Unit4 Review PDF

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Some Key Terms:  Purine – Adenine and Guanine  Pyrimidine – Cytosine and Thymine  Helicase – unwinds DNA  Topoisomerase – releases tension in the DNA during unwinding  Primase – produces RNA primers  DNA is synthesized in the 5’ to 3’ direction, and replicates along the parental strand in the 3’ to 5’ direction  DNA polymerase attaches to the 3’ hydroxyl group on the parental strand  Leading strand – continuous DNA replication o DNA polymerase III  Lagging strand – discontinuous DNA replication o Okazaki fragments o DNA polymerase I o DNA ligase – closes gap  Introns – noncoding regions  Exons – coding regions  Splicing – removes introns  Ribosome - EPA o E site - exit o P site – peptidyl-tRNA binding site o A site – aminoacyl-tRNA binding site  Point mutations – base sequence changes o Silent mutation – same amino acid sequence o Missense mutation – change of amino acid sequence o Nonsense mutation – change to STOP codon o Frameshift mutation – throw off reading frame  2 Types of Regulation o Negative regulation – something prevents transcription o Positive regulation – something facilitates (enhances) transcription  Operon o Promoter o Operator – downstream of promoter and binds a regulatory protein  Trp Operon – contains genes to make amino acid tryptophan  Repressible Operon – the end product can suppress transcription o Tryptophan absent, operon on o Tryptophan present, operon off  Lac Operon (bacteria) – inducible operon o Lactose absent, operon off o Lactose present, operon on  Methylation of histones – add methyl groups o Methylated – dense – closed to gene expression o Unmethylated – light – open to gene expression  Housekeeping genes – genes always on  Unacetylated – dense packing  Acetylated – light packing Some sample test questions for the 4th unit: 1. A transcription unit that is 8,000 nucleotides long may use 1,200 nucleotides to make a protein consisting of approximately 400 amino acids. This is best explained by the fact that a. There are termination exons near the beginning of mRNA b. There is redundancy and ambiguity in the genetic code c. Many noncoding stretches of nucleotides are present in mRNA d. Many nucleotides are needed to code for each amino acid e. Nucleotides break off and are lost during the transcription process 2. Which of the following is a function of a signal peptide? a. To terminate translation of the messenger RNA

b. To bind RNA polymerase to DNA and initiate transcription c. To direct an mRNA molecule into the cisternal space of the ER d. To signal the initiation of transcription e. To translocate polypeptides across the ER membrane 3. In positive control of several sugar-metabolism-related operons, the catabolite activator protein (CAP) binds to DNA to stimulate transcription. What causes an increase in CAP? a. Decrease in glucose and increase in cAMP b. Increase in glucose and decrease in cAMP c. Decrease in glucose and decrease in repressor d. Increase in glucose and increase in cAMP e. Decrease in glucose and increase in repressor 4. Gene expression might be altered at the level of post-transcriptional processing in eukaryotes rather than prokaryotes because of which of the following? a. Prokaryotic genes are expressed as mRNA, which is more stable in the cell b. Eukaryotic exons may be spliced in alternative patterns c. Eukaryotic coded polypeptides often require cleaving of signal sequences before localization d. Eukaryotic mRNAs get 5’ caps and 3’ tails e. Prokaryotes use ribosomes of different structure and size 5. Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on specificity in the a. Binding of ribosomes to mRNA b. Bonding of the anticodon to the codon c. Shape of the A and P sites of ribosomes d. Bonding of the anticodon to the codon and the attachment of amino acids to tRNAs e. Attachment of amino acids to tRNAs 6. What is the function of DNA polymerase III? a. To unwind the DNA helix during replication b. To seal together the broken ends of DNA strands c. To degrade damaged DNA molecules d. To add nucleotides to the 3’ end of a growing DNA strand e. To rejoin the two DNA strands (one new and one old) after replication 7. In an analysis of the nucleotide composition of DNA, which of the following will be found? a. A = C b. G + C = T + A c. A = G and C = T d. A + C = G + T 8. What is the function of topoisomerase? a. Relieving strain in the DNA ahead of the replication fork b. Elongating new DNA at a replication fork by adding nucleotides to the existing chain c. Unwinding of the double helix d. Stabilizing single-stranded DNA at the replication fork e. Adding methyl groups to bases of DNA 9. Which of the following does not occur in prokaryotic gene expression, but does in eukaryotic gene expression? a. RNA polymerase binds to the promoter b. A poly-A tail is added to the 3’ end of an mRNA and a cap is added to the 5’ end c. mRNA, tRNA, and rRNA are transcribed d. RNA polymerase requires a primer to elongate the molecule e. Transcription can begin as soon as translation has begun even a little 10. What is the effect of a nonsense mutation in a gene? a. It alters the reading frame of the mRNA b. It introduces a premature stop codon into the mRNA c. It has no effect on the amino acid sequence of the encoded protein d. It prevents introns from being excised e. It changes an amino acid in the encoded protein

11. In eukaryotes there are several different types of RNA polymerase. Which type is involved in transcription of mRNA for a globin protein? a. Primase b. Ligase c. RNA polymerase I d. RNA polymerase III e. RNA polymerase II 12. Which of the following statements describes proto-oncogenes? a. They are produced by somatic mutations induced by carcinogenic substances b. They are underexpressed in cancer cells c. Their normal function is to suppress tumor growth d. The are introduced to a cell initially by retroviruses e. They can code for proteins associated with cell growth 13. Cytosine makes up 42% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine? a. 42% b. 16% c. 31% d. 8% e. It cannot be determined from the information provided 14. Alternative RNA splicing a. Increases the rate of transcription b. Is a mechanism for increasing the rate of transcription c. Can allow the production of proteins of different sizes from a single mRNA d. Is due to the presence or absence of particular snRNPs e. Can allow the production of similar proteins from different RNAs 15. An Okazaki fragment has which of the following arrangements? a. Primase, polymerase, ligase b. 5’ RNA nucleotides, DNA nucleotides 3’ c. 3’ RNA nucleotides, DNA nucleotides 5’ d. DNA polymerase I, DNA polymerase III e. 5’ DNA to 3’ 16. In eukaryotes, general transcription factors a. Are required for the expression of specific protein-encoding genes b. Inhibit TNA polymerase binding to the promoter and begin transcribing c. Bind to sequences just after the start site of transcription d. Bind to other proteins or to a sequence element within the promoter called the TATA box e. Usually lead to a high level of transcription even without additional specific transcription factors 17. The tryptophan operon is a repressible operon that is a. Turned on only when glucose is present in the growth medium b. Turned on only when tryptophan is present in the growth medium c. Turned off only when glucose is present in the growth medium d. Permanently turned on e. Turned off whenever tryptophan is added to the growth medium 18. Which of the following is the first event to take place in translation in eukaryotes? a. The small subunit of the ribosome recognizes and attaches to the 5’ cap of mRNA b. Base pairing of activated methionine-tRNA to AUG of the messenger RNA c. Covalent bonding between the first two amino acids d. Elongation of the polypeptide e. Binding of the larger ribosomal subunit to smaller ribosomal subunits 19. Which of the following set of materials are required by both eukaryotes and prokaryotes for replication? a. Ligase, primers, nucleases b. Nucleosome loosening, four dNTPs, four rNTPs c. Topoisomerases, telomerases, polymerases d. Double-stranded DNA, four kinds of dNTPs, primers, origins e. G-C rich regions, polymerases, chromosome nicks

20. That lactose operon is likely to be transcribed when a. There is more glucose in the cell than lactose b. The cyclic AMP and lactose levels are both high within the cell c. There is glucose but no lactose in the cell d. The cyclic AMP levels are low e. The cAMP level is high and the lactose level is low 21. Which of the following would you expect of a eukaryote lacking telomerase? a. Production of Okazaki fragments b. A high probability of somatic cells becoming cancerous c. A reduction in chromosome length in gametes d. Inability to repair thymine dimers e. High sensitivity to sunlight 22. Two parental devices that eukaryotic cells use to regulate transcription are a. DNA amplification and histone methylation b. DNA methylation and histone amplification c. DNA acetylation and methylation d. DNA methylation and histone modification e. Histone amplification and DNA acetylation 23. In eukaryotic cells, transcription cannot begin until a. Several transcription factors have bound to the promoter b. The two DNA strands have completely separated and exposed the promoter c. DNA nucleases have isolated the transcription unit d. The 5’ caps are removed from the mRNA e. The DNA introns are removed from the template 24. Which of the following help(s) to hold the DNA strands apart while they are being replicated? a. DNA polymerase b. Exonuclease c. Primase d. Single-strand binding proteins e. Ligase 25. The functioning of enhancers is an example of a. Transcriptional control of gene expression b. A eukaryotic equivalent of prokaryotic promoter functioning c. The stimulation of translation by initiation factors d. Post-translational control that activates certain proteins e. A post-transcriptional mechanism to regulate mRNA 26. In E. coli, there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin. Which of the following would you expect as a result of this mutation? a. Replication will require a DNA template from another source b. Replication will occur via RNA polymerase alone c. The DNA will supercoil d. No proofreading will occur e. No replication fork will be formed 27. What is the function of the release factor (RF)? a. It releases the ribosome from the ER to allow polypeptides into the cytosol b. It supplies a source of energy for termination of translation c. It releases the amino acid from its tRNA to allow the amino acid to form a peptide bond d. It separates tRNA in the A site from the growing polypeptide e. It binds to the stop codon in the A site in place of a tRNA 28. Which of the following, when taken up by the cell, binds to the repressor so that the repressor no longer binds to the operator? a. Ubiquitin b. Repressor c. Inducer d. Corepressor e. Promoter

29. Which of the following statements is true about protein synthesis in prokaryotes? a. Translation requires antibiotic activity b. Prokaryotic cells have complicated mechanisms for targeting proteins to the appropriate cellular organelles c. Extensive RNA processing is required before prokaryotic transcripts can be translated d. Unlike eukaryotes, prokaryotes require no initiation or elongation factors e. Translation can begin while transcription is still in progress 30. There is a mutation in the repressor that results in a molecule known as a super-repressor because it represses the lac operon permanently. Which of these would characterize such a mutant? a. It makes a repressor that binds CAP b. It makes molecules that bind to one another c. It cannot make a functional repressor d. It cannot bind to the operator e. It cannot bind to the inducer 31. The role of a metabolite that controls a repressible operon is to a. Bind to the promoter region and decrease the affinity of RNA polymerase for the promoter b. Bind to the repressor protein and activate it c. Increase the production of inactive repressor proteins d. Bind to the repressor protein and inactivate it e. Bind to the operator region and block the attachment of RNA polymerase to the promoter 32. Transcription of the structural genes in an inducible operon a. Starts when the pathway’s product is present b. Starts when the pathway’s substrate is present c. Occurs continuously in the cell d. Does no result in the production of enzymes e. Stops when the pathway’s product is present 33. A frameshift mutation could result from a. A base insertion only b. Deletion of three consecutive bases c. Either an insertion or a deletion of a base d. A base substitution only e. A base deletion only 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.

C E A B D D D A B B E E D C B D E A D B C D

23. 24. 25. 26. 27. 28. 29. 30. 31. 32.

A D A E E C E E B B 33. C...