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 attachment of amino acids to tRNAs.

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

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

At a specific area of a chromosome, the sequence of nucleotides below is present where the chain opens to form a replication fork: 3' C C T A G G C T G C A A T C C 5' An RNA primer is formed starting at the underlined T (T) of the template. Which of the following represents the primer sequence?
A) 5' G C C T A G G 3'

B) 3' G C C T A G G 5'

C) 5' A C G T T A G G 3'

D) 5' A C G U U A G G 3'

E) 5' G C C U A G G 3'

D

What can be determined directly from x-ray diffraction of crystallized DNA?

the diameter of the helix

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

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

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

What is the function of topoisomerase?

A topoisomerase is an enzyme which regulates the winding and unwinding of DNA. The function is that they regulate the topology of the DNA.

Which of the following is a function of a poly-A signal sequence?

A. It codes for a sequence in eukaryotic transcripts that signals enzymatic cleavage ~1035 nucleotides away.

B. It allows the 3' end of the mRNA to attach to the ribosome.
C. It is a sequence that codes for the hydrolysis of the RNA polymerase.
D. It adds the poly-A tail to the 3' end of the mRNA.
E. It adds a 7-methylguanosine cap to the 3' end of the 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 III
E) 5' DNA to 3'

C

What is the function of DNA polymerase III?

To add nucleotides to the end of a growing DNA strand.

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

If a cell were unable to produce histone proteins, which of the following would be a likely effect?
A) There would be an increase in the amount of "satellite" DNA produced during centrifugation.
B) The cell's DNA couldn't be packed into its nucleus.
C) Spindle fibers would not form during prophase.
D) Amplification of other genes would compensate for the lack of histones.
E) Pseudogenes would be transcribed to compensate for the decreased protein in the cell.

B

Which enzyme catalyzes the elongation of a DNA strand in the 5' → 3' direction?

DNA polymerase

ring splicing, which molecular component of the spliceosome catalyzes the excision?

RNA

Which would you expect of a eukaryotic cell lacking telomerase?
A) a high probability of becoming cancerous
B) production of Okazaki fragments
C) inability to repair thymine dimers
D) a reduction in chromosome length
E) high sensitivity to sunlight

D

How do we describe transformation in bacteria?

The infection of cells by a phage DNA molecule.

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

For a science fair project, two students decided to repeat the Hershey and Chase experiment, with modifications. They decided to label the nitrogen of the DNA, rather than the phosphate. They reasoned that each nucleotide has only one phosphate and two to five nitrogens. Thus, labeling the nitrogens would provide a stronger signal than labeling the phosphates. Why won't this experiment work?

Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins.

The leading and the lagging strands differ in that

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

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?

8%

Which of the following sets of materials are required by both eukaryotes and prokaryotes for replication?
A) double-stranded DNA, 4 kinds of dNTPs, primers, origins
B) topoisomerases, telomerase, polymerases
C) G-C rich regions, polymerases, chromosome nicks
D) nucleosome loosening, 4 dNTPs, 4 rNTPs
E) ligase, primers, nucleases

A

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?
A) The mRNA could not exit the nucleus to be translated.
B) The cell recognizes the absence of the tail and polyadenylates the mRNA.
C) The molecule is digested by restriction enzymes in the nucleus.
D) The molecule is digested by exonucleases since it is no longer protected at the 5' end.
E) The molecule attaches to a ribosome and is translated, but more slowly.

D

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

A release factor is a protein that allows for the termination of translation by recognizing the termination codon or stop codon in an mRNA sequence.

The nitrogenous base adenine is found in all members of which group?
A) proteins, triglycerides, and testosterone
B) proteins, ATP, and DNA
C) ATP, RNA, and DNA
D) alpha glucose, ATP, and DNA
E) proteins, carbohydrates, and ATP

C

It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information in which of the following?
A) sequence of bases
B) phosphate-sugar backbones
C) complementary pairing of bases
D) side groups of nitrogenous bases
E) different five-carbon sugars

A

Which of the following help to hold the DNA strands apart while they are being replicated?

A) primase

B) ligase

C) DNA polymerase
D) single-strand binding proteins

E) exonuclease

D

Polytene chromosomes of Drosophila salivary glands each consist of multiple identical DNA strands that are aligned in parallel arrays. How could these arise?
A) replication followed by mitosis
B) replication without separation
C) meiosis followed by mitosis
D) fertilization by multiple sperm
E) special association with histone proteins

B

Why do histones bind tightly to DNA?

Histones are positively charged, and DNA is negatively charged.

Individuals with the disorder xeroderma pigmentosum are hypersensitive to sunlight. This occurs because their cells have which impaired ability?

They cannot repair thymine dimers.