There are four different levels of protein structures. The structures are the primary structure, secondary structure, tertiary structure and the quaternary structure. In the primary structure the amino acids share electrons so the bond is covalent. Hydrophobic, and hydrophilic reactions often occur between in this level. Hydrogen bonds can also take place in this level. In the secondary structure the polypeptides chains can form alpha helices or B pleated sheets. Alpha helices are spiral shaped and B pleated sheets alternate “in and out”. Whether the structure is a alpha helix or a B pleated sheet is determined by the bonds between the different amino acids. In the tertiary structure the polypeptides fold into different shapes. These shapes are very important because the shape determines if it can perform its function. A protein can become denatured because of many things; such as: the temperature or water. If a protein is denatured , the structure and the bonds begins to break. Once the bonds are broken the protein can’t perform all of its functions. Some proteins transport different molecules through a cell membrane. If the protein is denatured, its shape has changed and it will not be able to transport these molecules properly. In the quaternary structure 2 polypeptides (or more) are condensed to form a large protein. The different bonds such as the hydrophobic, ionic and the hydrogen bonds are what hold the polypeptides together. Since these bonds are weak, usually no large changes occur in this structure.