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Biology 1101 – Midterm 2 – Fall 2023 Your signature below certifies that you have complied with the Code of Academic Integrity of the University of Pennsylvania in taking this exam. This code will be strictly enforced! Signature___________________________________________________________ Your Name (print ): __________________________________________________ EXAM VERSION: __C____ • DO NOT OPEN YOUR EXAM UNTIL YOU ARE TOLD TO DO SO. • This is a closed book exam. You will have 90 minutes to complete the exam. • Make sure you have a complete exam: 40 questions, 10 pages. • Please be sure to budget your time so that you can complete the entire exam. • This is a multiple choice exam. For multiple choice questions you should choose the SINGLE BEST answer. If you think that there is an error in the formatting of the test, please alert a proctor. However, please note that proctors will not answer questions about the wording or content of test questions.

1. During the fight or flight response, some cells respond to adrenaline by converting glycogen to glucose. This conversion of glycogen to glucose is an example of: A. monomers being linked together to form polymers B. polymers being broken down into monomers C. conversion of linear polymers into branched polymers 2. Adrenaline (epinephrine) is a: A. G protein coupled receptor B. steroid hormone C. polar small molecule D. growth factor peptide 3. G protein coupled receptors are attractive targets for new drugs because: A. receptor dimerization is easy to block using small molecules B. ligands interact with GPCRs at the outer edge of the receptor away from the membrane C. GPCR binding to adenylyl cyclase is sensitive to slight changes in ligand binding D. The interface of interaction with ligands is large and can be blocked by small molecules 4. Which of the following is NOT TRUE regarding the heterotrimeric G proteins involved in adrenaline signaling? A. They are associated with the intracellular side of the adrenaline receptor B. They have three subunits – alpha, beta, and gamma C. They are inactive in the GDP-bound form D. The alpha subunit can directly phosphorylate cyclic AMP 5. Adenylyl cyclases are typically activated by: A. Cyclic AMP binding B. A subunit of a heterotrimeric G protein C. GTP hydrolysis in the G protein α-subunit D. A negative feedback loop 6. The signaling molecule ACTH is released by the pituitary gland in the brain and binds to receptors on the surface of cells in the adrenal gland (near the kidneys). This is an example of: A. autocrine signaling B. signaling through gap junctions C. paracrine signaling D. endocrine signaling

7. Chemical signaling across neuronal synapses is an example of: A. Autocrine signaling B. Paracrine signaling C. Endocrine signaling D. Plasmodesmata signaling 8. Fill in the blanks using the appropriate sequence of words: Polar signaling molecules like ______ bind to receptors ______ the cell, while nonpolar signaling molecules like ______ bind to receptors ______ the cell. A. steroid hormones; on the surface of; adrenaline; inside B. steroid hormones; inside; adrenaline; on the surface of C. adrenaline; on the surface of; steroid hormones; inside D. adrenaline; inside; steroid hormones; on the surface of 9. Direct transmission of a chemical signal from outside of a cell to inside of a cell typically involves (choose the broadest answer) A. activation of a protein kinase B. diffusion of a second messenger to activate proteins C. a conformational change in a protein D. changing the expression of a gene in the nucleus 10. When the signaling molecule 5-HT binds to the G-protein coupled receptor 5-HT4, the concentration of cAMP increases inside the cell. What is the most likely explanation for this increase in cAMP? A. The 5-HT4 receptor forms a dimer, leading to activation of Ras B. A G protein is activated, leading to activation of adenylyl cyclase C. 5-HT triggers movement of cAMP from smooth ER into the cytoplasm. 11. The chemical reactions shown below are coupled. Which is TRUE about these reactions? Glucose + fructose --> sucrose ΔG = +27 kJ/mol ATP + H 2 O --> ADP + P i ΔG = -30 kJ/mol A. Energy is released from the breakdown of ATP and used in the synthesis of sucrose. B. Energy is released from the breakdown of sucrose and used in the synthesis of ATP. C. The top reaction is spontaneous D. The top reaction is exergonic 12. The conversion of glycogen into glucose in the liver is most likely:

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A. Endergonic since it involves a dehydration reaction B. Endergonic because bonds between sugars are broken C. Exergonic as there is a large increase in overall entropy D. Exergonic because this reaction is anabolic (sugar producing) 13. Chemical reactions that result in increases in entropy have a free energy change that is negative. A. Generally true B. Generally false C. Unclear from information given Credit was given for any answer. For your information, if you are interested, free energy changes are influenced by two independent variables, changes in enthalpy and changes in entropy. It is unclear how the overall free energy will change in a reaction without information about both. 14. Which is TRUE about the activity of the enzyme DNA polymerase during DNA replication? A. It catalyzes the formation of phosphodiester bonds B. It can add nucleotides to both ends (5’ and 3’) of the growing nucleic acid C. It unwinds the double helix to make room for replication 15. Osteocytes are a type of fully differentiated bone cell that are permanently in G zero (G 0 ) phase. This means that these cells: A. are about to undergo apoptosis B. are constantly dividing C. can't re-enter the cell cycle D. must contain damaged DNA 16. The Ras G12C mutation A. Can’t bind to GTP as efficiently as non-mutated Ras B. Can’t hydrolyze GTP to GDP as efficiently as non-mutated Ras C. Can’t activate Raf as efficiently as non-mutated Ras D. Is a poor drug target for Ras-based cancers 17. Which best describes the relationship between Ras/MAPK signaling and cyclin gene expression? A. Ras functions as a transcription factor by binding to the promoter of a cyclin gene B. The expression of cyclin causes activation of the Ras/MAPK signaling pathway

C. Cyclin gene expression occurs after phosphorylated Erk enters the nucleus D. Cyclin phosphorylates Erk, which causes Erk to enter the nucleus 18. Which of the following would most likely lead to tumor formation? A. An RTK that can perform cross-phosphorylation in the absence of a ligand B. A Ras protein that is “stuck” in the GDP-bound state C. A Raf protein which has lost its ability to act as a kinase D. A mutation that causes the tumor suppressor p53 to be overactive 19. Cyclin E activity is important for progression from G1 to S phase of the cell cycle. Based on your knowledge of cyclins, what is the likely mechanism used by cyclin to push cells into S phase? A. Cyclin E phosphorylates a CDK, which acts as a transcription factor B. Cyclin E monitors for DNA damage and triggers apoptosis if damage is detected C. Cyclin E binds to a CDK, which phosphorylates proteins needed for DNA replication 20. The results of an experiment involving an Rb knockout mouse (in which no Rb protein is produced) is shown below. Based on the graph, what can you conclude? A. Mean tumor size is larger in mice with Rb, so Rb is required to promote cell division B. Mean tumor size is larger in mice without Rb, so Rb is required to promote cell division C. Mean tumor size is larger in mice with Rb, so Rb is required to inhibit cell division D. Mean tumor size is larger in mice without Rb, so Rb is required to inhibit cell division 21. If a significant portion of chromosome 14 is not successfully copied during DNA replication, at which checkpoint is a dividing cell most likely to arrest? A. G1/S checkpoint B. G2/M checkpoint C. M checkpoint D. None – the cell is unlikely to arrest

22. A DNA replication fork is shown below. If we assume helicase is moving left to right to open the double helix, which statement is TRUE about new DNA synthesis along the TOP strand? A. It proceeds to the left and is continuous. B. It proceeds to the right and is continuous. C. It proceeds to the left and is discontinuous. D. It proceeds to the right and is discontinuous. 23. During mitosis, attachment of the mitotic spindle to kinetochores occurs primarily in: A. telophase B. anaphase C. metaphase D. prometaphase E. prophase 24. An oncogene called “myc” is a major contributor to tumor formation in humans. What is likely TRUE about the myc oncogene? A. The myc oncogene acts as a tumor suppressor. B. The myc proto-oncogene acts as a tumor suppressor. C. The myc oncogene has a mutation that makes the protein non-functional. D. The myc proto-oncogene acts as a positive regulator of the cell cycle. 25. PDGF is a growth factor that acts as a ligand for a receptor tyrosine kinase. Which of the following is likely NOT TRUE about PDGF? A. PDGF causes its receptor to form a dimer. B. PDGF binding leads to cross phosphorylation of its receptor. C. PDGF activates a heterotrimeric G protein. D. PDGF activates the MAPK signaling pathway.

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26. Here is a reaction discussed briefly in class: In this reaction, the negative ΔG is expressed as A. Enthalpy changes from substrates to products and entropy changes to surrounding molecules. B. Entropy changes from substrates to products and enthalpy changes to surrounding molecules. C. Entropy changes from substrates to products and little to no changes to surrounding molecules. Credit was given for any answer. For your information, if you are interested, because the chemical bonds but not the number of molecules change in this reaction, there will be enthalpy changes but likely little entropy changes to the reactants, and the heat released from the reaction will lead to an increase in the thermal motion of surrounding molecules (an increase in enthalpy). 27. Enzymes can couple reactions, which makes endergonic reactions possible. Which of the following IS NOT considered an endergonic reaction? A. Synthesis of fatty acids from two-carbon building blocks B. ATP synthesis from ADP and phosphate C. Breaking a phosphodiester bond in cAMP to form AMP D. Phosphorylation of the β-adrenergic receptor by a kinase (“BARK”) 28. A strictly competitive enzyme inhibitor such as the Raf kinase inhibitor Venurafinab binds to: A. the kinase active site B. an allosteric site on the kinase C. likely both the active site and an allosteric site 29. Which is typically NOT a characteristic of the transition state complex between an enzyme and its substrate(s)?

A. Multiple non-covalent bonds between the enzyme and the substrate B. The substrate(s) very closely interacting with the enzyme active site C. Shape changes in both the enzyme active site and the substrate(s) D. A set of stable interactions during this phase of the chemical reaction 30. A molecule of ATP is shown below. Which statement accurately describes the chemical structure of ATP? A. Three phosphate groups, a pentose sugar, and a purine B. Three phosphate groups, a hexose sugar, and purine C. Three phosphate groups, a deoxyribose sugar, and a pyrimidine D. Three phosphate groups, a ribose sugar, and a pyrimidine 31. One important function of a typical mesenchymal cell is that it can synthesize and secrete extracellular matrix components. A. Generally true B. Generally false C. Unclear from the information given Credit was given for any answer. For your information, if you are interested, a major function of mesenchymal cells (fibroblasts and the pericytes that surround blood vessels) is that they synthesize and secrete extracellular matrix components. 32. When glucose is taken up from digested food in your gut and then moved into the bloodstream, the order of glucose movement spatially is through: A. basal lamina, epithelial cell, stroma, blood vessels B. basal lamina, stroma, epithelial cell, blood vessels C. epithelial cell, basal lamina, stroma, blood vessels D. stroma, epithelial cell, basal lamina, blood vessels 33. Skin cells (epidermal cells) are particularly rich in intermediate filaments because it is especially important that the skin cell cytoskeleton is:

A. Easily remodeled to heal wounds B. Capable of an epithelial to mesenchymal transition C. Highly resistant to tearing and shear forces D. Capable of rapid transition into the cell cycle 34. A set of actin filaments are tightly linked to cadherins through a complex of proteins to: A. Maintain a strong connection to the extracellular matrix B. Enable strong physical attachment to other cells C. Allow direct and rapid cell signaling D. Transiently hold onto extracellular matrix during cell movement 35. In recitation, we discussed a recent paper examining epithelial to mesenchymal transition in a mouse model of breast cancer cells. Data from that recitation problem is shown below. Recall that E-cadherin is expressed in epithelial cells. Based on these data, what can you conclude? A. SnailLO cells express E-cadherin, so they are epithelial B. SnailLO cells express Twist, so they are mesenchymal C. SnailLO cells express vimentin, so they are mesenchymal D. SnailLO cells do not express E cadherin, so they are mesenchymal 36. Which best describes the relationship between cAMP and PKA in adrenaline signaling? A. PKA phosphorylates and activates cAMP B. cAMP is a kinase that phosphorylates PKA C. cAMP triggers release of PKA from smooth ER into the cytoplasm D. cAMP binds to the regulatory subunits of PKA 37. Which of the following is LEAST LIKELY to terminate/turn off an intracellular signaling pathway? A. phosphodiesterase activity

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B. hydrolysis of GTP to GDP by a G protein C. removal of phosphates by phosphatases D. increase in cytoplasmic calcium concentration 38. Plasmodesmata are similar to gap junctions in that they both: A. form a tight seal between epithelial cells B. are considered part of the basal lamina C. connect the cytoplasm of two adjacent cells 39. One aspect of current thinking about cancer is that primary tumors are a type of “delinquent organ”. Why might primary tumors that develop initially from epithelial cells be considered organs? Because: A. the cancer cells themselves are different from one another even though they come from a single mutated cell. B. the stroma of primary tumors includes white blood cells and fibroblasts that favor tumor proliferation and survival. C. the cancer cells can eventually migrate to distant parts of the body to form metastases so they are not considered a tissue. Credit was given for any answer. For your information, if you are interested, this is a basic tenet of cancer biology- that a tumor is not just composed of the tumor cells but also of other types of tissue that are recruited or repurposed by signaling from the tumor cells. The mixture of these different cell types resembles a normal organ, and some of the signaling that leads to a full blown primary tumor likely originates in normal organogenesis. 40. Tumors in breasts can be first detected because they feel firm (like lumps). This firmness is because of a modified form of the extracellular matrix. The extracellular molecule most likely to be directly responsible for the increased firmness is: A. collagen B. keratin C. actin D. tubulin

key VC BIOL1101 F23 MT2

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