Biology
A double-stranded RNA genome isolated from a virus was found to contain 15% uracil. What percentage of guanine should exist in this virus''s genome?
■15%
■35%
■70%
■85%
35% (The percentage of uracil must equal that of adenine due to base-pairing. This accounts for 30% of the genome. The remaining 70% must be split evenly between guanine and cytosine, so they each account for 35% of the genome.)
Some enzymes require the presence of a nonprotein molecule to behave catalytically. An enzyme devoid of this molecule is called a(n):
■holoenzyme.
■apoenzyme.
■coenzyme.
■zymoenzyme.
apoenzyme (An enzyme devoid of its necessary cofactor is called an apoenzyme and is catalytically inactive.)
Biologically important carboxylic acids include pyruvic acid, citric acid, and the C-terminus of amino acid chains. Which of the following carboxylic acids will be the most acidic?
A) CH3CHClCH2COOH
B) CH3CH2CCl2COOH
C) CH3CH2CHClCOOH
D) CH3CH2CH2COOH
B (The acidity of carboxylic acids is significantly increased by the presence of highly electronegative functional groups. Their electron-withdrawing effect increases the stability of the carboxylate anion, favoring proton dissociation. This effect increases as the number of electronegative groups on the chain increases, and it also increases as the distance between the acid functionality and electronegative group decreases. This answer has two halogens bound to it, at a smaller distance from the carboxyl group compared to the other answers.)
Which of the following is the ideal gas law?
A) PE = mgh
B) F = ma
C) PV = nRT
D) V = IR
C) PV = nRT. PV = nRT is the ideal gas law (choice C is correct). PE = mgh is the equation for gravitational potential energy (choice A is incorrect). Newton’s second law states that force is equal to mass multiplied by acceleration (choice B is incorrect). V = IR is Ohm’s Law for circuits (choice D is incorrect).
Increases in which of the following hormones causes sleepiness?
■Cortisol
■Growth hormone
■Melatonin
■Oxytocin
Melatonin (As light diminishes throughout the day, the pineal gland increases secretion of melatonin, resulting in sleepiness. Cortisol levels, choice (A), increase throughout the early morning, resulting in wakefulness. Growth hormone secretion, choice (B), peaks during slow-wave sleep. Oxytocin, choice (D), is associated with uterine contractions in childbirth, milk letdown, and bonding behavior.)
A student is trying to determine the type of membrane transport occurring in a cell. She finds that the molecule to be transported is very large and polar, and when transported across the membrane, no energy is required. Which of the following is the most likely mechanism of transport?
■Active transport
■Simple diffusion
■Facilitated diffusion
■Exocytosis
Facilitated diffusion (We are asked to identify the type of transport that would allow a large, polar molecule to cross the membrane without any energy expenditure. This scenario describes facilitated diffusion, which uses a transport protein (or channel) to facilitate the movement of large, polar molecules across the nonpolar, hydrophobic membrane. Facilitated diffusion, like simple diffusion, does not require energy, which explains why no ATP was consumed during this transport process.)
An α-helix is most likely to be held together by:
■disulfide bonds.
■hydrophobic effects.
■hydrogen bonds.
■ion attractions between side chains.
hydrogen bonds (The α-helix is held together primarily by hydrogen bonds between the carboxyl groups and amino groups of amino acids. Disulfide bridges, choice (A), and hydrophobic effects, choice (B), are primarily involved in tertiary structures, not secondary. Even if they were charged, the side chains of amino acids are too far apart to participate in strong interactions in secondary structure.)
Sodium hypochlorite (NaClO) is used as a disinfectant and has also been shown to treat chronic skin inflammation. What is the oxidation number of chlorine in NaClO?
■-1
■0
■+1
■+2
+1 (In NaClO (sodium hypochlorite), sodium carries its typical +1 charge, and oxygen carries its typical -2 charge. This means that the chlorine atom must carry a +1 charge in order to balance the overall charge of zero.)
Which of the following best describes the units for current?
A) Amperes
B) Volts
C) Farads
D) Ohms
A) Amperes. The units for current are given by amperes (choice A is correct). Volts are the units for voltage (choice B is incorrect). Farads are the units for capacitance (choice C is incorrect). Ohms are the units for resistance (choice D is incorrect).
Over the last few decades, the United States population has become:
A) bigger, older, and more diverse.
B) bigger, younger, and more diverse.
C) smaller, older, and less diverse.
D) smaller, older, and more diverse .
A (With a decrease in mortality rate and a higher immigration rate than emigration rate, the United States population continues to grow, with an increasing average age and increasing racial and ethnic diversity.)
Which of the following is NOT a difference that would allow one to distinguish a prokaryotic and a eukaryotic cell?
A) Ribosomal subunit weight
B) Presence of a nucleus
C) Presence of a membrane on the outside surface of the cell
D) Presence of membrane-bound organelles
C (The main differences between prokaryotes and eukaryotes include: prokaryotes do not have a nucleus, while eukaryotes do, eliminating choice (B); prokaryotes have ribosomal subunits of 30S and 50S, while eukaryotes have ribosomal subunits of 40S and 60S, eliminating choice (A); and prokaryotes do not have membrane-bound organelles, whereas eukaryotes do, eliminating choice (D). The presence of a membrane on the outer surface of the cell could not distinguish a prokaryotic cell from a eukaryotic one because both gram-negative bacteria and animal cells share this feature. Thus, choice (C) is the correct answer.)
Which of the following is least likely to cause denaturation of proteins?
A) Heating the protein to 100 °C
B) Adding 8 M urea
C) Moving it to a more hypotonic environment
D) Adding a detergent such as sodium dodecyl sulfate
C (High salt concentrations and detergents can denature a protein, as can high temperatures. But moving a protein to a hypotonic environment—that is, a lower solute concentration— should not lead to denaturation.)
For the most part, biological pH is slightly basic. However, the stomach is very acidic, and its contents must be swiftly neutralized by basic bicarbonate ions upon entering the small intestine, which has a basic pH. How many liters of 2 M Ba(OH)2 are needed to titrate a 4 L solution of 6 M H3PO4?
■1.33 L
■12 L
■18 L
■56 L
18 L (Use the equivalence point equation:
NaVa = NbVb
Ba(OH)2 can dissociate to give two hydroxide ions, so its normality is 2 M × 2 = 4 N. H3PO4 can dissociate to give three hydronium ions, so its normality is 6 M × 3 = 18 N. Plugging into the equation, we get (18 N)(4 L) = (4 N)(Vb). Therefore, Vb is 18 L.)
A plane of light hits a mirror at an angle of 37°. What is this angle called?
A) Snell’s angle
B) Angle of incidence
C) Angle of reflection
D) Angle of refraction
B) Angle of incidence. The initial light hitting the mirror forms the angle of incidence (choice B is correct; choices A and D are incorrect). The reflected light forms an angle of reflection (choice C is incorrect).
Which of the following neurotransmitters is associated with both schizophrenia and Parkinson's disease?
■GABA
■Serotonin
■Dopamine
■Enkephalins
Dopamine (Schizophrenia is associated with high levels of dopamine, or high sensitivity to dopamine. Parkinson's disease is associated with destruction of the dopaminergic neurons in the basal ganglia.)
What role does peptidyl transferase play in protein synthesis?
A) It transports the initiator aminoacyl-tRNA complex.
B) It helps the ribosome to advance three nucleotides along the mRNA in the 5′ to 3′ direction.
C) It holds the proteins in its tertiary structure.
D) It catalyzes the formation of a peptide bond.
D (Peptidyl transferase is an enzyme that catalyzes the formation of a peptide bond between the incoming amino acid in the A site and the growing polypeptide chain in the P site. Initiation and elongation factors help transport charged tRNA molecules into the ribosome and advance the ribosome down the mRNA transcript, as in choices (A) and (B). Chaperones maintain a protein's three-dimensional shape as it is formed, as in choice (C).)
Which of the following INCORRECTLY pairs a digestive hormone with its function?
A) Trypsin—hydrolyzes specific peptide bonds
B) Lactase—hydrolyzes lactose to glucose and galactose
C) Pancreatic amylase—hydrolyzes starch to maltose
D) Lipase—emulsifies fats
D (Lipase is involved in the digestion of fats, but its function is not to emulsify fats—this is the job of bile. Rather, lipase chemically digests fats in the duodenum, allowing them to be brought into duodenal cells and packaged into chylomicrons. The other associations given here are all correct.)
The body's pH is tightly regulated because specific enzymes function best within a narrow pH range. What is the approximate pH of a 1.2 × 10-5 M aqueous solution of NaOH?
■4.92
■7.5
■9.08
■12.45
9.08 (NaOH is a strong base; as such, there will be 1.2 × 10-5 M OH- in solution. Based on this information alone, the pOH must be between 4 and 5, and the pH must be between 9 and 10. Using the shortcut, pOH ≈ 5 - 0.12 = 4.88. pH = 14 - pOH = 9.12 (actual = 9.08).)
The Heisenberg uncertainty principle states that which of the following cannot be measured simultaneously?
A) Velocity and acceleration
B) Position and displacement
C) Acceleration and composition
D) Velocity and position
D) Velocity and position. The Heisenberg uncertainty principle states that velocity and position cannot be measured simultaneously (choice D is correct; choices A, B, and C are incorrect).
A stroke patient comprehends speech but cannot move her mouth to form words. Which of the following brain areas is likely affected?
■Broca's area
■Wernicke's Area
■Arcuate fasciculus
■Superior temporal gyrus
Broca's area (Broca's area governs the motor function of language. A stroke that affects Broca's area will leave receptive language intact, but word formation will be affected. A stroke affecting Wernicke's area, choice (B), will make it so the individual is unable to comprehend speech. A stroke affecting the arcuate fasciculus, choice (C), will result in an inability to repeat words heard but spontaneous language production is intact. The superior temporal gyrus, choice (D), is where Wernicke's area is located.)
Which ion channels are responsible for maintaining the resting membrane potential?
A) Ungated channels
B) Voltage-gated channels
C) Ligand-gated channels
D) No ion channels are involved in maintenance of the resting membrane potential.
A (The resting membrane potential is displayed by cells that are not actively involved in signal transduction. Ungated or "leak" channels permit limited free flow of ions, while the sodium-potassium pump is also active and corrects for this leakage. Ligand-gated and voltage-gated channels are involved in cell signaling and in the pacemaker potentials of certain cells, but cause deviation from—not maintenance of—the resting membrane potential.)
In high doses, aspirin functions as a mitochondrial uncoupler. How would this affect glycogen stores?
A) It causes depletion of glycogen stores.
B) It has no effect on glycogen stores.
C) It promotes additional storage of glucose as glycogen.
D) Its effect on glycogen stores varies from cell to cell.
A (Uncouplers inhibit ATP synthesis without affecting the electron transport chain. Because the body must burn more fuel to maintain the proton-motive force, glycogen stores will be mobilized to feed into glycolysis, then the TCA, and finally oxidative phosphorylation.)
Biochemical reactions that involve the transfer of electrons produce an electromotive force.
Given the following standard reduction potentials:
Zn2+ + 2e- → Zn E = -0.763 v
Ag+ + e- → Ag E = 0.337 v
What is the standard electromotive force of the following reaction?
Zn2+ + 2Ag → 2Ag+ + Zn
■-2.2 V
■-1.1 V
■+1.1 V
■+2.2 V
-1.1 v (To determine the standard electromotive force of a cell, simply subtract the standard reduction potentials of the two electrodes. In this case, the cathode is zinc because it is being reduced; the anode is silver because it is being oxidized.
Thus, E°cell = E°red,cathode - E°red,anode = -0.763 - 0.337 = -1.10 V. While we must multiply the silver half-reaction by two to balance electrons, the actual value for the reduction potential does not change. Remember that the standard reduction potential is determined by the identity of the electrode, not the amount of it present.)
A mouse is given 50 mg of oxaliplatin. If the half-life of the drug is 6 hours, how much will remain in the mouse at 24 hours?
A) 12.50 mg
B) 6.250 mg
C) 3.125 mg
D) 1.562 mg
C) 3.125 mg. After 6 hours, 25 mg remain. After 12 hours, 12.5 mg remain. After 18 hours, 6.250 mg remain. After 24 hours, 3.125 mg remain (choice C is correct; choices A, B, and D are incorrect).
The swimming times for all members of a swim team are tracked over a six-month period in team-only practices and at public meets. For 14 of the 16 members, top times were clocked at the meets. What social phenomenon does this evidence support?
■Social facilitation
■Peer pressure
■Identification
■Group polarization
Social facilitation (For 14 out of the 16 members, the record times were obtained during public meets. The fact that the team members performed better when in front of a crowd supports the notion of social facilitation.)