Levels of protein structure (a) Primary structure Amino end H H R. H R4 H Re Carboxyl end H|| C C N. IH | H -- R, H R5 (b) Secondary structure R H H- R. H.... 0=C N-H. N-H.. ... H .• OC H N-H. R H C-R N-H -H H R Hydrogen bonds between amino acids at different locations in polypeptide chain H R HR a helix Pleated sheet (c) Tertiary structure (d) Quaternary structure Heme. Heme group B polypeptide FIGURE 9-3 A protein can have four levels of structure. (a) Primary structure. The sequence of amino acids defined by their R groups. (b) Secondary structure. The polypeptide can form a helical structure (an az helix) or a zigzag structure (a B-pleated sheet). The B-pleated sheet has two polypeptide segments arranged in opposite polarity, as indicated by the arrows. (c) Tertiary structure. The heme group is a nonprotein ring structure with an iron atom at its center. (d) Quatemary structure illustrated by hemoglobin, which is composed of four polypeptide subunits: two a subunits and two B subunits.
Gene Interactions
When the expression of a single trait is influenced by two or more different non-allelic genes, it is termed as genetic interaction. According to Mendel's law of inheritance, each gene functions in its own way and does not depend on the function of another gene, i.e., a single gene controls each of seven characteristics considered, but the complex contribution of many different genes determine many traits of an organism.
Gene Expression
Gene expression is a process by which the instructions present in deoxyribonucleic acid (DNA) are converted into useful molecules such as proteins, and functional messenger ribonucleic (mRNA) molecules in the case of non-protein-coding genes.
The primary protein structure is shown in Figure 9-3(a).
Where in the mRNA (near the 5′
or 3′
end) would a mutation in R2 be encoded?
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