At what temperature does Kw equal 10^-14 (mol/L)2?
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At 25°C.
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At what temperature does Kw equal 10^-14 (mol/L)2?
At 25°C.
Why is water considered an ideal biological solvent?
Due to its ability to dissolve a wide range of solutes, including polar and ionic compounds.
What makes water an ideal biological solvent?
Its ability to dissolve a wide range of substances due to its polarity.
What is pKa used to express?
The relative strengths of both acids and bases.
How do water molecules form hydrogen bonds?
By interacting with unshared electron pairs on other oxygen or nitrogen atoms.
At what pH values do buffers resist changes in pH most effectively?
Close to the pKa value.
What are some common electrophiles?
Carbonyl carbons in amides, esters, aldehydes, and ketones; phosphorus atoms of phosphoesters.
How is pOH calculated from the hydroxide ion concentration?
pOH = -log[OHˉ]
What is the process by which water ionizes?
Intermolecular proton transfer that forms a hydronium ion (H3O+) and a hydroxide ion (OH-).
What is the process called when water causes the cleavage of biopolymer bonds?
Hydrolysis.
Do nucleophiles and electrophiles necessarily possess a formal negative or positive charge?
No, they do not necessarily possess a formal negative or positive charge.
Why is knowledge of the dissociation of weak acids and bases necessary?
To understand the influence of intracellular pH on structure and biologic activity.
Why can an individual hydrogen or oxygen not be stated to be present as an ion or as part of a water molecule?
Because at one instant it is an ion, and an instant later it is part of a water molecule.
How are charge-based separations like electrophoresis best understood?
In terms of the dissociation behavior of functional groups.
What are some biomedical importance of water?
It serves as a solvent, participates in metabolic reactions, helps regulate body temperature, and provides cushioning for organs and tissues.
What is the equation for the ion product of water (Kw)?
Kw = [H+][OH-] = 10^-14
What does the Henderson-Hasselbalch equation calculate?
It calculates the pH of a solution containing a weak acid and its conjugate base.
What type of interactions influence the structure of biomolecules?
Noncovalent Interactions.
What is the relationship between the strength of an acid and its pKa value?
The stronger the acid, the lower its pKa value.
What does the dissociation of water represent?
The molar concentrations and the dissociation constant.
How are the relative strengths of bases expressed?
In terms of the pKa of their conjugate acids.
What does the symbol 'OH' represent in water?
Hydroxide ion.
What does the Henderson-Hasselbalch equation express?
The relationship between the pH of a buffer solution and the pKa.
What is the shape of a water molecule?
An irregular, slightly skewed tetrahedron with oxygen at its center.
What is the predominant chemical component of living systems?
Water.
What interactions are maximized between polar groups on biomolecules and water?
Charge-dipole, dipole-dipole, and hydrogen bonding interactions.
What is the useful new constant termed for the ion product of water?
Kw.
What is the strongest force that holds molecules together?
Covalent bond.
What are the components of the Henderson-Hasselbalch equation?
The concentration of the weak acid, the concentration of its conjugate base, and the acid dissociation constant (pKa).
What is the key feature of a hydrogen nucleus in a water molecule?
It is partially shielded.
What is the definition of buffering in the context of weak acids or bases?
The ability to resist a change in pH following addition of strong acid or base.
How does the double helix DNA structure interact with water?
It presents charged phosphate groups and polar hydroxyl groups from the ribose sugars to water while burying the relatively hydrophobic nucleotide bases inside.
What does it mean for a biomolecule to be amphipathic?
It means it possesses regions rich in charged or polar functional groups as well as regions with hydrophobic character.
In what pH range do a solution of a weak acid and its conjugate base buffer most effectively?
pKa ± 1.0 pH unit.
How do biomolecules fold to position polar and charged groups on their surfaces?
To maximize energetically favorable interactions with water and minimize energetically unfavorable contacts with hydrophobic groups.
What does pKa represent?
The negative logarithm of the acid dissociation constant (Ka).
How are the two strands of the DNA double helix held together?
Exclusively by noncovalent interactions, including hydrogen bonds and Van der Waals interactions.
What is the second step in solving the Henderson-Hasselbalch equation?
Multiply through by -1.
What are the types of Van der Waals forces?
Neutral A - Neutral B, eˉ - eˉ, δ+ - δ+.
What factor hinders proton release from nearby acidic groups, raising their pKa?
The presence of local negative charge.
What is the formula to calculate pH?
pH = -log[H+]
What is the relationship between Ka, [H+], and the concentrations of undissociated acid and its conjugate base?
When [R-COO-] = [R-COOH] or when [R-NH2] = [R-NH3+], then:
What is the pH of a solution with a hydrogen ion concentration of 3.2 × 10^-4 mol/L?
pH = 3.5
What are nucleophiles and electrophiles?
Nucleophiles are electron-rich molecules that attack electron-poor atoms (electrophiles).
Where are functional groups that are weak acids found?
In proteins, nucleic acids, coenzymes, and intermediary metabolites.
Is the molar concentration of water significantly affected by dissociation?
No, it is considered to be essentially constant.
How do we express the relative strengths of weak acids and bases?
In terms of their dissociation constants.
Why is water considered an ideal biological solvent?
Due to its ability to dissolve a wide range of substances.
What are the two categories of Van der Waals forces based on distance?
Weak Van der Waals force (> 4 Angstrom) and Strong Van der Waals force (2 - 4 Angstrom).
What makes water an ideal biological solvent?
Its high dielectric constant.
What is the dielectric constant of water at 25°C?
78.5.
What is the pH of a solution with a hydroxide ion concentration of 4.0 x 10^-4 mol/L?
pH = 10.6
How many moles of water are present in 1 liter of pure water?
55.56 moles.
What are the examples of biological buffers involved in maintaining a constant pH?
Phosphate, bicarbonate, and proteins.
What is the molar concentration of H+ ions in pure water?
1.0 × 10^-7 mol/L.
What does the symbol 'H' represent in water?
Hydrogen ion.
How do Van der Waals forces compare to hydrogen bonds in terms of strength?
Significantly weaker than hydrogen bonds.
What is the relationship between pH and pOH in a solution?
pH + pOH = 14
Why is water considered an excellent nucleophile?
Because its two lone pairs of sp3 electrons bear a partial negative charge.
How is pOH defined?
pOH = -log[OH-]
What type of bonds are formed between hydrogen and oxygen or nitrogen?
Covalent bonds.
How does water interaction influence the structure of biomolecules?
Water can form hydrogen bonds with biomolecules, affecting their conformation and stability.
Why is water considered an ideal biological solvent?
Due to its ability to dissolve a wide range of substances.
What do water molecules form?
Dipoles.
What are representative weak acids and their conjugate bases used for?
They are used to determine pKa values.
What is the probability that a hydrogen in pure water will exist as a hydrogen ion?
1.8 × 10^-9.
What does the extended DNA backbone maximize?
The distance between negatively charged phosphates, minimizing unfavorable electrostatic interactions.
What stabilizes the structure of biomolecules?
Multiple forces, including noncovalent interactions.
How is pKa defined?
pKa is defined as -log(Ka).
What is the second pKa for glutaric acid?
5.4.
What do acids do?
They are proton donors.
What is the principal fluid medium of the cell?
Water.
What type of bond links each hydrogen atom to the oxygen atom in a water molecule?
A single covalent bond.
In what concentration is water present in most cells?
Between 70 and 85 percent.
What is the role of proteases in the cell?
They catalyze the hydrolysis of proteins into their component amino acids.
What is the nature of noncovalent forces?
They can be either attractive or repulsive.
How do noncovalent interactions affect the chemical and biological properties of water?
They contribute to water's high surface tension, cohesion, and adhesion.
What type of interactions influence the structure of biomolecules?
Noncovalent Interactions.
What is a dipole?
A molecule with electrical charge distributed asymmetrically about its structure.
At what distance do Van der Waals forces typically occur?
2 - 4 Angstrom.
What are some other nucleophiles of biologic importance?
Oxygen atoms of phosphates, alcohols, and carboxylic acids; sulfur of thiols; nitrogen atom of amines and of the imidazole ring of histidine.
How does a weak acid ionize?
As [H+][Aˉ]/[HA]=Ka.
What are some examples of functional groups that are weak acids?
Carboxyl groups, protonated amino groups, and phosphate esters.
What does the high dielectric constant of water enable it to do?
Dissolve large quantities of charged compounds such as salts.
What is a nucleophile?
A species that donates an electron pair to form a chemical bond.
What is the protonated species called in weak acids?
The acid.
What is the molar concentration of OH- ions in pure water?
1.0 × 10^-7 mol/L.
How is pH defined?
pH is defined as -log[H+].
What is the dissociation constant K for pure water?
1.8 × 10^-9 * 55.56 = 1.0 × 10^-7.
What is the ion product Kw numerically equal to?
The product of the molar concentrations of H+ and OH- ions.
Over what distances do Van der Waals forces typically act?
2 to 4 Å (angstroms).
What is the range of pH for the extracellular fluid maintained by buffers?
Between 7.35 and 7.45.
What influences the pKa of a functional group in a medium?
The surrounding medium.
What is the first step in solving the Henderson-Hasselbalch equation?
Take the log of both sides.
What affects the pKa values of dissociating groups in the interiors of proteins?
Their local environment, including the presence or absence of water.
What influences the physical properties of water?
Hydrogen bonding.
What is the pKa for a weak acid?
The pH at which the concentration of the acid equals that of the base.
How does the effect of adjacent charge change with distance?
It decreases with distance.
What is the result of nucleophilic attack by water?
Cleavage of amide, glycoside, or ester bonds.
What is the molar concentration of water?
55.56 mol/L.
Who introduced the term pH and when?
Sörensen in 1909.
What type of forces stabilize biomolecules?
Multiple forces, including interactions with water.
How is a proton represented in solution?
As H+.
What is the unprotonated species called in weak acids?
Its conjugate base.
What is the purpose of protein folding and phospholipid bilayer in relation to water?
To maximize energetically favorable interactions with water and minimize energetically unfavorable contacts with hydrophobic groups.
What happens when the logarithms of both sides of the equation relating Ka and [H+] are taken and both sides are multiplied by -1?
The equation is rewritten as -logKa = pH.
What type of forces make significant contributions to the structure, stability, and functional competence of macromolecules in living cells?
Noncovalent forces.
How does the ability of water to solvate molecules influence biomolecule structure?
It influences the structure of the biomolecule.
What is a salt bridge in the context of biomolecules?
It is a term used to describe electrostatic interactions between oppositely charged groups within or between biomolecules.
For what type of solutions does Kw equal 10^-14 (mol/L)2?
For all aqueous solutions, even solutions of acids or bases.
What is pH and how does it affect living cells?
pH is a measure of the acidity or alkalinity of a solution. It affects living cells by influencing enzyme activity and protein structure.
Why does ethanol affect the pKa of a charged species in water?
Because ethanol decreases the ability of water to solvate a charged species.
What does the strength of an acid depend on?
The molecular structure of the acid.
Why is water considered an ideal biological solvent?
Due to its ability to dissolve a wide range of substances.
Why is water considered an ideal biological solvent?
Due to its ability to form dipoles and its role as a solvent for many biological molecules.
What constitutes a region of local negative charge in a water molecule?
The two unshared electron pairs of oxygen.
What are the pH values of 2.0 × 10^-2 mol/L KOH and 2.0 × 10^-6 mol/L KOH?
a) For 2.0 × 10^-2 mol/L KOH, the pH value is 12.7. b) For 2.0 × 10^-6 mol/L KOH, the pH value is 8.7.
What are some examples of buffers used in laboratory experiments?
MES, inorganic orthophosphate, HEPES, Tris.
What is the relationship between a weak acid and its conjugate?
For any weak acid, its conjugate is a strong base.
What are the ions represented by Na+ and Clˉ in water?
Sodium (Na+) and Chloride (Clˉ) ions.
What is the role of buffering in biologic maintenance of a constant pH?
To resist a change in pH by accepting or releasing protons.
What does hydrogen bonding favor in water molecules?
The self-association of water molecules into ordered arrays.
What does pH stand for?
The negative logarithm of the hydrogen ion concentration.
How many other water molecules does each water molecule associate with through hydrogen bonds in the liquid state?
3.5 others on average.
What is the second pKa for succinic acid?
5.6.
What gives rise to Van der Waals forces?
Attractions between transient dipoles generated by the rapid movement of electrons of all neutral atoms.
What is the molar concentration of pure water?
55.56 molar.
What is the pH of a solution with a hydroxide ion concentration of 4.0 × 10^-4 mol/L?
pH + pOH = 14
How is pH calculated from hydrogen ion concentration?
pH = -log(3.2 × 10^-4) = -0.5 + 4.0 = 3.5
What is the relationship between pH and pOH?
pH + pOH = 14
What is the concept of water dissociation?
The continuous recombination of hydronium and hydroxide ions to form water molecules.
What are hydrogen bonds?
Intermolecular bonds between hydrogen and oxygen or nitrogen of neighboring molecules, acting as a bridge between the participating molecules.
What is the Henderson-Hasselbalch equation used for?
Calculating the pH of a buffer solution.
What does the symbol 'δˉ' represent in water?
Partial negative charge.
What are the multimers in which protons exist in solution?
H5O2+ and H7O3+.
How do hydrogen bonds compare to covalent and ionic bonds in terms of strength?
Considerably weaker than covalent and ionic bonds, but stronger than most noncovalent bonds.
What is the pH scale used to measure?
The concentration of protons or acidity of aqueous solutions.
What is the relationship between Kw and K?
Kw is incorporated into the dissociation constant K to provide a useful new constant.
What is the pH of pure water at 25°C?
What is the probability of a hydrogen atom in pure water existing as a hydrogen ion?
Approximately 1.8 × 10^-9.
How are weak acids expressed in terms of pKa?
Weak acids are expressed as pKa, where pKa is related to Ka as pH is to [H+].
What does the Henderson-Hasselbalch equation describe?
The behavior of weak acids and buffers.
What does hydrogen bonding account for in water?
Relatively high viscosity, relatively high surface tension, and relatively high boiling point.
How does water's dielectric constant affect the strength of interaction between oppositely charged particles?
It decreases the force of attraction between charged and polar species relative to water-free environments with lower dielectric constants.
What is the relationship between the prevailing hydrogen ion concentration and the dissociation constant (Ka)?
When the associated (protonated) and dissociated (conjugate base) species are present at equal concentrations, the prevailing hydrogen ion concentration [H+] is numerically equal to the dissociation constant, Ka.
What is the numerical subscript assigned to each dissociation in polyprotic compounds?
A numerical subscript is assigned to each dissociation, numbered starting from unity in decreasing order of relative acidity.
What does low pH value correspond to?
High concentrations of H+.
What is the consequence of unbuffered CO2 produced by oxidative metabolism?
Severe acidosis.
How is pH calculated for a solution?
What is the product of the formation of biopolymers like proteins or glycogen?
Water.
What is the definition of pH?
The negative log of the hydrogen ion concentration.
During the formation of a peptide bond between two amino acids, what is the by-product of the reaction?
Water.
Why is the ability of water to ionize of central importance for life?
Because water can act both as an acid and as a base.
What is the expression for the dissociation constant (Ka) for weak acids?
Shown below are the expressions for the dissociation constant (Ka) for two representative weak acids, R-COOH and R-NH3+.
Why do hydrogen atoms have a partial positive charge in a water molecule?
Due to the strongly electronegative oxygen atom attracting electrons away from hydrogen.
Why is careful control of the activities of enzymes required in the cell?
To ensure that they act only at appropriate times.
What is the condition called when blood pH is greater than 7.45?
Alkalosis.
What do oxygen atoms of aldehydes, ketones, and amides provide for hydrogen bonding?
Lone pairs of electrons.
Why are amide and phosphoester bonds stable in the aqueous environment of the cell?
Due to the stability of these bonds, hydrolysis is not favored.
What type of bonds hold each individual DNA strand together?
Covalent bonds.
What do bases do?
They are proton acceptors.
What does the symbol 'δ+' represent in water?
Partial positive charge.
What happens to strong acids in strongly acidic solutions?
They completely dissociate into anions and protons.
What type of bonds do water molecules form?
Hydrogen bonds.
What is the biomedical importance of water as a nucleophile?
It is a reactant or product in many metabolic reactions.
What are the essential factors for the regulation of water balance?
Thirst mechanism, antidiuretic hormone, and evaporative loss.
How can the ionization of water be described?
Statistically.
How are the hydrogen atoms and unshared electrons arranged in a water molecule?
The hydrogen atoms and unshared electrons occupy the corners of the tetrahedron.
How does the strength of Van der Waals forces change with distance?
They decrease as the sixth power of the distance separating atoms.
What determines the rate at which a reaction will proceed toward its equilibrium point?
Enzymes in the cell, which are protein catalysts.
What is the name of the specific hydrogen bonding between nucleotide bases in DNA?
Watson-Crick base pairing.
What is the angle between the two hydrogen atoms in a water molecule?
104.5°.
What happens to weak acids in acidic solutions?
They dissociate only partially.
What do noncovalent forces involve interactions with, besides the biomolecule itself?
Water, which forms the principal component of the surrounding environment.
What significantly contributes to the properties of water?
Hydrogen ions and hydroxide ions.
What is a buffer and what is its role in living cells?
A buffer is a solution that resists changes in pH. Its role in living cells is to maintain a stable pH environment, crucial for cellular functions.
How are individual ions or molecules considered in the context of water dissociation?
They are not considered; instead, the probability of a given hydrogen being present as an ion or as part of a water molecule is referred to.
What are electrostatic interactions?
Interactions that occur between oppositely charged atoms or groups.
What causes the hydrogen nucleus to become weakly attracted to the lone pair of electrons of an oxygen or nitrogen of a neighboring molecule?
Sufficiently polar covalent bonds between hydrogen and oxygen or nitrogen.
What is the half-life of hydrogen bonds in water?
A few picoseconds.
How much energy is required to rupture a hydrogen bond in liquid water?
About 4.5 kcal/mol.
Give an example of a condition causing alkalosis.
Vomiting of acidic gastric contents.
What are some properties of water that account for its physical and chemical behavior?
High polarity, hydrogen bonding, high specific heat, and high heat of vaporization.
How does Kw change with temperatures below 25°C and above 25°C?
It is somewhat less than 10^-14 at temperatures below 25°C and somewhat greater than 10^-14 at temperatures above 25°C.
How do electrostatic interactions influence the shape and function of biomolecules?
They help influence the shape and function of biomolecules.
What enables water to dissolve many organic biomolecules?
Hydrogen bonding.
Which biomolecules can serve as both hydrogen acceptors and donors of unshielded hydrogen atoms for formation of hydrogen bonds?
Alcohols, carboxylic acids, and amines.
What does it mean to state that the probability that a hydrogen exists as an ion is 0.01?
It means that at any given moment in time, a hydrogen atom has 1 chance in 100 of being an ion and 99 chances out of 100 of being part of a water molecule.
What is the condition called when blood pH is less than 7.35?
Acidosis.
Give an example of a condition causing acidosis.
Diabetic ketosis and lactic acidosis.
How does adding ethanol to water affect the pKa of a carboxylic acid?
It increases the pKa.
What is the probability of a hydrogen atom in pure water being part of a water molecule?
Almost unity.
What happens to strong bases like KOH and NaOH?
They are completely dissociated even at high pH.
What effect does the dielectric constant have on pKa?
It may be observed by adding ethanol to water.
Which functional groups can participate in hydrogen bonding with water?
Aldehydes, ketones, amides, alcohols, carboxylic acids, and amines.
What do nucleases catalyze in the cell?
They catalyze the hydrolysis of the phosphoester bonds in DNA and RNA.
How does the medium affect the pKa relative to its value in water?
It may either raise or lower the pKa.
What is Kw used to calculate?
The pH of acidic and basic solutions.
How does the strength of electrostatic interactions compare to hydrogen bonds?
They are comparable in strength to hydrogen bonds but act over larger distances.
For every hydrogen ion or hydroxide ion in pure water, how many water molecules are there?
0.56 billion or 0.56 × 10^9 water molecules.
Give an example of an electrostatic interaction in determining the three-dimensional structure of proteins.
The interaction of NH3+ and COO-.
How does adding ethanol to water affect the pKa of an amine?
It decreases the pKa.
How do noncovalent interactions contribute to the stability of macromolecules?
They help in maintaining the three-dimensional structure of macromolecules, such as proteins and nucleic acids.
What do electrostatic interactions facilitate in terms of binding to proteins and nucleic acids?
They facilitate the binding of charged molecules and ions to proteins and nucleic acids.
