MCAT Chemistry Flashcards
1
Q
Define transferase
A
Moves functional groups from one molecule to another (such as kinases that move phosphate groups onto their substrates)
2
Q
Define lysase
A
Breaks molecules into two smaller molecules without using water or redox reactions
3
Q
Define isomerase
A
Converts molecule from one isomer to another (including stereoisomers and constitutional isomers)
4
Q
Define oxireductase
A
Catalyze oxidation-reduction reactions where electrons are transferred
5
Q
What functional group shows a peak in the 3200-3500 cm-1 region?
A
-OH (hydroxyl groups)
6
Q
What functional group shows a peak in the 1700-1750 cm-1 region?
A
C=O (carbonyl)
7
Q
What functional group shows a peak in the 1580-1640 cm-1 region?
A
C=C (alkenes)
8
Q
What is the equation used to generate the total standard potential of a galvanic (or voltaic) cell
A
Ecell=E°cathode-E°anode
9
Q
How does a galvanic (or voltaic) cell work?
A
Redox reactions can be carried out in special devices known as electrochemical cells. These cells must have two electrodes, which are where the redox half-reactions occur. The electrode where oxidation happens is known as the anode, while the electrode where the reduction happens is known as the cathode. Therefore, a surplus of electrons is generated at the anode (because electrons are lost during oxidation), and they travel to the cathode. In a galvanic (or voltaic) cell, a spontaneous redox reaction is used to generate a positive potential difference that can drive current. The total standard potential generated by a cell, Ecell, can be calculated from the standard reduction potentials of the half-reactions. The simplest way of defining Ecell is presented Ecell=E°cathode-E°anode
10
Q
What is the orbital hydrization of XeF4
A
sp3d2
11
Q
How is the rate of cation formation related to energy?
A
The rate of cation formation through deprotonation is directly related to the energy require to deprotonate the compound. Smaller ΔH f means faster rate of reaction for deprotonation
12
Q
What is Hess’s Law?
A
ΔH reaction = Σ ΔH products - ΣΔH reactants
13
Q
How can we determine whether or not a reaction is spontaneous?
A
ΔG=ΔH-TΔS ΔG>0 reaction is nonspontaneous ΔG=0 reaction is in equilibrium ΔG<0 reaction is spontaneous
14
Q
H2 gas typically acts as a reductant or an oxidant?
A
Reductant. Reduction can be conceptualized as either the gain of bonds to hydrogen or the loss of bonds to oxygen.
15
Q
Define Bronsted-Lowry acid
A
Proton (hydrogen ion) donor
16
Q
Define Bronsted-Lowry base
A
Proton (hydrogen ion) acceptor
17
Q
Define Lewis acid
A
Electron pair acceptor
18
Q
Define Lewis base
A
Electron pair donor
19
Q
Define Arrhenius acid
A
An Arrhenius acid is a substance that dissociates in water to form hydrogen ions (H+)
20
Q
Define Arrhenius base
A
An Arrhenius base is a substance that dissociates in water to form hydroxide (OH–) ions
21
Q
What is an amide?
A
22
Q
What is an imine?
A
23
Q
What is an imide?
A
24
Q
What is an amine?
A
25
Imide
26
imine
27
amide
28
amine
29
30
What are the unit conversions for the different units of pressure?
1 atm=760 mmHg=10^5 Pa
31
What is homotropic regulation?
Homotropic regulation is when a molecule serves as a substrate for its target enzyme, as well as a regulatory molecue of the enzyme's activity.
32
What is the modulator of hemoglobin and what kind is it?
O2 is a homotropic allosteric modulator of hemoglobin
33
What is the structure of hemoglobin?
In humans, hemoglobin typically consists of four globular protein subunits, attached together to form the quaternary structure of the overall moleculle. Each subunit contains one heme group, which is a structure consisting of a specific ring, termed a porphyrin ring. Each heme group contains one iton caiton, which binds oxygen in the Fe2+ state. Since each hemoglobin molecule therefore includes for iron cations, each hemoglobin can cerry up to four oxygen atoms.
34
What is hemoglobin?
A metalloptrotein that functions in the transport of oxygen to the body tissues and of carbon dioxide to the lungs for exhalation.
35
Where is hemoglobin found?
In red blood cells (erythrocytes)
36
What makes up an erythrocyte?
Hemoglobin. They are so packed with hemoglobin that they lack a nucleus or membrane-bound organelles
37
Where are erythrocytes produced?
Bone marrow
38
When is erythrocyte production increased?
Under low-oxygen conditions, erythrocyte production increases in response to the secretion of a kidney hormone, erythropoietin (EPO)
39
How does hemoglobin work?
Since each hemoglobin molecule includes four iron cations, each hemoglobin can cerry up to four oxygen atoms. Binding of oxygen to any of the four binding sites causes an increase in the oxygen affinity of the remaining sites, a phenomenon known as cooperativity. Cooperative binding can be recognized by its sigmoidal shape. The steep part of the S denotes the sharply increased binding affinity that occurs as a result of the initial binding
40
What is cooperative binding?
Binding of oxygen to any of the four binding sites of hemoglobin causes an increase in the oxygen affinity of the remaining sites, a phenomenon known as cooperativity. Cooperative binding can be recognized by its sigmoidal shape. The steep part of the S denotes the sharply increased binding affinity that occurs as a result of the initial binding
41
Are the majority of molecules in air polar or nonpolar?
nonpolar
42
What is kinetic molecular theory of gases?
Kinetic molecular theory of gases states that gaseous mixtures do not act differently from pure gases
43
What effect no humidity does temperature have in the composition of air?
With decreasing temperature, air is able to hold less total water. (Ex. If warm air could hold 100 g of water in a given volume, then 50% relative humidity would be 50 g of water in the air. And if cold air could only hold 40 g of water in the same given volume, then 50% relative humidity would be 20 g of water in the air. So with the same relative humidity, the cold high-altitude air has less mass of water.)
44
Define solubility
Solubility describes the degree to which particles, called soutes, dissolve in another substance (usually a fluid), called a solvent. Solubility it an equilibrium process between the non-dissolved form of a substnace (Ex. Hydrophilic substances are molecules that contain polar or charged groups and are capable of dissolving in water and other hydrophilic solvents, whereas hyrdrophic substances are nonpolar molecules that are capable of dissolving in nonpolar, hydrophobic solvents.)
45
What is Ksp?
Ksp is the solubility product constant. This is the equilibrium constant that describes the dissociation of a reaction
46
What is the Ksp expression for MgCl2 (s) Mg2+ (aq) + 2 Cl- (aq)
Ksp = [Mg2+][Cl-]^2
47
How does an increase in temperature affect the solubility of ionic substance in water? How about gases?
Solubility of ionic substances in water increase with temperature while the opposite pattern is observed for gases. Higher termpatures provide gases with more kinetic energy that they can use to escape the solution. Additionally, pressure favors the solubility of gases
48
At STP, how much volume does one mole of an ideal gas occupy?
At 1 atm 273K one mole of an ideal gas occupies a volume 22.4L
49
How does temperature relate to energy?
Temperature is an approximation of the average kinetic energy of the molecule in a gaseous sample (T~Keavg = 1/2 mv^2)
50
What are the most common units of volume (unit conversions included)
1 L = 10^3 mL = 10^3 cm^3
51
How do indicators work?
Indicators function in acid-base titrations to identify, via color change or a similar mechanism, that an expected pH, and thus the titration endpoint, has been reached. In order to function this way, an indicator must undergo a color change near the desired pH. This occurs becasue of a reversible change in teh protonation state of the indicator. It is desirable then that the pKa of a chosen indicator be within +- unit of the target pH.
52
What is analyte?
The unknown solution in titration
53
What is the titrant?
A solution of known concentration used in a titration to determine the concentration of the unknown solution (analyte)
54
What is the ideal pKa for an indicator in an acid-base titration
pKa of a chosen indicator should be within +- unit of the target pH (Ex. Indicator for acetic acid (weak acid) and NaOH (strong base) should be above 7, specifically 9.3)
55
Define the equivalence point during titration
The number of acid and base groups added to the solution is requivalent to the number of base/acid groups in the original unknown solution. NaVa=NbVb where N and V are the normality (mol/L) and the volume of the acidic and basic solutions, respectively.
56
Why is it important to convert molarity (M) to Normality (N) when determining the concentration at equivalence?
NaVa=NbVb It is important to convert from molarity (M) to normality (N) for polyprotic acids and polyvalent bases
57
What does the flat regions of titration curves represent?
The flat regions of titration curves represent buffering solutions (roughly equal mix of an acid/base and its conjugate)
58
What does the steep, near-vertical sections of the titration curve represent?
The steep parts of the titration curve contain equivalence points which indicate that enoguh of the titrant has been added to remove one equivalent (acid of base group) from each of the original molecules in the unknown solution.
59
What species will have multiple equivalence points?
Species with multiple acid or base groups (e.g. H3PO4 or Ca(OH)2)
60
What is positive control?
A positive control is a control group that is not exposed to the experimental treatment but that is exposed to some other treatment that is known ot produce the expected effect. (Eg. The scientists wished to test the effect of analogs on enzyme acitivity. Using a known inhibitor is an example of comparing the expected effects of the inhibitor to those of the analog treatment)
61
What is negative control?
A negative control group is a control group that is not exposed to the experimental treatment or to any other treatment that is expected to have an effect
62
What is randomized control?
In randomized controls, the groups that receive different experimental treatments are determined randomly.
63
What is a false negative?
A false negative is when a test result appears negative when it should have been positive. (Ex. If a particular test of a known ADAMTS inhibitos returns a result that shows no change in enzyme activity)
64
How much sample is left after 4 half-lives?
0.5^4=0.0625=6.25%
65
How is the remaining amount of sample determined after n half-lives? (equation)
(E.g. If we know 250g of 2000g sample remains we determine the number of half lives by 250/2000=1/8=(1/2)^n --\> n=3)
66
Define radioactive decay
Radioactive decay is the spontaneous transformation of oneatomic nucleus into another. This often involves a change from one element into a different element. The only way this transformation can happen is by changing the number of protons (and often neutrons) in the nucleus, since atomic identity is defined by the number of protons. This process is irreversible
67
What are the four primary types of decay?
alpha decay, beta decay (β+ and β−), gamma decay, and electron capture
68
Define alpha decay
In alpha decay, an alpha particle, containing two protons, two neutrons, and a +2 charge is emitted
69
Define β- decay
In β- decay, a neutron is converted into a proton in the nucleus and a β- particle (an electron) is ejected to maintain charge balance.
70
Define β+ decay
In β+ decay, a proton is converted into a neutron, and a β+ particle (a positron) is emitted to preserve charge.
71
Define γ decay
γ decay involves the emission of a γ ray, which is a high-energy photon, from an excited nucleus.
72
Define electron capture
In electron capture, a nucleus "grabs" an electron, which changes a proton into a neutron.
73
What happens when an atom does not gain or lose any protons and only the neutron count is changed?
A new isotope is formed
74
Define isotope
An isotope is a variety of an element that is distinguished from other varieties of the same element by having a different atomic mass; however, isotopes of a given element all share the same atomic number and chemical properties. These isotopes are often used in radiolabeling techniques in the biological sciences (e.g. 2^H or deuterium (D) to track amino acid uptake in protein translation)
75
What is half life?
Half life (t1/2) is the time required for one-half of the parent isotopes in a sample to decay into daughter (radiogenic) isotopes.
76
What is "cupric"?
"cupric" tells us that we are using the Cu^2+ (or copper [II]) cation
77
What is "ferrous" ion
Fe^2+
78
What is "ferric" ion
Fe^3+
79
What is oxide?
O^2-
80
What is hypochlorite
ClO-
81
What is chlorite?
ClO2^-
82
What is chlorate?
ClO3^-
83
What is perchlorate?
ClO4^-
84
What is nitrite?
NO2^-
85
What is nitrate?
NO3^-
86
What is phosphate?
PO4^3-
87
What is dihydrogen phosphate?
H2PO4^-
88
How is Ka associated with acidity strength?
A higher Ka is associated with strong acidity
89
How does Ka relate to pKa?
pK=-logK
90
What is the Henderson-Hasselbalch equation?
pH=pKa+log[B]/[A]
91
Define Ka (equation)
Ka=[H+][A-]/[HA]
92
What is the usual Ka of lactic acid and amino acids
10^-3 to 10^-6
93
What is the relationships between Ka and pKa?
pKa=-logKa
94
How does pKa relate to acid strength?
The smaller the pKa value, the stronger the acid
95
What is the isoelectric point?
The isoelectric point (pI) is the pH at which the net carge of the amino acid is zero, or when the carboxylate is deprotonated and the amin groups is still protonated. In other words, glycine is in its zwitterionic form
96
How can we calculate the isoelectric point for diprotic amino acids? Acidic amino acids? Basic amino acids?
The pI can be captured as the average of the two pKa values pI=1/2(pKa1+pKa2). For acidic amino acids, the pI is the average of the two lower pKa value. For basic amino acids, the pI is the average of the two highest pKa value.
97
How does the bicarbonate buffer system work?
H2O (aq) + CO2 (g) ⇌ H2CO3 (aq) ⇌ H+ (aq) + HCO3− (aq) Carbonic acid (H2CO3) has the conjugate base of HCO3−. Buffers work because the concentrations of the weak acid and its salt are large compared to the number of protons or hydroxide ions added or removed. When protons are added to the solution from an external source, some of the bicarbonate in the buffer is converted to carbonic acid, using up the protons added; when hydroxide ions are added to the solution, protons are dissociated from some of the carbonic acid in the buffer, converting it to bicarbonate and replacing the protons lost.
98
Describe an ideal buffer
Buffers resist pH changes best when the pH values are at or near the pKa value for the acid/base used, because that is when the conjugate acid and base have equal concentrations. Optimal buffering occurs when the pH is within approximately 1 pH unit from the pKa value of the system. The pH of a buffer solution can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log [conjugate base] / [acid].
99
Why does carbonic acid function as a buffer in the human body?
Carbonic acid works best at a pH below physiological conditions because its pKa1 (pKa1=6.3, pKa2=10.3) is much lower than the normal pH of blood (7.4)
