Cytosine makes up 42% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine?

A.) 8%

B.) 16%

C.) 31%

D.) 42%

E.) It cannot be determined from the information provided.

A

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

A.) 3' UCA 5'

B.) 3' UGA 5'

C.) 5' TCA 3'

D.) 3' ACU 5'

A

In an analysis of the nucleotide composition of DNA, which of the following will be found?

A.) A=C

B.) A=G

C.) A+ C= G+T

D.) G+C=T+A

C

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

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

B.) All organisms have experienced convergent evolution.

C.) DNA was the first genetic material.

D.) The same codons in different organisms translate into the different amino acids.

E.) Different organisms have different numbers of different types of amino acids.

A

What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized?

A.) The origins of replication occur only at the 5' end.

B.) Helicases and single-strand binding proteins work at the 5' end.

C.) DNA polymerase can join new nucleotides only to the 3' end growing strand.

D.) DNA ligase works only in 3' -> 5' direction.

E.) Polymerase can work on only one strand at a time.

C

Which of the following nucleotide triplets best represents a codon?

A.) a triplet separated spatially from other triplets

B.) a triplet that has no corresponding amino acid

C.) a triplet at the opposite end of tRNA from the attachment site of the amino acid

D.) a triplet in the same reading frame as an upstream AUG

E.) a sequence in tRNA at the 3' end

D

What is the role of DNA ligase in the elongation of the lagging strand during DNA replication?

A.) It synthesizes RNA nucleotides to make a primer.

B.) It catalyzes the lengthening of telomeres.

C.) It joins Okazaki fragments together.

D.) It unwinds the parental double helix.

E.) It stabilizes the unwound parental DNA.

C

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

A.) the protein product of the promoter

B.) start and stop codon

C.) ribosomes and tRNA

D.) several transcription factors

E.) aminoacyl- tRNA synthase

D

A new DNA strand elongates only in the 5' to 3' direction because

A.) DNA polymerase begins adding nucleotides at the 5' end of the template

B.) Okazaki fragments prevent elongation in the 3' to 5' direction.

C.) the polarity of the DNA molecule prevents addition of nucleotides at the 3' end

D.) replication must progress toward the replication fork

E.) DNA polymerase can only add nucleotides to the free 3' end.

E

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

A.) The sequence evolves very rapidly.

B.) The sequence does not mutate.

C.) Any mutation in the sequence is selected against.

D.) The sequence is found in many but not all promoters.

E.) The sequence is transcribed at the start of every gene.

C

The leading and the lagging strands differ in that

A.) the leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction.

B.) the leading strand is synthesized by adding nucleotides to the 3' end of the growing strand, and the lagging strand is synthesized by adding nucleotides to the 5' end.

C.) the lagging strand is synthesized continuously, whereas the leading strand is synthesized in short fragments that are ultimately stitched together.

D.) the leading strand is synthesized at twice the rate of the lagging strand.

A

RNA polymerase moves in which direction along the DNA?

A.) 5' to 3' along whichever strand its on.

B.) 3' to 5' along the template strand.

C.) 5' to 3' along the template strand.

D.) 5' to 3' along the double stranded DNA.

E.) 3' to 5' along the nontemplate strand.

B

The difference between ATP and the nucleotide triphosphates used during DNA synthesis is that

A.) the nucleoside triphosphates have the sugar deoxyribose; ATP has the sugar ribose

B.) the nucleoside triphosphate have two phosphate groups; ATP has three phosphate groups

C.) ATP contains three high-energy bonds; the nucleoside triphosphates have two

D.) ATP is found ony in human cells; the nucleoside triphosphate are found in all animal and plant cells

E.) triphosphate monomers are active in the nucleoside triphosphates; but not in ATP

A

What is a ribozyme?

A.) an enzyme that uses RNA as a substrate

B.) an RNA with enzymatic activity

C.) an enzyme that catalyzes the association between the large and small ribosomal subunits

D.) an enzyme that synthesizes RNA as part of the transcription process

E.) an enzyme that synthesizes RNA primers during DNA replications

B

A eukaryotic 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

A.) many noncoding stretches of nucleotides are present in eukaryotic DNA

B.) there is redundancy and amiguity in the genetic code

C.) many nucleotides are needed to code for each amino acid

D.) nucleotides are needed to code for each amino acid

E.) there are termination exons near the beginning of mRNA

A

An Okazaki fragment has which of the following arrangements?

A.) primase, polymerase, ligase

B.) 3' RNA nucleotides, DNA nucleotides 5'

C.) 5' RNA nucleotides, DNA nucleotides 3'

D.) DNA polymerase I, DNA polymerase II

E.) 5' DNA to 3'

C

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

A.) TTT

B.) UUA

C.) UUU

D.) AAA

C

What is meant by the description of "antiparrallel" regarding the strands that make up DNA?

A.) The twisting nature of DNA creates nonparallel strands.

B.) The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand.

C.) Base pairing create unequal spacing between the two DNA strands.

D.) One strand is positively charged and the other is negatively charged.

E.) One strand contains only purines and the other contains only pyrimidines.

B

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

A.) binding of ribosomes to mRNA

B.) shape of the A and P sites of ribosomes

C.) bonding of the anticodon to the codon

D.) attachment of amino acids to tRNAs

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

E

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

A.) some tRNAs have anticodons that recognize four or more different codons

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

C.) many codons are never used, so the tRNAs that recognize them are dispensable.

D.) the DNA codes for all 61 tRNAs but some are then destroyed

E.) competitive exclusion forces some tRNAs to be destroyed by nucleases

B

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

A.) elongation of the peptide

B.) base pairing of activated methionine-tRNA to AUG of the messenger RNA

C.) binding of the larger ribosomal subunit to smaller ribosomal subunits

D.) covalent bonding between the first two amino acids

E.) the small subunits of the ribosome recongnizes and attaches to the 5' cap of mRNA

E

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

A.) It changes an amino acid in the encoded protein

B.) It has no effect on the amino acid sequence of the encoded protein

C.) It introduces a premature stop codon into the mRNA.

D.) It alters the reading frame of the mRNA

E.) It prevents introns from being excised.

C

A frameshift mutation could result from

A.) a base insertion only

B.) a base deletion only

C.) a base substitution only

D.) deletion of three consecutive bases

E.) either an insertion or a deletion of a base

E

Of the following, which is the most current description of a gene?

A.) a unit of heredity that causes formation of a phenotypic characteristic

B.) a DNA subunit that codes for a single complete protein

C.) a DUNA sequence that is expressed to form a functional product: either RNA or polypeptide

D.) a DNA-RNA sequence combination that results in an enzymatic product

E.) a discrete unit of hereditary information that consists of a sequence of amino acids

C

In comparing DNA replication with RNA transcription in the same cell, which of the following is true only of replication?

A.) It uses RNA polymerase

B.) It makes a new molecule from its 5' end to its 3' end.

C.) The process is extremely fast once it is initiated.

D.) The process occurs in the nucleus of a eukaryotic cell

E.) The entire template molecule is represented in the product

E

In eukaryotic cells, transcription cannot begin until

A.) the two DNA strands have completely separated and exposed the promoter.

B.) several transcription factors have bound to the promoter

C.) the 5' caps are removed from the mRNA

D.) the DNA introns are removed from the template

E.) DNA nucleases have isolated the transcription unit

B

Which of the following is not true of a codon?

A.) It consists of three nucleotides.

B.) It may code for the same amino acid as another codon.

C.) It never codes for more than one amino acid.

D.) It extends from one end of a tRNA molecule.

E.) It is the basic unit of the genetic code.

D

The anitcodon of a particular tRNA molecule is

A.) complementary to the corresponding mRNA codon

B.) complementary to the corresponding triplet in rRNA

C.) the part of tRNA that bonds to a specific amino acid.

D.) changeable, depending on the amino acid that attaches to the tRNA

A

Which component is not, directly involved in translation?

A.) mRNA

B.) DNA

C.) tRNA

D.) ribosomes

B

If you were to observe the activity of methylated DNA, you would expect it to

A.) be replicating nearly continuously

B.) be unwinding in preparation for protein synthesis

C.) have turned off or slowed down the process of transcription

D.) be very actively transcribed and translated

E.) induce protein synthesis by not allowing repressors to bind to it

C

Gene expression might be altered at the level of post-transcriptional processing in eukaryotes rather than prokaryotes because of which of the following?

A.) Eukaryotic mRNAs get 5' caps and 3' tails.

B.) Prokaryotic genes are expressed as mRNA, which is more stable in the cell.

C.) Eukaryotic exons may be spliced in altenative patterns

D.) Prokaryotes use ribosomes of different structure and size

E.) Eukaryotic coded polypeptides often require cleaving of signal sequences before localization.

C