Chapter 5 Multiple Choice Questions

. Two proteins that are descended from a common ancestor in two different species – for example, human haemoglobin and horse haemoglobin – are

homologues and orthologues.

homologues and paralogues.

orthologues and paralogues.

all three: homologues, orthologues, and paralogues.

. As proteins evolve

although relatively few changes are observed in the amino-acid sequences, the three-dimensional structure may change completely, so that very distant relationships are often not recognizable by comparison of three-dimensional structures, but only by comparison of amino-acid sequences.

amino-acid sequence and three-dimensional structure diverge at approximately the same rate (that is, typically it is equally easy to recognize distant relationships from comparison of sequences, and from comparison of structures).

the three-dimensional structure diverges more quickly than amino-acid sequence (that is, it is typically possible to recognize distant relationships from comparison of sequences, than from comparison of structures).

amino-acid sequence diverges more quickly than three-dimensional structure (that is, it is often easier to recognize distant relationships from comparison of structures, than from comparison of amino-acid sequences).

. All but one of the following are exceptions to the rule that a set of consecutive bases in DNA is translated into the amino-acid sequence of a protein, in eukaryotes. Which is NOT an exception?

Posttranslational modification

RNA editing

Gene duplication

Variable splicing

. Suppose a certain protein contains, consecutively, four domains: N-terminus–Domain–Domain B--Domain C--Domain D--C-terminus. Which, if any of the following domain organizations would be impossible in a different protein? (Domain E is a fifth domain, not appearing in the original protein.)

N-terminus–Domain D–Domain C–Domain B–Domain A–C-terminus

N-terminus–Domain B–Domain B–Domain B–Domain B–C-terminus

N-terminus–Domain A–Domain E–Domain E–Domain D–C-terminus

All the other domain organizations, appearing in other choices, would in principle be possible.

. If two proteins have the same function

there may be no relationship between the sequences (except perhaps for a local region around the active site).

they must have very similar sequences but not necessarily very similar structures.

they must have both very similar sequences and very similar structures.

they must have very similar structures but not necessarily very similar sequences.

. It is possible to expand the genetic code, by reassigning a STOP codon to stand for a non-canonical amino acid. This requires

not necessarily introducing a novel tRNA or a novel tRNA synthetase.

introducing both a novel tRNA and a novel tRNA synthetase.

introducing a novel tRNA but not necessarily a novel tRNA synthetase.

introducing a novel tRNA synthetase but not necessarily a novel tRNA.

. All but one of the following are observed types of local DNA sequence changes. Which is NOT observed?

Inversion

Change in copy number

Conversion to complementary DNA sequence

Tandem duplication

. If the amino-acid sequences of two homologous proteins differ in approximately 50% of the residues in an optimal alignment, approximately what root-mean-square deviation of the Cá atoms of the core would you expect to observe?

0.1 Å

0.3 Å

1.0 Å

4.0 Å

. Directed evolution and a priori protein design have produced novel proteins, not found in nature, to provide enzymes with properties not available from natural proteins, include all but one of the following. Which one has NOT been produced?

Subtilisin active in organic solvent: 60% dimethylformamide

Retroaldol condensation

Catalysis of the Diels-Alder reaction

Phosphorylation of glucose without coupling to another reaction such as hydrolysis of ATP

. For a set of homologous proteins from different species, all the following statements except one are true. Which one is false?

The pattern of divergence of the amino-acid sequence matches the pattern of divergence of the functions of the proteins.

The pattern of divergence of the three-dimensional structures typically matches the pattern of taxonomic divergence of the species.

The pattern of divergence of the amino-acid sequence typically matches the pattern of divergence of the three-dimensional structures.

The pattern of divergence of the amino-acid sequence typically matches the pattern of taxonomic divergence of the species.

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