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Biochemistry > Chapter 2 Biochemistry > Flashcards

Chapter 2 Biochemistry Flashcards

1
Q

Hydrogen Bond

A

Electrostatic attraction between the oxygen atom of one water molecule and the hydrogen of another.

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2
Q

Water has a higher ____, ____, and ____ than most other common solvents.

A

Melting point, boiling point, and heat of vaporization.

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3
Q

Weak acids do/do not fully disassociate in water. Describe the concentration of reactants vs. products.

A

Do not fully disassociate. HA concentrations are much higher compared to strong acids and in equilibrium with concentration of A- and H3O+.

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4
Q

Strong acids do/do not fully disassociate. Describe the concentration of reactants vs. products.

A

Fully disassociate. HA concentrations are nonexistent compared to concentrations of A- and H3O+.

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5
Q

Hydrogen bonds are relatively strong/weak.

A

Relatively Weak

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6
Q

What is the bond disassociation energy of hydrogen bonds?

A

~23 kJ/mol in liquid H2O.

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7
Q

Hydrogen bonds are what percent covalent and what percent electrostatic?

A

10% covalent (due to overlapping bond orbitals) and 90% electrostatic.

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8
Q

Describe the lifetime of hydrogen bonds. What does fleeting mean?

A

Lifetime of each hydrogen bond is just 1 to 20 picoseconds in liquid. Fleeting means “When one hydrogen bond breaks, another forms”.”

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9
Q

What makes ice less dense than liquid water?

A

The crystal lattice structure found in ice.

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10
Q

Describe the number of hydrogen bonds formed in liquid vs. ice.

A

Liquid: Each H2O molecule forms hydrogen bonds with ~3.4 other molecules.
Ice: Each H2O molecule forms 4 hydrogen bonds.

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11
Q

Entropy (S)

A

Represents the randomness or disorder of the components of a chemical system.

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12
Q

Enthalpy (H)

A

Heat content, roughly reflecting the number and kind of bonds (breaking and making).

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13
Q

To bring about the synthesis of macromolecules from their monomeric units, what must be supplied to the system?

A

Free Energy (G)

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14
Q

Free Energy (G)

A

Represents the total energy of a system that can do work at constant temperature and pressure.
△G=△H-T△S

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15
Q

During melting or evaporation (solid →liquid →gas), describe the enthalpy, entropy, and free energy of the system.

A

Enthalpy (H) increases (heat is absorbed by the system). Entropy also increases as the particles become more disordered the closer you get to a gas state. At room temperature, melting and evaporation occur spontaneously meaning △G must be negative.

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16
Q

Hydrogen bonds readily form between an _____/______ and a ________.

A

Electronegative atom/hydrogen acceptor; hydrogen atom covalently bonded to another electronegative atom/hydrogen donor.

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17
Q

An unusual characteristic of H20 is:
A) Greater density in solid form (ice) than in liquid form (water).
B) High heat of vaporization.
C) Low specific heat.
D) Not readily forming intermolecular interactions.

A

B) High heat of vaporization.

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18
Q

Hydrogen atoms covalently bonded to which other element DO NOT participate in hydrogen bonding?

A

Carbon

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19
Q

What are four example compounds that are able to form hydrogen bonds with water?

A

Alcohols, Aldehydes, Ketones, and compounds containing N-H bonds.

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20
Q

Which atom does not commonly form hydrogen bonds between or within biological molecules?
A) Oxygen
B) Hydrogen
C) Carbon
D) Nitrogen

A

C) Carbon

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21
Q

When are hydrogen bonds strongest? Why? (Geometry)

A

When the acceptor atom is in line with the covalent bond between the donor atom and hydrogen. It maximizes electrostatic interaction.

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22
Q

Which statement about hydrogen bonds is false?
A) They only occur between water molecules.
B) They are weak compared to covalent bonds.
C) They cause acid-base reactions in aqueous solutions to be very rapid.
D) They have optimal geometry.

A

A) They only occur between water molecules.

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23
Q

Hydrophilic

A

Describes compounds that dissolve easily in H2O; generally charged or polar compounds.

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24
Q

Hydrophobic

A

Nonpolar molecules such as lipids and waxes.

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25
Q

Amphipathic

A

Contain regions that are polar (or charged) and regions that are nonpolar.

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26
Q

Dissolving table sugar into iced tea is an energetically favorable reaction due to a(n):
A) Increase in enthalpy as heat moves into the sugar.
B) Decrease in free energy due to broken weak interactions between sugar molecules.
C) Increase in entropy as the sugar dissolves.
D) Increase in free energy because there is no longer a salvation layer around the sugar crystal.

A

C) Increase in entropy as the sugar dissolves.

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27
Q

Nonpolar compounds:
A) Force surrounding H20 molecules to become disordered.
B) Increase entropy (△S) when dissolved in water.
C) Decrease enthalpy (△H) when dissolved in water.
D) Interfere with the hydrogen bonding among H2O molecules.

A

D) Interfere with the hydrogen bonding among H2O molecules.

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28
Q

Nonpolar compounds _______ with the hydrogen bonding among H2O molecules. Describe the enthalpy (H), entropy (S), and free energy (△G) of this process.

A

Interfere. Increases enthalpy (H), decreases entropy (S). Free energy change for dissolving a nonpolar solute in water is unfavorable (△G = +).

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29
Q

What happens when a non polar compound is dissolved in water?

A

H2O molecules for a highly ordered, cagelike shell around each solute molecule (maximizes solvent-solvent hydrogen bonding). H2O molecules are not as highly oriented as those in clathrates.

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30
Q

Clathrates

A

Crystalline compounds of nonpolar solutes and water.

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31
Q

How do amphipathic compounds behave in aqueous solutions?

A

Polar / hydrophilic region interacts favorably with H2O and tends to dissolve. Nonpolar / hydrophobic region tends to avoid contact with H2O and cluster together.

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32
Q

Micelles

A

Thermodynamically stable structures of amphipathic compounds in water.

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33
Q

Hydrophobic Effect

A

Amphipathic compounds in aqueous solutions: Nonpolar regions cluster together and polar regions arrange to maximize interactions with each other and the solvent.

34
Q

For macromolecules, the most stable structure usually maximizes/minimizes weak interactions.

A

Maximizes

35
Q

How are H2O molecules involved in the crystal structure of biomolecules/macromolecules?

A

H2O molecules are often found bound so tightly to biomolecules that they are part of the crystal structure. This is due to the maximization of weak interactions.

36
Q

What possible colligative properties do solutes alter when dissolved in a solvent? What determines the level of effect?

A

Vapor pressure, boiling point, melting point (freezing point), osmotic pressure. Effect depends on the number of solute particles (molecules or ions) in a given amount of water.

37
Q

Concentrated solutes produce ____________.

A

Osmotic Pressure

38
Q

What are the 3 effects of extracellular osmolarity on water movement in cells?

A

Isotonic, Hypotonic, Hypertonic

39
Q

Isotonic Solution

A

Osmolarity equal to that of a cell’s cytosol. (No net water movement)

40
Q

Hypertonic Solution

A

Higher osmolarity than that of the cytosol. (Water moves out of the cell and cell shrinks)

41
Q

Hypotonic Solution

A

Lower osmolarity than that of the cytosol. (Water moves into the cell and cell expands)

42
Q

What is osmotic pressure (Π)?

A

Force necessary to resist water movement.

43
Q

What is the van’t Hoff equation?

A

Π = icRT
Π = Osmotic Pressure
i = van’t Hoff’s factor
c = molar concentration of solute (mol/L)
R = gas constant
T = absolute temperature (Kelvin)
ic = osmolarity

44
Q

Explain the van’t Hoff factor.

A

A measure of the extent to which the solution disassociates into 2+ ionic species (i). For non ionizing solutes, i=1. For solutes that disassociate into two ions, i=2. (I.E. In dilute NaCl solutions, the solute completely disassociates into Na+ and Cl-, doubling the number of particles.)

45
Q

LQ: I need to calculate the osmotic pressure of a solvent. I know the concentration of the solute and the temperature of the solution. What else do I need?
A) Whether the solute disassociates into 2+ ion species.
B) The vapor pressure of the solvent.
C) The boiling point of the solvent.
D) Whether the solvent is hydrophilic or hydrophobic.

A

A) Whether the solute disassociates into 2+ ion species.

46
Q

LQ: Which condition would cause red blood cells to burst due to excess water passing through the plasma membrane?
A) Placing the cells in a solution of higher osmolarity than is present within the cells.
B) Placing the cells in a solution of amphipathic molecules.
C) Adding a charged solute, such as NaCl, to the cell suspension.
D) Placing the cells in hypotonic solution.

A

D) Placing the cells in a hypotonic solution.

47
Q

H2O molecules have a slight tendency to undergo _________ to yield a hydrogen ion (a proton) and a hydroxide ion.

A

Reversible Ionization

48
Q

Proton hopping results in high/low ionic mobility.

A

High Ionic Mobility

49
Q

Hydrogen ions are immediately hydrated to form ________.

A

Hydronium Ions (H3O+)

50
Q

Describe the process of proton hopping.

A

Hydronium ion gives up a proton, a water molecule some distance away acquires one, becoming a hydronium ion.

51
Q

What is neutral pH in terms of water?

A

Exactly equal concentrations of H+ and OH-, as in pure water.

52
Q

Are solutions with pH > 7 acidic or basic/alkaline?

A

Alkaline / Basic.

53
Q

Are solutions with pH < 7 acidic or basic/alkaline?

A

Acidic

54
Q

Describe the concentrations of H+ vs. OH- in acidic solutions.

A

Concentration of H+ is greater than concentration of OH-.

55
Q

Describe the concentrations of H+ vs. OH- in basic/alkaline solutions.

A

Concentration of OH- is greater than concentration of H+.

56
Q

Acidosis and effects.

A

pH of blood plasma below the normal value of 7.4. Common in people with severe / uncontrolled diabetes and responsible for amputations. Extreme acidosis can be life threatening.

57
Q

Alkalosis and effects.

A

pH of blood plasma above the normal value of 7.4. Causes electrolyte imbalance, seizures, passing out. Extreme alkalosis can be life threatening.

58
Q

LQ: The pH of an aqueous solution:
A) Must remain at 7.
B) Is not affected by adding OH-.
C) Depends solely on the ionization of water.
D) Is a function of hydrogen ion concentration (to a reasonable approximation).

A

D) Is a function of hydrogen ion concentration (to a reasonable concentration).

59
Q

Conjugate Acid-Base Pair

A

A proton donor and its corresponding proton acceptor.

60
Q

What is the term for how water can act as an acid and a base?

A

Amphiprotic

61
Q

Acid _________ proton in water (___________).

A

releases; proton donor

62
Q

Base _______ proton in water (_________).

A

accepts; proton acceptor

63
Q

LQ: When H2O ionizes:
A) The △G°=0 kJ/mol.
B) It has a measurable Keq.
C) Its concentration (7 M) does not appreciably change.
D) Free H+ ions are present in solution.

A

B) It has a measurable Keq.

64
Q

How does pKa tell us the strength of an acid?

A

Tells us how tightly a proton is held by an acid. The stronger the tendency to dissociate a proton, the stronger the acid, and the lower its pKa.

65
Q

LQ: Weak acids:
A) Only partially ionize in water.
B) Have a pKa < 7.
C) React very slowly with bases.
D) Are formed by the dilution of strong acids.

A

A) Only partially ionize in water.

66
Q

Define titration curve and describe what happens at its midpoint.

A

A plot of pH against the amount of NaOH added and it reveals the pKa of a weak acid. At the midpoint, the pH of the equimolar solution is equal to the pKa of the starting acid.

67
Q

LQ: The pKa of a weak acid:
A) Is a function of its concentration.
B) Is the pH at which it has no net charge.
C) Is <0 at pH>7.
D) Can be determined from its titration curve.

A

D) Can be determined from its titration curve.

68
Q

Buffers

A

Aqueous systems that tend to resist changes in pH when small amounts of acid (H+) or base (OH-) are added.

69
Q

What does a Buffer System consist of?

A

Consists of a weak acid (the proton donor) and its conjugate base (the proton acceptor) or vis-versa.

70
Q

Name 2 ways our bodies utilize buffers.

A

Maintain blood pH and physiological pH inside cells.

71
Q

Buffering Region

A

The flat zone of a titration curve.

72
Q

At what region in a titration curve is a buffer effective?

A

+/- 1 pH of the pKa.

73
Q

At which concentration of conjugate bases and acids is the best region for buffering?

A

When conjugate base and acid concentrations are equal.

74
Q

LQ: What is the actual function of a buffer system such as acetate/acetic acid?
A) To maintain a constant pH in the event that the concentration of an acid or base increases.
B) To maintain the solution at the pKa.
C) To ensure that the solution has no free H+ or OH- within a specific range.
D) To keep the solution within one pH unit of the pKa.

A

A) To maintain a constant pH in the event that the concentration of an acid or base increases.

75
Q

What is the function of the Henderson-Hasselbalch equation?

A

Describes the same of the titration curve of any weak acid (Describes the behavior of the weak acids in solution).

76
Q

LQ: I need to calculate the pH of a weak acid. I know the concentration of the acid and its conjugate base, and my solution is at 30° C. Using the Henderson-Hasselbalch equation, what else do I need?
A) The Kd for H+ of the acid.
B) The total H+ concentration (that is, free and bound to the acid).
C) The free-energy change for the release of the H+.
D) The pKa of the acid.

A

D) The pKa of the acid.

77
Q

How does your body protect against changes in pH?

A

Proteins containing histadine (side chain pKa of 6.0) residues buffer effectively near neutral pH.

78
Q

LQ: Which statement about buffers is false?
A) They have a maximum buffering capacity at pH 7.
B) They are weak acids and bases.
C) [A-] = [HA] when pH = pKa.
D) They can sometimes be biological macromolecules.

A

A) They have a maximum buffering capacity at pH 7.

79
Q

Optimum pH

A

The characteristic pH at which enzymes typically show maximum catalytic activity.

80
Q

What are the two digestive enzymes discussed within optimum pH?

A

Pepsin (Stomach) and Trypsin (Small Intestine)

Biochemistry (3 decks)

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