Alexandria University Medical Research Institute Semester: fall Biochemistry Department Academic year: 2019 – 2020 PhD Degree Time allowed: 2 hours Course title: Biochemistry Date: 31 / 12/ 2019 Course code: 1701801 Total marks: 60 Final exam Model answer ______________________________________________________________________________ All questions are to be answered Question I: (30 Marks) A. Multiple Choice Questions (25 Marks, 0.5 mark each) Encircle the correct answer: 1- Receptor-mediated endocytosis is carried out by specific proteins complex of the membrane. They are termed as: a- Membrane Globules. b- Coated vesicles. c- Coated pits. d- Carrier proteins. 2- A membrane- bound enzyme that catalyzes the formation of cAMP from ATP is: a- Adenyl cyclase. b- MAP cyclase. c- Kinase cyclase. d- ATP phosporelase. 3- Which of the following statement is true for the gab junctions? a- Made up of two subunits of connexons. b- Movement of gases takes place freely. c- It is made of connexin protein. d- Allows free movement of large molecules across cells. 4- Pore- like connections between adjacent cells is an example of a- Gap junction. b- Desmosomes. c- Tight junction. d- Cell junction. Page 1 of 18 5- Desmosomes is composed of a- Fibers. b- Soft tissue. c- Hard tissue. d- Bones. 6- Junction that prevents two cell compartments from mixing is a- Gap junction. b- Desmosomes. c- Tight junction. d- Cell junction. 7- Gap junction allows exchange of a- Solutions. b- Solutes. c- Solvent. d- Water only. 8- Adherens junctions are specialized cell junctions that form by linking the …………to transmembrane proteins known as …………….. a- Microtubule cytoskeleton; integrins. b- Microtubule cytoskeleton; cadherins. c- Actin cytoskeleton; cadherins. d- Intermediate filament cytoskeleton; integrins. 9- Which of the following statements is NOT TRUE about gap junctions? a- Gap junctions have some functionality of permitting cells to adhere to one another. b- Gap junctions form channels that are comprised of connexin proteins. c- Gap junctions permit the travel of small molecules back and forth between adjacent cells. d- Gap junctions prevent molecules and ions from traveling between cells in the extracellular space. 10- Which of the following proteins forms channels that permit electrical communication between cells across gap junctions? a- Connexin. b- Cadherin. c- Tubulin. d- Ephrin. Page 2 of 18 11- What are the two major proteins that comprise tight junctions? a- Claudins and adherins. b- Occludins and connexins. c- Claudins and occludins. d- Claudins and protocadherins. 12- What is the main purpose of gap junctions? a- Prevents cells from separating from one another. b- Allows large molecules to move between cells. c- Prevents water from moving between cells. d- Allows molecules and ions to travel between cells. 13- Which cellular junction will be most useful in preventing the movement of material between cell membranes? a- Hemidesmosomes. b- Desmosomes. c- Gap junctions. d- Tight junctions. 14- Depolarization: a- Is associated with increase in membrane permeability to Na+. b- Is terminated with closure of voltage activated K+ channels. c- Is followed by muscle relaxation. d- Is caused by K+ efflux. 15- Action potential: a- Is a graded potential. b- Is produced by sub threshold stimulus. c- Starts with repolarization caused by outward movement of Cl-. d- Is conducted slower in thin nerve fibers. 16- Myelin sheath: a- Present in the myelinated and unmyelinated nerve fibers. b- Formed of lipoprotein complex and acts as electric insulator. c- It is formed of successive wrappings of the membrane of Schwann cells. d- It is the cause of decreased conduction of nerve impulse. Page 3 of 18 17- During depolarization: a- Voltage activated Na+ channels open. b- The membrane becomes impermeable to Na+. c- When membrane potential reaches -55 m.v Na+ and K+ fluxes occur at the same time. d- K+ ions diffuse outside. 18- The resting membrane potential is caused by: a- Diffusion of K+ ions outside the nerve fibers. b- Diffusion of Na+ ions inside the nerve fibers. c- Opening of the chemically activated ion channels. d- Opening of the voltage activated ion channels. 19- Repolarization: a- Occurs at first gradual then becomes fast. b- Results from closure of sodium gates and opening of potassium gates. c- Is represented by the ascending limb of the spike. d- Is followed by appearance of response. 20- Saltatory conduction: a- Occurs in myelinated nerve fibers. b- Occurs by jumping of charges from one node of Ranvier to another. c- Is relatively slow 0.5-2.0 meter / second. d- Occurs in the neuro-muscular junction. 21- ………. send signals away from neurons whereas …….. receive signals from other neurons. a- Axons; synapses b- Synapses; dendrites c- Axons; dendrites d- Dendrites; axons Page 4 of 18 22- The point at which the terminal button and another neuron communicate is called ……; communication here is made possible by the release of …………….. a- Synapse; hormones. b- Presynaptic membrane; neurotransmitters. c- Axon hillock; hormones. d- Synapse; neurotransmitters. 23- When the charge across the membrane of a neuron is about …….., the charge is called the ……... This is because there are ……….... a- 60-70 mV; action potential; more negative ions inside the cell. b- 70-100 mV; action potential; more positive ions inside the cell. c- 60-70mV; resting potential; more positive ions inside the cell. d- 60-70mV; resting potential; more negative ions inside the cell. 24- If sodium continues to enter a cell ……... This is called …………... a- The intracellular charge reverses from positive to negative; Repolarization. b- The intracellular charge reverses from positive to negative; Hyperpolarization. c- The intracellular charge reverses from positive to negative; Depolarization. d- The intracellular charge reverses from negative to positive; Hyperpolarisation. 25- If the stimulation of a cell is strong, the strength of the action potential produced would be: a- Stronger than that produced by weak stimulation. b- No different to that produced by weak stimulation. c- Weaker than that produced by weak stimulation. d- Twice that produced by weak stimulation. 26- When depolarisation occurs …………; this allows the release of ……….. into the …………….... a- Potassium channels open; neurotransmitters; synaptic gap. b- Calcium channels open; neurotransmitters; synaptic gap. c- Sodium channels open; neurotransmitters; synaptic gap. d- Calcium channels open; dopamine; cell body. Page 5 of 18 27- In a signal transduction where the trimeric G protein with α, ß and γ is involved. Which subuit of the protein will activate the adenylate cyclase enzyme? a- Gamma subunit. b- Beta subunit. c- Alpha subunit. d- All three. 28- Continuous conduction: a- Occurs in myelinated nerve fibers. b- Occurs by jumping of charges from one node of Ranvier to another. c- Is relatively slow 0.5-2.0 meter / second. d- Occurs in the neuro-muscular junction. 29- Saltatory conduction: a- Occurs in unmyelinated nerve fibers. b- May reach up to 120 meter / second. c- Occurs by jumping from one neuron to another. d- Decreases gradually with distance till it disappears. 30- In all or non rule: a- A minimal stimulus produces a maximal response. b- The response in a single nerve fiber increases with increase intensity of stimulus. c- The nerve trunk either respond maximally or not respond at all. d- Minimal stimulus produces minimal response. 31- About growth factors, all the following are correct EXCEPT: a- They are polypeptides. b- All growth factors are specific for a particular cell type. c- They function as growth stimulators. d- They function as growth inhibitor. Page 6 of 18 32- Bone homeostasis requires: a- T GF-b and bone morphogenic protein. b- T GF-a and bone morphogenic protein. c- TNF-a. d- Fibroblast growth factors. 33- Immune system is almost paralyzed if: a- Interferons are absent. b- Absence of VEGF. c- T cells are inactivated by AIDS virus. d- B cells growth and differentiation is inactive by AIDS virus. 34- An important cytokine that resists viral replication is: a- Insulin like growth factor. b- Epidermal growth factor. c- Interferon–α. d- Vascular endothelial growth factor. 35- Growth factors induce cellular functions EXCEPT: a- Growth and Survival. b- Differentiation. c- Death. d- Calcium homeostasis. 36- The JAK-STAT system consists of : a- A receptor b- Janus kinase c- Signal transducer and activator of transcription. d- All of the above. 37- For a 70-Kg man, in which one of the periods listed below do ketone bodies supply the major portion of the caloric needs of brain? a- Absorptive state. b- Overnight fast. c- Three-week fast. d- Four-day fast. Page 7 of 18 38- Enzymic changes in the absorptive state include: a- Allosteric effectors. b- Covalent modification. c- Induction and repression of enzyme synthesis. d- All of the above. 39- Input from several signaling pathways of growth factors at one time: a- May affect the concentration of common second messenger. b- Enhance the activity of the cell. c- Cause the changes in second messenger to be misinterpreted. d- All of the above. 40- Growth factor that act in a paracrine manner: a- Affect behavior of distant cells. b- Affect behavior of cells that release the growth factors. c- Affect behavior of adjacent cells. d- None of the above. 41- Regarding tumor cells: a- The receptor is activated in absence of a growth factor . b- Secrete growth factors. c- Overexpress its receptors. d- All of the above. 42- ……….. are secreted by target cells and binds to special receptors located on neurons that synapse with target cells: a- Nerve growth factor. b- Vascular endothelial growth factor. c- Fibroblast growth factor. d- Angiogenin. 43- One group of group factors that foster the multiplication and/or development of various types of cells includes: a- Nerve growth factor. b- Insulin like growth factor. c- Epidermal growth factor. d- All of the above. Page 8 of 18 44- Growth factor receptor is an example of which type of receptors? a- G-protein coupled receptor.