. The omega-3 fat docosahexaenoic acid (DHA) is especially important for brain and eye development. In this case, it’s often recommended that pregnant and breastfeeding women eat enough omega-3 fatty acids.

Salmon and sardines, in particular are good sources of omega-3 essential fatty acids, while halibut is a great source of protein.

The forms of lipid in fish are triglycerides or triacylglycerols. Triglycerides in pelagic fish contain the long-chain polyunsaturated fatty acid EPA (eicosapentoic acid) and DHA (docosahexanoic acid), which have many health benefits including normal development of the brain and retina in infants and prevention of heart disease in adults.

Research has linked fish consumption with many health benefits, including a lowered risk for arthritis, heart attacks, high blood pressure, prostate cancer in men and strokes. Many large observational studies show that people who eat fish regularly have a lower risk of heart attacks, strokes, and death from heart disease.

The WHO/FAO in 2003 recommendation on the consumption of fish is that “regular fish consumption (1-2 servings per week) is protective against coronary heart diseases and ischemic stroke and is recommended. The serving should provide an equivalent of 200-500 mg of EPA and DHA.”

Fish are also a great source of protein, which is critical to maintaining healthy muscles, organs, and blood vessels. Protein helps support cell division, hair growth, and even hormone signaling.
Fish - an important source of a variety of nutrients

Basic unit of protein and its function

The word protein is derived from Greek word, “proteios” which means primary. As the name shows, the proteins are of paramount importance for biological systems. Proteins are biochemical molecules consisting of polypeptides joined by peptide bonds between the amino and carboxyl groups of amino acid residues.

Proteins are made up of hundreds or thousands of smaller units known as amino acids. Most organisms use 20 naturally-occurring amino acids to build proteins. The linear sequence of the amino acids in a protein is dictated by the sequence of the nucleotides in an organisms’ genetic code. Amino acids can combine to form long linear chains known as polypeptides. Each type of polypeptide chain has a unique amino acid sequence.

The sequence of amino acids determines each protein’s unique 3-dimensional structure and its specific function such as catalysis of biochemical reactions, mechanical support and immune protection, movement, transport of ligand, transmits nerve impulses, and control growth and differentiation.

The proteins function to regulate specific steps in metabolism – one step, one protein. Hence, many proteins are needed.

The polypeptide must fold into a specific three-dimensional structure before it can perform its biological functions. The function of all proteins depends on their ability to specifically interact with other molecules. Such specificity is possible because polypeptides with different amino acid sequences fold into different tertiary structures.

Proteins are not entirely rigid molecules. They undergo conformational changes upon ligand binding. Each kind of protein evolved to interact with a specific molecule or ligand. For example, transport proteins (such as hemoglobin) bind to specific ligands (in this case oxygen) and transport the ligand to a site where it is needed. Hemoglobin, the transporter of oxygen is a tetrameric protein (alpha 2, beta 2), with each monomer having a heme unit. Binding of oxygen to one heme facilitates oxygen binding by other subunits.

Storage proteins such as myoglobin, another oxygen-binding protein, allow the cell to store higher concentrations of the ligand than otherwise would be possible.

Catalytic proteins— the enzymes—convert the ligands into other molecules. They act as biochemical catalysts. The first step in enzymatic catalysis is the binding of the enzyme to the substrate. This, in turn, depends on the structural conformation of the active site of the enzyme, which is precisely oriented for substrate binding

Many proteins have structural or mechanical functions. Structural proteins interact with specific molecules, often endowing the bound molecules with special biological properties. For instance, one class of proteins, the histones, binds to DNA to form compact nucleoprotein structures called nucleosomes, while a second class of proteins combines with RNA to form the ribonucleoprotein complex known as the ribosome.

Structural proteins collagen is the most abundant protein in mammals and is the main fibrous component of skin, bone, tendon, cartilage and teeth.

Proteins are also important in cell signaling, immune responses, cell adhesion, and the cell cycle.
Basic unit of protein and its function

 

Milk and dairy foods

Milk is the secreted fluid of the mammary glands of female mammals. It contains nearly all the nutrients necessary to sustain life. Since the earliest times, mankind has used the milk of goats, sheep and cows as food. Milk is basically composed of water (~87 percent), milk fat (~4 percent) and non-fat solids (~9 percent).

In addition to milk, several dairy products such as cream, butter, yogurt, kefir, and cheese have been produced and consumed worldwide for millennia.

Fresh milk is highly perishable, bulky, and easily contaminated (it is a favorable medium for bacterial growth). Because it is so susceptible to contamination and adulteration (with water), fluid milk production, treatment and distribution is widely subject to controls.

Milk tastes mildly sweet, while its odor and flavor are normally quite faint. Cow milk generally contains between 3 and 4 g of fat/100 g, although values as high as 5.5 g/100 g have been reported in raw milk. Most milks consumed now contain a standardized fat content of around 3.5 g/100 g.

Milk fat occurs in the form of droplets or globules, surrounded by a membrane and emulsified in milk serum (also called whey). The fat globules (called cream) separate after prolonged storage or after centrifugation. The fat globules float on the skim milk. Homogenization of milk so finely divides and emulsifies the fat globules that cream separation does not occur even after prolonged standing.

The major proteins found in milk are casein and whey proteins, with casein (αs1-, αs2-, β-, and κ-casein) accounting for approximately 78 percent of the protein in cow milk and whey proteins accounting for about 17 percent of the total protein

Milk and dairy products are nutrient-dense foods, supplying energy and high-quality protein with a range of essential micronutrients (especially calcium, magnesium, potassium, zinc, and phosphorus) in an easily absorbed form. Milk minerals are crucial for human health and development as well as in dairy processes as cheese-making and for all traits involving salt-protein interactions.

In recent decades, technological advances have supported the development of new dairy-based products. Broadly, dairy products can be categorized as basic products, such as fermented milk, cheese and yoghurt, and value-added products, such as low-fat and fortified milks.

Milk can be internationally traded either in dry, evaporated or condensed whole milk form or as dry skimmed milk powder (NFDM). These whole milk products may be reconstituted to fluid milk by mixing with water. Skimmed milk powder is reconstituted by mixing with butteroil (anhydrous milk fat) or vegetable fats and water to obtain a mixture of about 3.5 to 4 percent fat and 9 percent non-fat-solids. Well-reconstituted milk is said to be practically indistinguishable from fresh milk.
Milk and dairy foods

Protein content in fish

Fish and seafood products, have a high nutritional value regarding beneficial amounts of protein, lipids as well as essential micronutrients.

Aquatic animal foods are a rich source of protein and currently supplies 17% of all the protein consumed in the world. Fish is also a good source of easily digestible protein, and its amino acid profile usually contains most of the essential amino acids which is required to humans for balanced diet.

A 100 g cooked serving of most types of fish and shellfish provides approximately 18–20 g of protein, or about a third of the average daily recommended protein intake.

The amount of protein in fish muscle is usually between 16 and 21 %, but values lower than 16 % or as high as 28 % are occasionally found in some species. Proteins are important for growth and development of the body, maintenance and repairing of worn out tissues. Fish is known to be a source of protein rich in essential amino acids (lysine, methionine, cystine, threonine, and tryptophan). Eighteen amino acids were identified in tuna species, and glutamic acid was the most predominant.

Aquatic animal foods have a higher protein content than most terrestrial meats. In addition, aquatic protein is highly digestible and rich in several peptides and essential amino acids that are limited in terrestrial meat proteins, as for example methionine and lysine.

In addition to the high nutritional value, fish proteins also have good functional properties such as water-holding capacity, gelling, emulsification, and textural properties for the products such as fish mince and surimi, the water-holding capacity and the gelling properties which determine the textural attributes of the products are important quality parameters.
Protein content in fish

Kjeldahl method for protein analysis

Proteins have a major role in the growth and maintenance of the human body and are, along with carbohydrates and lipids, the energy giving nutrients in the diet. In addition, proteins also pose a wide range of other functions in the body, such as enzymatic activity and transport of nutrients and other biochemical compounds across cellular membranes.

The Kjeldahl method was developed in 1883 by a brewer called Johann Kjeldahl. A food is digested with a strong acid so that it releases nitrogen which can be determined by a suitable titration technique. The amount of protein present is then calculated from the nitrogen concentration of the food.

The same basic approach is still used today, although a number of improvements have been made to speed up the process and to obtain more accurate measurements. It is usually considered to be the standard method of determining protein concentration. Protein is determined by the analysis of the nitrogen content. From this, the protein content is calculated. Protein consists of amino acids which contain nitrogen (N) in the amino group.

The Kjeldahl method has three different steps: digestion, distillation, and titration. In this method, most organic nitrogen-containing samples are digested with sulfuric acid to ammonium sulfate; the ammonium is then liberated by raising the pH and measured by titration.

The Kjeldahl method was performed according to method 981.10 of the AOAC International. Approximately 1 g of raw material was hydrolyzed with 15 mL concentrated sulfuric acid (H2SO4) containing two copper catalyst tablets in a heat block at 420 ◦C for 2 h.

After cooling, H2O was added to the hydrolysates before neutralization and titration. The amount of total nitrogen in the raw materials were multiplied with both the traditional conversion factor of 6.25 and species-specific conversion factors in order to determine total protein content. The species-specific conversion factors were 5.6 for fish and shrimp, 5.4 for flours and 4.59 for seaweed, respectively.
Kjeldahl method for protein analysis

What is red meat?

Red meat is commonly considered to include beef, veal, pork and lamb (fresh, minced and frozen). In recent years, red meat has attracted much debate regarding its impact on health and the environment. Consumption trends of meat vary greatly around the world. Significant increases in consumption are apparent in developing countries with Latin America, the Caribbean and East Asia seeing particularly large increases.

Red meat continues to play an important role in the human diet today; it contains high biological value (easily absorbed and utilized) proteins and essential micronutrients, including vitamins and minerals. The composition of the meat varies based on the animal species, sex, age, and diet, as well as the climate and activity during its growth. Total nitrogen, fat, and iron levels increase as the animal approaches maturity. It also makes a significant contribution to the monounsaturated and omega 3 fatty acids in our diet.

In addition, the ratio of polyunsaturated fatty acids (PUFAs) to saturated fatty acids (SFAs) decreases with the maturity of the animal.

In terms of micronutrients, red meat (particularly beef and lamb) is an excellent source of bioavailable iron and zinc, and also provides selenium, vitamin D, and B vitamins, with red meat being one of our major sources of vitamin B12. Red meat also contains bioactive compounds such as taurine, carnitine, creatine and some endogenous antioxidants.
What is red meat?

Classification of glycoproteins

Glycoproteins result from the covalent association of carbohydrate moieties with protein. The amino acids and carbohydrates comprising the glycoprotein molecules are organised in two general ways. One type has a protein core, frequently molecular weight less than 100,000 to which are attached a few oligosaccharides residues.

The other type has a much higher molecular weight and is mainly carbohydrate in content and is organised as hundreds of small oligosaccharides residues covalently linked to a peptide core.

Classifications of glycoproteins is based in the type of glycosidic linkage involved in the attachment of carbohydrate to the peptide backbone.
*Glycoproteins having one carbohydrate group in each protein group
Ovalbumin MW 44.5x1000
Soybean hemagglutinin MW 110x1000
Ceruloplasmin MW 143x1000
Transferrin MW 92x1000

*Glycoproteins having a few carbohydrates groups in each protein unit
Ovomucoid MW 28x1000
Fibrinogen MW 330x1000
Fetuin MW 46x1000
D-glucose oxidase MW 186x1000
Thyroglobulin MW 600x1000

*Glycoproteins having many carbohydrate groups in each protein unit
Epithelial mucins MW 1000x1000
Blood group substance A MW 416x1000
Classification of glycoproteins

What is biological value of protein?

Since proteins are of such great importance to animals and man, many plants are grown because of nutritional value of their proteins.

However not all proteins have the some biological value. Biological value can be defined as the percentage of the absorbed nitrogen retained in the body.

Protein quality refers to the ability of a dietary protein to supply the amino acid needs of the body. The fact that a specific food is a rich source of protein does not indicate that the food has any particular value in supporting growth or maintenance. Some proteins are rich in certain essential amino acids, and thus have a high biological value, whereas other proteins are devoid of some of these amino acids or contain them in very small amounts.

For example, gelatin is a protein that is sometimes used in cooking. This protein is available in a pure powdered form; however, the use of gelatin as a food and as the sole source of protein cannot supply the body’s amino acid needs.

In those areas of the world where the main protein source is vegetable protein that lacks certain amino acids, protein deficiency diseases often occur, particularly in children.

 A protein with biological value of 70 or more is considered capable of supporting growth, assuming caloric value of the diet is adequate. This means that 70% of the nitrogen absorbed is retained.
What is biological value of protein? 

Elements of protein

Carbon, hydrogen and oxygen dominate biomass composition, but neither proteins nor nucleic acids could be built with just those three elements.

Proteins are major components of all organisms. Proteins have several essential roles in animals and plants.
*Enzymes
*Structural
*Defense
*Transport
*Hormones
*Storage

All proteins contain nitrogen, carbon, hydrogen and oxygen. Many also contain sulfur; some contain phosphorus and a few contain other elements such as zinc, iron and copper.

Groundnuts: Good source of protein

Although protein vary somewhat in composition, the typical elemental analysis in 16% nitrogen, 50% carbon, 7% hydrogen, 22% oxygen and 0.5%-3% sulfur.

Nucleic acid cannot be formed without phosphate groups, and phosphorus is also essential for intracellular energy conversion via adenosine triphospahte (ATP).

Twenty amino acids are used for protein synthesis. Plants can make all of these from carbon captured during photosynthesis, in addition to nitrogen and sulfur taken up from the soil.
Elements of protein

Nutrition of rice

Rice is predominantly a carbohydrate, high energy food. It may be the major as aspect of a diet, or incorporated into the main dish, side dish, or dessert and is commonly used in the preparation of ready to eat breakfast cereals.

Rice is especially important to persons with wheat allergies and is commonly eaten as a first food by infants, as it offers the least cereal allergy.

Rice may be eaten as the whole grain, or polished shedding the bran. The nutritional value of rice with respect to vitamins is affected by the content so individual vitamins present and the amount removed or destroyed by milling or processing.

The once-prevalent deadly disease beriberi resulted from eating polished rice (thiamin removed in the milling process) as a staple food.

Today, most white rice is enriched with vitamins and minerals, to add back nutrients lost in milling.

Unpolished, whole rice is more subject to flavor deterioration and insect infestation than polished, white rice.

The protein content is about 7% which is not an appreciable amount. The protein level of rice is similar to those of potato and yam on a dry weight basis is the lowest among the cereals.

But since it is consumed in large quantities, rice supplies a good amount of protein. Rice also has the lowest dietary fiber content.

The primary place of origin of rice is Southeast Asia, where averages of more than 200 pounds per person a year are eaten.

China, India, Japan and Vietnam are some of the major rice consuming countries.
Nutrition of rice 

The role of protein as a color

The role of protein in color of foods is not clear cut. In most instances it may either play a role through its interaction or as part of a complex molecules.

The brown color produced during the heating of many different foods comes, in part, from the Maillard reaction.

Maillard Reaction is a browning reaction between an amino group and a reducing group of a carbohydrate.

This reaction contributes to the golden crust of baked products, the browning of meats and the dark color of roasted coffee.

Proteins are directly involved in the color of the protein happens to be a pigment. Selected color pigments, such as chlorophyll are bound in the chloroplasts in a protein lipid matrix.

The meat turn grayish brown during cooking when protein holding the pigment becomes denatured. While milk appears white as light reflects odd the colloidal dispersion of milk protein.

The color of raw salmon flesh is a translucent deep pink red, which on smoking turns a more opaque light pink, as the conformation of the protein changes during processing light scattering within the fish increases.

The visible light range is only a small portion of the electromagnetic energy spectrum which ranges from wavelengths of 60 m for radio waves to 0.0001 nm for gamma waves.

The role of protein as a color

Protein deficiency in human body

Protein is one of the three ‘macronutrients’ (protein, carbohydrates, and fats) that human bodies need in balanced amounts.

Proteins are constantly being turned over in body tissues as old cells die and are replaced by new ones. Approximately 300 g of new protein is made each day in the human body.

The disease syndrome of kwashiorkor first described in 1933 is believed to be due to protein deficiency, but it occurs to varying degrees in conjunction with calorie deficiency. The dramatic clinical picture of kwashiorkor (edema, hypoalbuminemia, and a fatty lover with or without skin and hair changes) represents acute decompensation of a relatively long-standing deficiency state, usually precipitated by infection.

The disease syndrome is variable source the degree in both calorie and protein malnutrition, as well as the nutrients, will influence the biochemical and clinical changes.

MYOGLOBIN

The term protein deficiency can be defined as state of relative or absolute deficiency of body proteins or one or more of the essential amino acids. The deficiency can result from a protein-deficient due to other disease and in general can also result from a global deficit of food.

In uncomplicated protein deficiency, for example, protein catabolism should be minimal when total energy is the limiting factor, however, protein catabolism must increase to cover energy needs.

Severe marasmus or choric starvation , is characterized by growth retardation , loss of body fat, and muscle wasting. Studies of mass starvation during World War II and in chronically deprived populations suggest that severe deficits of calories and protein result in decreased fertility, in a deceased in the length and weight of the newborn, and in increased rates of neonatal mortality.

When total caloric intake has been adequate or nearly adequate, as is possible when starchy low protein foods are dietary staples, the symptoms are more toward changes associated with protein deficiency pellagra-type dermatitis, fatty liver, changes in texture and pigmentation of hair, gastro intestinal disturbances and diarrhea with resulting loss of electrolytes.

Protein deficiency in human body

Protein deficiency symptoms

The nutritional disease kwashiorkor was first described in the medical literature in the 1930s and a very tentative suggestion made that it might due to dietary protein deficiency.

In protein deficiency, when the diet supplies too little protein or lacks a specific essential amino acid relative to the others, the body slows it synthesis of proteins whole increasing its breakdown of body tissue protein to liberate the amino acids it needs to build other proteins of critical importance.

The first sign of protein deficiency is likely to be weak muscles – the body tissue most reliant on protein.

A protein deficiency may also show up in the blood. Red blood cells live for only 12 days. Protein is needed to produce new ones.

People who do not get enough protein may become anemic, having fewer red blood cells than they needed.
Protein deficiency symptoms

Structure of protein

In 1960, the British biochemist John Kendrew used a method called ‘X-ray diffraction’ to photograph myoglobin at a 2 A resolution and became the first man to determine the three-dimensional structure of a protein.

The basic structure common to all proteins is the peptide linkage which is formed by condensation the carboxyl group of one of amino acid with the amino group of another.

In this way chains are created, which contains only 3 amino acids, to complex polymers of 1000 or more. At physiological temperatures in aqueous solution, the polypeptide chains of proteins fold into a form that in most cases is globular.

The sequence in which amino acids are arranged in the peptide chain is known as the primary structure of the molecule. In biochemistry, this is always given starting with the N-terminal and ending with the C-terminal amino acid, because this is the order in which amino acids are added during protein synthesis in the cells.

The amino acid chain is the primary and central component of the protein, but not necessarily the only component. Some protein may include other atoms or small molecules which are required for their function and. or stability. The proper sequence of amino acids tends to be a critical factor in protein function.

Protein molecules serve as some of the major structural elements of living system. This function depends on specific association of protein subunits with themselves as well as with other proteins, carbohydrates and so on, enabling even complex systems like actin fibril to assemble spontaneously.
Structure of protein

Transport Proteins in human body

The functions of all protein depend on their ability to specially interact with other molecules.

Transport proteins may function by acting as carriers or they may provide protein-lined passages (pores) through which water-soluble materials of small molecular weight may diffuse.

Protein act as conduits to bring compounds into a cell either by passive (or facilitated) diffusion, in which no energy is needed to pass down a concentration gradient, or by active transport, for which energy is required. 

The uptake of amino acids and monosaccharides occurs against a concentration gradient and requires ATP, thus, it is example of active transport.

Hemoglobin is an example of an oxygen transport protein and is part of these oxygen delivery systems. 

Transport such as hemoglobin bind to specific ligands (oxygen) and transport the ligand to a site where it is needed.

Other transport proteins move about in the body fluids, carrying nutrients and other molecules from one organ to another. Those that carry lipids in the lipoproteins are examples. 

Special proteins also carry fat-soluble vitamins, water-soluble vitamins, and minerals. Other example of oxygen transport protein are, myoglobin (Fe), hemerythrin (Fe), and hemocyanin (Cu).

Passive transport involved with transport of substances occurs down their concentration and electrical gradient. This does not use any energy.

A glucose transporter is an example of a passive transport protein, this protein changes shape when it binds to a molecule of glucose.

The shape change moves the solute to the opposite side of the membrane, where it detaches. Then, the transporter reverts to its original shape.

Transport Proteins in human body

Amino Acids

Proteins are sequences of amino acids. All amino acids contain at least one amino group (-NH2) in the alpha position and one carboxyl, and all (except Glycine) contain an asymmetric carbon atom. For this reason, they may exist as isomers.

There are 20 different amino acids each consisting of a backbone to which a side group is attached. The amino acid backbone is the same for all amino acids, but the side group varies. It is side group that makes each amino acid unique.

Most naturally occurring amino acids are of the L-configurations, although D-amino acids are not uncommon in some microorganisms.

The presence of a D-amino acid oxidase in mammalian tissue, however, suggests that the D-forms may play some yet unrecognized role in mammalian protein metabolism.

Nine of amino acids are called essential amino acids, because human body cannot make them and must get them though diet. The body can manufacture the remaining 11 amino acids, called nonessential amino acids. 

When amino acid backbones joined end to end, a protein forms. The bonds that from between adjoining amino acids are called peptide bonds. Proteins often contain from 35 to several hundred or more amino acids.

Amino acids are not stored in the body in any appreciable amounts; therefore, proper nutrition requires eating enough protein just about every day to meet the body’s needs for essential amino acid.
Amino Acids

Filled Milk

Filled milk is a milk or cream to which a fat other than butter fat has been added. A typical milk consists of skim milk or nonfat dry milk to which a vegetable fat has been added.It’s cheaper and contains less cholesterol than whole milk.

The water phase contains milk solids. These solids usually give a good flavor background, which usually makes addition of a milk or cream flavor unnecessary.

Usually the protein ingredient comes from soybeans, through sometimes the soya proteins is combined with a chalky protein substance called sodium caseinate, which is derived from real milk.

It is a homogenized product and its fat content should not less than 3 per cent and SNF 8,5 per cent.

This product was very unpopular initially, the ‘Filled Milk Act’ was passed by the US Congress in 1923 to prohibit interstate and foreign shipments of such products.

Congress claimed that filled milk was unhealthy, and that it was manufactured to look like real milk, thus confusing consumers.

By 1970s, the drive to reduce the intake of cholesterol on the diet resulted in an increased demand for filled milk products.

Filled Milk