Genetics Test Date: _________________
GENETICS – SOME PRACTICE QUESTIONS
HOW TO COMPLETE THESE PRACTICE QUESTIONS!
 Write out clear answers to these questions!
 Use the powerpoint, class notes, and friends to help you out
 Bring specific questions to your teacher if you are having difficulty
DNA: The Molecular Basis of Life!
The following is a segment taken from a strand of DNA: 5’ – ATGCCTA-3’. Write out the complementary strand for this
segment. Be sure to show directionality.
2. Copy Table 2 into your notes and fill in the missing information
Table 2
Enzyme
Function
DNA gyrase
DNA helicase
DNA polymerase I
DNA polymerase III
DNA ligase
RNA primase
1.
3.
4.
5.
6.
Compare the mechanisms by which the leading and lagging strands are replicated. Explain why it is necessary for two
mechanisms to exist.
Matthew Meselson and Franklin Stahl observed a total of three bands (heavy, light and intermediate) in the density
gradient they obtained in their experiment. At which point in their experiment did they observe each type of band? What
was the constituent isotope that each band contained?
Messelson and Stahl’s experiment indicated that DNA replicates semiconservatively. What percentage of DNA double
helixes would contain one of the original parent strands after four generations of replication?
Answer question below by writing on the diagram with 5’ or 3’.
PROTEIN SYNTHESIS
Protein Synthesis: An Overview
1. State the central dogma of molecular genetics.
2. Compare DNA and RNA and outline their similarities and differences.
3. Differentiate between transcription and translation in terms of their purpose and location.
4. Describe the role of the following molecules in protein synthesis: mRNA, tRNA, rRNA.
5. The DNA code is read in groups of three nucleotides called codons. Explain why reading the code in pairs of
nucleotides is not sufficient.
6. The following is the sequence of a fragment of DNA:
GGATCAGGTCCAGGCAATTTAGCATGCCCCAA
Transcribe this sequence into mRNA.
7. Using the genetic code, decipher the following mRNA sequence:
5’ – GGCAUGGGACAUUAUUUUGCCCGUUGUGGUGGGGCGUGA – 3’
Transcription
8. Explain the role of the following in transcription: RNA polymerase, poly-A polymerase, and splicesomes.
9. A short fragment of a particular gene includes the following sequence of nucleotides:
3’ – TACTACGGTAGGTATA – 5’
Write out the mRNA sequence.
10. A short fragment of a particular gene includes the following sequence of nucleotides:
3’ – GGCATGCACCATAATATCGACCTTCGGCACGG – 5’
a) Identify the promoter region.
b) Explain the purpose of the promoter region in transcription.
11. Differentiate between introns and exons.
12. In eukaryotes, mRNA must be modified before it is allowed to exit the nucleus.
a) Describe the modifications that are made to eukaryotic primary transcript.
b) Explain how these modifications ensure that mRNA survives in the cytoplasm and is translated into a
functioning protein.
Translation
13. Differentiate between the following:
a) P site and A site
b) Codon and anticodon
c) Start codon and stop codon
14. Three types or RNA must be functioning properly to ensure normal protein synthesis. Identify the three types of RNA
that are needed and explain the critical role that each one plays during translation.
15. List the possible anticodons for threonine, alanine, and praline.
16. The following sequence was isolated from a fragment of mRNA:
5’ – GGC CCA UAG AUG CCA CCG GGA AAA GAC UGA GCC CCG – 3’
Translate the sequence into protein starting with the start codon.
Control Mechanisms
17. Define the following terms: operon, operator, corepressor, repressor.
18. Explain why it is to a cell’s advantage to have some of its genes under regulation.
19. Describe the state of the lac operon system if the level of lactose is low, indicating the activity and state of all major
enzymes and proteins found in this system. What changes take place if lactose is suddenly made available as a nutrient
to the bacteria?
20. Describe the state of the trp operon system if the level of tryptophan is high, indicating the activity and stat of all
major enzymes and proteins found in this system. What changes take place if the tryptophan levels fall?
Mutations
21. Define the following terms: mutation, frameshift mutation, point mutation, nonsense mutation, missense mutation
22. Explain why mutations, such as nitrogen-based additions, are often much more harmful than nitrogen-based
substitutions.
23. Which of the two types of mutations, nonsense or missense, would be more harmful to an organism? Justify your
answer using your knowledge of protein synthesis.
24. Name three factors that can produce gene mutations.
25. Using the genetic code, list all the codons that can possibly be latered to become a stop codon by sutstitution by one
base.