Quiz 2

The following statements about translation are TRUE:

1. AUG, which encodes methionine, is used to initiate protein synthesis 2. Most amino acids have more than one codon 3. An amino acid may have more than one tRNA to which it can attach

The following are methods used by cells to regulated the amount of protein in a cell:

1. Genes can be transcribed into mRNA with different efficiencies 2. many ribosomes can bind to a single mRNA molecule 3. proteins can be tagged for degradation

The following statements about the coupling of an amino acid with tRNA are TRUE:

1. it is catalyzed by tRNA synthetase 2. the enzyme catalyze this reaction has proofreading ability 3. the reaction requires ATP

5' cap and 3' poly (A) tail in mature mRNA may

1. protect mRNA from enzymatic degradation 2. assist export of mRNA from the nucleus ot hte cytoplasm 3. assist in translation

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'

Which of the following help(s) to stabilize mRNA by inhibiting its degradation

5' cap and poly (A) tail

An incoming aminoacytl-tRNA carrying the next amino acid in the chain will bind to the

A-site by forming base pairs through its anti-codon with the codon in the mRNA

During the peptide chain elongation process of translating an mRNA into a protein, the growing polypeptide chain attached to a tRNA is bound to the

P-site of the ribosome

Using RNA as a template for protein synthesis instead of translating proteins directly from the DNA is advantageous to the cell because

RNA can be translated by many ribosomes at the same time

The phenonmenon in which RNA molecules in a cell are destroyed if they have a sequence complimentary to an introduced small RNA fragment is called

RNA interference

Reaction known to be carried out by a ribozyme:

RNA splicing

Which of the following reactions are known to be carried out by a ribozyme?

RNA splicing

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 nucleases (RNAases) since it is no longer protected by the 5' end

Which of the following types of mutation, resulting in an error in the mRNA just after the AUG start of translation, is likely to have the most serious effect on the polypeptide product?

a deletion of 2 nucleotides

Which of the following statements about translation is FALSE?

all three bases in a codon an an anti-codon form strict standard base pairs

What is a ribozyme?

an RNA with enzymatic activity

MicroRNA (mRNA) are a class of small RNA sequences that

bind to complementary sequences of target mRNA, resulting in the destruction of targets mRNA

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

bonding of the anticodon to the codon

The peptidyl transferase enzyme

catalyzes the formation of anew peptide bond between the growing polypeptide chain and the newly arriving amino acid

Ribosome

catalyzes the formation of peptide bonds that link the amino acids together into a polypeptide chain

The anticodon of a particular tRNA molecule is

complementary to the corresponding mRNA codon

A ribosome

contains the catalytic activity that joins amino acids together

Once transcribed, eukaryotic mRNA typically undergoes substantial alteration that includes

excision of introns

What are the coding segments of a stretch of eukaryotic DNA called?

exons

The distinct characteristics of different cell types in a multicellular organism are produced mainly by the differential regulation of the

expression of specific genes

What are polyribosomes?

groups of ribosomes reading a single mRNA simultaneously

Muscle cells and nerve cells in one species of animal owe their differences in structure to

having different genes expressed

Which of the following statement about the coupling of an amino acid with tRNA is FALSE?

it is catalyzed by tRNA hydrolase

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

Which of the following methods is NOT used by cells to regulate the amount of a protein in a cell?

nuclear pore complexes can regulate the speed at which newly synthesized proteins are exported from the nucleus in the cytoplasm

Synthesis of pre-rRNA occurs in the

nucleolus

The complex of several ribosomes and a mRNA engaged in simultaneous translation is called

polyribosome

The sigma factor of bacterial RNA polymerase

recognizes promoter sites in the DNA

The stop codon binds the protein called

release factor

Once an mRNA is produce, its message can be decoded on a

ribosome

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

several transcription factors (TFs)

The end of a protein-coding message is signaled by the presence of a

stop codon

You will find an anti codon in

tRNA

This is the site in the DNA located near the end of the final exon, encoding an RNA sequence that determines the 3' end of the transcript:

terminator

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

Although gene expression can be regulated at multiple levels, the most important step is at the level of

transcription

In both eukaryotes and prokaryotes, gene expression is primarily regulated at the level of

transcription