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
