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This folding is stabilized by hydrogen bonds between peptide linkages. These sections of polypeptide chains are repeatedly coiled or folded into patterns that add to the protein’s overall conformation. There are two types of secondary structures. They are alpha helixes and beta pleated sheets. Alpha helixes are helical coils stabilized by a hydrogen bond between every fourth peptide bond. They are usually found in fibrous protein such as keratin and collagen, Beta pleated sheets are structures where two regions of the polypeptide chain lie parallel to each other.
Again hydrogen bonds between the parts of the backbone in the parallel regions hold the structure together. The cores of many globular proteins are made to beta pleated sheets. The 3-D shape of a protein is otherwise known as the tertiary structure. Superimposed on the patterns of secondary structure is a protein’s tertiary structure, consisting of irregular contortions from bonding side chains of the various amino acids. There are many types of bonds that are found in this structure including hydrogen, ionic, hydrophobic interactions, and van deer Walls interactions.
Stronger bonds such as the disulfide bridges form from covalent bonds between side chains of cytosine pairs. The sulfur of one cytosine bonds to the sulfur Of the seconds and the disulfide bridge fastens parts Of the protein together. Once monopole amino acid side chains are close together, van deer Walls attractions reinforce hydrophobic interactions. Meanwhile, hydrogen bonds between polar side chains also help stabilize tertiary structure. The structure that results from interaction between and among several polypeptide chains are called Quaternary structures.
Subunits that fit together eighty are sometimes found in globular proteins. Hemoglobin is an example of a globular protein with quaternary structure because it is made up of two kinds of polypeptide chains with two of each kind per molecule. Not all proteins have a quaternary structure. Enzymes are very selective as to which reaction they’ll catalyst. This means that enzymes are highly specific. Catalysts are specific to a particular substrate and that depends on the three dimensional shape of it or its tertiary structure.
A substrate is the substance an enzyme acts upon. Each substrate has a specific happen that will only fit into the active site of a particular enzyme. The active site is the restricted region of an enzyme that binds the substrate to the enzyme. It is usually a pocket or groove on the protein’s surface. There is one model called the lock and key. This is demonstrated by the substrate fitting exactly into the enzymes active site similar to how a key kits perfectly into the lock. This is because the key has a particular shape and is the only one that Will turn the lock.
This is comparable to how a substrate has a special shape and it is the only one hat Will fit into a particular enzyme’s active site. There is another model called the induced fit. This explains that the enzyme changes its shape slightly in order to grasp the substrate. This is related to how a baseball glove wraps around the ball in order to hold it in tight. The example below shows how the enzyme sucrose will break up sucrose but not lactose due to the shape of the substrate and active site. This sums up how the structural organization within proteins are responsible the specificity of an enzyme breaking down a substrate