Lecture 2 Flashcards
where did live evolve
in water
T/F Organisms typically contain 40–50% water
False, Organisms typically contain 70–90% water
what is a critical determinant of the structure and function of proteins, nucleic
acids, and membranes
water
how many electron pairs are there around a oxygen atom in water
4
in which orbital are the 4 electron in in water
sp3
how many lone pairs are found on an oxygen molecule
2
what is the geometry of the water molecule
Water geometry is a distorted tetrahedron
what causes the net dipole on an oxygen atom
The electronegativity of the oxygen atom induces a net dipole moment
what contributes to waters ability to act as both an acid or a base
• Because of the dipole moment, water can serve as
both a hydrogen bond donor and acceptor
what kind of molecules do we typically see H bonding ?
• Typically involves two electronegative atoms (frequently
nitrogen and oxygen)
When are H bonds the strongest
Hydrogen bonds are strongest when the bonded molecules are
oriented to maximize electrostatic interaction
• Ideally the three atoms involved are in a line
T/F Water can serve as both – an H donor
– an H acceptor
True
What the maximum # of H bonds per molecule
4
Describe waters bp , surface tension and mp
Up to four H-bonds per water molecule gives water its
– anomalously high boiling point
– anomalously high melting point
– unusually large surface tension
Describe the lifetime of hydrogen bonding
Hydrogen bonding in water is cooperative and has a lifetime
of 1 to 20 picoseconds
Describe the difference in strength between an H bond and a covalent bond
Hydrogen bonds between neighboring molecules are longer and weaker
(20 kJ/mol) relative to the H–O covalent bonds (420 kJ/mol)
what is the bond angle of water
104.5
what kind of structure does ice form
a regular lattice
T/f a lattice structure has high enthalpy
false, • Hexagonal ice forms a regular lattice,
and thus has a low entropy
how many bonds does ice form
4
how many bonds does water from
3.4
how many bonds does vapor form
0
What allows ice to floar
the 4 H bonds form a crystal lattace structure which makes ice less dense than water, and thus ice floats on water
what kind of substances is water a good solvent for
Water is a good solvent for charged and polar
substances
what kind of substances is water a poor solvent for
Water is a poor solvent for nonpolar substances
is water a good solvent
amino acids and peptides
yes
is water a good solvent? – aromatic moieties
no
is water a good solvent? – carbohydrates
yes
is water a good solvent? – – small alcohols
yes
is water a good solvent?– nonpolar gases
no
is water a good solvent? – aliphatic chains
no
How can water dissolve salt
High dielectric constant reduces attraction
between oppositely charged ions in salt crystal; The NaCl crystal lattice is disrupted as water
molecules cluster about the Cl– and Na+
ions. The ionic charges are
partially neutralized, and the electrostatic attractions necessary for lattice
formation are weakened.
Does Entropy decrease or increase as ordered crystal lattice is dissolved
Entropy increases as ordered crystal lattice is dissolved
hemoglobin and myoglobin) are referred to as
• Some organisms have water-soluble carrier
proteins(hemoglobin and myoglobin) to
transport Oxygen.
is there sharing of electrons in non covalent interaction
no , Noncovalent interactions do not involve sharing a pair of electrons.
what are the 4 types of non covalent interaction
ionic
hydrogen bonds
vander waals
hydrophobic effect
what is an ionic bond
Electrostatic interactions between permanently charged
species, or between the ion and a permanent dipole
what is a hydrogen bond
Electrostatic interactions between uncharged, but polar
molecules
what is a van der waals interaction
– Weak interactions between all atoms, regardless of polarity
– Attractive (dispersion) and repulsive (steric) component
Hydrophobic Effect
Complex phenomenon associated with the ordering of water
molecules around nonpolar substances
T/f h bonds helps with binding of substrates to enzymes
True!
T/f H bonds help with Binding of hormones to receptors
True
T/f H bonds help with Matching of mRNA and tRNA
True
In a H bond which atom is typically the acceptor
The
hydrogen acceptor is usually oxygen or nitrogen
Does bulk water have high or low entropy?
high
does water near a hydrophobic solute have high or low entropy
low
do hydrophobic solutes have high or low solubility.
Low entropy is thermodynamically unfavorable, thus
hydrophobic solutes have low solubility
Define the hydrophobic effect
Refers to the association or folding of nonpolar
molecules in the aqueous solution
T/F hydrophobic effect contributes to protein folding
– protein-protein association
– formation of lipid micelles
– binding of steroid hormones to their receptors
True
T/f the hydrophobic effect arises from some attractive
direct force between two nonpolar molecules
FALSE!! The hydrophobic effect does NOT arise because of some attractive
direct force between two nonpolar molecules
does the water surrounding nonpolar solutes have high or low entropy
lower entropy
T/F Nonpolar portions of a amphipathic molecule aggregate so that
fewer water molecules are ordered
True! The released water molecules will be more random and the
entropy increases
• All nonpolar groups are sequestered from water, and the released water molecules increase the entropy further
which is more favored a cluster or lipid molecules or a micelle?
a micelle, because ALL of the hydrophobic groups are sequestered . n. By clustering together in micelles, the
fatty acid molecules expose the smallest possible hydrophobic surface area to the
water, and fewer water molecules are required in the shell of ordered water
What force is this referring to : When two uncharged atoms are brought very close
together, their surrounding electron clouds influence
each other.
Van Der walls
what are the 2 components of the van der wall interaction
Attractive force (London dispersion) depends on the polarizability
– Repulsive force (Steric repulsion) depends on the size of
atoms
at longer distances does attraction of repulsion dominate in van der walls force
Attraction dominates at longer distances (typically
0.4–0.7 nm)
at shorter distances does attraction or repulsion dominate
• Repulsion dominates at very short distances
T/F van der walls forces are strong individually
false , they are Weak individually easily broken, reversible
T/f van der walls force can happen between any 2 atoms
True! It is universal
and occur between any two atoms that are near each other
what are the 3 colligative properties
Boiling point, melting point, and osmolarity
do colligative properties depend on the nature of the solute
No! – Do not depend on the nature of the solute, just
the concentration
what are the 4 non colligative properties
– Viscosity, surface tension, taste, and color
Do colligative or non colligative properties depend on the nature of the solute
non colligative
T/F cytoplasm of cells have high osmotic pressure
true
Describe osmostic pressure
Osmotic pressure is measured as the force that must be applied to return the solution in the
tube to the level of that in the beaker.
what is osmosis
movement of water
a cell is in an isotonic environment . Describe what will occur
no net water movement
a cell is in a hypertonic environment describe what will occur
water moves out of the cell and it shrinks
a cell is in a hypotonic environment describe what will occur
water moves in, which causes cell to swell and burst
are most water molecules ionized
no, Most water molecules remain un-ionized, thus pure water has
very low electrical conductivity
• The equilibrium is strongly to the left
what does the extent of dissociation depend on for water
• Extent of dissociation depends on the temperature
T/F protons from water typically exist freely in solution
false , Protons do not exist free in solution.
• They are immediately hydrated to form hydronium (oxonium) ions.
what is the K eq for water
55.5 M
T/F The pH and pOH must always add to 14
true
T/F PH can be negative
True, pH can be negative ([H+] = 6 M)
the ionic product of water is based on what concept
the ionic product of water
T/F • Weak electrolytes dissociate only partially in water.
True ! They are more reluctant to give up their H
The extent to which a substance dissociates is determined by what
Extent of dissociation is
determined by the acid
dissociation constant Ka
If an acid is strong will it have a small or larger pka
small
a conjugate acid-base pairs consist of what two things
Conjugate acid-base pairs consist of a proton
donor and a proton acceptor
buffers are a mixture of what two things
Buffers are mixtures of weak acids and their anions (conjugate base)
when the pH = pKa
(acid dissociation constant) what does this mean
At pH = pKa
(acid dissociation constant), there is a
50:50 mixture of conjugate acid and its conjugate
base
At what point does a buffer lose its capacity
Buffering capacity is lost when the pH differs from
pKa by more than 1 pH unit
what are the 3 buffer systems that we have in the body
phosphate, concentration in millimolar range
– bicarbonate, important for blood plasma
– histidine, efficient buffer at neutral pH
if someone is hyperventilating will they experience acidosis of alklosis
alkalosis. They are breathing out too much co2, this means that the reaction will be pushed to the left ( to create more co2) which mean H+ concentration will decrease ( gets more basic)
if someone is not exhaling enough would someone be more likely to experience alkalosis or acidosis
acidosis . This means there is excess co2 in the blood which will push the equation to the right , casuing H+ to increase.
