Quiz 10 (ch 16 + 17)

The nitrogenous base adenine is found in all members of which group?

ATP, RNA, and DNA

Which of the following shows the correct base pairing of deoxyribonucleotides that occurs in nature?

C with G

What is meant by the statement that "the genetic code is not ambiguous"?

Each codon specifies just one amino acid.

What is the function of the release factor?

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

What is the role of DNA ligase during DNA replication

It joins DNA fragments together.

Which of the following are needed for the initiation of transcription?

RNA polymerase Correct! all of these answers are correct Nice job! transcription factors a promoter sequence

Which of the following shows the correct base pairing of deoxyribonucleotides that occurs in nature?

T with A

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.

The order in which chromatin packing occurs is as follows:

The DNA wraps around histones, forming nucleosomes; the histones within each nucleosome interact with adjacent nucleosomes and with the DNA between nucleosomes to form a 30-nm fiber; the chromatin forms loops by attaching to scaffold proteins, forming a 300-nm fiber

An experimenter moves the operator for the lactose operon to the far end of the operon (past all of the structural genes in the lactose operon). Which of the following would likely occur when the cell is exposed to lactose?

The structural genes will be transcribed continuously.

Which of the following shows the correct base pairing of ribonucleotides that occurs in nature?

U with A

Which of the following mutations would be most likely to have a harmful effect on an organism?

a single nucleotide insertion downstream of, and close to, the start of the coding sequence

If an organism uses the "conservative" model of DNA replication, rather than the normal "semi-conservative" model of DNA replication,

after DNA replication occurs, one of the two double-stranded DNA molecules will consist of two "daughter" DNA strands and the other will consist of two "parental" DNA strands

Which of the following are NOT components of a nucleotide?

an "R" group

Ribosomal RNAs, or rRNAs

are not translated to form proteins

The ends of linear chromosomes are known as

telomeres

During translation, tRNAs leave the ribosome from

the E site

How do the nucleotides used to make RNA molecules differ from those used to make DNA molecules?

the nucleotides used to make RNA molecules have ribose instead of deoxyribose as their sugar and uracil instead of thymine as one of their nitrogenous bases

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?

12

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

3' CCA 5'

A part of an mRNA molecule with the following sequence is being read by a ribosome: 5' CCG-ACG 3' (mRNA). The anticodon loop of the first tRNA that will complement this mRNA is

3' GGC 5'

Given the locally unwound double strand below, in which direction does the RNA polymerase move?

3' → 5' along the template strand

If a DNA sample were composed of 10% thymine, what would be the percentage of guanine?

40%

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?

5' A C G U U A G G 3'

What would be the sequence of the DNA molecule made by replication of the DNA molecule shown below? 5' AAGGCTT 3'

5' AAGCCTT 3'

The nucleotide sequence of the coding strand of a DNA molecule is shown below. What will be the nucleotide sequence of the RNA molecule made from this segment of DNA? 5' AATTCGGG 3'

5' AAUUCGGG 3'

The nucleotide sequence of the coding strand of a DNA molecule is shown below. What will be the nucleotide sequence of the RNA molecule made from this segment of DNA? 5' ATGCGTA 3'

5' AUGCGUA 3'

The nucleotide sequence of the template strand of a DNA molecule is shown below. What will be the nucleotide sequence of the RNA molecule made from this segment of DNA? 5' AATTCGGG 3'

5' CCCGAAUU 3'

A peptide has the sequence NH2-phe-pro-lys-gly-phe-pro-COOH. Which of the following sequences in the coding strand of the DNA would code for this peptide?

5' TTT-CCC-AAA-GGG-TTT-CCC 3'

Which of the following statements is TRUE?

5' and 3' untranslated regions (UTRs) are parts of exons, but do not code for proteins.

The nucleotide sequence of the template strand of a DNA molecule is shown below. What will be the nucleotide sequence of the RNA molecule made from this segment of DNA? 5' ATGCGTA 3'

5'UACGCAU 3'

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

A + C = G + T

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.

During translation (polypeptide elongation), charged tRNAs enter the ribosome at the

A site

Which of the following shows the correct base pairing of deoxyribonucleotides that occurs in nature?

A with T

A particular triplet of bases in the coding strand of a gene is TTT. If an mRNA is made from this gene, the anticodon on the tRNA that will bind the codon on the mRNA is

AAA.

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

AAA.

A space probe returns with a culture of a microorganism found on a distant planet. Analysis shows that it is a carbon-based life-form that has DNA. You grow the cells in 15N medium for several generations and then transfer them to 14N medium and grown them for another generation. Which pattern in the figure shown below would you expect if the DNA was replicated in a conservative manner?

B

A particular triplet of bases in the coding strand of a gene is GGG. If an mRNA is made from this gene, the anticodon on the tRNA that will bind the codon on the mRNA is

CCC.

Which of the following statements is TRUE?

Correct Answer all of these answers are correct You Answered 5' UTRs are part of exons 3' UTRs are part of exons coding regions are part of exons

In the late 1950s, Meselson and Stahl grew bacteria in a medium containing "heavy" nitrogen (15N) and then transferred them to a medium containing 14N. Which of the results in the figure shown below would be expected after one round of DNA replication in the presence of 14N?

D

Suppose you are provided with an actively dividing culture of E. coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base?

DNA in both daughter cells would be radioactive.

A biochemist isolates, 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 molecule consists of a normal strand paired with numerous segments of DNA a few hundred nucleotides long. What has she probably left out of the mixture?

DNA ligase

Which of the following enzymes removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3' end of DNA fragments resulting from DNA replication of one of the two DNA strands?

DNA polymerase I

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

DNA polymerase III

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

DNA polymerase can join new nucleotides only to the 3' end of a growing strand.

Eukaryotic telomeres replicate differently than the rest of the chromosome. This is a consequence of which of the following?

DNA polymerases can only add deoxyribonucleotides to the 3' end of an existing nucleotide chain

Which of the following statements regarding DNA polymerases is TRUE?

DNA polymerases can only add nucleotides to the 3' end of a nucleotide chain Correct Answer all of these statements are true DNA polymerases can add nucleotides to the 3' end of an RNA molecule DNA polymerases can NOT initiate synthesis of a new deoxyribonucleotide chain

E. coli cells grown on 15N medium are transferred to 14N medium and allowed to grow for two more generations (two rounds of DNA replication). DNA extracted from these cells is centrifuged. Which of the samples shown in the figure below shows the density distribution of DNA you would expect in this experiment?

E

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

Exons

Which of the following statements about RNA processing is FALSE?

Exons are cut out before mRNA leaves the nucleus.

A particular triplet of bases in the template strand of DNA is GGG. The anticodon on the tRNA that binds the mRNA codon is

GGG.

Which of the following statements about histones is FALSE?

Histones help transport mRNA molecules out of the nucleus

What kind of chemical bond is found between paired bases of the DNA double helix?

Hydrogen

The "universal" genetic code is now known to have exceptions. Evidence for this can be found if which of the following is true?

If UGA, usually a stop codon, is found to code for an amino acid such as tryptophan (usually coded for by UGG only).

How do some scientists feel that telomerase might be used to slow the aging process?

If telomerase activity was increased in our cells, the rate at which our chromosomes shorten as we age might be decreased.

Which of the following statements describes the eukaryotic chromosome?

It consists of a single linear molecule of double-stranded DNA plus proteins.

What is meant by the statement that "the genetic code is redundant"?

Most amino acids are specified by more than one codon.

Why are there concerns about using increased telomerase activity to slow down the aging process?

One concern is that increasing telomerase activity could increase cancer rates.

Which of the following statements regarding primases is TRUE?

Primases can initiate synthesis of a new nucleotide chain Primases add nucleotides to the 3' end of a nucleotide or nucleotide chain Correct! all of these statements are true Good work! Primases catalyze the formation of an RNA molecule

Why do some scientists feel that telomerase might be used to slow the aging process?

Telomere extension in mice and worms has reversed some signs of aging.

In comparing DNA replication with transcription, which of the following is true only of DNA replication?

The entire template molecule is represented in the product.

When the genome of a particular species is said to include 20,000 protein-coding regions, what does this imply?

There are also genes for RNAs other than mRNA.

In an experiment, DNA is allowed to replicate in an environment with all necessary enzymes, dATP, dCTP, dGTP, and radioactively labeled dTTP (3H thymidine) for several minutes and then switched to nonradioactive medium. It is then viewed by electron microscopy and autoradiography. The figure shown below represents the results. The grains in the figure represent radioactive material within the replicating eye. Which of the following is the most likely interpretation?

There are two replication forks going in opposite directions.

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

UUU.

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 two nucleotides

Which of the following would you expect of a eukaryote lacking telomerase?

a reduction in chromosome length in gametes

According to the "semi-conservative" model of DNA replication,

after DNA replication occurs, each of the two double-stranded DNA molecules will consist of one "daughter" and one "parental" DNA strand

When a DNA molecule is replicated,

all of these answers are correct Good work! replication generally occurs by a "semi-conservative" mechanism the DNA strands in the original molecule are known as the "parental" DNA strands the DNA strands that are made by copying the parental DNA strands are known as the "daughter" strands

Which of the following statements regarding primases is TRUE

all of these statements are true Good work! Primases catalyze the formation of an RNA molecule Primases can initiate synthesis of a new nucleotide chain Primases add nucleotides to the 3' end of a nucleotide or nucleotide chain

Translation of mRNA

almost always begins at an AUG codon, which specifies methionine

The enzyme that catalyzes the formation of a covalent bond between a tRNA and a specific amino acid is

an aminoacyl tRNA synthetase

When the ribosome reaches a stop codon on the mRNA, no corresponding tRNA enters the A site. If the translation reaction were to be experimentally stopped at this point, which of the following would you be able to isolate?

an assembled ribosome with a polypeptide attached to the tRNA in the P site

The formation of hydrogen bonds between complementary nucleotides is known as

base pairing

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.

The group of three nucleotides that specifies an amino acid is known as a

codon

The pairs of nucleotides that interact to join together two DNA strands are known as

complementary nucleotides

The "polyA" tail that is added to the 3' end of eukaryotic mRNA molecules

consists of a string of adenosine ribonucleotides

The elongation of the leading strand during DNA synthesis

depends on the action of DNA polymerase.

Transfer RNAs, or tRNAs

form 3-dimensional shapes as a result of ionic bonds between different parts of the molecule. Correct Answer None of these answers is correct. are important components of ribosomes are translated to form short polypeptides that are part of ribosomes.

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

hydrogen bonding between base pairs

The two strands of a double-stranded DNA molecule are held together by

hydrogen bonds

You briefly expose bacteria undergoing DNA replication to radioactively labeled nucleotides. When you centrifuge the DNA isolated from the bacteria, the DNA separates into two classes. One class of labeled DNA includes very large molecules (thousands or even millions of nucleotides long), and the other includes short stretches of DNA (several hundred to a few thousand nucleotides in length). These two classes of DNA probably represent

leading strands and Okazaki fragments.

Which of the following statements about translation is TRUE?

mRNA molecules are read by the translation machinery in the 5' to 3' direction. Correct! All of these statements are true. Nice job! The 5' and 3' UTRs of an mRNA molecule are not translated. Translation of an mRNA begins at an AUG codon

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 represents the order of increasingly higher levels of organization of chromatin?

nucleosome, 30-nm chromatin fiber, looped domain

DNA polymerases can add deoxyribonucleotides to

only the 3' end of an existing nucleotide chain

Histones are

part of nucleosomes

The covalent linkages joining together nucleotides in a DNA molecule are known as

phosphodiester linkages

Which of the following enzymes initiates the synthesis of a new nucleotide chain during DNA replication?

primase

Which of the following enzymes synthesizes short segments of RNA?

primase

Histones are

proteins around which the DNA in chromosomes wrap

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.

Which of the following describes the sequence of events that occurs during DNA replication of a double-stranded DNA molecule?

separation of the DNA strands at DNA replication origins, unwinding of the DNA double helix, synthesis of RNA primers, synthesis of DNA, ligation of DNA fragments

The DNA molecule is able to carry a vast amount of hereditary information in which of the following?

sequence of bases

In eukaryotic cells, transcription cannot begin until

several transcription factors have bound to the promoter.

The sequence of an RNA molecule will be complementary to the sequence of the

template strand from which that RNA molecule was made

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.

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

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

During translation, after the ribosome breaks the bond between the growing polypeptide chain and the tRNA in the P site and then forms a covalent (peptide) bond between the growing polypeptide chain and the amino acid attached to the tRNA in the A site,

the ribosome shifts over one codon on the mRNA, such that the codon specifying the next amino acid is now lined up with the A site

During translation, after the ribosome breaks the bond between the growing polypeptide chain and the tRNA in the P site and then forms a covalent (peptide) bond between the growing polypeptide chain and the amino acid attached to the tRNA in the A site,

the tRNA that was in the P site is now in the E site and leaves the ribosome

What is the function of DNA polymerase III?

to add nucleotides to the 3' end of a growing DNA strand

The proteins that help RNA bind the DNA at the promoter site are known as

transcription factors