Chapter 2 Flashcards
. In contrast, nonpolar biomolecules are poorly
soluble in water because
they interfere with water-water
interactions but are unable to form water-solute interactions.
Hydrogen bonds
account for the relatively high melting point of water, because
much thermal energy is required to break a sufficient proportion
of hydrogen bonds to destabilize the crystal lattice of ice.
why are hydrogen bonds highly directional
see pg 262
Water dissolves salts such as NaCl by
y hydrating and stabilizing the Na \+ and Cl − ions, weakening the electrostatic interactions between them and thus counteracting their tendency to associate in a crystalline lattice
what else does water readily dissolve and give examples
Water also readily dissolves
charged biomolecules, including compounds with functional
groups such as ionized carboxylic acids (—COO
−
), protonated
amines (—NH
+
3
), and phosphate esters or anhydrides. Water
replaces the solute-solute hydrogen bonds linking these
biomolecules to each other with solute-water hydrogen bonds,
thus screening the electrostatic interactions between solute
molecules.
Nonpolar compounds such
as benzene and hexane are hydrophobic meaning
they are unable to
undergo energetically favorable interactions with water
molecules, and they interfere with the hydrogen bonding among
water molecules.
When two uncharged atoms are brought very close together,
their
surrounding electron clouds influence each other. Random
variations in the positions of the electrons around one nucleus
may create a transient electric dipole, which induces a transient,
opposite electric dipole in the nearby atom. T
. The two dipoles
weakly attract each other,
bringing the two nuclei closer. These
weak attractions are called van der Waals interactions (also
known as London dispersion forces). As the two nuclei draw
closer together, their electron clouds begin to repel each other
when are the nuclei said to be in van der waals contact
At
the point where the net attraction is maximal,
Macromolecules such as proteins, DNA, and RNA contain so many
sites of potential hydrogen bonding or ionic, van der Waals, or
hydrophobic clustering that the cumulative effect can be
enormous.
what is te most stable structure for macromolecules
For macromolecules, the most stable (that is,
the native) structure is usually that in which these weak
interactions are maximized. ( weak interactions being examples of vdw, hydrophobic clustering- its in card 10)
what is essential to the function for many proteins
For many proteins, tightly bound water molecules are
essential to their function.
osmotic pressure graph on pg 281
kk
explanation of the vant hoff equation on pgs 281-282
kk
good practice question on pg 285
kk
good summary on pg 286
kk
The very different electronegativities of H and O make water a
highly polar molecule, capable of forming hydrogen bonds with
itself and with solutes. Hydrogen bonds are fleeting, primarily
electrostatic, and weaker than covalent bonds.
Alcohols, aldehydes, ketones, and compounds containing N—H
bonds all form
hydrogen bonds with water and are therefore
water soluble
By screening the electrical charges of ions and by increasing
the entropy of the system, water
dissolves crystals of ionizable
solutes.
N2, O2, and CO2 are… nh3 and h2s are…
nonpolar and poorly soluble in water…ionizable and therefore very water soluble.
Nonpolar (hydrophobic) compounds- how they dissolve, what can’t they do and what does their presence cause. what do they do to avoid water
dissolve poorly in water;
they cannot hydrogen-bond with the solvent, and their presence
forces an energetically unfavorable ordering of water molecules
at their hydrophobic surfaces. To minimize the surface exposed to
water, nonpolar and amphipathic compounds such as lipids form
aggregates (micelles and bilayer vesicles) in which the
hydrophobic moieties are sequestered in the interior, an
association driven by the hydrophobic effect, and only the more
polar moieties interact with water.
van der Waals interactions exist when
two nearby nuclei
induce dipoles in each other. The nearest approach of two atoms
defines the van der Waals radius of each.
Weak, noncovalent interactions, in large numbers, decisively
influence
the folding of macromolecules such as proteins and
nucleic acids.
(related to card 23, they were part of the same point)The most stable macromolecular conformations
are those in
which hydrogen bonding is maximized within the
molecule and between the molecule and the solvent, and in which
hydrophobic moieties cluster in the interior of the molecule away
from the aqueous solvent.
When two aqueous compartments are separated by a
semipermeable membrane (such as the plasma membrane
separating a cell from its surroundings), water moves across that
membrane to
o equalize the osmolarity in the two compartments.
(part of the same point as card 25) what produces osmotic pressure
When two aqueous compartments are separated by a
semipermeable membrane (such as the plasma membrane
separating a cell from its surroundings), water moves across that
membrane to equalize the osmolarity in the two compartments.
This tendency for water to move across a semipermeable
membrane produces the osmotic pressure
When weak acids are dissolved in water,
they contribute
H
+ by ionizing; weak bases consume H
+ by
becoming protonated.
The ionization of water can be measured by its electrical
conductivity;
pure water carries electrical current as H3O \+ migrates toward the cathode and OH − migrates toward the anode.
ph chart on pg 298
kk
why is Measurement of pH is one of the most important and
frequently used procedures in biochemistry.
The pH affects the structure and activity of biological macromolecules, so a small change in pH can cause a large change in the structure and function of a protein
acids and bases def
Acids (in the Brønsted-Lowry definition) are proton donors, and
bases are proton acceptors
When a proton donor such as acetic
acid (CH3COOH) loses a proton… also what is a conjugate acid-base pair
it becomes the corresponding
proton acceptor, in this case the acetate anion (CH3COO
−
). A
proton donor and its corresponding proton acceptor make up a
conjugate acid-base pair (Fig. 2-15), related by the reversible
reaction
equation at the bottom of pg 302
what is a titration curve and what does it reveal
in this example on pg 306, a titration curve is a plot of pH against the amount of NAOH added. a titration curve reveals the pka of the weak acid./
see the example on pg 307-30-8
kk
Pure water ionizes slightly, forming
equal numbers of
hydrogen ions (hydronium ions, H3O
+
) and hydroxide ions.
The extent of ionization is described by an equilibrium
constant, Keq = {H}{OH}/[h20), from which the ion product of
water, Kw, is derived.
At 25 °C, Kw = [H \+ ] [OH − ] = (55.5 M)(Keq) = 10^ −14 M 2
The pH of an aqueous solution reflects, on a logarithmic scale,
the concentration of hydrogen ions:
Weak acids partially ionize to release a hydrogen ion, thus… also what do weak bases do and what is the extent of these processes characteristic of?
lowering the pH of the aqueous solution. Weak bases accept a
hydrogen ion, increasing the pH. The extent of these processes is
characteristic of each particular weak acid or base and is
expressed as an acid dissociation constant:
acid dissoc constant
keq= [H+]{A-]/[HA]= Ka
pka expresses
on a logarithmic scale, the relative strength
of a weak acid or base: the equation is ]pka= log 1/[Ka]= -log Ka
The stronger the acid,/base… also how do u find the pka on a titration curve
the smaller its pKa; the stronger the
base, the larger the pKa of its conjugate acid. The pKa can be
determined experimentally; it is the pH at the midpoint of the
titration curve.
buffer
are aqueous systems that tend to resist changes in pH when small amounts of acid (H \+ ) or base (OH − ) are added.
buffering region
Notice that the titration curve of acetic acid has a relatively flat
zone extending about 1 pH unit on either side of its midpoint pH
of 4.76. In this zone, a given amount of H
+
or OH
−
added to the
system has much less effect on pH than the same amount added
outside the zone. This relatively flat zone is the buffering region
of the acetic acid–acetate buffer pair. At the midpoint of the
buffering region, where the concentration of the proton donor
(acetic acid) exactly equals that of the proton acceptor (acetate),
the buffering power of the system is maximal; that is, its pH
changes least on addition of H
+
or OH
−
.
what is the henderson hasselbach equation useful for
This equation is simply a useful way of
316
restating the expression for the ionization constant of an acid.
henderson hasslebach fits
the titration curve of all weak acids and enables
us to deduce some important quantitative relationships. For
example, it shows why the pKa of a weak acid is equal to the pH of
the solution at the midpoint of its titration.
henderson hasslebach
The shape of the titration curve of any weak acid is described by
the Henderson-Hasselbalch equation, which is important for
understanding buffer action and acid-base balance in the blood
and tissues of vertebrate
. So, an amount of NaOH that increases the pH of
water from 7 to 12 increases
the pH of a buffered solution, as in
(b), from 7.0 to just 7.2. Such is the power of buffering!
The pH of a bicarbonate buffer system depends on
the concentrations of H2CO3 and HCO − 3 , the proton donor and acceptor components. The concentration of H2CO3 in turn depends on the concentration of dissolved CO2, which in turn depends on the concentration of CO2 in the gas phase, or the partial pressure of CO2, denoted pCO2 . Thus, the pH of a bicarbonate buffer exposed to a gas phase is ultimately determined by the concentration of HCO − 3 in the aqueous phase and by pCO2 in the gas phase.
acidosis and alkalosis- pgs 330-332
kk
A mixture of a weak acid (or base) and its salt resists
changes in pH caused by the addition of H \+ or OH − . The mixture thus functions as a buffer.
The pH of a solution of a weak acid (or base) and its salt is
given by
the Henderson-Hasselbalch equation:
In cells and tissues, phosphate and bicarbonate buffer systems
maintain
intracellular and extracellular fluids near pH 7.4.
Enzymes generally work optimally near this physiological pH.
Medical conditions such as untreated diabetes that lower the
pH of blood, causing
acidosis, or raise it, causing alkalosis, can be
life-threatening.
whats something that could cause alkalosis
hyperventilation - see somewhere around pg 330 ish i think
