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17 Cards in this Set

  • Front
  • Back

A section of a DNA or RNA molecule that codes for a specific polypeptide in protein synthesis is a...


In bacteriophage T4, what is the name of the mutation that proflavin induces?


What does mating the WT-like T4 mutant with a WT phage yield in terms of progeny, and what does this ultimately mean?

When mutant WT-like T4 is mated with WT T4, the progeny either have the original FC0 proflavin-induced mutation or a new mutation on the same gene, termed FC1. This means that the WT-like mutant contains both FC0 and FC1 mutations that are INTRAGENIC SUPRESSORS of each other, meaning that they are mutations within the same gene that cancel each other out and bring the T4 back to WT-like, non-mutant behavior.

What are the 3 stop codons? What are they - somewhat inappropriately - called?

UAG and UAA and UGA; nonsense codons

Codons that specify the same amino acid are termed...


Explain the two ways in which the triplet code is not random.

1: A change in the first codon tends to specify similar, if not the same, amino acid

2: Second position pyrimidines code for hydrophobic amino acids, and purines code for polar amino acids

T/F: As a consequence of the genetic code's degeneracy, however, many point mutations at a third codon position are phenotypically silent; that is, the mutated codon specifies the same amino acid as the wild type.


T/F: The "standard" genetic code is not entirely universal because it changes in mitochondria and protozoa.


In Crick's Nature of the Genetic code experiments, the WT-like double mutant was cross again with the WT to yield progeny with either the FC0 or FC1 mutation. Why would you then cross these progeny once more with FC0?

Because then those progeny with FC1 would again have both FC0 and FC1, and if their WT-like behavior was recovered after this cross then you could be sure that it was only that single deletion/addition that is affecting the phenotype.

What were the two important issues in the homopolymer system used be Nirenberg and Matthaei?

The [Mg2+] was high so that codon-free translation could start; they identified which aa was incorporated into the chain by radiolabeling each aa and seeing which one would become TCA precipitable (which was evidence of polymer formation) in response to which homopolymer RNA was fed into the system.

Why doesn't poly(G) code for an aa?

Because it aggregates and forms complex structures instead of being translated

T/F: After using just poly(U) mRNAs, additional experiments were done with defined copolymers using RNA prepared from transcription off of synthetic DNA templates.


What was the triplet binding assay by Nirenburg?

Trinucleotides with specific codons were placed with ribosomes and tRNA's with radiolabeled aa's; the complementary tRNA would become associated with the filter and thus its aa corresponding to the correct codon could be detected

Why are overlapping genes usually not feasible in higher organisms like eukaryotes?

Because a single mutation would then cause a mutation in more than one product which could be harmful

T/F: Although the genetic code is conserved among different organisms, the codon usage varies significantly which can lead to difficulty with over-expressing human or other mammalian genes in E. coli.


The codon within the mRNA is recognized by the anticodon loop of the tRNA via...

A hydrogen bonding interaction (base pairing) - (note that the recognition of the third codon position is less discriminating)

Many tRNAs contain an _ substitution (a postsynthetic modification introduced into the RNA) at the first position of the anticodon which base pairs with the wobble position of the codon.