Chapter 2 and Exam 1 multiple choice

An amphiphilic molecule: A. Has both polar and non-polar groups. B.Has neither polar nor non-polar groups. C. Has polar groups. D. Has non-polar group

A. Has both polar and non-polar groups.

Modifications of amino acids in proteins: A. Occurs post-translationally B. Occurs before the amino acid is incorporated into the protein C. Can involve formation of an ether with the hydroxyl groups of serine, Thr or Tyr D. Has no effect on protein function E. None of the above

A. Occurs post-translationally

Which of the following statements accurately describes hydrogen bonds in water at room temperature? A. The hydrogen bonds are a constantly changing network. B. There is a network of interactions where each water molecule is hydrogen bonded to 3 other water molecules. C. There is an organized and regular network of interactions between water molecules.

A. The hydrogen bonds are a constantly changing network.

Which statement about the pK is not true? A. The pK is equal to the pH at the maximum slope of the titration curve. B. The pK is equal to the pH at the midpoint of the titration. C. The pK is equal to the pH at the maximal buffering capacity. D. The pK is equal to the pH when [A-] = [HA].

A. The pK is equal to the pH at the maximum slope of the titration curve.

Which of the following correctly lists bonding interactions in terms of their increasing strength: A. Van der Waals interactions<hydrogen bonding<ionic interactions<covalent bonds B. Covalent bonds<hydrogen bonds<ionic interactions<Van der Waals interactions C. Van der Waals interactions<ionic interactions<hydrogen bonding<covalent bonds D. Hydrogen bonds<ionic interactions<covalent interactions<Van der Waals interactions

A. Van der Waals interactions<hydrogen bonding<ionic interactions<covalent bonds

Which of the following statements is not accurate when considering water and biological molecules? A. Water is more likely to act as a hydrogen bond donor than a hydrogen bond acceptor. B. Polar substances are soluble because of their interaction with water. C. The hydrogen bonding pattern of water is disrupted by the presence of hydrophobic molecules.

A. Water is more likely to act as a hydrogen bond donor than a hydrogen bond acceptor.

Which of the following statements is not accurate when considering water and biological molecules? A. Water is more likely to act as a hydrogen bond donor than a hydrogen bond acceptor. B. The hydrogen bonding pattern of water is disrupted by the presence of hydrophobic molecules. C. Polar substances are soluble because of their interaction with water.

A. Water is more likely to act as a hydrogen bond donor than a hydrogen bond acceptor.

Which of the following functional groups could NOT act as a hydrogen bond donor? A. An ester. B. Both aldehyde and ester. C. An aldehyde. D. A hydroxyl group. E. An amino group.

B. Both aldehyde and ester.

Which statement about a chemical reaction at equilibrium is false? A. ∆G = 0 B. The concentration of products equals the concentration of reactants. C. Forward and reverse reactions proceed (continue), but the concentrations of reactants and products do not change. D. ∆H = T∆S

B. The concentration of products equals the concentration of reactants.

water forms a cage like structure around the hydrophobic structure

Clathrate Structure

Which property of liquid water is also true for solid water? A. The density of liquid water, 1.0 g•mL-1. B. Liquid water tends to form hydrogen bonded rings of three to seven molecules. C. Liquid water consists of a rapidly fluctuating, three-dimensional network of hydrogen-bonded molecules. D. Liquid water has an extensive hydrogen bond network.

D. Liquid water has an extensive hydrogen bond network.

Consider a solution separated from pure water by a semipermeable membrane that permits the passage of water, but not solutes. Which statement is false? A. Osmotic pressure could be eliminated if enough solute were added to the region of pure water. B. Osmosis is the movement of solvent from a region of high solvent concentration to a solution of lower solvent concentration. C. Osmotic pressure is the pressure that must be applied to the solution to prevent the inflow of water. D. Osmotic pressure depends upon the size of the solute molecules.

D. Osmotic pressure depends upon the size of the solute molecules.

relatively weak charge-charge interactions between 2 ionized groups

Electrostatic Interactions

A solution in which the concentration of solutes is essentially equal to that of the cell which resides in the solution; there will be no net water movement because the osmolarity in and outside the cell is the same

Isotonic Solution

relates the pH of a solution to the pKa and the concentrations of acid and conjugate base: pH= pKa + log (A- / HA)

The Henderson-Hasselbach equation

Hydrophobic interactions are the driving force in the formation of micelles of amphipathic compounds in water, T/F?

True

T/F: Hydrogen bonds account for anomalously high boiling points of water

True

T/F: Hydrophobic interactions are the driving force in the formation of micelles of amphipathic compounds in water.

True

A __________ is a solution that resists pH changes.

buffer

Hydrogen-bonded atoms are separated by van der Waals distances, T/F?

false

The properties of water are typical for molecules of its size, T/F?

false

Weak acids have dissociation constants that are greater than one, T/F?

false

Osmosis is the movement of the solute across a semipermeable membrane from a region of high concentration to a region of low concentration, T/F?

false, movement of a solvent

What is mainly present in solution at equilibrium?

mainly HA

What are spheroidal globules of up to several thousand amphiphilic molecules, in which the hydrophobic groups are buried and the polar groups form the surface?

micelles

Which of the following properties of water doesn't contribute to the fitness of the aqueous environment for living organisms?

the very low molecular weight of water

A plot of pH versus the [OH-] added to a solution of a weak acid is called a.....

titration curve

A hydronium ion (H3O+) has the potential to be a hydrogen bond acceptor, T/F?

true

In general, a hydrogen bond can be represented as D-H•••A, where D-H is a weakly acidic "donor" group such as O-H, N-H, or sometimes S-H, and A is a weakly basic "acceptor" atom such as O, N, or occasionally S, T/F?

true

Molecules in liquid water are each hydrogen bonded to four nearest neighbors, as they are in ice. These hydrogen bonds are distorted, however, so the networks of linked molecules are irregular and varied whereas they are ordered in ice, where each water molecule is tetrahedrally surrounded by four nearest neighbors to which it is hydrogen bonded, T/F?

true

Solutions in which [H+] = [OH-] are said to be neutral, T/F?

true

Solutions in which [H+] > 10-7 are said to be acidic, T/F?

true

The Henderson-Hasselbalch equation, given by pH = pK + log ([A-]/[HA]), is very useful for calculating the pH of solutions of weak acids, T/F?

true

The hydrophobic effect is due largely to entropy changes in the solvent water, T/F?

true

Water solvates both positive and negative ion, T/F?

true

Noncovalent associations between neutral molecules are due to forces known generally as ______________ forces.

van der Waals

Osmosis is movement of a: A) charged solute molecule (ion) across a membrane. B) gas molecule across a membrane. C) nonpolar solute molecule across a membrane. D) polar solute molecule across a membrane. E) water molecule across a membrane.

water molecule across a membrane

Which is the conjugate base? 1) RCOOH RCOO- 2) RNH2 RNH3+ 3) H2PO4- H3PO4 4) H2CO3 HCO3-

1) RCOO- 2) RNH2 3) H2PO4- 4) HCO3-

Define pKa for a weak acid in the following 2 ways: 1) in relation to its acid dissociation constant, Ka, and 2) by reference to a titration curve for the weak acid.

1) pKa = -log Ka ; 2) pKa is the value of pH at the inflection point in a plot of pH vs. extent of titration of the weak acid. At the pKa, the concentration of ionized acid equals the concentration of unionized acid

Rank the following bond/interaction distances correctly in order from shortest to longest: A. Covalent bond, hydrogen bond, van der Waals interactions. B. Hydrogen bond, van der Waals interactions, covalent bond. C. Van der Waals interactions, covalent bond, hydrogen bond. D. Van der Waals interactions, hydrogen bond, covalent bond. E. Covalent bond, van der Waals interactions, hydrogen bond.

A. Covalent bond, hydrogen bond, van der Waals interactions.

Which statement is NOT a principle of the theory of evolution? A. Evolution is largely completed B. Evolution requires some built-in sloppiness, i.e. random mutations in genetic information C. Evolution is not directed toward a particular goal D. Evolution is constrained by its past E. All of the above are principles in the theory of evolution

A. Evolution is largely completed

Which of the following statements is not accurate when considering water and biological molecules? A. Non-polar substances associate with water to maximize their exposed surface area. B. Water can act as a hydrogen bond donor. C. Polar substances are soluble because of their interaction with water. D. Water can act as a hydrogen bond acceptor.

A. Non-polar substances associate with water to maximize their exposed surface area.

A solution that contains appreciable amounts of a weak acid and its conjugate base such that upon addition of strong acid/base or upon dilution the pH doesn't change appreciably

Buffers

Which pair of amino acids have complementary R-groups? A. K and R B. C and E C. E and K D. Q and D E. P and D

C. E and K

Which statement best explains why water can solvate both negative and positive ions? A. It can ionize. B. It can hydrogen bond. C. It is dipolar. D. It is very small.

C. It is dipolar.

Which of the following statements about water is false? A. Water molecules make hydrogen bonds readily with each other and with other polar substances. B. Water is a cohesive substance. C. The hydrophobic effect results when solutes are unable to break hydrogen bonds between water molecules. D. Water has a high melting point relative to its molecular mass. E. Nonpolar substances decrease the entropy of water molecules.

C. The hydrophobic effect results when solutes are unable to break hydrogen bonds between water molecules.

Which of the following cellular components could be separated from each other by differential centrifugation? A. a mixture of soluble cytosolic proteins from each other B. a soluble mitochondrial protein and another soluble protein inside the mitochondrion C. a soluble cytosolic protein and a soluble mitochondrial protein D. various nucleic acids from each other E. none of the above

C. a soluble cytosolic protein and a soluble mitochondrial protein

Which of the following would not typically be involved in hydrophobic interactions? A. lipid bilayer B. phenyl groups C. hydroxyl groups D. isoleucine-R group E. fatty acid micelle

C. hydroxyl groups

Which is the weakest interaction? A. A covalent bond between the O and H atoms of water. B. A hydrogen bond between two water molecules. C. An ionic interaction between a carboxylic acid and an amine. D. A van der Waals interaction between two methyl groups.

D. A van der Waals interaction between two methyl groups.

Which one of the following statements about the Beta-sheet is FALSE? A. Beta sheet is a type of secondary structure that is stabilized by H-bonds B. Beta sheets can be parallel or anti-parallel C. The AA R groups in a beta sheet alternate between the 2 sides of the sheet D. Beta sheet structure cannot be at the surface of a globular protein because all of the amino acids in a beta sheet must be nonpolar E. the beta sheet contains H-bonds between carbonyl oxygen of one residue and an amide hydrogen of a residue on an adjacent strand

D. Beta sheet structure cannot be at the surface of a globular protein because all of the amino acids in a beta sheet must be nonpolar

Which of the following groups of amino acids is LEAST likely to be buried in the center of a water-soluble globular protein? A. Tyr, Phe, Trp B. Gly, Asn, Val C. Pro, Ala, His D. Glu, Asp, Lys E. Ile, Leu, Phe

D. Glu, Asp, Lys

Which statement about the Bronsted-Lowry formulation of acid-base chemistry is false? A. A base is a substance that can accept a proton. B. An acid is a substance that can donate a proton. C. A- is the conjugate base of the acid HA. D. H3O+ is the conjugate base of the acid H2O.

D. H3O+ is the conjugate base of the acid H2O.

Which statement is NOT an important aspect of the hydrophobic effect? A. The ∆H is near zero or positive when hydrophobic molecules are excluded from water. B. The larger the surface area of a hydrophobic molecule, the greater the loss of entropy by interacting solvent water. C. The entropy of water increases when hydrophobic molecules are excluded from water. D. Hydrophobic molecules have a strong affinity to interact with each other instead of water.

D. Hydrophobic molecules have a strong affinity to interact with each other instead of water.

Why are the ionic mobilities of H+ and OH- in an aqueous environment much greater than that of other ions? A. They are smaller than most other ions. B. They have less mass than other ions. C. They have unit charge. D. The hydrogen ion can hop from one water molecule to another.

D. The hydrogen ion can hop from one water molecule to another.

Which statement best explains why nonpolar substances have low solubility in water? A. They are much denser than water. B. They have strong mutual attractions. C. They are much larger than water. D. They cannot form hydrogen bonds to water.

D. They cannot form hydrogen bonds to water.

Which statement is NOT a reason for the centrality of water in biochemistry? A. Water is oxidized to oxygen during photosynthesis. B. Water and its ionic components participate in many biochemical reactions. C. The medium for most biochemical reactions is water. D. Water in oceans covers most of the surface of our planet

D. Water in oceans covers most of the surface of our planet

Which of the following types of bonding interactions is NOT classified as non-covalent? A. Hydrogen bonding. B. Electrostatic interactions. C. Van der Waals. D. Dipole-Dipole interactions. E. None of the above

E. None of the above

Which of the following statements about water is FALSE? A. Substances with polar functional groups are generally soluble in water. B. Water will act as a hydrogen bond acceptor with hydroxyl groups. C. Water carries a dipole because of the geometry of the two oxygen-hydrogen bonds. D. A network of electrostatic interactions exists between the molecules in water. E. The hydrophobic effect is driven largely by the entropy of the non-polar substance.

E. The hydrophobic effect is driven largely by the entropy of the non-polar substance.

Consider the peptide represented by the following: EYTALIPR If the sequence were unknown to you, what would reacting this peptide with trypsin help to determine? A. the peptide absorbs maximally at 280nm B. the peptide is soluble in water C. the peptide has a -1 net charge in solution at pH7 D. that Glu is the N-terminal amino acid E. if the peptide contains either a lysine or arginine

E. if the peptide contains either a lysine or arginine

Explain the fact that ethanol (Ch3Ch2OH) is more soluble in water than ethane (Ch3Ch3)

Ethanol can form hydrogen bonds with water molecules but ethane cant due to the OH group on the ethanol that contains a more electronegative atom oxygen

weak electrostatic attractions between a pair of electrons on one electronegative atom and a hydrogen atom covalently linked to a second electronegative atom

Hydrogen Bonds

the forces that tend to bring together two hydrophobic groups , reducing the total area of the 2 groups that is exposed to surroundings molecules of the polar solvent (water)

Hydrophobic Interactions

The tendency of water to minimize its contacts with hydrophobic molecules is termed the.....

Hydrophobic effect

when comparing two solutions, the solution with the greater concentration of solutes; water will move out of the cell and it will shrink

Hypertonic Solution

Having a lower concentration of solute than another solution; water will move into the cell causing the cell to swell and maybe burst

Hypotonic Solution

If ice were denser than water, how would that affect life on earth?

Ice formed at the surface of bodies of water would sink hence streams/lakes/etc. would freeze from the bottom up. The water with ice on the bottom would be forever cold and in the limit they would freeze solid, precluding life

A solution of known concentration is used to determine the concentration of another solution.

Titration

Hydrogen bonds readily form in aqueous solutions, T/F?

True

T/F: Hydrophobic interactions contribute to the structure of water-soluble proteins.

True

weak interactions between the electric dipoles that 2 close-spaced atoms induce in each other

Van der Waals Forces

According to the Brönsted-Lowry definition, a ___________ is a substance that can accept a proton.

base

London dispersion forces are long range, but weak forces, T/F?

false, short range and weak

Water is a neutral molecule that ionizes to a great extent, T/F?

false, to a small extent

Substances that can undergo more than one ionization are known as _____________ acids.

polyprotic