Protein- Structure, Properties and Function

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Structure, properties, and functions of protein

Proteins are defined as the most flexible macromolecules in living systems and perform vital roles in nearly all biological processes. Amino acids are the building blocks of the proteins. They act as catalysts, transport and store other oxygen molecules, provide mechanical support and immune protection, produce motion, transmit nerve impulses, and regulate growth and differentiation.

  • The organic compounds in the living organism are the most common proteins. They happen in each cell region and comprise roughly 50% of the dry cell weight.
  • The structure and role of life are dependent on proteins.
  • The root of ‘protein’ word? The name protein derives from the Greek word protein, which means the first position.
  • In the group of organic compounds most important to life, Berzelius (Swede Chemist) proposed the term protein.
  • The expression protein for the abundant and high molecular nitrogen weight of animals and plants was used in 1838 by the Netherlands chemist Mulder.
Protein- Structure, Properties and Function
Protein

STRUCTURE OF PROTEINS

The polymers of L-a-amino acids are proteins. The arrangement of proteins or protein folding which can be separated into 4 layers of the organization, is very complex.

(1)Primary structure

Linear amino acid series comprising the protein backbone (polypeptides). The primary structure of a protein consists of the amino acid sequence along the polypeptide chain. The main structure, generally abbreviated by 1- or 3-letter codes is the succession of amino acid residues. Covalent peptide bonds binding the amino acids together preserve the primary structure of a protein.

(2)Secondary structure

Protein spatial organization by spinning the chain of the polypeptide. Twisting or folding polypeptides into extremely normal sub-structures requires the secondary structure of proteins. The secondary structure is the right-handed alpha helix 3-D configuration or alternate arrangements like a beta-pleated sheet. 

(3)Tertiary structure

A stable protein’s three-dimensional structure. The 3-D folding of the alpha helix is the tertiary structure, created by structures such as proline corners, cysteine residue disulfide bridges, and electrostatic bonds. More than only an alpha helix and a pleated layer is used in this folding. There are other chemical interactions that can help describe the tertiary structure of the 3 dimensions.The secondary protein structure may be:
Alpha- Helix
Beta-SheetThe alpha-helix is a coiled right-handed strand. In an alpha-helix, the side-chain substituents of the amino acid groups extend to the outside.

In the ß-sheet, the hydrogen bonding is between strands (inter-strand) instead of between strands (intra-strand).Pairs of strands lying side-by – side are part of the sheet conformation.

(4)Quaternary structure

Certain proteins consist of two or three chains of polypeptides known as subunits. The spatial organization of these subunits is known as a quaternary structure. The structural hierarchy of proteins is equivalent to a building’s structure. The 3-D folding of the alpha helix (shown as a purple ribbon) is the tertiary structure, created by structures such as proline corners, cysteine residue disulfide bridges, and electrostatic bonds. More than only an alpha helix and a pleated layer is used in this folding. There are other chemical interactions that can help describe the tertiary structure of the 3 dimensions. Hemoglobin is a protein like the one in this illustration that has 4 polypeptide chains (called subunits) you may be familiar with. The quaternary structure would be a structure of identical and different spaces.

(5)Polypeptide

For a polypeptide that comprises more than 50 amino acids, the term protein is commonly used. However, some scholars have used ‘polypeptide’ in recent years, even though the number of amino acids is a few hundred. In an assemblage of polypeptide chains with a quaternary structure, they tend to use protein.

Protein- Structure, Properties and Function
Structure Of Proteins

STANDARD AMINO ACIDS

  • There are 300 amino acids in the wild – About 20 of them are present in the protein design, which isolates them from various life forms – animal, plant, and microbial – known as regular amino acids.
  • This is because the genetic code is universal and only 20 amino acids can be added as the protein is synthesized in the cells.
  • DNA, the genetic material in the egg, regulates the mechanism in part.
  • Any of the amino acids introduced undergo changes to form their derivatives during the protein synthesis.
  • The repeating sequence of atoms is referred to as the polypeptide backbone around the center of the polypeptide chain. These parts of the amino acids that are not active in making a peptide bond are bound to this repeated chain and give each amino acid its distinctive properties.

PROPERTIES OF PROTEINS

  • Solubility: Instead of true solutions in water, proteins form colloidal solutions. This is because of the large volume of protein molecules.
  • Molecular weight: Proteins differ according to their molecular weights, which depend on the amount of residues of amino acids.
  • Isoelectric pH: Isoelectric pH was defined as a property of amino acids.
  • The pH of a protein is determined by the structure of the amino acids (especially its ionizable groups). The pl is highly determined by acidic amino acids (asp, glu) and fundamental amino acids (his, lys, arg).
  • Protein occurs as tweeters or dipolar ions in Isoelectric pH. They have limited solubility, maximum precipitability, and less buffer potential in electrically neutral (do not migrate in the electrical field).
  • Acidic and essential proteins (e Lys + e Arg)/e Glu + e Asp): proteins of which the ratio is higher than 1 are referenced as fundamental proteins. The ratio is less than 1. For acidic proteins.
  • Protein precipitation: In colloidal solution, proteins occur due to polar group hydration (-COO, -NH3, -OH).
  • Dehydration or neutralization of polar groups may precipitate proteins.
  • Precipitation at pH: Proteins are less soluble at isoelectric pH in general.  When the pH is changed to pH (4.6 for casein), some proteins (e.g. casein) readily precipitate. Curd production from milk is a great example of sluggish milk protein precipitation, casein at pl. This is attributable to the lactic acid formed by the fermentation of bacteria that lowers the casein pH to pl.
  • Precipitation by salting out: The protein precipitation process is known as salting out by adding neutral salts such as ammonium sulfate or sodium sulfate. This phenomenon is clarified on the basis of salt dehydration of protein molecules. This induces intensified protein interaction, resulting in precipitation and molecular aggregation.
  • The amount of salt needed for the precipitation of proteins depends on the protein molecule’s size (molecular weight).

CLASSIFICATION OF PROTEINS

On the basis of nature of molecules, solubility, shape, and structure, the proteins can be classified into-

(1)Simple Proteins

A protein that contains amino acids as the main or only full hydrolysis result and occasional small carbohydrate compounds.

  • Fibrous protein– Fibrous proteins consist of long-lasting and fibrous chains in nature, or they have structure similar to sheets. The fibres and sheets are physically solid and insoluble in water. Ex- collagen, elastin, actin, and myosin,  α-keratin
  • Globular protein- Globular proteins are small, relatively spherical structure . These are water soluble and appear to be part of metabolic functions. Ex-  haemoglobin, insulin, Histones, albumins.

(2) Conjugated proteins

A compound of a complex protein with a nonprotein moiety. Ex-  lipoproteins, phytochromes, cytochromes, glycoproteins, phosphoproteins, metalloproteins,  opsins, hemoproteins, flavoproteins, and chromoproteins.

(3) Derived proteins

The degradation products extracted from the proteins are considered derived proteins when proteins are hydrolyzed by acids, alkaline, or enzymes. The derived proteins classification is then done by-

  • Primary derived protein:  These are derivatives of proteins that do not significantly change the size of the protein molecule. Ex- Proteans, Metaproteins, Coagulated proteins
  • Secondary derived proteins: These are formed by hydrolysis of simple or conjugated proteins by acid or enzymes. Ex- Proteosesn or albunoses, peptones, polypeptides.

FUNCTIONS OF PROTEINS

  • In living, cell proteins serve a broad range of specialized and essential roles.
  • These functions may usually be grouped into static functions (structural and dynamic).
  • Structural functions: Some of the proteins have brick and mortar roles and are responsible mainly for structure and body strength.
  • Collagen and elastin present in the bone, vascular and other organs of the epidermal tissue, and keratin.
  • Dynamic functions: proteins have a more complex nature in terms of dynamic functions.
  • This includes proteins, which serve as enzymes, hormones, blood clotting factors, immunoglobulins, membrane receptors, storage proteins, and even genetic regulation functions.
  • The proteins that execute complex roles are properly considered as cell horses.
  • Protein is an amino acid polymer Protein that gives rise to L-a-amino acids at complete hydrolysis (with concentrated HCl for many hours).
  • This is a common property of all the proteins. Therefore, proteins are polymers L-a-amino acids.

References

  1. https://www.ncbi.nlm.nih.gov/books/NBK21177/
  2. https://www.ncbi.nlm.nih.gov/books/NBK26830/
  3. https://content.byui.edu/file/a236934c-3c60-4fe9-90aa-d343b3e3a640/1/module3/readings/proteins.html
  4. https://www.researchgate.net/figure/The-hierarchical-structure-of-proteins-The-primary-structure-is-defined-by-the-sequence_fig1_236237111