Bio unit 16 and 17

A eukaryotic cell lacking active telomerase would a. experience a gradual reduction of chromosome length with each replication cycle. b. have a greater potential to become cancerous. c. be unable to take up DNA from the surrounding solution. d. be unable to connect Okazaki fragments. e. be unable to identify and correct mismatched nucleotides.

a

A transcription unit that is 8,000 nucleotides long may use 1,200 nucleotides to make a protein consisting of 400 amino acids. This is best explained by the fact that a. many noncoding nucleotides are present in mRNA. b. there is redundancy and ambiguity in the genetic code. c. many nucleotides are needed to code for each amino acid. d. nucleotides break off and are lost during the transcription process. e. there are termination exons near the beginning of mRNA.

a

After DNA replication is completed, a. each new DNA double helix consists of one old DNA strand and one new DNA strand. b. there are four double helices. c. each new DNA double helix consists of two new strands. d. each of the four DNA strands consists of some old strand parts and some new strand parts. e. one DNA double helix consists of two old strands and one DNA double helix consists of two new strands.

a

Cytosine makes up 38% of the nucleotides in a sample of DNA from an organism. Approximately, what percentage of the nucleotides in this sample will be thymine? a. 12 b. 24 c. 38 d. 31 e. It cannot be determined from the information provided.

a

During RNA processing, a(n) _____________________ is added to the 3' end of the RNA. a. long string of adenine nucleotides b. AAUAAA c. 3' untranslated region (UTR) d. modified guanine nucleotide (GTP) e. 5' untranslated region (UTR)

a

The spontaneous loss of amino groups from adenine in DNA results in hypoxanthine, an uncommon base, opposite thymine. What combination of proteins could repair such damage? a. nuclease, DNA polymerase, DNA ligase b. nuclease, telomerase, primase c. telomerase, helicase, single-stranded binding protein (SSBP) d. telomerase, primase, DNA polymerase e. DNA ligase, replication fork proteins, adenylyl cyclase

a

What are polyribosomes? a. groups of ribosomes reading a single mRNA simultaneously b. ribosomes containing more than two subunits c. ribosomes associated with more than one tRNA d. multiple copies of ribosomes associated with giant chromosomes e. aggregations of vesicles containing ribosomal RNA

a

Which of the following is not true of a codon? a. It extends from one end of a tRNA molecule. b. It is the basic unit of the genetic code. c. It never codes for more than on amino acid. d. It may code for the same amino acid as another codon. e. It consists of three nucleotides.

a

Individuals with the disorder xeroderma pigmentosum are hypersensitive to sunlight because their cells have an impaired ability to a. exchange DNA with other cells. b. repair thymine dimers. c. undergo mitosis. d. replicate DNA. e. recombine homologous chromosomes during meiosis.

b

Multiple origins of replication on the DNA molecules of eukaryotic cells serve to a. assure the correct orientation of the two strands in the newly growing double helix. b. shorten the time necessary for DNA replication. c. remove errors in DNA replication. d. create multiple copies of the DNA molecule at the same time. e. reduce the number of "bubbles" that occur in the DNA molecule during replication.

b

The elongation of the leading strand during DNA synthesis a. produces Okazaki fragments. b. depends on the action of DNA polymerase. c. progresses away from the replication fork. d. does not require a template strand. e. occurs in the 3' to 5' direction.

b

We now know that the one gene-one-enzyme hypothesis is not entirely accurate because a. many genes code for proteins that are not enzymes. b. All the choices are correct. c. None of the choices are correct. d. many genes code for RNA molecules that have no enzymatic activity. e. a single gene codes for a single polypeptide chain, and many enzymes are made up of more than one polypeptide chain.

b

What enzyme catalyzes the attachment of an amino acid to tRNA? a. ribozymes b. aminoacyl-tRNA synthetase c. RNA polymerase d. nuclease e. ligase

b

What type of bonding is responsible for maintaining the shape of the tRNA molecule? a. ionic bonding between phosphates b. hydrogen bonding between base pairs c. covalent bonding between sulfur atoms d. van der Waals interactions between hydrogen atoms e. peptide bonding between amino acids

b

Which of the following is true for both prokaryotic and eukaryotic gene expression? a. The mRNA transcript is the exact complement of the gene from which it was copied. b. RNA polymerase binds to the promoter region to begin transcription. c. After transcription, a 3' poly-A tail and a 5' cap are added to mRNA. d. mRNA is synthesized in the 3' to 5' direction. e. Translation of mRNA can begin before transcription is complete.

b

A base substitution mutation in a gene sometimes does not result in a different protein. Which of the following factors could account for this? a. the fact that such mutations are usually accompanied by a complementary deletion b. the mutation affects only the sequence of amino acids, so the protein stays the same c. some amino acids are produced from more than one codon d. a correcting mechanism that is part of the mRNA molecule e. the rarity of such mutations

c

In eukaryotic cells, transcription cannot begin until a. the 5' caps are removed from the mRNA. b. the two DNA strands have completely separated and exposed the promoter. c. several transcription factors have bound to the promoter. d. the DNA introns are removed from the template. e. DNA nucleases have isolated the transcription unit.

c

In the nucleosome, the DNA is wrapped around a. a thymine dimer. b. ribosomes. c. histones. d. satellite DNA. e. polymerase molecules.

c

What is the function of topoisomerase? a. the addition of methyl groups to bases of DNA b. elongation of new DNA at a replication fork by addition of nucleotides to the existing chain c. relieving strain in the DNA ahead of the replication fork d. unwinding of the DNA helix e. stabilizing single-stranded DNA at the replication fork

c

Which component is not directly involved in translation? a. GTP b. mRNA c. DNA d. tRNA e. ribosomes

c

Which of the following help to hold the DNA strands apart while they are being replicated? a. exonuclease b. primase c. single-strand binding proteins d. DNA polymerase e. ligase

c

Which of the following people conducted experiments that demonstrated that DNA is the genetic material of bacteriophages? a. Griffith b. McCarty and MacLeod c. Hershey and Chase d. Watson and Crick e. Franklin and Wilkins

c

A biochemist isolate, purifies, and combines in a test tube a variety of molecules needed for DNA replication. When she adds some DNA to the mixture, replication occurs, but each DNA molecules consists of a normal strand paired with numberous segments of DNA a few hundred nucleotides long. What has she probably left out of the mixture? a. DNA polymerase. b. Okazaki fragments. c. primase. d. DNA ligase. e. mucleotides.

d

A frameshift mutation could result from a. a base deletion only. b. a base substitution only. c. a base insertion only. d. either an insertion or a deletion of a base. e. deletion of three consecutive bases.

d

An extraterrestrial life form is discovered. It has a genetic code much like that of organisms on Earth except that there are five different DNA bases instead of four and the base sequences are translated as doublets instead of triplets. How many different amino acids could be accommodated by this genetic code? a. 32 b. 5 c. 64 d. 25 e. 10

d

Choose the answer that has these events of protein synthesis in the proper sequence. 1. An aminoacyl-tRNA binds to the A site. 2. A peptide bond forms between the new amino acid and a polypeptide chain. 3. tRNA leaves the P site, and the P site remains vacant. 4. A small ribosomal subunit binds with mRNA. 5. tRNA translocates to the P site. a. 4, 1, 3, 2, 5 b. 2, 4, 5, 1, 3 c. 5, 4, 3, 2, 1 d. 4, 1, 2, 5, 3 e. 1, 3, 2, 4, 5

d

The anticodon of a particular tRNA molecule is a. changeable, depending on the amino acid that attaches to the tRNA. b. the part of tRNA that bonds to a specific amino acid. c. complementary to the corresponding mRNA triplet in rRNA. d. complementary to the corresponding mRNA codon. e. catalytic, making the tRNA a ribozyme.

d

What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized? a. DNA ligase works only in the 3' to 5' direction. b. Polymerase can work on only one strand at a time. c. Helicases and single-strand binding proteins (SSBPs) work at the 5' end. d. DNA polymerase can join new nucleotides only to the 3' end of the growing strand. e. The origins of replication occur only at the 5' end.

d

Which enzyme catalyzes the elongation of a DNA strand in the 5' to 3' direction? a. topoisomerase b. helicase c. DNA ligase d. DNA polymerase e. primase

d

Which of the following mutations would be most likely to have a harmful effect on an organism? a. a single nucleotide deletion near the end of the coding sequence b. a nucleotide-pair substitution c. a single nucleotide deletion in the middle of an intron d. a single nucleotide insertion downstream of, and close to, the start of the coding sequence e. a deletion of three nucleotides near the middle of a gene

d

How would the shape of a DNA molecules change if adenine paired with guanine and cytosine paired with thymine? The DNA molecule would a. be longer. b. be shorter. c. have regions where no base-pairing would occur. d. be circular. e. have irregular widths along its length.

e

In a nucleotide, the nitrogenous base is attached to the sugar's ___________ carbon and the phosphate group is attached to the sugar's __________ carbon. a. 1'; 3' b. 1'; 2' c. 2'; 3' d. 2'; 1' e. 1'; 5'

e

In analyzing the number of different bases in a DNA sample, which result would be consistent with base-pairing rules? a. G = T b. A = C c. A + T = G + T d. A = G e. A + G = C + T

e

In his work with pneumonia-causing bacteria and mice, Griffith found that a. the polysaccharide coat of bacteria caused pneumonia. b. heat-killed pathogenic cells caused pneumonia. c. a protein coat from pathogenic cells was able to transform nonpathogenic cells. d. bacteriophages injected DNA into bacteria. e. some substance from pathogenic cells was transferred to nonpathogenic cells, making them pathogenic.

e

RNA polymerase and DNA polymerase differ in that a. RNA polymerase is much more accurate than DNA polymerase. b. RNA polymerase uses RNA as a template, and DNA polymerase uses a DNA template. c. RNA polymerase binds to single-stranded DNA, and DNA polymerase binds to double-stranded DNA. d. RNA polymerase does not need to separate the two strands of DNA in order to synthesize an RNA copy, whereas DNA polymerase must unwind the double helix before it can replicate the DNA. e. RNA polymerase can initiate RNA synthesis, but DNA polymerase requires a primer to initiate DNA synthesis.

e

Spliceosomes are composed of a. polymerases and ligases. b. introns and exons. c. the RNA transcript and protein. d. snRNPs and snurps. e. snRNPs and other proteins.

e

Synthesis of a new DNA strand usually begins with a. DNA ligase. b. an Okazaki fragment. c. a DNA primer. d. a thymine dimer. e. an RNA primer.

e

Using a mRNA codon table, identify a 5' to 3' sequence of nucleotides in the DNA template strand for an mRNA coding for the polypeptide sequence Phe-Pro-Lys. a. 5'-AAACCCUUU-3' b. 5'-AAAACCTTT-3' c. 5'-UUUGGGAAA-3' d. 5'-GAACCCCTT-3' e. 5'-CTTCGGGAA-3'

e

Which of the following is not true of RNA processing? a. RNA splicing can be catalyzed by spliceosomes. b. Ribozymes may function in RNA splicing. c. Nucleotides may be added at both ends of the RNA. d. A primary transcript is often much longer than the final RNA molecule that leaves the nucleus. e. Exons are cut out before mRNA leaves the nucleus.

e

Why is the new DNA strand complementary to the 3' to 5' strands assembled in short segments? a. the replication forks block the formation of longer strands b. it is more efficient than assembling complete new stands c. DNA polymerase can assemble DNA only in the 3' to 5' direction d. only short DNA sequences can extend off the RNA primers e. DNA polymerase can assemble DNA only in the 5' to 3' direction

e