Exam 1 Flashcards
The O-H bonds in water are polar due to the high electronegativity of hydrogen.
False.
Water is a polar molecule due to its bent geometry.
True.
In the liquid state, each water molecule has the potential to form hydrogen bonds with four other water molecules.
True.
Compounds that dissolve readily in water are termed hydrophilic and include electrolytes as well as nonelectrolytes.
True.
Electrolytes (e.g. NaCl) are polar and dissociate into anions & cations, each surrounded by water molecules that form a solvation sphere. Nonelectrolytes also become hydrated by water due to hydrogen bond formation between water and polar –OH groups.
The osmotic pressure of an aqueous 0.001 M starch solution is greater than that of an aqueous 0.001 M glucose solution.
False.
Polar molecules can induce polarity in nonpolar molecules.
True.
An aqueous solution of pH 3.0 contains H2O, H+, and OH-.
True.
An acid that dissociates to the extent of 88% in water would be termed a strong acid.
False.
An acid is weak if it dissociates less than 100% in water.
A solution that contains 0.05 mol of lactic acid and 0.05 mol of potassium lactate per liter of solution has a pH of 3.86.
True.
The major buffer system of the blood is the bicarbonate-carbonic acid buffer system.
True.
The shell of water molecules that surrounds a dissolved ion or molecule is called a hydrosphere.
False.
It is called a solvation sphere.
Although they operate over similar distances, hydrogen bonds are much stronger than van der Waals forces.
True.
In a buffer system, increasing the concentration of the conjugate base relative to that of the conjugate acid increases pH.
True.
Hydrophobic interactions explain why the olive oil in an open bottle does not readily evaporate.
False.
Hydrophobic interactions explain why hydrophobic molecules aggregate when placed in an aqueous environment.
____ is the tendency of an atom to attract to itself the shared electrons is a covalent bond.
Electronegativity
. ____ agents are certain ions and molecules that are poorly solvated in water and enhance the solubility of nonpolar compounds by disordering the water molecules.
Chaotropic
____ molecules contain both hydrophobic and hydrophilic groups.
Amphipathic
Soap molecules dissolved in water tend to form aggregates called ____.
Micelles
A shell of water molecules that forms around ions as they become dissolved is called a/an ____.
Solvation sphere
Attractive forces between molecules, collectively called ____, can occur due to dipole-dipole attractions, ion-dipole attractions, and interactions between two nonpolar atoms or molecules that result in transiently induced dipoles, which are known as London dispersion forces.
Van der waals
The unit(s) of Kw, the ion-product constant of water, is/are ____.
M2
An acid or base that dissociates less than 100% in water is described as being ____.
weak
The unit(s) of Ka, the dissociation constant for a weak acid, is/are ____.
M
A solution that contains equal or nearly equal quantities of a weak acid and its conjugate base is called a/an ____.
buffer
The condition called ____ results when a person’s blood pH becomes lower than normal.
acidosis
Compounds that dissolve in water to produce ions that can conduct a current through the resulting solution are called ____.
electrolytes
The strongest buffer in the bloodstream (including both plasma and red blood cells) after the carbon dioxide-carbonic acid-bicarbonate system is ____.
hemoglobin
Within the hydrophobic interior of a protein, the attraction between two oppositely charged functional groups is often called a _____.
salt bridge
In a medium of pH 2.0, aspartic acid has a net positive charge.
True.
At physiological pH, lysine will have at least one ionizable group that is uncharged.
False.
At physiological pH, all three lysine’s ionizable groups will be charged.
The amino acids with the most hydrophilic R-groups are overall uncharged at physiological pH.
False.
Most hydrophilic amino acids are arginine & lysine. Their R-groups are charged at physiological pH.
One mole of aspartic acid in its fully protonated form would require three moles of OH- to convert it to the fully unprotonated form.
True.
All 20 amino acids used to make natural proteins are optically active.
False.
Glycine is not, and has no chiral center since its side chain is an H atom.
The isoelectric point for most of the amino acids that have nonpolar side chains is about six.
True.
Since the common amino acids have the L-stereo configurations, one may assume that they will rotate plane-polarized light in a left-handed (levorotatory) direction.
False.
Direction of rotation of polarized light must be determined empirically. L- refers to the structural similarity to L-glyceraldehyde
The addition of 0.015 mole of L-valine to a solution containing 0.015 mole of D-valine would produce a solution that would exhibit twice the degree of rotation of polarized light that the D-valine solution had before the addition.
False.
The equal and opposite optical activities of D- and L-valine components would cancel. Equal amounts of 2 enantiomers constitute a racemic mixture.
A linear molecule made from amino acids linked end to end, containing four peptide bonds in its structure, is called a tetrapeptide.
False.
It’s a pentapeptide. The # of aa residues dictates the prefix used. Five residues would involve four peptide bonds.
All of the α-L amino acids with only one chiral carbon have the (S) designation in the RS system.
False.
Cysteine is the only exception. L-cysteine is R-cysteine because of side chain.
When electrophoresis is performed on a mixture of methionine and aspartic acid buffered at pH 5.25, methionine will move toward the cathode and aspartic acid will move toward the anode.
False.
pH of 5.7 is isoelectric point for methionine, so it will not migrate.
In SDS-PAGE, proteins are separated from each other primarily on the basis of their size and not their charge.
True.
SDS denatures proteins and associates w/ protein molecules giving all molecules a (-) charge proportional to their length. Thus, charge/mass ratios are the same for all SDS-proteins. Migration rates depend on size & charge/mass ratios. Since proteins coated w/ SDS anions have same charge/mass ratio, and migrate according to size only.
Complete amino acid analysis of a peptide is possible using acid hydrolysis with, for example, 6 M HCl at 110°C for 16-72 hours.
False.
This process converts L-glutamine & L-asparagine to L-glutamic and L-aspartic acid. L-tryptophan is destroyed, and some L-serine, L-threonine, and L-tyrosine are lost.
It is easier to determine the amino acid sequence of a protein by sequencing the DNA of the gene that codes for that protein than by purifying and directly sequencing the protein itself.
True.
!!! However, sequencing DNA does not permit identification of post-translationally modified aa !!!
Two proteins from different species that have very similar sequences are said to be ____.
homologous
An amino acid in a dipolar ion form can be called a/an ____.
zwitterion
The pH at which a given amino acid carries a net zero charge is referred to as ____.
isoelectric point
The covalent linkage formed by the oxidation of the side chains of two cysteine residues in a peptide or protein is called a/an ____.
disulfide bridge
A measure of the relative hydrophobicity or hydrophilicity of a given amino acid is called its ____.
hydropathy
The immediate surroundings of a side chain of a given amino acid residue in a protein are called its ____.
microenvironment
D-leucine and L-leucine may be called a pair of ____.
enantiomers
The specific sequence of amino acid residues in a peptide or protein is called its ____.
primary structure
The method to determine the sequence of a peptide by reacting phenylisothiocyanate with the N-terminal amino acid residue is called ____.
Edman degradation procedure
The sequence of a protein or peptide is given direction by indication the primary structure from its ____ to its ____.
N-terminus, C-terminus
____ has the R-group with the highest pKa value of the 20 common amino acids.
Arginine
____ and ____ are amide derivatives or aspartic acid and glutamic acid.
Asparagine, glutamine
Secondary structural features of a protein are stabilized by covalent bonds.
False
Hydrogen bonds stabilize areas of secondary structure
Nearly all peptide bonds in proteins studied to date have been found to have the trans conformation.
True
Trans is more favorable. Exception w/ peptide bond involving nitrogen of proline.
The tertiary structure of a globular protein is its overall three-dimensional shape.
True.
Metabolic proteins such as enzymes are globular proteins.
True.
Myoglobin binds O2 more readily than does hemoglobin.
True
Myoglobin is half saturated at pO2 of 2.8 torr, but a pO2 of 26 torr is required for half saturation of hemoglobin.
Fetal hemoglobin has a lower P50 than does adult hemoglobin, which indicates that fetal hemoglobin binds O2 less strongly than does adult hemoglobin.
False.
Indicates that fetal hemoglobin binds O2 more readily than does adult hemoglobin, making for efficient O2 transfer to the fetus
Oxygen-binding characteristics of hemoglobin proved to be quite different from those of myoglobin due to radical differences in the primary structure of their respective protein chains.
False.
The primary structures of the protein chains are very similar
The rise per amino acid residue in a segment of α-helix is called the pitch.
False
Pitch = distance along α-helix that constitutes one turn of the helix and involves ~ 3.6 aa residues.
The heme group of hemoglobin binds oxygen more strongly alone than it does when present in the hemoglobin molecule.
False
An isolated heme does not bind oxygen, but is oxidized from Fe2+ to Fe3+.
Recognizable combinations of α-helices and β-strands that appear in a number of different proteins are called domains.
False
They are called motifs.
Domains = independently folded regions, and may consist of combinations of motifs.
The hydrophilic side chains of amino acid residues normally locate themselves toward the exterior of globular proteins.
True
Allows interaction of these water-loving groups w/ the water molecules that surround the protein.
Denaturation destroys the biological activity of a protein by breaking many covalent bonds in the protein.
False
No covalent bonds are broken, however activity is lost due to loss of native tertiary structure.
The quaternary structure of proteins is maintained predominantly by noncovalent interactions.
True
Salt bridges, hydrogen bonding, hydrophobic interactions, and disulfide bonds help maintain association of monomers of an oligomeric protein.
Hemoglobin binds oxygen more strongly as the pH is lowered.
False
Low pH causes lowered oxygen affinity
Collagen is an example of a fibrous protein that contains only one type of secondary structure. In case of collagen, this is an α-helix.
False
Collagen is composed of three left handed helical chains coiled around each other in a right-handed fashion
Protein folding is impossible without aid from chaperone proteins.
False.
____ is the name of a new area of study that involves large sets of proteins.
Proteomics
The Bohr effect explains why hemoglobin has a ____ affinity for oxygen when levels of carbon dioxide and H+ are elevated.
decreased
The predominant type of secondary structure seen in myoglobin is ____.
α-helix
Denaturation of a protein by addition of a reducing agent indicates that ____ is/are present in the protein.
Disulfide bond
The form of the protein chain that occurs upon denaturation is called ____.
random coil
Proteins that possess quaternary structure are called ____.
Oligomeric proteins
The actual site of oxygen binding in the heme of myoglobin occurs between ____ and ____.
Fe2+ of heme group, histidine residue
Chaotropic agents, such as urea, cause denaturation of a protein mainly by disrupting ____.
Hydrophobic interactions
The process by which a protein that has been denatured assumes its native shape is called ____.
renaturation
The sigmoidal curve for binding of oxygen by hemoglobin illustrates the phenomenon of ____.
Positive cooperative binding
An organic molecule in erythrocytes that lowers the affinity of hemoglobin for oxygen is ____.
BPG
Scurvy is a condition arising from the inability to make functional collagen. On a molecular level, hydroxylysine and hydroxyproline are not formed due to the absence of ____. This results in collagen that is not properly crosslinked.
Vit. C
The interaction between the R-groups of a valine and leucine residue in a monomeric protein would contribute to ____ structure.
tertiary
In the immune response, foreign compounds called ____ cause the synthesis of proteins called ____ that combine with and precipitate the foreign compounds and mark them for destruction.
Antigens, antibodies
The activity of some proteins, such as hemoglobin, is modulated by specific small molecules called ____. Such proteins are called ____.
Allosteric modulators, allosteric proteins
The only biological catalysts are the proteins called enzymes.
False
Ribozymes possess catalytic activity
All enzymes require cofactors such as FAD and coenzymes A.
False
Many don’t require cofactors
An enzyme that catalyzes the addition of a phosphoryl group to glucose would likely not catalyze the same reaction for glycerol.
True
Enzymes are specific. Often D-sugar is recognized, but NOT L-form.
Any form of contact between an enzyme and its substrate will lead to reaction.
False
Substrate must fit specifically in the active site.
The formation of an enzyme-substrate complex is an unsupported hypothesis.
False
Observed via X-ray crystallography
A multi-substrate, enzyme-catalyzed reaction in which a product is released before all substrates have been bound to the enzyme is an example of a sequential kinetic mechanism.
False
Example of ping-pong mechanism
Km and Vmax values can best be determined graphically from a plot of initial velocity, v0, versus substrate concentrations, [S]. This type of plot is known as a Michaelis-Menten plot.
False
Not best way. Lineweaver-Burk plot gives better approximation of these values
The higher the Km value, the greater the affinity of an enzyme for its substrate.
False
Lower
The Km values of enzymes for their substrates are usually slightly higher than the intracellular concentration of their substrates.
True
Intracellular enzymatic rates are sensitive to small changes in substrate concentrations
A plot of kinetic data, vo vs. [S], that produces a sigmoidal curve indicates that cooperative interactions occur between enzyme subunits.
True.
Most regulatory enzymes are oligomeric proteins that catalyze reactions at a committed step in a pathway.
True.
Irreversible enzyme inhibitors form covalent bonds with side chains of the enzyme active site residues.
True
This permanently disables the enzyme unless the inhibitor is chemically removed.
A noncompetitive inhibitor does not cause a change in the maximum velocity of an enzyme-catalyzed reaction but it does result in an increase in the apparent Km value.
False
Noncompetitive = decrease Vmax, no Km change Competitive = increase Km, no Vmax change
The region of an enzyme molecule with which the substrate must interact in order for catalysis to occur is called the ____.
Active site
The short-lived species formed when enzyme and substrate interact initially is the ____.
Enzyme substrate complex
Enzymes that catalyze the conversion of a molecule into is structural isomer would belong to the IUBMB category of ____.
isomerases
The number of catalytic events catalyzed per second per enzyme molecule (or per active site) is called the ____.
Kcat
The ratio kcat/km is called the ____ and is a measure of the ____.
Specificity constant, specificity of enzyme for its substrate
Some enzymes are subject to control of activity by the addition and removal of phosphate groups. This is called regulation by ____.
Covalent modification
Due to its structure, a/an ____ inhibitor binds in the active site of an enzyme.
competitive
An inhibitor that does not alter the Km of the enzyme is a/an ____ inhibitor.
noncompetitive
An inhibitor that alters both the Km and Vmax of the enzyme system is a/an ____ inhibitor.
uncompetitive
Inhibition of a regulatory enzyme by an end product of the pathway is called ____ inhibition.
feedback
Sites where allosteric effectors bind to enzymes are called ____.
Allosteric or regulatory sites
An allosteric effector can be either a/an ____ or a/an ____.
Activator, inhibitor
Acetylsalicylic acid, commonly known as aspirin, reacts with a serine residue in the active site of the enzyme cyclooxygenase. The acetyl group is transferred to the serine residue. This would be an example of ____ inhibition.
irreversible
