Ch 2 Water Flashcards
What percentage of the mass of living things is water?
60 - 70%
This indicates the essential role of water in biological systems.
How is body water distributed in cells?
2/3 inside cells, 1/3 outside cells
What is the primary role of water in biological systems?
Water is the solvent for biological systems.
What is a hydrophilic compound?
A water-loving compound that interacts with and dissolves in water.
What types of compounds are considered hydrophilic?
- Polar compounds
- Ionic compounds
What is a hydrophobic compound?
A water-hating compound that avoids water.
What types of compounds are considered hydrophobic?
- Non-polar compounds
- Oils and fats
What makes water a polar molecule?
Electrons are unequally shared between oxygen and hydrogen.
Define electronegativity.
The tendency of an atom to attract electrons.
What is the significance of hydrogen bonds in biochemistry?
They provide organization to macromolecules but are weak enough to be readily broken.
What is a hydrogen bond?
A dipole-dipole bond between an electronegative atom and a hydrogen atom.
True or False: Water can act as both a weak acid and a weak base.
True
What is the relationship between [H+] and [OH–] in a solution?
[H+] and [OH–] are inversely related.
What is the pH of pure water at 25°C?
7.0
What does a strong acid do in solution?
Completely ionizes in aqueous solution.
What does a weak acid do in solution?
Is incompletely ionized in aqueous solution.
Define pK.
A measure related to an acid’s tendency to ionize.
What is the ionization constant of water (Kw)?
Kw = [H+][OH–] = 10–14 at 25°C.
What is the pH scale?
A logarithmic scale that measures hydrogen ion concentration.
What is the significance of pH being a logarithmic scale?
A difference of one pH unit represents a tenfold difference in [H+].
What is the formula for calculating pH?
pH = -log[H+]
What does the term ‘amphipathic’ refer to?
Molecules that have both hydrophilic and hydrophobic regions.
What is the Henderson-Hasselbalch equation used for?
Calculating pH based on the concentrations of an acid and its conjugate base.
What happens to ionic compounds when they dissolve in water?
They are pulled apart due to ion-dipole interactions.
Fill in the blank: Water can donate or accept a _______.
proton
What is the physiological pH of human blood?
7.4
What is the relationship between the concentration of H+ and OH– in neutral water?
[H+] = [OH–] = 10–7 M
What does the acid dissociation constant (Ka) measure?
The strength of an acid in terms of its ionization in water.
How does the electronegativity of oxygen compare to carbon and hydrogen?
Oxygen is more electronegative than both carbon and hydrogen.
What effect does adding an acid have on the pH of a solution?
Decreases pH
What effect does adding a base have on the pH of a solution?
Increases pH
What is the definition of an acid in biochemistry?
A substance that can donate a proton
What is the definition of a base in biochemistry?
A substance that can accept a proton
What does K_a represent?
The acid dissociation constant
What is the relationship between K_a and acid strength?
The larger the K_a value, the stronger the acid
How is pK_a calculated?
pK_a = -log K_a
What does a lower pK_a value indicate?
A stronger acid
What is the pK_a of an acid with a K_a value of 3.3 x 10^-3?
2.5
How does adding an acid affect pH?
Increases [H+] and decreases pH
How does adding a base affect pH?
Decreases [H+] and increases pH
What is a buffer?
A weak acid whose pH resists change upon addition of either more acid or more base
What components make up a buffer?
A weak acid and its conjugate base
What is the principal buffer in cells?
H2PO4-/HPO4^2-
What is the Henderson-Hasselbalch equation used for?
To relate pH to pK_a and the concentrations of acid and conjugate base
When is a buffer’s maximum buffering capacity achieved?
When pK_a equals pH, and [HA] = [A-]
What happens to the pH if [A-] is higher than [HA]?
The pH is higher than the pK_a
What happens to the pH if [A-] is lower than [HA]?
The pH is lower than the pK_a
What is the effective buffer range?
About 1 pH unit above or below the pK_a
What ratio of HA to A- occurs 1 pH unit below the pK_a?
90% HA: 10% A-
What ratio of HA to A- occurs 1 pH unit above the pK_a?
10% HA: 90% A-
What is the bicarbonate buffer system’s role in blood?
It helps maintain blood pH
What effect does hyperventilation have on blood pH?
Increases blood pH
What effect does hypoventilation have on blood pH?
Decreases blood pH
What is carbonic acid’s pK_a value?
Around 6.36
What is the significance of carbonic anhydrase?
One of the fastest enzymes, catalyzing reactions at rates of 10^4 to 10^6 reactions per second
Fill in the blank: Buffers resist changes in pH by either _______ H+ when an acid is added, or _______ H+ when a base is added.
[binding] [releasing]
