Deck 12: The Genetic Code and Transcription

Question 1

Significant in the deciphering of the genetic code was the discovery of the enzyme polynucleotide phosphorylase.What is this enzyme used for?

A)manufacture of synthetic RNA for cell-free systems
B)ribosomal translocation
C)peptide bond formation
D)production of ribosomal proteins
E)degradation of RNA

Answer 1

A

Question 2

When scientists were attempting to determine the structure of the genetic code,Crick and coworkers found that when three base additions or three base deletions occurred in a single gene,the wild-type phenotype was sometimes restored.These data supported the hypothesis that ________.

A)the code is triplet
B)the code contains internal punctuation
C)AUG is the initiating triplet
D)the code is overlapping
E)there are three amino acids per base

Answer 2

A

Question 3

An intron is a section of ________.

A)protein that is clipped out posttranslationally
B)RNA that is removed during RNA processing
C)DNA that is removed during DNA processing
D)transfer RNA that binds to the anticodon
E)carbohydrate that serves as a signal for RNA transport

Answer 3

B

Question 4

Which of the following two terms relate most closely to split genes?

A)5'-cap,3'-poly-A tail
B)introns,exons
C)elongation,termination
D)transcription,translation
E)heteroduplex,homoduplex

Question 5

When considering the initiation of transcription,one often finds consensus sequences located in the region of the DNA where RNA polymerase(s)binds.Which of the following is a common consensus sequence?

A)TATA
B)GGTTC
C)TTTTAAAA
D)any trinucleotide repeat
E)satellite DNAs

Question 6

In which cellular organelle do the three posttranscriptional modifications often seen in the maturation of mRNA in eukaryotes occur?

A)nucleus
B)cytoplasm
C)mitochondrion
D)lysosome
E)Golgi

Question 7

Sidney Brenner argued that the code was nonoverlapping because he considered that coding restrictions would occur if it were overlapping.A second major argument against an overlapping code involved the effect of a single nucleotide change.In an overlapping code,how many adjacent amino acids would be affected by a point mutation? In a nonoverlapping code,how many amino acid(s)would be affected?

Question 8

Introns are known to contain termination codons (UAA,UGA,or UAG),yet these codons do not interrupt the coding of a particular protein.Why?

A)UAA,UGA,and UAG are initiator codons,not termination codons.
B)Exons are spliced out of mRNA before translation.
C)These triplets cause frameshift mutations,but not termination.
D)More than one termination codon is needed to stop translation.
E)Introns are removed from mRNA before translation.

Question 9

If one compares the base sequences of related genes from different species,one is likely to find that corresponding ________ are usually conserved,but the sequences of ________ are much less well conserved.

A)exons; introns
B)introns; exons
C)introns; chaperons
D)chaperons; exons
E)introns; proteins

Question 10

Describe the direction of information flow in living systems.Use appropriate,scientific terms in your description.

Question 11

What is the initiator triplet in both prokaryotes and eukaryotes? Which amino acid does this triplet recruit?

A)UAA; no amino acid called in
B)UAA or UGA; arginine
C)AUG; arginine
D)AUG; methionine
E)UAA; methionine

Question 12

In 1964,Nirenberg and Leder used the triplet binding assay to determine specific codon assignments.A complex of which of the following components was trapped in the nitrocellulose filter?

A)ribosomes and DNA
B)free tRNAs
C)charged tRNA,RNA triplet,and ribosome
D)uncharged tRNAs and ribosomes
E)sense and antisense strands of DNA

Question 13

The genetic code is fairly consistent among all organisms.The term often used to describe such consistency in the code is ________.

A)universal
B)exceptional
C)trans-specific
D)overlapping
E)None of the answers listed is correct.

Question 14

The genetic code is said to be triplet,meaning that there ________.

A)are three amino acids per base in mRNA
B)are three bases in mRNA that code for an amino acid
C)may be three ways in which an amino acid may terminate a chain
D)are three "nonsense" triplets
E)None of the answers listed is correct.

Question 15

Which of the following contains the three posttranscriptional modifications often seen in the maturation of mRNA in eukaryotes?

A)5'-capping,3'-poly(A)tail addition,splicing
B)3'-capping,5'-poly(A)tail addition,splicing
C)removal of exons,insertion of introns,capping
D)5'-poly(A)tail addition,insertion of introns,capping
E)heteroduplex formation,base modification,capping

Question 16

It has been recently determined that the gene for Duchenne muscular dystrophy (DMD)is more than 2000 kb (kilobases)in length; however,the mRNA produced by this gene is only about 14 kb long.What is a likely cause of this discrepancy?

A)The exons have been spliced out during mRNA processing.
B)The DNA represents a double-stranded structure,whereas the RNA is single-stranded.
C)More amino acids are coded for by the DNA than by the mRNA.
D)The introns have been spliced out during mRNA processing.
E)When the mRNA is produced,it is highly folded and therefore less long.

Question 17

When examining the genetic code,it is apparent that ________.

A)there can be more than one amino acid for a particular codon
B)AUG is a terminating codon
C)there can be more than one codon for a particular amino acid
D)the code is ambiguous in that the same codon can code for two or more amino acids
E)there are 44 stop codons because there are only 20 amino acids

Question 18

What is the name given to the three bases in a messenger RNA that bind to the anticodon of tRNA to specify an amino acid placement in a protein?

A)protein
B)anti-anticodon
C)cistron
D)rho
E)codon

Question 19

A class of mutations that results in multiple contiguous (side-by-side)amino acid changes in proteins is probably caused by which one of the following types of mutations?

A)frameshift
B)transversion
C)transition
D)base analog
E)recombinant

Question 20

The relationship between a gene and a messenger RNA is that ________.

A)genes are made from mRNAs
B)mRNAs are made from genes
C)mRNAs make proteins,which then code for genes
D)genes are structurally identical to mRNAs
E)mRNA is directly responsible for making Okazaki fragments

Question 21

"Breaking the genetic code" has been referred to as one of the most significant scientific achievements in modern times.Describe (in outline or brief statement form)the procedures used to break the code.

Question 22

What is polycistronic mRNA?

Question 23

Describe how the sigma subunit (factor)of E.coli RNA polymerase participates in transcription.

Question 24

Of the following three types of nucleic acids-DNA,mRNA,tRNA-which is most likely to contain modified bases?

Question 25

Describe the function of N-formylmethionine in prokaryotes.

Question 26

There is some indication that the code is in some way ordered; a certain pattern exists.Describe an observation that supports this view.

Question 27

The relationship between codon and anticodon can be characterized as involving ________.

Question 28

Describe a difference between the RNA polymerases of eukaryotes and prokaryotes.

Question 29

The finding that virtually all organisms use the same genetic code provides the basis for declaring that the code is universal.Name at least two exceptions to such universality.

Question 30

From the late 1950s to the mid-1960s,numerous experiments using in vitro cell-free systems provided information on the nature of the genetic code.Briefly outline significant experiments in the determination of the genetic code.

Question 31

What two experimental procedures allowed deciphering of the ordered triplet assignments of the genetic code?

Question 32

Referring to the genetic code,what is meant by "wobble"?

Question 33

In the context of molecular genetics,how does one reconcile the terms overlapping genes and nonoverlapping code?

Question 34

What is meant by punctuation in terms of the genetic code?

Question 35

A base at the first position of an anticodon on the tRNA would pair with a base at the ________ position of the mRNA.

Question 36

What is a nonsense mutation?

Question 37

List four base triplets that are clearly responsible for punctuation (initiation,termination).

Question 38

What is meant by the term heterogeneous nuclear RNA (hnRNA)?

Question 39

Suppose that in the use of polynucleotide phosphorylase,nucleotides A and C are added in a ratio of 1A:5C.What is the probability that an AAA sequence will occur?

Question 40

Regarding the efficient initiation of transcription by RNA polymerase II,which specific "upstream" signals appear to be involved?

Question 41

Heterogeneous nuclear RNA is a primary transcript in eukaryotes that is processed prior to involvement in translation.

Question 42

The triplet AUG is commonly used as a start codon during translation.

Question 43

An intron is a section of an RNA that gets spliced out.

Question 44

Messenger RNA is usually polycistronic in eukaryotes.

Question 45

In eukaryotes,which three factors appear to encourage the specific association of RNA polymerase(s)to a specific region of DNA?

Question 46

The code is nonoverlapping,meaning that,assuming "standard translation," a given base participates in the specification of one and only one amino acid.

Question 47

RNA processing occurs when amino acids are removed from nascent proteins.

Question 48

Transcription factors function to help move ribosomes along the mRNA.

Question 49

A 3' poly-A tail and a 5'-cap are common components of prokaryotic RNAs.

Question 50

A 5'-cap describes the addition of a base,usually thymine,to the 5' end of a completed peptide.

Question 51

The enzyme polynucleotide phosphorylase is capable of generating a random assembly of ribonucleotides.