Quiz 2

Question 1

Covalent bonds

Answer 1

Hold atoms together so that molecules are formed

Question 2

Weak forces

Answer 2

Create interactions that are constantly forming and breaking under physiological conditions
1. Van der waals (closest fit )
2. Hydrogen bonding ( short and straight )
3. Ionic interactions ( opposite charges )

Question 3

Molecular recognition

Answer 3

Is mediated by weak chemical forces

for example: hydrogen bonds forms double bonded DNA

Question 4

Restricts organism to a narrow range of environmental conditions

Answer 4

Weak forces.
- changes in its temperature pressure or pH can easily disrupt weak forces

Question 5

Van der waals

Answer 5

Is enhanced in molecules that are structurally complementary

Question 6

Important hydrogen bonds

Answer 6

Straight short (~3A)
[ higher in energy ,harder to break thus bond angle important for directionality ]

Question 7

H-bond donors

Answer 7

Electronegative atoms O and N attached to H

Question 8

H-bond acceptors

Answer 8

The electronegative atoms O and N

Question 9

Ionic bonds

Answer 9

• unlike h bonds, they do not require specific angles
• weak interactions contribute to stability of proteins

Question 10

Water molecules

Answer 10

• polar
• high dielectric constant : solvates polar groups well [ attraction of charges and partial charges are responsible ]
• forms H bonds with polar, uncharged solutes

Question 11

Ice

Answer 11

• water molecules that are hydrogen bonded in a crystalline array
• 4 H bonds

Question 12

Attractive forces acting on biological molecules

Answer 12

• ionic interactions
• hydrogen bonds
• van der waals interactions

Question 13

Non polar substances

Answer 13

• do not dissolve in water

Question 14

Hydrophobic effect [1]

Answer 14

• exclusion of non polar groups as a way to maximize entropy of water molecules
• non polar molecules aggregate together to free many molecules of water, vastly increasing entropy

[increased freedom of water molecules by decreasing surface area of the non polar solute]

Question 15

Amphiphilic

Answer 15

• form micelles or bilayers that hide their hydrophobic groups while exposing their hydrophilic groups to water
  Polar heads and non polar tails

Question 16

Osmosis

Answer 16

Solvent molecules diffuse across membranes which are permeable to them from regions of higher concentration to regions of lower concentrations
- diffusion of solvents

Question 17

Dialysis

Answer 17

Solute diffuse across a semipermeable membrane from regions of higher concentrations to regions of lower concentration
- diffusion of solutes

Question 18

Important for water

Answer 18

• Bent structure is key, makes it polar
• Non- tetrahedral bond angles define directionality of interactions
• H- bond donors and H-bond acceptors
• Able to form 4 H bonds per water molecule [ice forms 4]

Question 19

Liquid water

Answer 19

2-3 H bonds per water molecule at any given time
H bonds of liquid water are too transient to form all 4 at once

Question 20

Ions

Answer 20

Carry around a hydration shell of water molecules
[always hydrated in water]

Question 21

Water H bonds with

Answer 21

• hydroxyl group
• carbonyl group
• carboxyl group
• amino group

Question 22

hydrophobic effect

Answer 22

• non polar molecules aggregate together to free many molecules of water vastly INCREASING ENTROPY[favored] , without losing any of the enthalpy

Question 23

Water-water H bonds are enthalpicaly favorable (hydrophobic effect)

Answer 23

The increase in the order of water is even more strongly entropically opposed

Question 24

Dissociation constant

Answer 24

10^-14
- varies with strength of an acid

Question 25

Acidity of a solution is expressed as pH value

Answer 25

pH =-log[H+]

Question 26

Acid

Answer 26

A compound that can donate a proton

Question 27

Base

Answer 27

A compound that accepts a proton

Question 28

Henderson—Hasselbach equation

Answer 28

Relates the pH of a solution of a weak acid to the pK and the concentrations of the acid and its conjugate base

Question 29

A titration curve demonstrates

Answer 29

• if the concentrations of an acid and its conjugate are close, the solution is buffered against changes in pH when acid or base is added

Question 30

Many biological molecules contain

Answer 30

Ionizable groups ( they are sensitive to changes in pH )

Question 31

How does water get acidic

Answer 31

A protonated solute [acid] was added to water, deprotenated and increased the [H+]

Question 32

How does water turn basic

Answer 32

The addition of a base takes a proton from water leaving behind an increased [OH-] and correspondingly lower [H+]

Question 33

Weak acids

Answer 33

Significant concentration of both ionized (A-) and protonated (HA) species in equilibrium

HA -><- H+ + A-

pKa is the pH when [A-]=[HA]

Question 34

For any acid HA

Answer 34

• the relationship between the pKa, the concentrations existing at equilibrium, and the solution pH is given by
  pH = pKa + log10([A-]/[HA])

Question 35

Buffers

Answer 35

• solutions that resist changes in pH as acid and base are added ( as protons are added or dissociated )
• protect function of bio molecules
• most buffers consist of weak acid and its conjugate base
• can only be used reliably within one pH unit of their pKa

Question 36

The plot of pH versus H+ dissociated is

Answer 36

Flat near the pKa

Question 37

Buffer action

Answer 37

Is a continuous cycle of protonation and deprotanation as long as both [HA] and [A] are in present abundance
Both abundant at the pKa and up to one log of H+ on either side

Question 38

Buffers hold ___

Answer 38

pH constant to preserve activity