BSC1010 Exam 2 ~ Practice Test Questions

Here is a sketch of an incomplete replication fork, as might be seen in E. coli. At which letter—(a), (b), (c), (d), or a combination of letters—would you expect to see the enzyme class commonly called topoisomerase? A. (a) B. (b) C. (c) D. (d) E. (b) and (c)

A. (a)

Here is a schematic of transcription and translation occurring simultaneously as described by Miller et al. (1970) in E. coli. For each of the following questions, select the correct cluster of answers. (a) Is letter A at the 5 or 3 end (state which) of the DNA strand? (b) Is letter B at the 5 or 3 end (state which) of the RNA strand? (c) Is the amino acid nearest letter C the same type as the one nearest letter E (yes or no)? A. (a) 5; (b) 5; (c) yes B. (a) 3; (b) 5; (c) yes C. (a) 3; (b) 3; (c) yes D. (a) 5; (b) 3; (c) no E. (a) 3; (b) 3; (c) no

A. (a) 5'; (b) 5'; (c) yes

Actin filaments have polarity. This means that the two ends can be identified due to structural differences. The plus end is the end to which subunits are added more rapidly, or the end of polymerization. Which of the following would enable you to identify the plus end of actin filaments? A. Add radiolabeled actin subunits to a mixture of actin filaments in which conditions are favorable for polymerization. B. Add radiolabeled actin subunits to a mixture of actin filaments in which conditions favor depolymerization. C. Inspect the actin filaments using electron microscopy. D. Determine the ionic charge of the ends of the actin filaments.

A. Add radiolabeled actin subunits to a mixture of actin filaments in which conditions are favorable for polymerization.

If the GC content of a double-stranded DNA molecule is 60%, what are the molar percentages of the four bases (G, C, T, A)? A. G = 30%; C = 30%; A = 20%; T = 20% B. G = 20%; C = 20%; A = 30%; T = 30% C. G = 10%; C = 50%; A = 20%; T = 20% D. G = 0%; C = 60%; A = 0%; T = 40% E. There is not enough information to answer this question.

A. G = 30%; C = 30%; A = 20%; T = 20%

The TATA box (-10 or Pribnow box) has all the following characteristics except: A. It is both transcribed and translated. B. It is upstream from most genes. C. It is part of the binding site for the RNA polymerase. D. It is part of a consensus (common) sequence of the promoter.

A. It is both transcribed and translated.

Flagella are found in both eukaryotic cells and prokaryotic cells. Despite the structural and functional similarities of these cell types, scientists suspect that the structures have evolved independently. Why don't they think there is a common evolutionary origin for prokaryotic and eukaryotic flagella? A. Prokaryotic flagella move by rotating, whereas eukaryotic flagella undergo an undulating motion. Furthermore, eukaryotic flagella are covered by a plasma membrane and prokaryotic flagella are not. B. Prokaryotic flagella do not protrude outside the cell wall, whereas eukaryotic flagella are membrane-bound extensions of cytoplasm. C. Prokaryotic flagella are an adaptation to scarce nutrient supply, whereas eukaryotic flagella are designed to protect. D. Prokaryotic flagella do not require energy in the form of ATP.

A. Prokaryotic flagella move by rotating, whereas eukaryotic flagella undergo an undulating motion. Furthermore, eukaryotic flagella are covered by a plasma membrane and prokaryotic flagella are not.

This table gives the results of assays of percentages of bases from nucleic acids isolated from different sources. For each source, what type of nucleic acid (RNA or DNA) is most likely specified? State whether it is likely to be single or double stranded. The nucleic acid from source #1 is _________ and most likely __________. A. RNA; single stranded B. RNA; double stranded C. DNA; single stranded D. DNA; double stranded E. all of the above

A. RNA; single stranded

Given there are three "termination codons" that do not code for a given amino acid, you might expect there would be 61 tRNAs. But the actual number is smaller (about 40), because: A. Some tRNAs have anticodons that can recognize two or more different codons. B. Many tRNAs are often degraded during isolation and purification. C. The code is universal. D. AUG is the starting triplet only in prokaryotes. E. The base sequence and three dimensional structure for any given tRNA species varies sufficiently to allow for ambiguous codon recognition.

A. Some tRNAs have anticodons that can recognize two or more different codons.

As scientists were attempting to determine the structure of the genetic code, Crick and co-workers found that when three base additions or three base deletions occurred in a single gene, the wild-type phenotype was sometimes restored. These data indicated: 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.

A. The code is triplet.

Spherocytosis is a defect associated with a defective cytoskeletal protein in red blood cells. What do you suspect is one consequence of defective cytoskeletal proteins in red blood cells? A. abnormal cell shape B. insufficient energy supply in the cell C. a lack of cellular proteins available to transport oxygen D. adhering of blood cells to blood vessel walls, causing the formation of plaque

A. abnormal cell shape

Small eukaryotic proteins that are known to add specificity to polymerase-dependent RNA synthesis are known as A. basal transcription factors B. gene terminators C. stabilizers D. translation factors E. elongation factors

A. basal transcription factors

At the ends of chromosomes in eukaryotes, a problem exists with repeated DNA replication on the __________ strand. A __________ enzyme is responsible for providing a solution to this problem. A. lagging; telomerase B. leading; replicase C. lagging; replicase D. leading; polymerase

A. lagging; telomerase

A class of mutations that results in multiple contiguous (side-by-side) amino acid changes in proteins is probably caused by the following type of mutation: A. reading frame shift B. transversion C. transition D. base analogue E. recombinant

A. reading frame shift

What is the function of the nuclear pore complex? A. regulates movement of materials across the nuclear membrane B. assembles ribosomes from raw materials that are synthesized in the nucleus C. communicates with components of the endomembranal system D. synthesizes and repairs DNA, the unit of genetic information

A. regulates movement of materials across the nuclear membrane

One function of the Golgi stacks is to ship vesicles/products to their final destination. Which of the following clues might indicate that different signal sequences are responsible for determining the final destination of a particular vesicle? A. the discovery of different receptors on membranes of the various organelles or destinations to which materials are shipped B. using radioactivity to track materials from the endoplasmic reticulum to the Golgi C. using radioactivity to track the movement of vesicles from the trans face of the Golgi to their final destination D. tracking the movement of a particular protein through the stacks of the Golgi

A. the discovery of different receptors on membranes of the various organelles or destinations to which materials are shipped

Here is a sketch of an incomplete replication fork, as might be seen in E. coli. At which letter—(a), (b), (c), (d), or a combination of letters—would you expect to see the more continuous synthesis of DNA (the leading strand)? A. (a) B. (b) C. (c) D. (d) E. (b) and (c)

B. (b)

Early in the evolution of life-forms, there likely were fewer than 20 amino acids. If "primitive proteins" were composed of only 14 different kinds of amino acids, what would be the fewest number of nucleotides needed for a code that could specify the 14 different amino acids? Assume that all four nitrogenous bases are available for coding. A. 1 B. 2 C. 3 D. 14 E. 4

B. 2

How many amino acids would be coded for by this sequence? A. 3 B. 5 C. 6 D. 10 E. 15

B. 5

Which of the following represents a major difference between prokaryotic cells and eukaryotic cells? A. Prokaryotes, not eukaryotes, have cell walls. B. Eukaryotic cells tend to have much more extensive inner membrane systems and larger numbers of intracellular organelles than do prokaryotes. C. Prokaryotes are unable to carry out aerobic respiration, a process that requires a complex inner-membrane system. D. Prokaryotes are a more homogenous group of organisms than are eukaryotes, which include protozoa, plants, and animals.

B. Eukaryotic cells tend to have much more extensive inner membrane systems and larger numbers of intracellular organelles than do prokaryotes.

How did the P site of the ribosome get its name? A. It is where the promoter resides. B. It is the site where peptide bond formation takes place. C. It is where peptidyl tRNAs reside. D. It is the site where the growing polypeptide chain is phosphorylated.

B. It is the site where peptide bond formation takes place.

How is the nuclear membrane related to the endoplasmic reticulum? A. Ribosomes that exit the nucleus through the nuclear pore complex attach to ribosome receptor locations on the endoplasmic reticulum, thus providing a means of communication between the two structures. B. The inner and outer bilayers of the nuclear envelope are separated by a space that is continuous with the endoplasmic reticulum, thus providing direct contact between the two structures. C. The nucleolus is present in the nucleus, but communicates directly with the endoplasmic reticulum. D. The nuclear lamina anchors the endoplasmic reticulum, providing structural support and communication through direct contact.

B. The inner and outer bilayers of the nuclear envelope are separated by a space that is continuous with the endoplasmic reticulum, thus providing direct contact between the two structures.

The anticodon of ACG within an mRNA is A. TGC B. UGC C. AGC D. UCG E. TCG

B. UGC

In the figure above, the amino acid is most likely to bind at which position(s)? A. b and a B. b C. a and c D. c and d E. d

B. b

Which of the following two terms relates most closely to split genes? A. 5-cap; 3-poly-A tail B. introns; exons C. elongation; termination D. transcription; translation E. heteroduplex; homoduplex

B. introns; exons

A template strand of a gene has this base sequence: 3-TACAT#CCGATAGGGTCAT-5. Exposure to radiation causes a mutation in this gene. The thymine at the site of the mutation (#) is deleted. This will most likely result in A. mRNA codons preceding the mutation to be misread B. mRNA codons following the mutation to be misread C. no change of any kind D. no change in the polypeptide coded by this gene E. the AUG triplet functioning as a chain terminator

B. mRNA codons following the mutation to be misread

It has been hypothesized for some time that by having eukaryotic mRNAs spliced (removal of introns), an opportunity exists for alternative splicing (i.e., removal of different combinations of introns/exons) to produce A. more than one polymerase at a replication fork B. more than one mRNA from the same genetic locus C. several RNAs to generate several DNA segments D. many tRNA species to avoid the wobble seen during translation

B. more than one mRNA from the same genetic locus

Given the structure of DNA, what component of that structure is most directly associated with encoding genetic information? A. the sequence of phosphates B. nitrogenous bases and their sequence C. the arrangement of phosphodiester linkages D. the order of the deoxyribose sugars E. all of the above are correct

B. nitrogenous bases and their sequence

Here is a sketch of a replication bubble, as you might see in E. coli. Arrows indicate the direction of the replication forks. If letter (b) represents the 5' end of the strand it is nearest, where is(are) the most likely place(s) to see the Okazaki fragments? A. positions closest to letters (f) and (a) B. positions closest to letters (c) and (a) C. position closest to (c) only D. position closest to (d) only E. positions closest to letters (d) and (e)

B. positions closest to letters (c) and (a)

What is the best description of the "loops" in the tRNA molecule? A. unpaired DNA bases B. regions created as the result of hydrogen bonding between base pairs C. regions of the molecules that remain as single-stranded RNA due to the absence of complementary base pairs D. regions provided for binding to the mRNA codon

B. regions created as the result of hydrogen bonding between base pairs

What is the site of synthesis of proteins for export? A. free ribosomes B. ribosomes that attach to the endoplasmic reticulum C. the Golgi complex D. ribosomes that are attached to the outer mitochondrial membrane

B. ribosomes that attach to the endoplasmic reticulum

The ribosomes are moving from ________ to ________, and letter F points to ________. A. left to right; tRNA B. right to left; mRNA C. right to left; rRNA D. left to right; mRNA

B. right to left; mRNA

The first and last amino acids produced by this mRNA sequence would be, respectively, A. serine; glycine B. threonine; arginine C. glycine; serine D. arginine; serine E. threonine; proline

B. threonine; arginine

The nucleic acid from source #3 is _________ and most likely __________. A. RNA; single stranded B. RNA; double stranded C. DNA; single stranded D. DNA; double stranded E. all of the above

C. DNA; single stranded

Which of the following represents the correct order of events as they occur in the process of DNA replication? A. Helicase opens helix, pol III synthesizes RNA primer of leading strand, and pol I excises primer and fills gap. B. Primase synthesizes primer, pol I excises primer, and pol III elongates primer and synthesizes leading and lagging strands. C. Helicase opens helix, pol III elongates primer and synthesizes leading and lagging strands, and DNA ligase links fragments of DNA. D. Primase synthesizes RNA primer, pol III synthesizes lagging and leading strands, and helicase opens helix.

C. Helicase opens helix, pol III elongates primer and synthesizes leading and lagging strands, and DNA ligase links fragments of DNA.

How did the A site of the ribosome get its name? A. It is where amino acids are affixed to tRNAs, producing aminoacyl tRNAs. B. It is where the amino group on the growing polypeptide chain is available for peptide bond formation. C. It is the site occupied by incoming aminoacyl tRNAs. D. It is surrounded by -helices of ribosomal proteins.

C. It is the site occupied by incoming aminoacyl tRNAs.

Here is a simplified diagram of several components of the translation machinery. The ribosome is moving from left to right in this figure. Which of the following statements about this diagram is true? A. Letter A points to the mRNA. B. Letter B points to the tRNA. C. Letter C points to the 3' end of the mRNA. D. Letter D points to the ribosome. E. Letter E points to the "N" terminus of the growing polypeptide chain.

C. Letter C points to the 3' end of the mRNA.

A nonsense mutation is one in which: A. Multiple amino acid substitutions occur in the mutant protein. B. A single amino acid substitution occurs in the mutant protein. C. The mutant protein is shorter than normal. D. Each frameshift has called in an AUG triplet. E. None of the above apply.

C. The mutant protein is shorter than normal.

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.

C. There can be more than one codon for a particular amino acid.

The small intestine is the site of digestion and absorption of nutrients. A single layer of epithelial cells lines the small intestine. In the duodenum (the first section of the small intestine), these epithelial cells secrete large quantities of digestive enzymes. Which of the following features would be typical of these epithelial cells? A. They contain large numbers of lysosomes. B. They have more smooth endoplasmic reticulum than rough endoplasmic reticulum. C. They contain large quantities of rough endoplasmic reticulum. D. They have larger nuclei than cells that secrete large quantities of lipids.

C. They contain large quantities of rough endoplasmic reticulum.

What constitutes an individual's genome? A. all of its proteins B. all of its mRNAs C. all of its DNA D. all of its organelles

C. all of its DNA

Once DNA strands are separated by DNA helicase, _______________ block the reformation of a double helix by the template strands. A. RNA primer strands B. topoisomerase enzymes C. single-stranded DNA-binding proteins D. RNA polymerase complexes

C. single-stranded DNA-binding proteins

What do UAA, UAG and UGA code for? A. methionine B. phenylalanine C. stop sequence in the RNA message D. aminoacyl tRNA synthetase E. N-formyl methionine

C. stop sequence in the RNA message

The discontinuous aspect of DNA replication (i.e., that occurring on the lagging strand) is fundamentally caused by: A. polymerase slippage B. trinucleotide repeats C. the 5' => 3' polarity restriction D. topoisomerases cutting the DNA in a random fashion

C. the 5' => 3' polarity restriction

What is an anticodon? A. the part of an RNA message that signals the termination of translation B. the part of an RNA message that signals the start of translation C. the part of a tRNA that binds to a complementary codon in mRNA D. the part of a tRNA that accepts an amino acid, via a reaction catalyzed by tRNA synthetase

C. the part of a tRNA that binds to a complementary codon in mRNA

Which of these describes the function of RNA polymerase? A. amplifies the "message" by making multiple copies of an mRNA molecule after it has been transcribed from DNA B. converts a protein sequence to mRNA C. transcribes DNA to mRNA D. translates DNA into protein

C. transcribes DNA to mRNA

In a sample of double-stranded DNA from a particular organism, if 15% of the nitrogenous base is thymine, what percentage should be cytosine? A. 15% B. 30% C. 70% D. 35% E. 40%

D. 35%

Assume that you have determined the percentages of bases in DNA samples from a variety of organisms, each having DNA in the customary double-stranded form. What relationships would you expect to find in the percentage data? (Choose all that apply.) A. A = C B. A = G and C = T C. A + C = G + T D. A + T = G + C E. Both B and C are true.

D. A + T = G + C

What does the one-gene, one-enzyme hypothesis state? A. Genes are composed of stretches of DNA. B. Genes are made of protein. C. Genes code for ribozymes. D. A single gene codes for a single protein.

D. A single gene codes for a single protein.

Which of the following was considered important evidence that RNA was an intermediary between DNA and protein biosynthetic processes? A. RNA is located in the nucleus (with DNA) and the cytosol (with ribosomes). B. RNA is synthesized, but is then degraded fairly rapidly. C. DNA does not colocalize with ribosomes in the cytosol. D. All of the above are correct.

D. All of the above are correct.

Cancer can occur when DNA is damaged. Which of the following statements is true regarding the cause of damage to DNA molecules? A. The structure of DNA can be damaged only by environmental toxins such as cigarette smoke, aflotoxins, and other toxins in food. B. Excision repair enzymes are able to prevent all mutation in DNA. C. Small quantities of ultraviolet radiation have no effect on DNA structure. D. DNA molecules can break down in the absence of environmental toxins or radiation.

D. DNA molecules can break down in the absence of environmental toxins or radiation.

The nucleic acid from source #2 is _________ and most likely __________. A. RNA; single stranded B. RNA; double stranded C. DNA; single stranded D. DNA; double stranded E. all of the above

D. DNA; double stranded

In the triplet code, which of the following is true? A. Each DNA base codes for three amino acids. B. Each gene codes for three proteins. C. It takes three genes to code for one protein. D. Each amino acid in a protein is coded for by three bases in the DNA. E. Each triplet has many different meanings.

D. Each amino acid in a protein is coded for by three bases in the DNA

DNA replication is said to be semiconservative because: A. Half of the DNA in a new cell comes from one gamete and the other half from the other gamete. B. The same process of DNA replication is used by all organisms. C. The number of nucleotides within genes remains constant. D. Each new DNA molecule is composed of one old strand and one new strand. E. The total amount of DNA within an individual remains the same.

D. Each new DNA molecule is composed of one old strand and one new strand.

How can a gene be longer than an mRNA produced by that gene? For instance, the gene for Duchenne muscular dystrophy (DMD) is over 2000 kb (kb = kilobases) long, but the mRNA that this gene produces and that is found in polyribosomes is approximately 14 kb long. What causes this discrepancy? A. The exons have been spliced out during mRNA processing. B. The DNA represented a double-stranded structure and the RNA is single stranded. C. There are more amino acids coded for by the DNA than 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.

D. The introns have been spliced out during mRNA processing.

The tRNA shown in Figure 16.12 in your textbook depicts the typical "L" shape of this molecule. Which of the following will most likely result if some hydrogen bonds in the region labeled "hydrogen bonds" in the figure were broken using some type of chemical treatment? A. The tRNA will not be able to bind the amino acid properly. B. The tRNA will not have the correct anticodon. C. The anticodon will remain the same, but the amino acid bound to the tRNA will be different. D. The tRNA will not fit into the ribosome properly.

D. The tRNA will not fit into the ribosome properly.

Which of the following statements is not true regarding translation in bacteria? A. Translation requires the presence of initiation factors and both the small and large subunits of the ribosome. B. The peptide bonds between adjacent amino acids are formed within the large ribosomal subunit. C. The first amino acid in a polypeptide chain is methionine. D. Translation proceeds from the 3' end toward the 5' end of the mRNA.

D. Translation proceeds from the 3' end toward the 5' end of the mRNA.

What is the purpose of the cell wall, for both prokaryotes and plant cells? A. to provide a means of cell-cell interaction B. to enable the cell to obtain nutrients from its environment C. to regulate the passage of solutes into and out of the cell D. to protect the cell from the effects of a hypotonic environment

D. to protect the cell from the effects of a hypotonic environment

The figure above is of: A. messenger RNA B. ribosomal RNA C. DNA D. transfer RNA

D. transfer RNA

Here is a diagram (not to scale) of DNA in the process of replication. Choose the answer below that correctly identifies structures shown in the figure. A. 1 = 3' end; 2 = lagging side; 3 = leading side; 6 = topoisomerase B. 1 = 5' end; 2 = lagging side; 3 = leading side; 6 = helicase C. 1 = 3' end; 2 = leading side; 4 = 3 end; 6 = helicase D. 1 = 3' end; 2 = leading side; 3 = lagging side; 5 = topoisomerase E. 1 = 5' end; 2 = leading side; 3 = lagging side; 6 = topoisomerase

E. 1 = 5' end; 2 = leading side; 3 = lagging side; 6 = topoisomerase

This diagram shows the major components of the central dogma of molecular biology as described in your text. The three numbered arrows represent which three major processes related to that central dogma? A. 1 = replication; 2 = translation; 3 = transcription B. 1 = transcription; 2 = replication; 3 = transcription C. 1 = regeneration; 2 = translation; 3 = transcription D. 1 = translation; 2 = regeneration; 3 = transcription E. 1 = replication; 2 = transcription; 3 = translation Using this code table, consider the following template strand of a DNA molecule Template strand: 3' TGATGGCCGGGGGCC 5'

E. 1 = replication; 2 = transcription; 3 = translation

A bacterial protein is 300 amino acids long. Remembering that DNA is typically double stranded, which of the following could be the number of nucleotides in the section of DNA that codes for this protein? A. 3 B. 100 C. 300 D. 500 E. 1800

E. 1800

In the diagram shown for question 11, to what structures do arrows 5 and 1 point? A. 5 = topoisomerase; 1 = 5' end B. 5 = helicase; 1 = 3' end C. 5 = RNA; 1 = 3' end D. 5 = Okazaki fragment; 1 = 3' end E. 5 = helicase; 1 = 5' end

E. 5 = helicase; 1 = 5' end

Which of the following is a basic structural difference between plant cells and animal cells? A. Plant cells contain chloroplasts, but animal cells do not. B. Animal cells contain lysosomes, but plant cells do not. C. Plants have cell walls, and animal cells do not. D. Animal cells have a cytoskeleton to give the cell shape; the cell wall plays a role in determining plant cell shape. E. All of the above.

E. All of the above.

A biochemist isolated and purified what she thought were the various molecules needed for DNA replication. She then recombined them in appropriate concentrations to replicate DNA in vitro. Replication occurred; and when she isolated the product DNA, heated it to break the hydrogen bonds between complementary strands, and electrophoresed the products, she noted that there were not only some long strands but also numerous short segments of DNA a few hundred nucleotides long. What probably went wrong with the in vitro replication system she created? A. There were no RNA primers. B. No Okazaki fragments formed. C. Too many nucleotides were added. D. The DNA polymerase synthesized only in the 5 3 direction. E. Failure of DNA ligase occurred.

E. Failure of DNA ligase occurred.

Introns are known to contain termination codons (UAA, UGA, or UAG) yet 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, not termination. D. More than one termination codon is needed to stop translation. E. Termination codons within an intron are not involved in translation, because the introns are removed before translation.

E. Termination codons within an intron are not involved in translation, because the introns are removed before translation.

In 1928, Griffith injected living S (smooth) Streptococci into mice, and the mice died. When he injected living R (rough) Streptococci into mice, the mice lived. When he injected heat-killed smooth bacteria into mice, the mice lived. What was the result when he mixed heat-killed S bacteria with live R bacteria and injected this mixture into mice? A. The mice lived. B. The mice died, indicating that the heat-killed S bacteria came back to life. C. The mice lived, and living S bacteria could be obtained from the blood of the living mice. D. The mice died, indicating that DNA replicated semiconservatively. E. The mice died, and living S cells could be isolated from the blood of the dead mice.

E. The mice died, and living S cells could be isolated from the blood of the dead mice.

What is the name given to the three bases in a messenger RNA that hydrogen bond 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

E. codon

The following is a short segment of an mRNA molecule. The polypeptide it codes for is also shown: 5 AUGGUGCUGAAG 3: methionine-valine-leucine-lysine A mutation in the DNA occurs so that the fourth base (counting from the 5 end) in the messenger RNA now reads A rather than G. What sequence of peptides will the mRNA now code for? (You do not need a copy of the genetic code to answer the question.) A. methionine-valine-leucine-lysine B. methionine-lysine-leucine-lysine C. methionine-leucine-leucine-lysine D. methionine-valine-methionine-lysine E. methionine-methionine-leucine-lysine

E. methionine-methionine-leucine-lysine

Letter D points to A. messenger RNA B. DNA C. SnRNP D. SnRNA E. tRNA

E. tRNA