As shown earlier in this blog, amino acids serve as building blocks for polypeptide chains which, in turn assemble to form protein structures. Proteins are the most abundant and functionally diverse molecules in living systems; some of these roles include structural support, hormonal signalling, immune response system, transport of essential molecules as see in in haemoglobin, enzymatic activity, bloodclotting amongst others. This section of the course was immensely informative as it provided a biochemical basis for several processes that we as humans often take for granted. The lectures, as always, were very forthcoming and the material reinforced through the relevant podcasts and additional reading.
Protein structure was a central theme in this section. The levels of structure include primary,secondary,tertiary and quaternary.
Primary structure refers to the actual amino acid sequencing, connected via peptide bonds between the alpha carboxyl group of one amino acid and the alpha amino group of another.
Secondary structure refers to the arrangement of the polypeptide backbone into beta pleated sheets or alpha helices. More information on these structures will be given with the aid of diagrams in a subsequent blog post.
Tertiary structure refers to the spatial arrangement of amino acids that are far apart in linear sequence as well as those residues that are adjacent. The polypeptide chain folds spontaneously and the 3 dimensional structure is maitained via hydrophobic interactions, electrostatic forces, hydrogen bonding and, in some cases, the covalent disulfide bond.
Quaternary structure refers to the spatial arrangement of polypeptide subunits with noncovalent interactions ( hydrophobic,hydrogen bonds, electrostatic forces) being vital. Some covalent links may occur.
References: Champe, Pamela C. and Richard A. Harvey. 1987. Lippincott’s Illustrated Reviews : Biochemistry. Philadelphia : J.B. Lippincott and Company.