Unit Five Practice Exam Key

Unit 5 Practice Exam


1. A nucleotide consists of all of the following except

A. A phosphate group

B. A nitrogenous base

C. An amino acid

D. A ribose sugar

E. All of these are part of a nucleotide


2. A single strand of DNA contains nucleotides connected by

A. Hydrogen Bonds - connects 2 strands together

B. Weak Bonds

C. Peptide Bonds - connect amino acids together

D. Phosphodiester bonds

E. A and B


3. One strand of DNA is 5'-ACGTGCAT-3'. The complementary DNA strand is







4-8 use the following as answers. Each answer may be used once, more than once or not at all

A. DNA Polymerase

B. DNA ligase

C. Helicase

D. Primase

E. Telomerase


4. This enzyme seals together Okazaki fragments - B


5. This enzyme synthesizes new strands of DNA - A


6. This enzyme separates the 2 DNA strands - C


7. This enzyme proofreads DNA making sure no errors are made during DNA synthesis -A


8. This enzyme adds a short segment of RNA nucleotides to begin synthesis of a new strand- D


9. All of the following are true about errors in the DNA sequence except

A. Errors occur during synthesis of strands, but are corrected by proofreading

B. Errors occur when we are exposed to radiation, and are usually fatal - nucleases, DNA polymerase, and DNA ligase can repair damaged DNA

C. Errors are very rare during the replication of DNA

D. Deletions or additions of a nucleotide are much more serious than substitutions

E. Errors occur when we are exposed to x-rays, but are corrected by nucleases and other enzymes


10. How does transcription begin?

A. The separation of the 2 DNA strands by helicase

B. The unwinding of the DNA by topoisomerase

C. The binding of RNA polymerase to the promoter - RNA polymerase can separate the strands on its own

D. The binding of DNA polymerase

E. With the synthesis of a primer


11. RNA processing includes all of the following except

A. Substitution of U nucleotides for T nucleotides - U nucleotides are added during transcription - this is not a modification of the initial pre-mRNA

B. Addition of a 5' cap

C. Addition of a Poly A tail

D. Splicing of introns

E. All of the above occur during RNA processing


12. All of the following is true about introns except

A. They are found only in eukaryotes

B. They have no evolutionary purpose

C. They are interspersed with coding segments of a gene

D. They are transcribed but then removed

E. They are recognized by snRNPs


13. An mRNA transcript GCGAUGGGCATUUAGCGA enters a ribosome. How large will the peptide be?

A. 3 amino acids - only AUG - GGC - ATU will be translated into a polypeptide.  The stop codon UAG does not code for an amino acid

B. 4 amino acids

C. 5 amino acids

D. 6 amino acids

E. Impossible to tell from this situation


14. Viruses

A. Can only reproduce inside of a host cell

B. Are more genetically similar to their host than to other viruses

C. Can contain RNA or DNA

D. Can have very serious effects on a host organism

E. All of the above


15. All of the following are ways bacteria cells recombine DNA except

A. Conjugation

B. Meiosis - sexual reproduction

C. Transformation

D. Transduction

E. All of the above are ways bacteria recombine DNA


16. Which of the following best describes a repressible operon?

A. The gene is normally expressed

B. Presence of a molecule can stop the transcription of that gene

C. The gene is normally not expressed

D. The gene is turned on but the presence of an activator molecule

E. A and B


17. A person has a defective gene for histone proteins. What level of DNA structure would be most hindered?

A. The double helix

B. Nucleosomes - DNA wrapped around histone proteins

C. Chromatin Fibers - would also be inhibited, but because of B

D. Looped domains

E. Chromosomes


18. Which of the following is not a common way of regulating gene expression?

A. DNA methylation

B. Control of transcription factors

C. Histone acetylation

D. Polypeptide modifications

E. These are all methods of regulation


19. Differences between prokaryotic and eukaryotic DNA include all of the following except

A. The presence of introns in eukaryotic DNA

B. The circular nature of prokaryotic DNA

C. The length of the DNA

D. The type of sugar in DNA

E. These are all differences between prokaryotic and eukaryotic DNA


20. Transcription factors are important in what step of transcription?

A. Initiation - the binding of RNA polymerase to the DNA

B. Elongation - the addition of nucleotides to the RNA molecule, needs only RNA polymerase

C. Termination - needs termination factors

D. A and B

E. A, B and C


21. In prokaryotes RNA processing

A. In the nucleus

B. In the cytoplasm

C. In the ribosome itself

D. In the nucleolus

E. RNA processing doesn't occur in prokaryotes


22. Okazaki fragments are

A. Short mRNA strands

B. Primers used for the beginning of DNA replication

C. Short segments on the lagging strand during DNA replication

D. Segments of the leading strand during DNA synthesis

E. None of the above


23. Which of the following is not necessary for the pathway from gene to polypeptide to occur

A. Ribosomes

B. RNA polymerase


D. DNA polymerase - this is needed to replicate and maintain DNA, but not to transcribe it

E. A promoter region in DNA


24. Which of the following is not true about ribosomes?

A. They are slightly different in prokaryotes and eukaryotes

B. They are found in the nucleus

C. They consist of two subunits

D. They are more abundant in cells that make many proteins

E. Many ribosomes can operate on one mRNA molecule at once


25. Which of the following is not necessary for cloning a gene?

A. A plasmid

B. A bacterial cell

C. Restriction Enzymes

D. A method of transforming bacterial cells

E. All of the above are necessary


26. A biologist has a short sequence of DNA from 3 individuals and wishes to match them with a sample of the same DNA segment. The easiest way for him to accomplish this is to

A. Use restriction enzymes and gel electrophoresis

B. Clone the genes

C. Perform a microassay

D. Sequence the DNA

E. None of the above


27. Differences between a genomic library and cDNA library include all of the following except

A. The genomic library includes introns

B. The genomic library includes satellite DNA

C. The genomic library includes non-coding regions

D. The genomic library is made using reverse transcriptase

E. The genomic library contains all genes in an organism


28. A biologist performed a microassay on brain tissue. She was most likely trying to discover

A. If the brain tissue was the same as a sample tissue she had

B. Sequence the DNA found in the brain tissue

C. Identify which genes are expressed in the brain tissue

D. Create a genomic library of the brain tissue

E. Create a cDNA library of the brain tissue


29. The benefit of PCR in identifying viruses is that

A. PCR is highly selective in which genes it copies due to the primer - we can target the HIV

B. PCR can make many copies of the virus, so that we can locate a small amount of HIV - we can selectively amplify HIV

C. PCR specifically targets viral DNA - not true

D. A and B

E. A, B and C


30. Suppose all of the Thymine nucleotides in a cell were labelled with a fluorescent dye. We would find this dye

A. In all RNA strands that were transcribed

B. In all daughter DNA molecules after replication - RNA has no T nucleotides, but all new DNA strands molecules will have new Ts

C. In one of the two daughter DNA molecules after every replication (this would be conservative replication)

D. A and B

E. A and C


31. All of the following are transcribed from DNA except

A. Exons


C. Introns


E. All of the above are transcribed from DNA - Though introns are later removed.  rRNA is ribosomal RNA that aids in translation, but like all mRNA it is transcribed from DNA


32. A triplet segment of DNA is AAA. The anticodon on the tRNA that will carry the amino acid



C. Any anticodon beginning with UU

D. Any anticodon beginning with TT

E. AAA - The mRNA codon transcribed is UUU, therefore the tRNA anticodon is AAA.


33. Anticodons are found


B. in mRNA

C. in tRNA

D. in rRNA

E. in snRNPS


34. There are 61 mRNA codons that specificy an amino acid, but only 45 tRNAs. This is explained by the fact that

A. some tRNAs have anticodons that recognize two or more codons

B. The rules for base pairing of the 3rd nucleotide in a codon are more flexible than the rules for the first 2

C. The “wobbling” of tRNA anticodons

D. A and B

E. A, B and C - A and B are due to the Wobbling Effect


35. A single nucleotide is lost from the middle of a mRNA molecule during transcription

A. snRNPs will splice and remove the incorrect amino acid

B. nucleases will correct the error

C. One amino acid will be incorrect, but the polypeptide will most likely not be affected

D. The entire polypeptide will be dysfunctional - this is a frameshift mutation, the whole reading frame is thrown off

E. Depends on the gene


Questions 36-39 use the following as answers

A. Reverse transcriptase

B. Restriction enzymes

C. RNA polymerase

D. DNA polymerase

E. A and D


36. Used by retroviruses - A


37. Used in PCR - D


38. Used in cloning - B


39. Used in Southern Blotting - B


40. In the lytic cycle viruses do all of the following except

A. Incorporate themselves into the host's genome - this is the lysogenic cycle

B. Use the host's polymerases to copy their nucleic acid

C. Use the host's ribosomes to copy their proteins

D. Destroy the hosts

E. All of the above are done in the lytic cycle


41. Which of the following statements is true?

A. Animals can easily be regenerated from any animal cell grown in the right culture

B. Animal cells differentiate whereas plant cells do not

C. Differentiation of cells is mostly due to different genes being present

D. Plant cells can be regenerated from a single cell grown in the right medium

E. Stem cells are highly specialized and differentiated cells


42. The scientists who cloned Dolly had to find a way to

A. Un-differentiate the cells to be cloned

B. Make cells grow without the presence of an ovum

C. Sequence the sheep genome

D. Create a diploid sperm cell

E. Insert sheep DNA into bacteria


43. The most important control step in the differentiation of cells and the expression of genes is

A. The processing of RNA

B. Translation

C. Protein modifications

D. Transcription - Controlled by operons in prokaryotes and transcription factors in eukaryotes

E. DNA replication


44. Viruses

A. Evolved before bacteria

B. Are all related to each other

C. Most likely evolved from mobile elements in their host's genome

D. Can easily reproduce on their own

E. Cause syphillis