1. Protein structure is complex and is organized hierarchically into four differ
ID: 52400 • Letter: 1
Question
1. Protein structure is complex and is organized hierarchically into four different levels. In the space provided below, please describe each level of protein structure, as well as the types of chemical bonds that are involved in maintaining each structural level. To receive full credit, you must be as complete in your description as possible.
A. Amino acids. Please draw general structure and explain how the different amino acids found in Nature differ from one another.
B. Primary structure. Draw the formation of the bond that maintains this level of protein structure, and indicate what the amino and carboxyl termini are in the resulting molecule. Highlight all of the atoms that are part of the bond that maintains this structure.
C. Secondary structure:
Beta Sheet.
Alpha helix. Include in your answer why this is a common structure found in the region of a protein that spans a biological membrane. How do alpha helices differ between multi-pass compared to single pass transmembrane proteins.
D. Tertiary structure
E. Quaternary structure
F. What is a domain in a protein? Use an example to illustrate this concept.
Explanation / Answer
Amino acids:
A). Amino acids contain one hydrogen atom, one amine group (-NH2), one carboxylic acid group (-COOH) and a side chain (R group) attached to the central carbon atom. Proteins are the long chain amino acids, which are linked together by peptide bonds. The side chain varies from one amino acid to another and thus there are 20 amino acids which differ in their particular R group.
B) These R groups may be polar, charged and hydrophobic. All the proteins have multiple levels of structure known as, “primary, secondary, tertiary and quaternary structure.” The sequence of amino acids in a protein is called its “primary structure.”
C). When portions of amino acid chain take on a certain orientation in space, like an alpha helix, beta plated sheet, the “secondary structure” occurs.
D). “Tertiary structure” of a protein is its three dimensional structure, that results from the twisting and folding of its secondary structure. Tertiary structure is because of the interactions, which take place between the R groups of amino acids making up helices and beta plated sheets within the polypeptide. The function of a protein is determined by its tertiary structure.
E). Quaternary structure occurs if the protein contains more than one polypeptide chains (sub units). The arrangement of these subunits is described by the quaternary structure, Eg: hemoglobin.
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