Deck 12: The Genetic Code and Transcription

Question 1

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

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

Answer 1

A

Question 2

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

Answer 2

C

Question 3

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

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

Answer 3

A

Question 4

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

Question 5

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

Question 6

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

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

Question 7

An intron is a section of _.

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

Question 8

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

Question 9

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

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

Question 10

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

Question 11

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) heteroduplex, homoduplex
E) transcription, translation

Question 12

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

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

Question 13

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

Question 14

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

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

Question 15

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

Question 16

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

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

Question 17

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 18

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

Question 19

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

Question 20

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

Question 21

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

Question 22

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 23

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

Question 24

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

Question 25

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

Question 26

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

Question 27

"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 28

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

Question 29

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

Question 30

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

Question 31

What was the name of the molecule that Jacob and Monod (1961) postulated carried genetic information from DNA to the site of protein manufacture?

Question 32

What is polycistronic mRNA?

Question 33

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

Question 34

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 35

Describe the function of N -formylmethionine in prokaryotes.

Question 36

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

Question 37

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

Question 38

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

Question 39

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 40

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

Question 41

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

Question 42

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

Question 43

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

Question 44

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

Question 45

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

Question 46

Transcription factors function to help move ribosomes along the mRNA.

Question 47

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

Question 48

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

Question 49

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

Question 50

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

Question 51

Messenger RNA is usually polycistronic in eukaryotes.