Unit 4

Suppose you are provided with an actively dividing culture of Escherichia coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base?

DNA in both daughter cells would be radioactive.

According to the base pairing rules of DNA, if the sequence of bases on one strand was AGGCTTA, what would be the sequence of bases on the complementary strand?

TCCGAAT

An experimenter has altered the 3' end of the tRNA corresponding to the amino acid methionine in such a way as to remove the 3' AC. Which of the following statements correctly describes the most likely result of this change?

The amino acid methionine will not be covalently bound to the altered tRNA.

Proteins that bind to DNA and turn on operons by making it easier for RNA polymerase to bind to a promoter are called

activators.

Why does a DNA strand grow only in the 5ʹ to 3ʹ direction?

because DNA polymerases can only add nucleotides to the 3' end of the growing molecule

What is the role of a molecule that controls a repressible operon?

bind to the repressor protein and activate it

We would expect that a 15-nucleotide sequence that includes a stop codon at the end (as part of the 15-nucleotide sequence) will direct the production of a polypeptide that consists of

four amino acids.

In a prokaryote, a group of genes with related functions, along with their associated control sequences, defines a(n)

operon

RNA splicing involves the

removal of introns from the molecule

The expression of the tryptophan operon is controlled by a(n)

repressor that is active when it binds to tryptophan.

Transcription in eukaryotes requires which of the following in addition to RNA polymerase?

several transcription factors

There are 61 mRNA codons that specify an amino acid, but only 45 tRNAs. This is best explained by the fact that

the rules for base pairing between the third base of a codon and tRNA are flexible.

What is the function of DNA polymerase III?

to add nucleotides to the 3' end of a growing DNA strand

Both prokaryotic and eukaryotic cells use ________ to turn certain genes on or off.

transcription factors

DNA replication

uses each strand of a DNA molecule as a template for the creation of a new strand