Exam 3 Practice Question Key PDF

Preview

Summary

BIOS practice problems that will prepare you for the exam....

Description

Bios 41

Exam 3 Practice Questions

McLaughlin

1. Which of the following statements about the proteasome is false? (a) Ubiquitin is a small protein that is covalently attached to proteins to mark them for delivery to the proteasome. (b) Proteases reside in the central cylinder of a proteasome. (c) Misfolded proteins are delivered to the proteasome, where they are sequestered from the cytoplasm and can attempt to refold. (d) The protein stoppers that surround the central cylinder of the proteasome use the energy from ATP hydrolysis to move proteins into the proteasome inner chamber. 2. Which of the following molecules is thought to have arisen first during evolution? (a) protein (b) DNA (c) RNA (d) all came to be at the same time 3. In eukaryotes, but not in prokaryotes, ribosomes find the start site of translation by ____________________________. (a) binding directly to a ribosome-binding site preceding the initiation codon. (b) scanning along the mRNA from the 5′ end. (c) recognizing an AUG codon as the start of translation. (d) binding an initiator tRNA. 4. A mutation in the tRNA for the amino acid lysine results in the anticodon sequence 5′-UAU-3′ (instead of 5′-UUU-3′). Which of the following aberrations in protein synthesis might this tRNA cause? (a) read-through of stop codons (b) substitution of lysine for isoleucine (c) substitution of lysine for tyrosine (d) substitution of lysine for phenylalanine 5. Below is the sequence from the 3′ end of an mRNA. 5′-CCGUUACCAGGCCUCAUUAUUGGUAACGGAAAAAAAAAAAAAA-3′ If you were told that this sequence contains the stop codon for the protein encoded by this mRNA, what is the anticodon on the tRNA in the P site of the ribosome when release factor binds to the A site? a) 5′-CCA-3′ b) 5′-CCG-3′ c) 5′-UGG-3′ d) 5′-UUA-3′

1

Bios 41

Exam 3 Practice Questions

McLaughlin

6. The plasma membrane serves many functions, many of which depend on the presence of specialized membrane proteins. Which of the following roles of the plasma membrane could still occur if the bilayer were lacking these proteins? (a) intercellular communication (b) selective permeability (c) cellular movement (d) import/export of molecules 7. Both glycoproteins and proteoglycans contribute to the carbohydrate layer on the surface of the cell. Which of the following is not true of glycoproteins? (a) They can be secreted into the extracellular environment. (b) They have only one transmembrane domain. (c) They have long carbohydrate chains. (d) They are recognized by lectins. 8. Membrane lipids are capable of many different types of movement. Which of these does not occur spontaneously in biological membranes? (a) switching between lipid layers (b) lateral movement (c) rotation (d) flexing of hydrocarbon chains 9. Which type of lipids are the most abundant in the plasma membrane? (a) phospholipids (b) glycolipids (c) sterols (d) triacylglycerides 10. Which of the following might decrease the transcription of only one specific gene in a bacterial cell? (a) a decrease in the amount of sigma factor (b) a decrease in the amount of RNA polymerase (c) a mutation that introduced a stop codon into the DNA that precedes the gene’s coding sequence (d) a mutation that introduced extensive sequence changes into the DNA that precedes the gene’s transcription start site Such changes would probably destroy the function of the promoter, making RNA polymerase unable to bind to it. Decreasing the amount of sigma factor or RNA polymerase [choices (a) or (b)] would affect the transcription of most of the genes in the cell, not just one specific gene. Introducing a stop codon before the coding sequence [choice (c)] would have no effect on transcription of the gene, because the transcription machinery does not recognize translational stops.

2

Bios 41

Exam 3 Practice Questions

McLaughlin

11. Which of the following statements is false? (e) A new RNA molecule can begin to be synthesized from a gene before the previous RNA molecule’s synthesis is completed. (f) If two genes are to be expressed in a cell, these two genes can be transcribed with different efficiencies. (g) RNA polymerase is responsible for both unwinding the DNA helix and catalyzing the formation of the phosphodiester bonds between nucleotides. (h) Unlike DNA, RNA uses a uracil base and a deoxyribose sugar. 12. Which of the following statements about the carbohydrate coating of the cell surface is false? (a) It is not usually found on the cytosolic side of the membrane. (b) It can play a role in cell–cell adhesion. (c) The arrangement of the oligosaccharide side chains is highly ordered, much like the peptide bonds of a polypeptide chain. (d) Specific oligosaccharides can be involved in cell–cell recognition. The sugars in an oligosaccharide side chain attached to the cell surface can be joined together in many different ways and in varied sequences. 13. Match the following types of RNA with the main polymerase that transcribes them.

A—1; B—3; C—3; D—2; E – 2

14. List three ways in which the process of eukaryotic transcription differs from the process of bacterial transcription. Any three of the following are acceptable. 1. Bacterial cells contain a single RNA polymerase, whereas eukaryotic cells have three. 2. Bacterial RNA polymerase can initiate transcription without the help of additional proteins, whereas eukaryotic RNA polymerases need general transcription factors. 3. In eukaryotic cells, transcription regulators can influence transcriptional initiation thousands of nucleotides away from the promoter, whereas bacterial regulatory sequences are very close to the promoter. 4. Eukaryotic transcription is affected by chromatin structure and nucleosomes, whereas bacteria lack nucleosomes.

3

Bios 41

Exam 3 Practice Questions

McLaughlin

15. While many prokaryotic cells have a single membrane bilayer, all eukaryotic cells have a complex system of internal membrane-bound compartments. How might it be advantageous for the cell to have these additional compartments? Compartmentalization using intracellular membranes allows eukaryotic cells to separate a variety of cell processes. Although this requires a higher degree of coordination, the cell also gains a more stringent degree of control over these processes (examples include: the separation of transcription and translation; the separation of enzymes involved in protein modifications for secreted versus cytosolic substrates; the separation of proteolytic events in the lysosomes versus the cytosol etc.).

16. Glycolipids are found on the surface of healthy cells, and contribute to the cell’s defense against chemical damage and infectious agents. A. In which organelle are sugar groups added to membrane lipids? B. By what mechanism are glycolipids transported to the plasma membrane and presented to the extracellular environment? Draw a diagram to support your answer to part B. A. The Golgi apparatus. B. Membranes that contain newly synthesized glycolipids bud from the Golgi apparatus to form vesicles. These vesicles then fuse with the plasma membrane. The glycolipids that were facing the lumen of the Golgi will now face the extracellular environment (Figure A).

Figure A 17. Cell membranes are fluid, and thus proteins can diffuse laterally within the lipid bilayer. However, sometimes the cell needs to localize proteins to a particular membrane domain. Name three mechanisms that a cell can use to restrict a protein to a particular place in the cell membrane. Any combination of the following four answers is acceptable. 1. The protein can be attached to the cell cortex inside the cell. 2. The protein can be attached to the extracellular matrix outside the cell. 3. The protein can be attached to other proteins on the surface of a different cell. 4. The protein can be restricted by a diffusion barrier, such as that set up by specialized junctional proteins at a tight junction.

4

Bios 41

Exam 3 Practice Questions

McLaughlin

18. Give three reasons why DNA makes a better material than RNA for the storage of genetic information, and explain your answer. •

• •

The deoxyribose sugar of DNA makes the molecule much less susceptible than RNA to breakage, because of the lack of the hydroxyl group on carbon 2 of the ribose sugar. DNA is double-stranded and therefore the complementary strand provides a template from which damage can be repaired accurately. The use of “T” in DNA instead of “U” (as in RNA) protects against the effect of deamination, a common form of damage. Deamination of T produces an aberrant base (methyl C), whereas deamination of U generates C, a normal base. The presence of an abnormal base eases the cell’s job of recognizing the damaged strand.

19. One strand of a section of DNA isolated from the bacterium E. coli reads: 5′-GTAGCCTACCCATAGG-3′ A. Suppose that an mRNA is transcribed from this DNA using the complementary strand as a template. What will be the sequence of the mRNA in this region (make sure you label the 5′ and 3′ ends of the mRNA)? B. How many different peptides could potentially be made from this sequence of RNA, assuming that translation initiates upstream of this sequence? C. What are these peptides? (Use a codon table and give your answer using the one-letter amino acid code.) A. 5′-GUAGCCUACCCAUAGG-3′ B. Two. (There are three potential reading frames for each RNA. In this case, they are GUA GCC UAC CCA UAG … UAG CCU ACC CAU AGG … AGC CUA CCC AUA GG? … The center one cannot be used in this case, because UAG is a stop codon.) C. VAYP SLPIG Note: PTHR will not be a peptide because it is preceded by a stop codon.

5...