Category: Proteins

What are proteins?

They are formed by the complex polymerization of amino acids and are essential for every biochemical function of the living organisms.

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Types of proteins

With relation to the structure and number of amino acids present and the nature of bonding, they are broadly categorized into four classes.

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Functions of proteins

Proteins make up to 50% of the dry body weight and have specific functions. All the activities like structural support, growth, respiration, digestion, energy production, osmoregulation are brought about by proteins.

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What is protein synthesis?

In non-biological process of peptide production short peptides are produced in laboratories. There are two types of peptide production methods namely liquid phase production and solid phase synthesis.

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Daily protein requirements

The daily requirements are highly variable and are highly relative to the individual's gender, age, height and weight. The level of activity of a person and his lifestyle also have an effect over his necessities of macronutrients.

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High protein food sources

Corn and rice, the staple food sources of the third world are poor in proteins and are leading to obesity of the populations due to high carbohydrate content of these cereals.

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what is protein synthesis?

Home › Protein energy malnutrition › Protein deficiency › What is protein synthesis?

Proteins have diverse functions in the body and the body cells have the inherent ability to make them.

Living cells have evolved around their ability to produce proteins for their functions and growth. Right from the unicellular organisms to complex higher animals like mammals, all have the ability to make them from the amino acids present in the cytoplasm.

What is protein (polypeptide) synthesis?

All biological processes involve proteins present in the living cells. They are also essential nutrients for all life forms for their functions; Most of them are made by the body. There are many other uses of for them outside the body. Polypeptides are also manufactured by different chemical methods. These protein production processes inside the body as well as polypeptide manufacture chemically are broadly called protein synthesis.

What is protein bio-synthesis?

All organisms grow and reproduce. For these functions they have to utilize the nutrients and convert them into cell structures and body structures; the basis of which is protein. The body requires great number of them (1000s) for its many facets of activity. To directly source all these and use them is an impossible task for a living organism.

The body does not absorb the polypeptides as such but absorbs its broken down form as amino acids. The living body also has the capacity to make many of the amino acids. Amino acids numbering 22 constitute by their sequences and structural alignments all forms of polypeptides. With the exception of the unicellular organisms all the the higher organisms have nucleus in their cells (exception being red blood cells in many mammals). The cell nucleus contains specific numbers of chromosomes which are again specific to the particular organism. The chromosomes are in-turn made of DNA molecules.

part of a DNA double helix The DNA has the code for synthesis of polypeptides. By a complex process of bio-signals, the cell gets a message for the production of a particular molecule in certain quantity. Then a complex process occurs both inside and outside the cell nucleus giving rise to strands of polypeptides. This process is called protein bio-synthesis. The process and steps involved are discussed in post 'Protein synthesis steps and process'.

What is peptide synthesis?

Apart from the long strands of peptides formed by ribosomes inside the cells, biologically peptides are also produced outside the cells. The milk peptides are produced by enzymatic breakdown of milk protein by digestive enzymes as well as enzymes formed by lactobacilli. In non-biological process of peptide production short peptides are produced in laboratories. There are two types of peptide production methods namely liquid phase production and solid phase synthesis. A subject of great research interest is the synthesis of peptide antibodies.

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Functions of proteins

Home › Functions of proteins

Proteins are very important macromolecules with essential functions in the body.

Proteins make up to 50% of the dry body weight and have specific functions. All the activities like structural support, growth, respiration, digestion, energy production, osmoregulation are brought about by proteins. The chemical structures and chemical compositions regulate the roles of proteins.

Proteins in structural support

The structural proteins form the basic matrix of structural supports and protective covers.
Keratin, elastin and collagen are a few examples these types, carrying out the supportive and protective role.
Keratins (α and β) are the primary constituent of growths and structures of skin like hair (also wool), nails (also claws and hoofs), horns and beaks.
Elastin is very important for pressure wave propagation functions in arterial walls, especially in large elastic blood vessels like aorta.
Elastin contributes to the elasticity of skin, lung, bladder and elastic cartilage.
Collagen is fibrous, mostly found outside the cells and forms the extracellular matrix giving structure to the animal body.
It is the main component of the matrix of bone, cartilage, tendons, ligaments, fascia and skin.

Functions of proteins in movement and contraction

All our body movements are brought about by movement of muscles.
Muscles are categorized as skeletal muscle (bringing about skeletal movement, locomotion and maintenance of posture), smooth muscle (bring about involuntary movements like, movement of intestine, urinary bladder, stomach, esophagus, intestines, blood vessels) and cardiac muscle (for beating of the heart).
All these muscles are mainly made of muscle cells.
Muscle cells contain myofibrils which are organised into sub-units called sarcomeres.
The filaments of myofibrils are constructed from contractile proteins.
Thin type of myofibrils consists mainly of actin and the thick type of myofibril consists mainly myosin.

Proteins in control of growth differentiation

There are proteins having a regulatory role like growth differentiation.
Growth differentiation factors (GDF) are named GDF1 to GDF15.
These factors regulate complex processes in ovulation, embryonic development, muscle development (GDF8-myostatin) and inflammatory and apoptotic pathways (GDF15) during diseases and injuries.

Functions of proteins in gene expression

The messages and codes in the genes are not totally expressed at the same time.
They are switched on and off in respect to the phase of growth, organ under concern and biological timetable.
In expression of DNA and cell differentiation repressorproteins bind to specific DNA segments and prevent the formation of the particular product of that segment.
These DNA-binding proteins are coded by regulator genes.
The segment bound by repressor is called operator.
By binding to operator, the repressor prevents the creation of messenger RNA by the RNA polymerase.

Functions of proteins in tissue repair and maintenance

Continuous supply of amino acids and building of proteins is necessary for the tissue growth, repair and maintenance.
Constantly new tissues of hair, skin, nails and teeth are added to our body to replace the dead cells which have sloughed off.
Epidermis and blood cells have a life of about one month and are to be constantly replaced.
The cell in the gastro-intestinal system lining last only for 2 weeks.
There is an elaborate process of tissue regeneration all over the body with their use.
In special circumstances like injury and damage, increased activity of cell formation is induced and new tissue is formed.

Functions of proteins as hormones

These are messengers helping in regulating certain body chemical activities.
Many categories of hormones are secreted by endocrine glands like thyroid gland, pancreas, adrenal gland, ovary, testis and thymus gland for carying out many vital biological actities.
Complex hormones like melatonin and seratonin affect the sleep and mood whereas thyroid hormones affect the basal metabolic rate and synthesis of proteins.
Insulin regulates glucose utilisation whereas a myriad hormones regulate reproduction.

Functions of proteins as enzymes and catalysts

Proteins as enzymes and catalysts facilitate chemical reactions in the body.
Enzymes are large structures having essential kinetic functions in bringing about all biochemical reactions.
The functions of the gastrointestinal system are facilitated by different enzymes secreted for digestion of proteins, fats and carbohydrates.

Functions of proteins as antibodies and immune protection

Antibodies are proteins and are responsible for binding to specific foreign bodies and make them harmless, ineffective and eliminate them.
There are two types of main functions for immunoproteins made and used by the body, namely innate immune system and adaptive immune system.
In innate immune system the innate response is triggered by pattern recognition receptors (proteins) which identify pathogen-associated molecular patterns (PAMPs), which are associated with cellular stress or microbial pathogens. Cytokines (like interleukins, chemokines, interferons) which are glycoproteins are released to combat the antigen in various ways.

The Interleukins (secreted proteins /signaling molecules) create communication between white blood cells (leukocytes). Chemokines (chemotactic cytokines) are secreted by cells.
Their functions are to promote chemotaxis (chemically induced movement) of the nearby responsive cells towards the site of antigen.

Interferons (IFNS) have many antiviral activities like shutting down the synthesis of proteins in the host cells. In the functions of innate immune system, a complement system containing over 20 different proteins starts a biochemical cascade of attacking the surfaces of foreign cells.
This complements the functions of antibodies in killing the pathogens. In the innate immune system, white blood cells (leukocytes) like 'natural killer cells' which are cytotoxic lymphocytes kill the tumors and virus infected cells by releasing small cytoplasmic granules called perforin (cytolytic proteins) and granzyme (serine proteases) causing the target cell to die by apoptosis (programmed cell death).

Adaptive immune system has stronger immune response as well as immunological memory.
Each pathogen is remembered by signature antigen protein.
The responses are generated tailor made to specific antigen.

When a pathogen infects more than once the memory cells are quickly used to eliminate it.
Lymphocyte B cells and T cells carry receptor molecules which can recognize particular target antigen. Cytotoxins such as perforin are released into the target cell inducing it to undergo apoptosis.

Functions of proteins in Fluid and electrolyte balance and osmoregulation

Globulins and albumins are the important blood proteins molecules doing the functions of maintaining the fluid and electrolyte balance between the cells and the extracellular space.
The proteins present in the capillary beds (blood vessels of one-cell thickness) pull the blood fluid from the tissues into the capillary beds.
This osmotic pressure exerted by proteins is called colloid osmotic pressure or oncotic pressure.
These functions protects the body from fluid retention and edema.
If the blood plasma levels of proteins are reduced due to proteinuria (loss through urine) or as a result of malnutrition, oncotic pressure is reduced and fluid retention occurs leading to many health complications.
Proteins are abundant in biological membranes.
Cellular membranes form channels and pumps regulating fluids and ions inside and outside the cells.
Many cellular channels allow ions to move from higher concentration to lower concentration.
However for forcing ions from lower concentration to higher concentration (pumps-active transport) energy in the form of adenosine triphosphate (ATP) are required.
Proteins being amphoteric, perform the functions of buffering and maintaining the optimum blood pH.

Functions of proteins in transport and storage

One of the important functions of Proteins is the transport of essential molecules from one part of the body to other.

Functions of hemoglobin and myoglobin are primarily in transport of oxygen to the tissues.

Transferrin is transporter of iron and helps in the storage of iron in the liver.

Cytochrome C functions as electron transport and albumin transports fatty acids in the bloodstream.

Ovalbumin are storage proteins found in the egg white providing nutrition to the embryo.

Functions of proteins in metabolism and energy production

Though proteins are not primary source of energy, in the event of shortage of body fuels like carbohydrates and fats, they are utilized in energy production functions.
They provide the nitrogenous base adenine for ATP and also creatine phosphate in the cell metabolism functions.
Some amino acids by the process called gluconeogenesis are degraded to pyruvate and glucose for production of energy.
Some of the amino acids are reduced to ketone bodies (acetoacetate) which can be metabolised for energy by muscle and brain when blood glucose levels are low.

Functions of proteins as receptors and neurotransmitters

Many proteins do the functions of signal detection and its conversion into another type of signal.
The functions of proteins Rhodopsin in light detection and conversion of the photo-signals into neurosignals is well known.
Proteins play many important functions in generation as well as transmission of nerve impulses.
Many monoamines like dopamine, epinephrine, norepinephrine, serotonin, histamine, melatonin have neurotransmitters functions.
Many neuropeptides have been discovered and 'neuropeptide Y' is one of them having wide range of neurological functions in food intake, obesity and anorexia nervosa.
Acetylcholine receptor (AChR-an integral membrane) is one of the neuroreceptor proteins.
It is embedded in the 'postsynaptic density (PSD)' region at the membrane of postsynaptic neuron. These proteins function as neurotransmitter receptor.

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Types of proteins

Home › Protein energy malnutrition › Protein deficiency › Types of proteins

Proteins types are categorized as per their structure, chemical composition and biological function.

Proteins types in relation to the structure

Proteins are made up of long chains of amino acids the sequence of which is decided by gene expression. A simple polypeptide chain of amino acid is called monomeric chain and those with several polypeptide chains and bonds are called oligomeric types. With relation to the structure and number of amino acids present and the nature of bonding, they are broadly categorized into four classes. Primary structure:
This is a basic structure made up of amino acids chains and the sequence is defined by the gene expression.
Secondary structure:
In these proteins covalent bonding within and outside the chains is made and a structure, usually of helix shape, is formed.
Tertiary structure:
In these types of proteins the structure is much more complex.
These structures are three dimensional in nature with complex formations of folds and loops due to repulsion of like charged molecules and attraction of oppositely charged molecules.
Quaternary structure:
These types of proteins are very large complex molecules with many many polypeptide chains. There are two main classes of quaternary structure and they are scleroproteins and globular proteins.

Scleroproteins:

These are also called fibrous proteins. They form long rod or wire-like shaped filaments. these are not soluble in aqueous solutions.

They are usually inert and are storage or structural types of protein having role in supportive and protective function.

They are found in bone matrix, connective tissues, muscle fiber and tendons. Some of the examples of this class are collagen, elastin, keratin and fibroin (in silk).

Enzyme hexokinase ball and stick model (enlarge) Globularproteins:

These are also called spheroproteins having globe like structure and are soluble in aqueous solutions. Many types of enzymes, catalysts, hormones, transporters, signal transduction proteins, plasma, coagulation factors, growth factors and hemoproteins come under this category. Nucleosome, spliceosome, signal recognition particle and ribonucleoprotein are complexes with many components.

Types of proteins based on chemical composition

Depending upon the chemical composition, they are classified as simple or conjugated proteins.
Simple proteins:
Simple types contain only amino acids and do not contain any other chemical or chemical groups.
Conjugated proteins:
Many of these contain apart from amino acids other metal and chemical components and are named conjugated proteins.
The non amino acid parts are called prosthetic groups.
Some of the conjugated types and their prosthetic groups are given below.
Lipoproteins:

These conjugated protein types contain lipids in their biochemical assembly.
Lipid groups may be bound non-covalently or covalently.
Many protein like structural proteins, enzymes, transporters, antigens, toxins, adhesins, HDL (high density lipoproteins), LDL (low density lipoproteins), mitochondria and pathogen lipoprotein are lipoproteins.
Glycoproteins:

These conjugated proteins contain glycans (oligosaccharide chains) covalently attached to the side-chains of polypeptides.
These types are very important in integral membrane proteins.
There are many important glycoproteins like mucins (present in mucus), antibodies (immunoglobulins), glycoprotein llb/llla ( found on blood platelets and required for their aggregation), components of zona pellucida surrounding ovum, structural protein in the connective tissue, egg white, blood plasma, hormones (Follicle-stimulating hormone, Alpha-fetoprotein and Thyroid-stimulating hormone, Luteinizing hormone and Human chorionic gonadotropin and Erythropoietin).
Phosphoproteins:
These are chemically bonded to compounds containing phosphoric acid. Calcineurins are one of the examples.
Hemoproteins:
These conjugated types contain heme prosthetic group bound non covalently or covalently to the proteins.

Heme consists of iron atom contained in the center of a large heterocyclic organic ring called a porphyrin.

Many hemoproteins like hemoglobin, myoglobin, cytoglobin, hemocyanin, neuroglobin and leghemoglobin are required for oxygen transport.
Hemeproteins like peroxidases, ligninases and cytochrome c oxidase have the function of catalysis.
Hemeproteins, cytochrome c and catalase have a role in electron transfer whereas for active membrane transport cytochromes are needed.
Flavoproteins: 
These contain nucleic acid derivative of riboflavin like flavin mononucleotide (FMN) or flavin adenine dinucleotide (FAD).
These have many functions in DNA repair, photosynthesis, apoptosis and cellular respiration.
Metalloproteins:
These types have a metal ion as cofactor.
Many hemeproteins, enzymes (metalloenzymes), signal transduction factors come under these types.
Some of the metals in metalloproteins are iron (hemoglobin), zinc (carbonic anhydrase), cobalt (Vitamin B12 or cobalamin), copper (superoxide dismutase), magnesium (chlorophyll, Hexokinase, Glucose 6-phosphatase, DNA polymerase), calcium (calmodulin), vanadium (vanabins), nickel (Hydrogenase, Urease), manganese (arginase), selenium (Glutathione peroxidase) and molybdenum (nitrate reductase).
Opsins:
Opsins are conjugated types present in photoreceptor cells of the retina.
Opsins bind covalently to vitamin A based retinaldehyde chromophore and function the vision perception.

Other conjugated proteins like cytochrome have function in electron transport and phytochromes function in plants for photoreception regulating photoperiodism, circadian rhythms and germination of seeds.

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What are proteins? - What are proteins made of?

Home › Protein energy malnutrition › Protein deficiency › What are Proteins made of?

What are proteins?

Proteins are highly complex compounds made of nitrogenous organic macromolecules comprising a variety of α amino acids which are joined together by peptide bonds.

They are formed by the complex polymerization of amino acids and are essential for every biochemical function of the living organisms.
They are the building blocks of the living beings right from the simple forms like virus to higher animals with complex organ systems.
Nearly 50% of the dry weight of the organisms constitute these complex structures.

What are proteins made of?

Proteins are essentially formed from a number of amino acids which in turn are made of carbon, oxygen and hydrogen.
Nearly all them contain nitrogen and sulphur.
Specialised structures are formed with the incorporation of minerals like phosphorus, copper, zinc and iron.
Proteins molecules are large and have high molecular weights.
Proteins are made from 2-100 numbers of amino acids having molecular weight of about 10kDa are called peptides.
The combination sequence of these amino acids can produce innumerable proteins.
In the E.coli bacteria cell there are 3000 different known varieties.

The optical isomers of alanine, D-Alanine and L-Alanine
They are made of three very important structure levels namely primary, secondary and tertiary.

The primary level is the amino acid sequence and is determined by gene expression.

In the secondary level of structure, the angles of bonds (covalent) within and between the amino acids determines the geometrical shape usually helix.

The tertiary three dimensional level of structure of folds and loops is due to the repulsion of like charged amino acid groups and attraction of oppositely charged amino acid groups.

This structure is usually the basis for the biological activity of proteins. 

They are primarily the organic structure basis of skin, hair, tendons, bones, muscles and cartilage. 

All our organs and body fluids contain and made of them. 

The enzymes, hormones, blood and serum contain them and body functions like digestion, circulation are brought about by them.
Proteins are made from amino acids
Proteins are made with 22 amino acids of which eight are essential amino acids.
These amino acids are considered essential because the body cannot synthesise them.
The rest of the 14 amino acids are synthesised by the adult human body.
Essential amino acids for humans: Isoleucine,Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan and Valine Amino acids synthesised by adult body: Alanine, Asparagine, Aspartic Acid, Cysteine, Glutamic Acid, Glutamine, Glycine, Proline, Selenocysteine, Serine, Tyrosine, Arginine, Histidine and Pyrrolysine.
Of these cysteine, histidine, tyrosine and arginine are essential for infants and growing children as they are not produced by them.

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What are proteins? - What are proteins made of?

Proteins deficiency can lead to collapse of body functions.

Proteins are the body building blocks
Sufficient consumption of protein foods is stressed as proteins are essential for the proper growth of the body.
Proteins are the basis for almost all the body parts like muscles, skin, hair and nails.
Proteins are made up of many amino acids in particular sequences specific to each type of protein. In the intestines the proteins are broken down into amino acids and absorbed.
These amino acids are assembled into required proteins in the body for the growth and the repair of the body.
Excess amino acids are excreted from the body in the urine.
Human beings require about twenty amino acids of which ten are essential.
In the absence of these essential amino acids the body will not grow.
So in human nutrition particular attention is given for obtaining the balance by mixing two or three sources.
In pregnancy right from conception addition of many sources of proteins in the diet is recommended to get all the essential amino acids.
Animal sources of proteins contain almost all the essential amino acids.
This good aspect is offset by the huge amount of fats.
Plant sources are deficient in some essential amino acids. However soy beans has been found to contain all the required amino acids.

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Potassium - An essential mineral

Potassium is one of the very essential minerals for the human body.
It is a cation, most abundant inside the body cells.
Potassium is an electrolyte like sodium and calcium and is important for passing of nerve impulses in the nervous system.
It is important for osmoregulation and fluid balance maintenance in the cells and the blood.
Adrenal functions, muscular actions and renal functions depend on its availability.
This mineral also has a very important role in metabolism of proteins and carbohydrates.
Its deficiency, otherwise known as hypokalemia, show symptoms like generalized weakness, dry skin, muscle weakness and slow reflexes. 
The level of this mineral in the body is regulated by the kidneys.
Hypokalemia occurs in cases of severe vomiting and diarrhea, in usage of diuretics without proper monitoring, in diabetes without control and in alcoholism.
In case of sudden depletion of this mineral, heart problems will be encountered and if not replenished quickly heat failure and death can occur.
A balanced diet fulfills the requirements of potassium.
Excesses of potassium is excreted by the kidneys.
High potassium levels in the blood or hyperkalemia is experienced by people with impaired kidney function or severe infection.
Fish, meat, potatoes, tomatoes, green leafy vegetables, dry fruits and most of the fruits (especially banana) are good sources of potassium.
In hypertension treatment potassium supplement is used to replace harmful excess sodium.

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