In this chapter you were introduced to nonsense suppressor mutations in tRNA genes. However, suppressormutations also occur in protein-coding genes. Using thetertiary structure of the β subunit of hemoglobin shownin Figure 9-3(c), explain in structural terms how a mutation could cause the loss of globin protein function. Nowexplain how a mutation at a second site in the same protein could suppress this mutation and lead to a normalor near-normal protein. Levels of protein structure(a) Primary structureAmino endHHR.HR4HReCarboxyl endH||CCN.IH |H--R,HR5(b) Secondary structureRHH-R.H.... 0=CN-H.N-H.. ...H.• OCHN-H.RHC-RN-H-HH RHydrogen bonds between amino acidsat different locations in polypeptide chainH RHRa helixPleated sheet(c) Tertiary structure(d) Quaternary structureHeme.Heme groupB polypeptideFIGURE 9-3 A protein can have four levels of structure. (a) Primary structure. The sequence of amino acidsdefined by their R groups. (b) Secondary structure. The polypeptide can form a helical structure (an az helix) or azigzag structure (a B-pleated sheet). The B-pleated sheet has two polypeptide segments arranged in oppositepolarity, as indicated by the arrows. (c) Tertiary structure. The heme group is a nonprotein ring structure with aniron atom at its center. (d) Quatemary structure illustrated by hemoglobin, which is composed of four polypeptidesubunits: two a subunits and two B subunits.

Name: In this chapter you were introduced to nonsense suppressor mutations i
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Description: In this chapter you were introduced to nonsense suppressor mutations in tRNA genes. However, suppressormutations also occur in protein-coding genes. Using thetertiary structure of the β subunit of hemoglobin shownin Figure 9-3(c), explain in structur