Exam 14: From Dna to Protein: Gene Expression

Har Gobind Khorana at the University of Wisconsin synthesized artificial mRNAs such as poly CA (CACA … ) and poly CAA (CAACAACAA … ).He found that poly CA codes for a polypeptide consisting of alternating threonine (Thr) and histidine (His) residues.There are two possible codons in poly CA: CAC and ACA.One of these must encode histidine and the other threonine-but which is which? The answer comes from results with poly CAA, which produces three different polypeptides: poly Thr, poly Gln (glutamine), and poly Asn (asparagine).(An artificial mRNA can be read, inefficiently, beginning at any point in the chain; there is no specific initiation signal.Thus poly CAA can be read as a polymer of CAA, of ACA, or of AAC.) Compare the results of the poly CA and poly CAA experiments, and determine which codon corresponds with threonine and which with histidine.

Refer to the figure. The protein insulin, which plays a role in blood glucose regulation, is first synthesized as proinsulin, a single polypeptide chain with three domains, designated A, B, and C.Domain C connects domains A and B, which bind to one another through intramolecular disulfide bonds.Insulin is secreted as a polypeptide without domain C.In the figure, _______ represents the process that modifies proinsulin to yield insulin.

Heterozygotes for the defective enzyme _______ alkaptonuria, which means that the trait is _______.

If A, B, C, D, and E represent (in that order) sequence blocks in a pre-mRNA molecule, and B and D are introns, the sequence of the mature mRNA molecule is _______.

When eukaryotic DNA is hybridized with mRNA, the hybrid molecules contain loops of DNA, which are

You are least likely to see introns in a(n)

An example of an ambiguous genetic code is one

An mRNA molecule has 540 codons.How many nucleotides does it have in the coding region?

The adaptor between mRNA and a protein is

In eukaryotic cells, sugar residues are covalently attached to proteins through the process of glycosylation.This posttranslational modification occurs

Proteins are synthesized from _______ terminus to _______terminus in the _______ direction along the mRNA.

Mapping studies have showed that within a group of mutants with the same growth requirements (i.e., the same overt phenotype), individual mutations are on different chromosomes.This indicates that

The start codon is near the _______ end of the mRNA, and this corresponds with the _______ terminus of the polypeptide.

The transfer of information from DNA to RNA occurs during _______, while the transfer of information from RNA to protein occurs during _______.

The difference between mRNA and tRNA is that

Translation is the process by which information in _______ is propagated into information in _______.

Biologists often describe organisms that are easy to manipulate as _______ organisms.

The anticodon 3-UGI-5 can pair with

The promoter region of a gene has undergone an inversion with the 3′ end break point within the initiation site.This will affect the transcription of this gene in all of the following ways except

Suppose the 5ʹ-to-3ʹ coding strand of DNA is GTCTATGCATTA. What is the template DNA strand that would be used for transcription?