Tertiary and Quaternary Structure of Proteins

Tertiary and Quaternary Structure of Proteins


after learning the Primary and Secondary structure of proteins if you want to learn the tertiary and quaternary structure of proteins Consider watching this video Greetings to all, Myself Sharad Agrawal Welcome to my channel, VinAm Guidance In today’s video, we are going to discuss tertiary and Quaternary structure of proteins So lets begin As I had told in my previous video, the primary structure of proteins is simply a chain of polypeptide in which different amino acids are connected to each other via peptide bond In secondary structure polypeptides exist as alpha helix or beta pleated sheets parallel or antiparallel This was primary and secondary structure of proteins (check videos link in description below) In tertiary structure when a polypeptide folds itself and exists in a three dimensional confirmation then it is called tertiary structure. three dimensional is when something exists in all three coordinates (x, y and z) Thirds coordinate (z coordinate) So when a protein exists in all these three coordinates such kind of structure will be called tertiary structure But how is this tertiary structure stable which bonds, forces and interactions are responsible to make such structure stable, lets see Hydrophobic interactions Hydrogen bonding Ionic Interactions and weak Vander wall forces and Covalent interactions in terms of Disulfide bond so we will discuss covalent later In Hydrophobic interactions the R group (side chain) of amino acids Side chain of first amino acid interacts with side chain of another amino acid provided both of these side chains are also hydrophobic in nature in that case such interaction will be called hydrophobic interaction example Valine you can watch the video (Amino acid structures I and II), Link given in description and also in I button so the structure of valine was something like Alpha carbon, amino group, carboxylic group and side chain apart from this Leucine The side is hydrophobic here also so these hydrophobic side chains of different amino acids can interact with each other and make the structure stable Next is Hydrogen bonding one hydrogen atom share its electrons with two electronegative atoms such type of bonding is called hydrogen boniding and imparts stability to protein structure Ionic interactions occurs between two oppositely charged species Say sodium is positively charged and chloride is negatively charged Opposites attract each other offcourse But this is in context with NaCl In case of proteins In case of proteins oppositely charged species may undergo ionic interactions say OH looses its Hydrogen atom giving negative charge to O atom and any other positively charged amino acid can interact with each other via ionic interactions Similarly weak Vander wall forces that interact between close molecules Last but not the least – covalent bonding Although covalent bond is formed between different, different amino acids/molecules But in case of tertiary structure only disulfide covalent bond plays an important role and gives stability to tertiary structure of protein this disulfide bond is formed between two cysteine residues Have told this thing in previous videos also Structure of two cysteine molecules is being drawn this one cysteine molecule This is second cysteine molecule H atom of SH group is removed and a bond is formed between two sulfur molecules the sructure will be formed like … cystine this is the only difference between cysteine and cystine spelling difference as well cysteine includes e (in spelling) u can see the difference in structure also if H is attached to Sulfur, then no Disulfide bond is formed when this hydrogen is removed, a bond is formed between these two S atoms that is called disulfide bond and the structure will be called cystine such kind of covalent interactions are found in tertiary structures that gives them a lot of stability apart from this, no other covalent interaction is involved in imparting stability to protein structure Question generally asked Why disulfide bond is more prominently found in extracellular proteins rather than intracellular proteins Reason is Disulfide bond is formed by oxidation of two sulfur molecules (by removal of H atom) and this oxidation will occur in oxidizing environment only (most prominently found extracellularly) Suppose this is a cell and this is extracellular area where the environment will be oxidizing whereas inside a cell, in cytoplasm, the environment will be reducing Becoz of which Internal cysteines will not be oxidized by loosing hydrogen atom and extracellular cysteines will loose their hydrogen atoms to form disulfide bond Next after tertiary structure is quaternary structure of proteins when two or more than two polypeptide chains interact with each other a quaternary structure is formed So the polypeptide chains present will not be in linear fashion If this is the tertiary structure of one polypeptide chain and this is the tertiary structure of another polypeptide chain These chains can interact with each other to form quarternary structure. these may be two identical chains say first one is alpha chain second one could also be alpha chain also the second chain may be non-identical (say beta chain) encoded by a different gene So if the two chains are similar, in that case, the quaternary structure will be homomeric Homomeric structure and if the two chains are dissimilar/non-identical, then Heteromeric structure Heteromeric structure Hetero means different (Non-Identical) and in between these two chains, interactions will be same as studied in tertiary structure – Hydrophobic interactions, Vander wall interactions Ionic interactions plus covalent interactions Not only the disulfide bonds but other covalent interactions also these chains may be two, may be more than two depending on polymeric structure another term is Multimeric structure Example- Haemoglobin In Haemoglobin, there are two alpha chains and two beta chains mainly in adults 97% haemoglobin in adults is alpha2beta2 (dimer of alpha and beta) rest 3 % U must have been thinking what the rest 3% is Rest 3% is actually alpha2Delta2 (dimer of dimer alpha and delta) alpha2-beta2 – this is HbA1 This is HbA2 – alpha2delta2 Haemoglobin will be discussed more in next to next video Both myoglobin and haemoglobin will be discussed their association, dissociation curves, Bohrs effect etc. Where generally students feel difficulty Right now, I expect, you have understood and learned both tertiary and quaternary structure. So this much in today’s video Hope You liked this video, if you have any query, please post in comments section below Next video will be on collagen, elastin and keratin protein after which we will discuss Hb and Mb If you liked this video, please press the like button Subscribe to my channel Keep watching and keep learning, Thankyou

Comments

(11 Comments)

  • Pratibha Singh

    superb explanation.

  • daisy kumari

    sir supersecondary structure pr v banaye sir plz plz

  • Suresh Kumar

    Thanks sir very nice video

  • Aditya Patel

    Sir, which bond contribute more in order to stabilize the tertiary structure plz reply

  • Aditya Patel

    Sir, Can be more specific such as hydrophobic, Hydrogen bond, electrovalent or sth else in non-covalent bonding

  • Dharma is not religion. Dharma is Righteousness.

    Most amazing part of the video was that concept of why disulphide bond is found only in extracellular proteins. πŸ‘πŸ‘πŸ‘ Sabse kaam ki cheez pata lagi yahan se. Very good Sir. πŸ‘ŒπŸ‘ŒπŸ‘Œ

  • Prevesh Sehrawat

    Pedigree analysis video uploads kro sir ji.

  • Prevesh Sehrawat

    Sir please make video on HARDY WEINBERGB EQUATION Basicaly on Numericals.

  • Nouman KhAn

    Suscribe mY Chanal Tnk U

  • Hajra Naseer

    Sir U don't show clear examples of these bonds in tertiary structure

  • YOGESH anjan singer

    Thanku sir

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