Chapter 17 - From Gene to Protein

Question 1

Fill in the sequence in the flow of genetic information, often called the central dogma. Put the name of the process above each arrow.

_________ → _________ → _________

Answer 1

DNA ^{transcription} RNA ^translation protein

Question 2

Practice using the dictionary of the genetic cocde in your textbook. Determine the amino acid sequence for a polypeptide coded for by the following mRNA transcript (written 5’ → 3’):

AUGCCUGACUUUAAGUAG

Answer 2

Met Pro Asp Phe Lys stop

Question 3

Review the key steps of transcription in eukaryotes:

a.

b.

c.

Answer 3

a. Initiation: Transcription factors bind to promoter and facilitate the binding of RNA polymerase II, forming a transcription initation complex; RNA polymerase II separates DNA strands at initation site.
b. Elongation: RNA polymerase II moves along DNA strand, connecting RNA nucleotides that have paired to the DNA template to the 3’ end of the growing RNA strand.
c. Termination: After polymerase transcribes past a polyadenylation signal sequence, the pre-mRNA is cut and released.

Question 4

How does the mRNA that leaves the nucleus differ from the primary transcript pre-mRNA?

Answer 4

A 5’ cap consisting of a modified guanine nucleotide is added to the 5’ UTR. A poly-A tail consisting of up to 250 adenine nucleotides is attached to the 3’ UTR. Spliceosomes have cut out the introns and spliced the exons together.

Question 5

Using some of the codons and the amino acids you identified in Interactive Question 17.2, fill in the attached table.

Answer 5

Question 6

In the following diagram of polypeptide synthesis, name the stage, briefly describe what happens in the stage, and identify the component (a-f).

Answer 6

Codon recognition: An elongation factor (not shown) helps an aminoacyl tRNA into the A site where its anticodon base-pairs to the mRNA codon; two GTP increase accuracy and efficiency.

a. amino end of growing polypeptide
b. aminoacyl tRNA
c. large subunit
d. A site
e. small subunit
f. 5’ end of mRNA

Question 7

In the following diagram of polypeptide synthesis, name the stage, briefly describe what happens in the stage, and identify the component (g).

Answer 7

Peptide bond formation: Ribosome catalyzes peptide bond formation between new amino acid and polypeptide held in the P site.

g. peptide bond formation

Question 8

In the following diagram of polypeptide synthesis, name the stage, briefly describe what happens in the stage, and identify the component (h).

Answer 8

Translocation: The empty tRNA in the P site is moved to the E site and released; the tRNA now holding the polypeptide is moved from the A to the P site, taking the mRNA with it; one GTP is required.

h. E site

Question 9

In the following diagram of polypeptide synthesis, name the stage, briefly describe what happens in the stage, and identify the component (i-l).

Answer 9

Termination: Release factor binds to stop codon in the A site. Free polypeptide is released from the P site. Ribosomal subunits and other assembly components separate.

i. release factor
j. stop codon
k. P site of
l. free polypeptide

Question 10

What determines if a ribosome becomes bound to the ER?

Question 11

Define the following, and explain what type of point mutation could cause each of these mutations.

a. silent mutation
b. missense mutation
c. nonsense mutation
d. frameshift mutation

Answer 11

a. Silent: a base-pair substitution producing a codon that still codes for the same amino acid.
b. Missense: a base-pair substitution or frameshift mutation that results in a codon for a different amino acid.
c. Nonsense: a base-pair substitution or frameshift mutation that creates a stop codon and prematurely terminates translation.
d. Frameshift: an insertion or deletion or one, two, or more than three nucleotides that disrupts the reading frame and creates extensive missense and nonsense mutations.

Question 12

In Beadle and Tatum’s study of Neurospora, they were able to identify three classes of mutants that needed arginine added to the minimal media in order to grow. The production of arginine includes the following steps: precursor → ornithine → citrulline → arginine. What nutrient(s) had to be supplied for the mutants with a defective enzyme for the ornithine → citrulline step to grow?

a. the precursor
b. ornithine
c. citrulline
d. either ornithine or citrulline
e. the precursor, ornithine, and citrulline

Answer 12

c. citrulline

Question 13

Transcription involves the transfer of information from

a. DNA to RNA.
b. RNA to DNA.
c. mRNA to an amino acid sequence.
d. DNA to an amino acid sequence.
e. the nucleus to the cytoplasm.

Answer 13

a. DNA to RNA.

Question 14

If the 5’ → 3’ nucleotide sequence on the complementary (noncoding) DNA strand is CAT, what is the corresponding codon on mRNA?

a. UAC
b. CAU
c. GUA
d. GTA
e. CAT

Answer 14

b. CAU

Question 15

RNA polymerase

a. is the protein responsible for the production of ribonucleotides.
b. is the enzyme that creates hydrogen bonds between nucleotides on the DNA template strand and the complementary RNA nucleotides.
c. is the enzyme that transcribes exons but does not transcribe introns.
d. is a ribozyme composed of snRNPs.
e. moves along the template strand of DNA, elongating an RNA molecule in a 5’ →3’ direction.

Answer 15

e. moves along the template strand of DNA, elongating an RNA molecule in a 5’ →3’ direction.

Question 16

How is template strand for a particular gene determined?

a. It is the DNA strand that runs from the 5’ → 3’ direction.
b. It is the DNA strand that runs from the 3’ → 5’ direction.
c. It is established within the promoter.
d. It doesn’t matter which strand is the template because they are complementary and wil produce the same mRNA.
e. It is signaled by a polyadenylation signal sequence.

Answer 16

c. It is established within the promoter.

Question 17

Which enzyme sythesizes tRNA?

a. RNA replicase
b. RNA polymerase
c. aminoacyl-tRNA synthetase
d. ribosomal enzymes
e. ribozymes

Answer 17

b. RNA polymerase

Question 18

Which of the following is true of RNA processing?

a. Exons are excised before the mRNA is translated.
b. The RNA transcipt that leaves the nucleus may be much longer than the original transcript.
c. Assemblies of protein and snRNP’s, called spliceosomes, may catalyze splicing.
d. Large quantities of rRNA are assembled into ribosomes.
e. Signal peptides are added to the 5’ end of the transcript.

Answer 18

c. Assemblies of protein and snRNP’s, called spliceosomes, may catalyze splicing.

Question 19

Which of the following is not involved in the formation of a eukaryotic transciption initiation complex?

a. TATA box
b. transcriptionn factors
c. snRNA
d. RDA polymerase II
e. promoter

Answer 19

c. snRNA

Question 20

A prokaryotic gene 600 nucleotides long can code for a polypeptide chain of how many amino acids (at most)?

a. 100
b. 200
c. 300
d. 600
e. 1,800

Answer 20

b. 200

Question 21

All of the following are transcribed from DNA except

a. exons.
b. introns.
c. tRNA.
d. rRNA.
e. promoter

Answer 21

e. promoter

Question 22

What might introns have to do with the evolution of new proteins?

a. The excised introns are transcribed and translated as new proteins by themselves.
b. Introns are more likely to accumulate mutations than exons, and these mutations then result in the production of novel proteins.
c. Introns that are self-excising may also function as hydrolytic enzymes for other processes.
d. Introns provide more area where crossing over may occur (without interfering with the coding sequences) and thus increase the probability of exon shuffling between alleles.
e. Introns often correspond to domains in proteins that fold independently and have specific functions. Switching domains between nonallelic genes could produce novel proteins.

Answer 22

d. Introns provide more area where crossing over may occur (without interfering with the coding sequences) and thus increase the probability of exon shuffling between alleles.

Question 23

A ribozyme is

a. an exception to the one gene–one RNA molecule axiom.
b. an enzyme that adds the 5’ cap and poly-A tail to an mRNA.
c. an example of rearrangement of protein domains caused by RNA splicing.
d. an RNA molecule that functions as an enzyme.
e. an enzyme that produces both small and large ribosomal subunits.

Answer 23

d. an RNA molecule that functions as an enzyme.

Question 24

All of the following would be found in a prokaryotic cell except

a. mRNA.
b. rRNA.
c. simultaneous transcription and translation.
d. snRNA.
e. RNA polymerase.

Answer 24

d. snRNA.

Question 25

Which of the following is transcribed and then translated to form a protein product?

a. gene for tRNA
b. intron
c. gene for a transcription factor
d. 5’ and 3’ UTRs
e. gene for rRNA

Answer 25

c. gene for a transcription factor

Question 26

Transfer RNA

a. forms hydrogen bonds between its codon and the anticodon of an mRNA in the A site of a robosome.
b. binds to its specific amino acids in the active site of a aminoacyl-tRNA synthetase.
c. has catalytic actvity and is thus a ribozyme.
d. is translated from mRNA.
e. is produced inthe nucleolus.

Answer 26

b. binds to its specific amino acids in the active site of a aminoacyl-tRNA synthetase.

Question 27

Place the following events in the synthesis of a polypeptide in the proper order.

1. a peptide bond forms.
2. An aminoacyl tRNA mathces its anticodon the the codon in the A side.
3. At tRNA translocates from the A to the P site, and an unattached tRNA leaves the ribosome from the E side.
4. The large subunit attaches to the small subunit, with the initiator tRNA and the P site.
5. A small subunit binds to an mRNA and an initiator tRNA.
   a. 4-5-3-2-1
   b. 4-5-2-1-3
   c. 5-4-3-2-1
   d. 5-4-1-2-3
   e. 5-4-2-1-3

Answer 27

e. 5-4-2-1-3

Question 28

Translocation in the process of translation involves

a. the hydrolysis of a GTP molecule.
b. the movement of the tRNA in the A site to the P site.
c. the movement of the mRNA strand one triplet length.
d. the release of the unattached tRNA from the E site.
e. all of the above.

Answer 28

e. all of the above.

Question 29

Which of the following type of molecule catalyzes the formation of a peptide bond?

a. RNA polymerase
b. rRNA
c. mRNA
d. aminoacyl-tRNA synthetase
e. proteinase

Answer 29

b. rRNA

Question 30

Which of the following is not true of an anticodon?

a. It consists of three nucleotides.
b. It lines up in the 5’ → 3’ direction along the 5’ → 3’ mRNA strand.
c. It extends from one loop of a tRNA molecule.
d. It may pair with more than one codon.
e. Its base uracil base-pairs with adenine.

Answer 30

b. It lines up in the 5’ → 3’ direction along the 5’ → 3’ mRNA strand.

Question 31

Changes in a polypeptide following translation may involve

a. the addition of sugars or lipids to certain amino acids.
b. the action of enzymes to add amino acids at the beginning of the chain.
c. the removal of poly-A from the end of the chain.
d. the addition of a 5’ cap of a modified guanosine residue.
e. all of the above.

Answer 31

a. the addition of sugars or lipids to certain amino acids.

Question 32

Several proteins may be produced at the same time from a single mRNA by

a. the action of several ribosomes in a string, called a polyribosome.
b. several RNA polymerase molecules working sequentially.
c. signal peptides that associate ribosomes with rough ER.
d. containing several promoter regions.
e. the involvement of multiple spliceosomes.

Answer 32

a. the action of several ribosomes in a string, called a polyribosome.

Question 33

A signal peptide

a. is most likely to be found on cytosolic proteins produced by bacterial cells.
b. directs an mRNA molecule into the lumen of the ER.
c. is a sign to help bind the small ribosomal unit at the initiation codon.
d. would be the first 20 or so amino acids of a protein destined for a membrane location or secretion from the cell.
e. is part of the 5’ cap.

Answer 33

d. would be the first 20 or so amino acids of a protein destined for a membrane location or secretion from the cell.

Question 34

A base deletion early in the coding sequence of a gene would most likely result in

a. a nonsense mutation.
b. a frameshift mutation.
c. multiple missense mutations.
d. a nunfunctional protein.
e. all of the above.

Answer 34

e. all of the above.

Question 35

Which of the following best characterizes gene expression in archaea?

a. Their molecular machinery and processes are exactly like that of bacteria.
b. Their molecular machinery and processes are exactly like that of eukaryotes.
c. Their processes of transcription and translation differ substantially from both bacteria and eukaryotes.
d. Their mechanisms of gene expression are most similar to eukaryotes, although they share some similarities with bacteria.
e. Their processes of transcription and translation have not yet been studied.

Answer 35

d. Their mechanisms of gene expression are most similar to eukaryotes, although they share some similarities with bacteria.