Concours Commun d'Accès aux Facultés de Médecine, Pharmacie et Dentaire (Maroc)

During anaerobic glycolysis in human skeletal muscle cells, what is the net yield of ATP and reduced coenzyme per molecule of glucose consumed?

• A2 ATP and 0 net NADH,H+ (as NADH is reoxidized to NAD+ during lactate fermentation)
• B2 ATP and 2 NADH,H+
• C4 ATP and 2 NADH,H+
• D36 ATP and 10 NADH,H+

Where does the Krebs cycle (citric acid cycle) take place in eukaryotic cells?

• AMitochondrial matrix
• BMitochondrial intermembrane space
• CInner mitochondrial membrane
• DCytosol

During mitochondrial oxidative phosphorylation, what directly drives the synthesis of ATP by ATP synthase (Complex V)?

• AThe proton-motive force created by the H+ gradient across the inner mitochondrial membrane
• BThe direct transfer of high-energy phosphate from NADH to ADP
• CThe active transport of sodium ions across the outer mitochondrial membrane
• DThe direct oxidation of pyruvate by molecular oxygen

What is the theoretical ATP yield from the complete aerobic oxidation of one molecule of acetyl-CoA through one turn of the Krebs cycle and oxidative phosphorylation (assuming 2.5 ATP per NADH and 1.5 ATP per FADH2)?

• A10 ATP
• B12 ATP
• C15 ATP
• D24 ATP

In a skeletal muscle sarcomere during active isotonic contraction, which of the following bands or zones narrows and can completely disappear?

• AThe I-band and the H-zone
• BThe A-band only
• CThe A-band and the M-line
• DThe Z-discs only

What is the precise biochemical role of ATP binding (prior to hydrolysis) in the cross-bridge cycle of skeletal muscle?

• AIt causes the dissociation of the myosin head from the actin binding site
• BIt triggers the power stroke that moves the thin filament
• CIt induces calcium release from the sarcoplasmic reticulum
• DIt causes the phosphorylation of troponin C

During the first 2 to 5 seconds of maximum sprint effort, which immediate metabolic pathway regenerates cytosolic ATP most rapidly in skeletal muscle?

• APhosphocreatine breakdown catalyzed by creatine kinase
• BAerobic oxidation of free fatty acids in mitochondria
• CGlycogenolysis coupled to lactic acid fermentation
• DMyokinase-catalyzed synthesis from two molecules of ADP

In the regulation of muscle contraction, binding of Ca2+ to troponin C directly causes which structural modification?

• ADisplacement of tropomyosin away from the myosin-binding sites on actin monomers
• BPhosphorylation of the regulatory light chain of actin
• CCleavage of titin filament connections to the Z-disc
• DConformational change of the myosin tail into a coiled-coil structure

Meselson and Stahl grew Escherichia coli in 15N-labeled media, then transferred them to 14N media. What did the DNA density gradient centrifugation show after exactly ONE generation in 14N?

• AA single hybrid band of intermediate density (15N-14N)
• BTwo distinct bands: one heavy (15N-15N) and one light (14N-14N)
• CA single light band (14N-14N) only
• DThree bands: heavy, intermediate, and light in equal proportions

A segment of a DNA coding (non-template, sense) strand has the sequence 5'-ATG-GCA-TAC-TGA-3'. What is the corresponding mature mRNA sequence transcribed from this gene region?

• A5'-AUG-GCA-UAC-UGA-3'
• B5'-UAC-CGU-AUG-ACU-3'
• C5'-UCA-GUA-UGC-CAU-3'
• D5'-AGU-CAU-ACG-CCA-3'

A single nucleotide substitution in the coding region of a gene alters a codon from 5'-GAG-3' (glutamic acid) to 5'-AAG-3' (lysine). What type of mutation is this?

• AMissense mutation
• BNonsense mutation
• CSilent mutation
• DFrameshift mutation

During eukaryotic mRNA processing, what is the composition of the 5' cap and 3' tail added to the pre-mRNA transcript?

• AA 7-methylguanosine cap attached via a 5'-to-5' triphosphate bridge and a polyadenylate (…
• BA polyadenylate cap at the 5' end and a 7-methylguanosine tail at the 3' end
• CA triphosphate adenine cap and a cytosine-rich hairpin tail
• DA methylated deoxythymidine cap and an intron-stabilizing histone tail

In a dihybrid test cross (AaBb x aabb) involving two genes located on the same autosome, the testcross progeny show: 42% AB phenotype, 42% ab phenotype, 8% Ab phenotype, and 8% aB phenotype. What is the genetic distance between genes A and B?

• A16 cM (centimorgans)
• B8 cM
• C42 cM
• D84 cM

A couple who are both phenotypically unaffected have a first child affected by cystic fibrosis (an autosomal recessive condition). What is the probability that their second child will be a phenotypically normal carrier of the mutant allele?

• A1/2 (50%)
• B1/4 (25%)
• C3/4 (75%)
• D2/3 (66.7%)

A man with red-green color blindness (an X-linked recessive condition) marries a woman with normal vision whose father was color-blind. What is the probability that their first son will be color-blind?

• A1/2 (50%)
• B1/4 (25%)
• C1 (100%)
• D0 (0%)

Which of the following karyotype abnormalities causes Klinefelter syndrome in humans?

• A47,XXY
• B45,X0
• C47,XY,+21
• D47,XYY

Which human cell surface molecule presents endogenous viral peptide antigens to CD8+ cytotoxic T lymphocytes?

• AMajor Histocompatibility Complex class I (MHC-I / HLA-A, B, C)
• BMajor Histocompatibility Complex class II (MHC-II / HLA-DP, DQ, DR)
• CCD4 co-receptor molecule
• DToll-like receptor 4 (TLR4)

Which immunoglobulin isotype is the primary antibody secreted in external bodily fluids (saliva, tears, colostrum, and gastrointestinal mucus) to provide mucosal immunity?

• ADimeric IgA
• BPentameric IgM
• CMonomeric IgG
• DMonomeric IgE

Which cellular mechanism accounts for the cytotoxic destruction of virus-infected host cells by activated CD8+ cytotoxic T lymphocytes (CTLs)?

• ASecretion of perforin and granzymes, and activation of Fas/FasL-mediated apoptosis
• BOpsonization and phagocytosis by the CTL itself
• CDirect endocytosis of the intact target cell into a phagolysosome
• DSynthesis and massive secretion of neutral polysaccharide capsules

What is the primary target cell of Human Immunodeficiency Virus (HIV), and which viral surface glycoprotein binds to the host CD4 receptor?

• ACD4+ T helper lymphocytes; glycoprotein gp120
• BCD8+ cytotoxic T lymphocytes; glycoprotein gp41
• CErythrocytes; glycoprotein reverse transcriptase
• DB lymphocytes; glycoprotein CD28

During an immediate (Type I) hypersensitivity reaction (allergic response), which antibody class and effector cells are responsible for the sudden release of histamine?

• AIgE antibodies bound to high-affinity Fc-epsilon receptors on mast cells and basophils
• BIgG antibodies activating the classical complement pathway on eosinophils
• CIgM antibodies bound to cytotoxic T cells
• DIgA antibodies binding directly to smooth muscle muscarinic receptors

During the depolarization phase of a neuronal action potential, which ion channels open, and what direction do the ions move?

• AVoltage-gated Na+ channels open; Na+ flows into the cell down its electrochemical gradient
• BVoltage-gated K+ channels open; K+ flows into the cell
• CVoltage-gated Na+ channels open; Na+ is pumped out of the cell against its gradient
• DLigand-gated Cl- channels open; Cl- flows out of the cell

What is the primary cellular mechanism underlying the absolute refractory period in unmyelinated axons?

• AInactivation of voltage-gated Na+ channels by the closure of their intracellular inactiva…
• BComplete exhaustion of intracellular ATP required by the Na+/K+-ATPase pump
• CExcessive hyperpolarization caused by sustained Ca2+ influx
• DPhysical dissociation of myelin sheaths from axonal internodes

At the vertebrate neuromuscular junction, which event directly couples presynaptic action potential arrival to acetylcholine (ACh) vesicle exocytosis?

• AInflux of extracellular Ca2+ through presynaptic voltage-gated calcium channels
• BEfflux of K+ through presynaptic voltage-gated potassium channels
• CActive retrograde transport of choline from the synaptic cleft
• DDirect electrical coupling via presynaptic connexon gap junctions

Why does action potential propagation in myelinated axons (saltatory conduction) occur significantly faster and with greater metabolic efficiency than continuous conduction in unmyelinated axons?

• AMyelin increases membrane resistance and decreases capacitance, confining ionic currents…
• BMyelin contains active ATP-driven peristaltic pumps that physically squeeze the axoplasm…
• CVoltage-gated Na+ channels are uniformly distributed at extremely high density beneath th…
• DThe axial intracellular resistance of axoplasm is eliminated by the lipid bilayer

A progressive sinusoidal wave propagates along a taut rope at a speed v = 10 m/s with a frequency f = 50 Hz. What is the wavelength lambda, and what is the phase difference between two points on the rope separated by a distance d = 45 cm?

• Alambda = 20 cm; phase difference Delta phi = 4.5*pi rad (in phase quadrature)
• Blambda = 500 cm; phase difference Delta phi = 0.9*pi rad
• Clambda = 5.0 cm; phase difference Delta phi = 18*pi rad
• Dlambda = 20 cm; phase difference Delta phi = 2.25*pi rad

Straight sinusoidal water waves with wavelength lambda = 2.5 cm encounter a barrier with an aperture of width a = 2.0 cm. Which phenomenon is observed, and how does the wavelength of the waves beyond the barrier compare to the incident wavelength?

• ADiffraction occurs because a <= lambda; the wavelength beyond the barrier remains unchang…
• BRefraction occurs because a <= lambda; the wavelength decreases to 2.0 cm
• CDiffraction occurs; the wavelength beyond the barrier doubles to 5.0 cm
• DTotal reflection occurs because the aperture is narrower than the wavelength

What is the physical definition of a dispersive medium for mechanical or electromagnetic wave propagation?

• AA medium in which the wave propagation velocity depends on the wave frequency
• BA medium in which the wave amplitude increases exponentially with distance traveled
• CA medium in which mechanical waves can propagate without any energy dissipation
• DA medium in which longitudinal waves are converted entirely into transverse waves

In a medical diagnostic ultrasound scan, an ultrasonic pulse travels through human soft tissue at a speed v = 1540 m/s. An echo reflected from an organ boundary is detected Delta t = 40 microseconds after emission. At what depth is this organ boundary located?

• A30.8 mm (3.08 cm)
• B61.6 mm (6.16 cm)
• C15.4 mm (1.54 cm)
• D77.0 mm (7.70 cm)

Carbon-14 has a radioactive half-life T = 5,730 years. An archaeological wood sample exhibits a measured activity equal to 25% of the activity found in living wood today. What is the estimated age of the archaeological sample?

• A11,460 years
• B5,730 years
• C17,190 years
• D22,920 years

A radiopharmaceutical vial contains Iodine-131 (half-life T = 8.0 days) with an initial activity of 800 MBq. What will be the residual activity of the source after 24.0 days?

• A100 MBq
• B200 MBq
• C50 MBq
• D267 MBq

Phosphorus-30 (15 protons, mass number 30) undergoes beta-plus (beta+) decay. Applying Soddy's conservation laws, what are the identity of the daughter nucleus and the emitted particles?

• ASilicon-30 (Z=14, A=30), an emitted positron (e+), and an electron neutrino (nu_e)
• BSulfur-30 (Z=16, A=30), an emitted electron (e-), and an electron antineutrino
• CSilicon-29 (Z=14, A=29), an emitted proton, and a gamma photon
• DAluminum-26 (Z=13, A=26), an emitted alpha particle, and a neutrino

A Helium-4 nucleus has a mass of 4.00150 u. Given proton mass m_p = 1.00728 u, neutron mass m_n = 1.00866 u, and 1 u = 931.5 MeV/c^2, what is the binding energy per nucleon of the Helium-4 nucleus?

• A7.07 MeV/nucleon
• B28.30 MeV/nucleon
• C14.15 MeV/nucleon
• D8.52 MeV/nucleon

Consider the induced nuclear fission reaction: 235_92 U + 1_0 n -> 140_54 Xe + 94_38 Sr + k * 1_0 n. What is the integer value of k (the number of neutrons released)?

• A2
• B1
• C3
• D4

A radioactive sample contains N0 = 5.0 * 10^12 nuclei of an isotope with a radioactive half-life T = 69.3 seconds (take ln 2 ≈ 0.693). What is the initial radioactive activity A0 of the sample?

• A5.0 * 10^10 Bq (50 GBq)
• B5.0 * 10^12 Bq (5 TBq)
• C3.46 * 10^11 Bq (346 GBq)
• D7.21 * 10^9 Bq (7.21 GBq)

An RC series circuit consists of a resistor R = 200 kOhm and an initially uncharged capacitor C = 5.0 microFarad connected across an ideal DC voltage generator of electromotive force E = 12 V. What is the time constant tau of the circuit, and what is the capacitor voltage u_C at t = tau (taking 1 - e^-1 ≈ 0.632)?

• Atau = 1.0 s; u_C(tau) ≈ 7.58 V
• Btau = 1000 s; u_C(tau) ≈ 12.0 V
• Ctau = 0.025 s; u_C(tau) ≈ 4.42 V
• Dtau = 1.0 s; u_C(tau) ≈ 4.42 V

A capacitor with capacitance C = 40 microFarad is connected across a potential difference U = 100 V. What is the electrostatic energy stored in the electric field of the capacitor?

• A0.20 J (200 mJ)
• B0.40 J (400 mJ)
• C4.0 * 10^-3 J (4 mJ)
• D2.0 J

During the discharge of a capacitor C through an ohmic resistor R, what is the differential equation governing the capacitor voltage u_C(t), with orientation such that i(t) = C * du_C/dt?

• AR*C * (du_C / dt) + u_C = 0
• BR*C * (du_C / dt) - u_C = 0
• C(du_C / dt) + R*C * u_C = 0
• DR*C * (d^2 u_C / dt^2) + u_C = 0

An RL series circuit comprises an inductor with inductance L = 0.50 H and internal resistance r = 10 Ohm, connected in series with a resistor R = 40 Ohm and a DC generator of electromotive force E = 10 V. What is the inductive time constant tau, and what is the steady-state current I_max established in the circuit?

• Atau = 10 ms (0.010 s); I_max = 0.20 A (200 mA)
• Btau = 50 ms (0.050 s); I_max = 0.25 A (250 mA)
• Ctau = 10 ms (0.010 s); I_max = 1.0 A
• Dtau = 100 ms (0.10 s); I_max = 0.20 A

An inductor with self-inductance L = 0.40 H carries a steady electrical current I = 3.0 A. What is the magnetic energy stored in the magnetic field of the inductor?

• A1.8 J
• B3.6 J
• C0.60 J
• D1.2 J

An ideal oscillating LC circuit consists of an inductor L = 50 mH and a capacitor C = 2.0 microFarad. What is the proper period T0 of undamped electromagnetic oscillations in this circuit (taking pi ≈ 3.14)?

• AT0 ≈ 2.0 ms (1.99 ms)
• BT0 ≈ 1.0 ms
• CT0 ≈ 6.28 ms
• DT0 ≈ 0.31 ms

In a real series RLC circuit experiencing damped pseudo-periodic oscillations, what is the rate of change of total electromagnetic energy dE_T/dt, and what physical phenomenon does it describe?

• AdE_T / dt = -R * i^2; representing continuous thermal energy dissipation by the Joule eff…
• BdE_T / dt = 0; representing total electromagnetic energy conservation
• CdE_T / dt = +R * i^2; representing spontaneous magnetic amplification
• DdE_T / dt = -L * (di / dt); representing dielectric breakdown across capacitor plates

A solid block of mass m = 2.0 kg slides down a frictionless inclined plane inclined at an angle theta = 30 degrees to the horizontal (take g = 9.8 m/s^2, sin 30° = 0.50). What is the block's acceleration a, and what is its speed v after sliding a distance d = 10 m from rest?

• Aa = 4.9 m/s^2; v = sqrt(98) ≈ 9.9 m/s
• Ba = 9.8 m/s^2; v = 14.0 m/s
• Ca = 8.49 m/s^2; v = 13.0 m/s
• Da = 2.45 m/s^2; v = 7.0 m/s

A projectile is launched from ground level across flat terrain with an initial velocity v0 = 20 m/s at an angle alpha = 45 degrees above the horizontal (take g = 10 m/s^2). Neglecting air resistance, what are the maximum height H and the horizontal range R of the projectile?

• AH = 10 m; R = 40 m
• BH = 20 m; R = 40 m
• CH = 10 m; R = 20 m
• DH = 40 m; R = 80 m

A satellite of mass m moves in a stable circular orbit of radius r around a planet of mass M and radius R. What is the expression for its orbital speed v and orbital period T, consistent with Kepler's third law?

• Av = sqrt(G*M / r); T = 2*pi * sqrt(r^3 / (G*M))
• Bv = G*M / r; T = 2*pi * (r / (G*M))
• Cv = sqrt(G*M / r^2); T = pi * sqrt(r / (G*M))
• Dv = sqrt(2*G*M / r); T = 4*pi * sqrt(r^3 / (G*M))

A geostationary satellite appears stationary relative to an observer on Earth's surface. What are the orientation of its orbital plane and its approximate altitude h above Earth's surface (radius R_E = 6,370 km)?

• AEquatorial plane; altitude h ≈ 35,800 km
• BPolar plane passing over the North and South Poles; altitude h ≈ 35,800 km
• CEquatorial plane; altitude h ≈ 6,370 km
• DInclined at 45 degrees to the equator; altitude h ≈ 42,160 km

A sled of mass m = 10 kg enters a rough horizontal track with an initial speed v_i = 8.0 m/s. A constant kinetic friction force f = 20 N opposes its motion until it stops. Applying the work-energy theorem, what distance d does the sled slide before coming to rest?

• A16 m
• B32 m
• C8.0 m
• D64 m

A ball of mass m = 0.50 kg is projected vertically upward from ground level with an initial speed v0 = 14 m/s (take g = 9.8 m/s^2). Assuming air resistance is negligible, what is the maximum height h_max reached by the ball above the launch point?

• A10.0 m
• B20.0 m
• C5.0 m
• D14.0 m