AAMC Sample Test: Chem
Terms in this set (90)
What's the charge of an axon?
- negatively charged
What direction do electric field lines travel?
- from positive to negative
Electric Field Equation
E = F/q (in N/C)
E = kQ1Q2/(r^2)
- k = 9 X 10^9
F = qE + qvxB
Magnetic Field Lines
- run from North to South pole
Magnitude of Magnetic Field Equation
F = qvBsin(theta)
Right hand rule for Magnetic Field
Thumb: velocity (or current)
Fingers: B field
Equation for magnetic field with current
F = IlBsin(theta)
- I= current
- l = length of wire
One function of the myelin sheath is to...
a. insulate the axon from the surroundings
b. decrease the radius of the axon
c. produce Schwann cells
d. increase the capacitance of the axon
- myelin sheath assists with the propagation of nerve impulses (makes them faster)
- insulates the internal cytosol of the axon from the extracellular fluid
What happens when the nodes of Ranvier open in response to a stimulus?
- depolarization, which can only be transmitted along the axon since the myelin sheath insulates it
Structure of Axon
Nodes of Ranvier
- myelin sheath gaps exposed to extracellular space; uninsulated but enriched with ion channels that reengage the action potential
What are the myelinating glial cells in the CNS? PNS?
- CNS: oligodendrocytes
- ONS: Schwann Cells
- pressure and volume are inversely proportional if temperature if constant
- low pressure = high volume
- high volume = low pressure
- P1V1 = P2V2
- volume is proportional to temperature if pressure is constant
- V1/T1 = V2/T2
- V1T2 = V2T1
Combined Gas Law
(P1V1)/T1 = (P2V2)/T2
If the level of aqueous solution were 26 cm higher inside a buret than outside, compared to ambient pressure, the pressure of the gas inside the buret would be...
b. the same
c. 2 times greater
d. 26 times greater
- level of liquid inside is higher than outside, which means air pressure is higher outside than the pressure inside
- Vin > V out
- P in < P out
- PinVin = PoutVout
- Pin = (PoutVout)/Vin
- pressure builds on the inside by raising the volume level
Ideal Gas Law
PV = nRT
- P in kPa
- V in L
- n in mol
- T in Kelvin
- R = 8.314 (L kPa)/(mol K)
p = m/V
An ultrasound examination could show the motion of the fetus. In order to image this motion, the ultrasound examination devices requires what minimal information?
a. speeds of sound and of moving object
b. speed of sound and frequencies of sound waves emitted and observed
c. speeds of sound and of moving object, and frequencies of sound waves emitted and observed
d. speeds of sound and the moving object, and the frequencies and wavelengths of sound waves emitted and observed
B: speed of sound and frequencies of sound waves emitted and observed
- Doppler effect is used with ultrasound waves to provide fetal images
- Doppler effect relates frequency of ultrasound wave as detected by a moving detector to the frequency of the wave when the source is stationary, the speed of the source, and the speed of the detector
- effect produced by a moving source of waves in which there's an upward shift in frequency for observers towards whom the source is approaching
- downward frequency shift for observers from whom source is receding
Doppler effect when source is moving towards observer at rest
f' = [V/(V-Vs)]f
Doppler effect when source is moving away from observer at rest
f' = [V/(V+Vs)]f
What's the minimum amount of heat energy required to increase T from 373K to 573K? Specific heat capacity of iron is 460 J/kgK, mass is 4X10^-3 kg
Q = mcT
Q = (4X10^-3 kg)(460 J/kgK)(573-373K)
Q = 368 J
- count number of chiral centers (n)
- carbon with four non-identical groups attached
- carbons on double or triple bonds aren't chiral because they aren't bonded to four different groups
- solubility product constant
- equilibrium between solid and its respective ions in a solution
- higher solubility product constant = more soluble compound
If the product of the ions of a solid are greater than Ksp, what does that mean?
- if the product of ions is greater than Ksp, the solid is more likely to form (it'll be insoluble)
- explains formation of kidney stones
What does a high Ksp mean?
- more soluble the compound
- more likely the compound will dissolve into its constituent ions
Channel X only transmit the smallest substances dissolved in the extracellular fluid through the axon membrane. Which substance does Channel X transmit?
- sodium cations are the smallest
How does atom size change as you go down groups of the periodic table?
- atom size increases as you go down the group because you're adding extra layers of electrons
How does atom size change as you go across a period?
- atom size decreases as you go across the period: the more electronegative elements on the right pull the electrons closer to the nucleus, which decreases the radius
How does ionic radius change down a group?
- ionic radius gets bigger down a group
- Group 1: Li+ (smallest) < Na+ < K+ < Rb+ Cs+ (largest)
- Group 7: F- (smallest) < Cl- < Br- < I- (largest)
How does ionic radius change across a period?
- within a series of positive ions, the ionic radius decreases (when number of protons in the nucleus increases, electrons get closer together to decrease the size)
- within a series of negative ions, the ionic radius decreases
Which is larger: Na+ or Cl-?
- Na+ is smaller because you've lost a layer of electrons, which pulls the remaining electrons closer
- Chlorine gained electrons
What happens to radius when a cation is formed?
- when forming a cation, an electron is lost so the other electrons are more strongly attracted to the nucleus
- radius gets smaller
What happens when an anion is formed?
- added electron repels other electrons, which results in an increase in the size of the atom
What's the closest distance the electrodes used in an NCV test can be placed on a nerve in order to measure the voltage change as a response to a stimulus?
a. 0.01 m
b. 0.1 m
c. 1.0 m
d. 10 m
B: 0.1 m
- shortest time duration that can be detected is not less than the action potential time response of 1 msec.
- distance traveled by the impulse is 1 msec X 100 m/s = 0.1 m
What info about an axon is required to calculate the current associated with an NCV pulse?
a. conductivity, resistivity, and length
b. potential, conductivity, and radius
c. potential, resistivity, and radius
d. potential, resistance per unit length, and length
- I = V/R
- Resistance is calculated by length of the wire and thickness of the wire
What happens to resistance when length of wire increases? When thickness of wire decreases?
- resistance increases when length of wire increase
- resistance increases when thickness of wire decreases
What factors affect resistance of a conductor?
- resistivity, total length, cross sectional area, and temperature
R = (Lenght/Area)X(proportional constant)
If an unknown compound completely dissolves in water and weakly conducted electricity, and the hydrogen ion concentration of the unknown aqueous solution was 1X10^-5M, the unknown was probably a....
a. weak base
b. strong base
c. weak acid
d. strong acid
C: weak acid
- the hydrogen ion concentration is greater than 1X10^-7, but much less for the concentration of the unknown compound itself
- compound is only partially ionized to form hydrogen ions: weak acid
Squalene is produced in the body as a precursor to which important class of compounds?
c. steroid hormones
C: steroid hormones
- structure of squalene is suggestive of its transformation into the fused four-ring system common to cholesterol
What's the concentration of Cl- ions in a 0.1M solution of calcium chloride?
- CaCl2: produces twice as many Cl- ions as Ca2+ ions
Addition of which disaccharide to a solution of Ag2O in NH3(aq) will NOT result in the deposition of shiny silver mirror on the walls of the reaction vessel?
D: sucrose does NOT possess a hemiacetal functional group so it will NOT undergo mutarotation and NOT oxidized by Ag+
- where ring-opening can occur
- reducing sugars
In reverse-phase high performance liquid chromatography (polar phase and non polar phase), compound 2 (more polar) and compound 1 (less polar) are separated. Which accurately describes this process?
a. increasing the polarity of the mobile phase will decrease the retention time of compound 1 relative to compound 2
b. compound 1 will elute first because it is more polar than compound 2
c. decreasing affinity of compound 1 for stationary phase will increase its retention time relative to compound 2
d. compound 2 will elute first because it does not interact as favorably with the stationary phase as compound 1
- if compound 2 is more polar than compound 1, the more polar compound will elute first since this is reverse-phase chromatography
Thin Layer Chromatography (TLC)
- uses polar stationary phase and non polar mobile phases
- nonpolar phases interact less with the stationary phase so they elute first
Reverse Phase Chromatography
- opposite of TLC
- use non polar stationary phase and polar mobile phases
- polar compounds will interact less with stationary phases so they will elute first
NADPH + H+ + O2 + RH -> NADP+ + H2O + ROH
In this reaction, NADPH functions as...
a. oxidizing agent
b. reducing agent
B: reducing agent
- NADPH is acting as a hydride transfer agent which reduce oxygen
- NADPH loses electrons and is oxidized so it serves as a reducing agent
- gains electrons and are reduced in a reaction
- loses electrons and is oxidized in a chemical reaction
2HCl + Mg -> MgCl2 + H2
What type of reaction?
b. Lewis acid/Lewis base
c. Double replacement
- change in oxidation states
- Mg: 0 to 2+
Double Replacement Reaction
- occur when parts of two compounds are exchanged to make two new compounds
A+B- + C+D- -> A+D- + C+B-
Lewis Acid/Lewis Base Reactions
A+ (Lewis Acid) + B- (Lewis Base) -> AB
- Lewis Acid: electron acceptor
- Lewis Base: electron donor
- forms coordinate covalent bond
Which explains why the boiling point of HF is abnormally high when compared to the boiling points of other Group 7A hydrides?
a. HF bond is much less polar than the bonds between H and the other halogens
b. HF has the lowest molecular mass of Group 7A hydrides
c. HF is affected by hydrogen-bonding interactions to a much greater degree than the other group 7A hydrides
d. HF has the highest vapor pressure among the Group 7A hydrides
- hydrogen bonding is a special type of intermolecular force that happens when H is bonded to a highly electronegative elements such as N, O, and F
- since hydrogen bonding is a higher than anticipated dipole-diple interactions, it causes substances that exhibit it to have higher than expected boiling points and lower vapor pressures
If boiling point is high, what does that mean for vapor pressure?
- higher boiling points mean lower vapor pressure
Principle quantum number is a measure of which of the following?
a. approximate radial size of an electron cloud
b. approximate shape of an electron cloud
c. number of valence electrons that orbit a nucleus
d. number of protons and neutrons found in the nucleus of an atom
A: approximate radial size of an electron cloud
- n is most closely associated with potential energy of the electron
- potential energy is proportional to the square of the distance of two oppositely charged particles by Coloumb's Law
- n is also associated with the radial "size" of the electron cloud
Orbital Angular Momentum (l)
- determines shape of orbital and angular distribution
- each value of "l" indicates s, p, d, f subshells
Magnetic Quantum Number (ml)
- number of orbitals and their orientation within a subshell
- ranges from -l to +l
Which orbital has a higher ionization energy, n = 3 or n = 2?
n = 2 because closer the electron is to the nucleus, the smaller the atomic radius and the more energy it takes to expel an electron
What does a high Ka mean?
- Ka = acid dissociation constant
- high Ka = low pKa = more dissociation = more acidic
Mevalonate is expected to display prominent absorption in which regions of its infrared spectrum?
I and II
- mevalonic acid contains both CO2H and OH groups, but doesn't contain a conjugated CC bond
- Carboxyl C=O: 1700-1750
- OH: 3200-3500
- triggering molecular vibrations through IR light
- provides info about presence or absence of functional groups
Nuclear Magnetic Resonance (NMR)
- excitation of nucleus of atoms through radiofrequency irradiation
- extensive information about molecular structure and atom connectivity
- bombardment of sample with electrons and detection of resulting molecular fragments
- provides info about molecular mass and atom connectivity
- promotion of electrons to higher energy levels through irradiation with UV light
- evidence of conjugated pi systems and presence of double and triple bonds
What type of groups produce the strongest bands on the IR graph?
- polar bonds: C=O produces strongest bands
- medium polarity and asymmetric bonds produce medium bands (CN)
- weakly polar and symmetric bonds produce weak bands
IR Abosrption Range for NH, OH, CH, CC, CN, C=C, C=O, C=N
- IR Range: 600-4000 cm-1
- 2500-3500: NH, OH, CH
- 2200: C triple bonded to N and C
- 1600-1800: C=C, C=O, C=N
- Fingerprint Region: 600-1200 (C-C, C-O, C-N)
IR abosrption for C-H, O-H, C=O, C=C, C-O?
- C-H: 2850-3000
- O-H: 2500-3500
- C=O: 1680-1800
- C=C: 1590-1640
- C-O: 1000-1250
If neither reactant is chiral, what explains how a single stereoisomer is formed?
a. one of the reactants is chiral
B. both reactants are chiral
c. solvent medium is chiral
d. enzyme is chiral
- if neither enzyme is chiral, but a chiral product forms, this must be because the catalyst enzyme is chiral
What is NOT a product of squalene metabolism?
- squalene is structurally similar to the fused 4-ring system of steroids and is a metabolic precursor to this class of molecules
Myopia is a condition of the eye where the crystalline lens focuses the light rays to a position between the lens and the retina. To correct for this condition, a thin lens is placed in front of the eye that will help focus light on the retina. The type of lens required is...
- myopia: nearsightedness (inability to focus on distant objects) causes light to focus at a point in front of the retina
- diverging lens will spread out light before it reaches the lens of the eye, which will cause light to focus on a point closer to the re
Hyperopia: how is it corrected?
- farsightedness: inability of eye to focus on nearby objects
- images of nearby objects are focused at a location behind the retina
- use converging lens to refract light before it enters the eye so that the image is focused on the retinal surface
One method of isolating polypeptides and proteins from aqueous extracts if freeze drying. The aqueous solution of the polypeptide or protein is frozen. What procedure can be used to remove the water from the frozen sample?
a. sublimation under reduced pressure
b. distillation using steam
c. extraction with organic solvent
d. addition of magnesium sulfate
A: sublimation under reduced pressure
- only sublimation of water under reduced pressure will keep the mixture cold and will maintain protein in it
- transition of substance from solid to gas phase without passing through liquid phase
- separating mixtures based on differences in the conditions required to change the phase of components in the mixture
- liquid can be heated to force components into gas phase; gas phase is then condensed back into liquid form and collec
Density of a human body can be calculated from its weight in air, Wair, and its weight while submersed in water, Ww. The density of a human body is proportional to...
a. Wair/(Wair - Ww)
b. (Wair - Ww)/Wair
A: ratio of density of an object to the density of the fluid it's submersed in is equal to the ratio of the weight of the boject in the air to the difference of submersed weight and weight in the
Hydrostatic pressure of fluid
P = (density)(g)(h)
Pressure and Force equation
P = F/A
- buoyant force on an object is equal to the weight of the fluid displaced by the object
- volume is referring to the volume of the displaced fluid, not of the entire object
Fb = Wf = (density)(volume)(gravity) = pVg
Which two amino acids would contribute to the stabilization of ADP binding described in the passage?
a. Asn9 and Thr10
b. His11 and Arg27
c. Asp6 and Arg27
d. Asp6 and His11
B: His11 and Arg27
- both contain a positive charge so they'd have favorable ionic interactions with the negatively charged phospha
99Mo decays to 99Tc, releasing a beta particle and an antineutrino. The electrically charged particle emitted during the decay of 99Mo is...
- negatie beta particle is the name given to the electron emitted during the nuclear decay of a heavy nucleus
The advantage of the Doppler ultrasound technique over the standard ultrasound technique is that it allows
a. distinguishing between fluids and tissue
b. measuring the blood flow
c. measuring tissue density
d. measuring heart wall thickness
B: measures blood flow
- Doppler ultrasound takes advantage of Doppler Effect in which a sound wave emitted by, or reflected from a moving object, will change its frequency based on the relative speed of the object (flow of blood in a vessel)
Work equation in terms of Power
Power = W/t
Work = Power(t)
- usually in J
When choosing a buffer to use for an experiment conducted at pH 5.3, it would be best to choose one with a pKa of...
- a good buffer has a pKa within 1pH of desired experimental conditions
- resists changes in pH (maintains pH of a system)
- good buffers are usually soluble in water
An object with a mass of 0.1 kg absorbs 250J of heat while changing temeprature from 20C to 25C. What's the specific heat?
Q = mcT
c = (Q/MT) = (250)/(0.1 X 5) = 500 J/(kgC)
During glycolysis, pyruvate (CH3C(=O)CO2-) is reduced to lactate (CH3CH(OH)CO2-) by NADH. What's the balanced reaction for this reaction?
- use half reactions!
CH3C(=O)CO2- + 2H+ + 2e- -> CH3CH(OH)CO2-
NADH -> NAD+ + H+ + 2e-
CH3C(=O)CO2- + NADH + H+ -> CH3CH(OH)CO2- + NAD+