Module 12 Expression of Genes

A particular triplet of bases in the template strand of DNA is 5' AGT 3'. The corresponding codon for the mRNA transcribed is

3' UCA 5'.

The genetic code is essentially the same for all organisms. From this, one can logically assume which of the following?

A gene from an organism can theoretically be expressed by any other organism.

Which of the following does not occur in prokaryotic gene expression, but does in eukaryotic gene expression?

A poly-A tail is added to the 3' end of an mRNA and a cap is added to the 5' end.

Which component is not directly involved in translation?

DNA

A particular triplet of bases in the coding sequence of DNA is TTT. The anticodon on the tRNA that binds the mRNA codon is

UUU

What is a ribozyme?

an RNA with enzymatic activity

The following question refers to this figure of a simple metabolic pathway:According to Beadle and Tatum's hypothesis, how many genes are necessary for this pathway?

2

Use this representation to answer the following questions.Given the locally unwound double strand above, in which direction does the RNA polymerase move?

3' 5' along the template strand

The following questions refer to this table of codons.A possible sequence of nucleotides in the template strand of DNA that would code for the polypeptide sequence phe-leu-ile-val would be

3' AAA-GAA-TAA-CAA 5'.

Use the following model of a eukaryotic transcript to answer the next few questions.5' UTR E1 I1 E2 I2 E3 I3 E4 UTR 3'Which components of the previous molecule will also be found in mRNA in the cytosol?

5' UTR E1 E2 E3 E4 UTR 3'

A part of the promoter, called the TATA box, is said to be highly conserved in evolution. Which of the following might this illustrate?

Any mutation in the sequence is selected against.

Use the following information to answer the next few questions.A transfer RNA (#1) attached to the amino acid lysine enters the ribosome. The lysine binds to the growing polypeptide on the other tRNA (#2) in the ribosome already.Where does tRNA #2 move to after this bonding of lysine to the polypeptide?

E site

What is the function of GTP in translation?

GTP energizes the formation of the initiation complex, using initiation factors.

What is the function of the release factor (RF)?

It binds to the stop codon in the A site in place of a tRNA.

What is the effect of a nonsense mutation in a gene?

It introduces a premature stop codon into the mRNA.

Why might a point mutation in DNA make a difference in the level of protein's activity?

It might substitute an amino acid in the active site.

During splicing, which molecular component of the spliceosome catalyzes the excision reaction?

RNA

In eukaryotes there are several different types of RNA polymerase. Which type is involved in transcription of mRNA for a globin protein?

RNA polymerase II

Which of the following statements best describes the termination of transcription in prokaryotes?

RNA polymerase transcribes through the terminator sequence, causing the polymerase to separate from the DNA and release the transcript.

The tRNA shown in the figure has its 3' end projecting beyond its 5' end. What will occur at this 3' end?

The amino acid binds covalently.

In an experimental situation, a student researcher inserts an mRNA molecule into a eukaryotic cell after he has removed its 5' cap and poly-A tail. Which of the following would you expect him to find?

The molecule is digested by exonucleases since it is no longer protected at the 5' end.

The figure represents tRNA that recognizes and binds a particular amino acid (in this instance, phenylalanine). Which codon on the mRNA strand codes for this amino acid?

UUC

In order for a eukaryotic gene to be engineered into a bacterial colony to be expressed, what must be included in addition to the coding exons of the gene?

a bacterial promoter sequence

The most commonly occurring mutation in people with cystic fibrosis is a deletion of a single codon. This results in

a polypeptide missing an amino acid.

When translating secretory or membrane proteins, ribosomes are directed to the ER membrane by

a signal-recognition particle that brings ribosomes to a receptor protein in the ER membrane.

A mutation results in a defective enzyme A. Which of the following would be a consequence of that mutation?

an accumulation of A and no production of B and C

Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on specificity in the

bonding of the anticodon to the codon and the attachment of amino acids to tRNAs.

Alternative RNA splicing

can allow the production of proteins of different sizes from a single mRNA.

The anticodon of a particular tRNA molecule is

complementary to the corresponding mRNA codon.

A frameshift mutation could result from

either an insertion or a deletion of a base.

What type of bonding is responsible for maintaining the shape of the tRNA molecule?

hydrogen bonding between base pairs

A transcription unit that is 8,000 nucleotides long may use 1,200 nucleotides to make a protein consisting of approximately 400 amino acids. This is best explained by the fact that

many noncoding stretches of nucleotides are present in mRNA.

The following questions refer to this table of codons.What amino acid sequence will be generated, based on the following mRNA codon sequence?5' AUG-UCU-UCG-UUA-UCC-UUG 3'

met-ser-ser-leu-ser-leu

The following information should be used for the next few questions.A part of an mRNA molecule with the following sequence is being read by a ribosome: 5' CCG-ACG 3' (mRNA). The following charged transfer RNA molecules (with their anticodons shown in the 3' to 5' direction) are available. Two of them can correctly match the mRNA so that a dipeptide can form.The dipeptide that will form will be

proline-threonine.

A mutant bacterial cell has a defective aminoacyl synthetase that attaches a lysine to tRNAs with the anticodon AAA instead of the normal phenylalanine. The consequence of this for the cell will be that

proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU.

In eukaryotic cells, transcription cannot begin until

several transcription factors have bound to the promoter.

Which of the following is the first event to take place in translation in eukaryotes?

the small subunit of the ribosome recognizes and attaches to the 5' cap of mRNA

Which of the following is a function of a signal peptide?

to translocate polypeptides across the ER membrane

Which of the following variations on translation would be most disadvantageous for a cell?

translating polypeptides directly from DNA