Protein Quaternary Structures
protein quaternary structures
How can it be that a protein can have a tertiary structure but not have a quaternary structure?
Oh and also what is the action of conenzymes and what types of molecules are they?
Proteins can have tertiary structure and not quatranary because tertiary relates to the functional groups on the amino acids chain bonding with each other. Quatranary is multiple proteins which have bonded together.
If you have a protein made of only one polypeptide (amino acid) chain than it does not have quatranary structure because no other "proteins" or polypeptide chains are bonded to it.
Coenzymes are non polypeptide compunds that bond to an apoenzyme and serves as a cofactor (look those terms up, wikipedia or something) is a coenzyme. ATP serves as a coenzyme (which is a nucleic acid). Therefor it is not solely a protein and can be multiple types of molecules.
Importance of Hydrogen Bonding in Maintaining Protein Structure
Introduction
When building large structures, one must think of how to make sure the structure is long lasting, neat and ready serve its purpose. In very large structures, using the example of buildings, builders build several columns in the ground floor and triangle-like logs on the roof which do not interfere with the buildings' functionality as well as preventing the building from collapsing. Having a column right in the middle of a meeting room wouldn't be appropriate; so where these assisting blocks are put would also be needed to be considered. The same patterns are seen in proteins too where bonds form at specific places in specific amounts to make the protein strong enough to cope with the jobs they are doing. These bonds are called the Hydrogen bonds.
Hydrogen bonds are non-covalent meaning they are created by the electrostatic attractions between positive and negative charged atoms and form spontaneously without the need for enzyme catalysis (1). However they are quite weak so very little amount of energy is required to break these bonds. This could be an advantage as well as being a disadvantage, even though structures bonded by hydrogen bonds are not very strong, they are quite flexible which could be useful when the structure needs to change shape according to its function. This is where proteins come in to play.
Proteins are found everywhere in and between cells, doing so many jobs. They have a specific 3D shape which directly relates to its function, so there is a lot of diversity in proteins but every single one does a different job and do not interfere with each others'.
Hydrogen Bonds in Protein Structure
proteins are synthesized in the cytoplasm of a cell when the codon of mRNA from the nucleus binds with the anti-codon of tRNA which results in the synthesis of amino acids, which are the base units of proteins. Proteins have four levels of organisation called the primary, secondary, tertiary and quaternary structure (2). The primary structure relates to the sequence of the amino acids, the secondary structure is formed by the alpha helix and the beta sheet, the tertiary structure is the folding of the polypeptide chains and quaternary structure is the association of sub units of protein into larger ones. Hydrogen bonds are involved in the secondary, tertiary and the quaternary structure of proteins. How do the amino acids become proteins?
After the sequence of the amino acids are determined, the Alpha helix is formed which is the formation of hydrogen bonds between the C=O and N−H groups of amino acids. Then the Beta sheet comes into existence with the formation of hydrogen bonds between different polypeptide chains. The protein is already becoming a stable structure, with the hydrogen bonds forming at the right spots. Then the polypeptide chains start to fold according to where the hydrogen bonds were formed in the secondary structure; the hydrogen bonds also play a role in helping the protein keep the shape of its tertiary structure. As the polypeptide chains fold, they require support in order to be kept at the shape it has taken and again hydrogen bonds provide it, working with other bonds this time, including covalent bonds like disulphide bridges (3). Finally the quaternary structure exists only in proteins that contain more than one polypeptide. Hydrogen bonds are also found in the quaternary structure.
Conclusion
As we can see hydrogen bonds play a very important role in keeping the shape of proteins. Depending on the primary structure, they form at specific places and determine all the other levels of organization of proteins. Without them the tertiary structure would be different meaning the protein cannot bind and interact with the molecules it needs to which would result in a malfunctioning protein. Hydrogen bonds could be likened to match sticks, you can break one easily but if you bring ten of them together they become strong and more, even stronger; and without functioning proteins we wouldn't be alive!
(see: www.columbia.edu/cu/biology/courses/c2005/images/3levelpro.4.p.jpg)
References
(1) Elliott, W. Elliott, D. 2005. Biochemistry and Molecular Biology 3rd Ed. pp10-12 and pp52-55
(2) Snustad, P. Simmons, M. 2006. Principles of Genetics pp312-315
About the Author
If you have any questions you'd like to ask or need clarification on any of the things I wrote please email me at m.erz@hotmail.com
kit 3 lesson 1 protein folding.mov