MODULE 1: Chapter 2.2 Flashcards
What is the ultimate source of energy for life on Earth?
Solar energy
Why is water essential for life?
Because of its distinctive chemical properties and its central role in biochemical reactions
What percentage of the mass of most cells is water?
More than 70%
What are the three unusual properties of water that make it important for sustaining life?
- Less dense as a solid than as a liquid
- Liquid over a wide range of temperatures
- Excellent solvent due to hydrogen-bonding capabilities
What is the molecular formula of water?
H2O
What allows ice to float in water?
Water is less dense as a solid than as a liquid
What critical property of water is essential for aquatic life?
Liquid over a wide range of temperatures
What role do photosynthetic algae in the oceans play related to water?
They ultimately affect the oxygen content of our atmosphere
What is hydrogen bonding?
An interaction where a hydrogen atom covalently attached to an electronegative atom is shared between two electronegative atoms
What is the bond angle in a water molecule?
104.5°
What makes water a polar molecule?
The electronegativity difference between oxygen and hydrogen creates a partial negative charge on oxygen and partial positive charges on hydrogen
How many hydrogen bonds can a single water molecule form?
Up to four
What is the boiling point of water?
100 °C
How does the strength of a hydrogen bond compare to that of a covalent bond?
Hydrogen bonds are relatively weak compared to covalent bonds
What phenomenon describes the constant formation and breakage of hydrogen bonds in water?
Flickering clusters
What is proton hopping in the context of water molecules?
The movement of H⁺ ions through hydrogen bond ‘trades’ between adjacent H2O molecules
What is the density of ice compared to liquid water?
Ice has a density of 0.92 g/mL, which is less than the density of liquid water at 1.0 g/mL
What is the significance of ice floating on water for aquatic life?
It prevents lakes and oceans from freezing solid, allowing life to persist beneath the ice
What are antifreeze proteins and their function?
Proteins that prevent the formation of ice crystals in organisms by interacting with water
What is solubility?
The ability of a solute to dissolve to homogeneity in a solvent such as water
What happens when NaCl dissolves in water?
Na⁺ and Cl⁻ ions form weak ionic interactions with water molecules, preventing the ions from rejoining the crystal
What are the three basic types of weak noncovalent interactions in biochemistry?
- Hydrogen bonds
- Ionic interactions
- Van der Waals interactions
What is the role of weak noncovalent interactions in biochemical reactions?
They allow unstable structures to exist for short periods, facilitating biochemical reactions
How does the strength of a hydrogen bond compare to its length?
The length of a hydrogen bond is about twice that of a covalent bond, leading to reduced strength
What is the typical bond length of hydrogen bonds between nonhydrogen atoms?
∼2.5–3.0 Å
This bond length is about twice the length of a covalent bond.
What is the bond energy range for hydrogen bonds?
10–30 kJ/mol
Hydrogen bonds are significantly weaker than covalent bonds.
Which types of molecules most often form hydrogen bonds in biomolecules?
Oxygen- or nitrogen-containing molecules
Water molecules can serve as either donors or acceptors for hydrogen bonds.
Define ionic interactions.
Weak interactions between oppositely charged atoms or groups
These interactions are a type of electrostatic interaction.
What factors affect the strength of ionic interactions?
The environment of the ions and the distance between them
Ionic interactions are strongest in hydrophobic environments.
What is the bond energy range for van der Waals interactions?
1–10 kJ/mol
Van der Waals interactions are much weaker than hydrogen bonds.
What is the significance of van der Waals interactions in biology?
They can occur simultaneously with various atoms, resulting in great cumulative strength
Even weak interactions can have significant biological effects when numerous.
Describe the hydrophobic effect.
The tendency of hydrophobic molecules to pack close together away from water
This effect is energetically favorable as it reduces the ordered structure of water.
What happens to water molecules around hydrophobic regions?
They become more ordered, forming cage-like structures
This ordering is energetically unfavorable due to decreased entropy.
What is the effect of introducing polar substances like glucose into water?
Little effect on enthalpy (ΔH) or entropy (ΔS)
Polar substances can form multiple hydrogen bonds with water, maintaining similar energy states.
What occurs when nonpolar substances like limonene are added to water?
They disrupt hydrogen bonds between water molecules
This leads to a more positive ΔG due to restricted water motion.
What role do hydrophobic effects play in protein folding?
They cause nonpolar amino acids to collapse into the interior of proteins
This minimizes exposure to water and stabilizes protein structure.
What is the osmolarity of a solution?
The concentration of solute molecules in 1 L of solvent
Osmolarity affects colligative properties of the solution.
What are some colligative properties affected by osmolarity?
- Freezing point depression
- Boiling point elevation
- Vapor pressure lowering
- Osmotic pressure
These properties depend on the concentration of solute particles.
True or False: The angle of ionic interactions affects their strength.
False
Unlike hydrogen bonds, the strength of ionic interactions is not influenced by angle.
What is the optimal distance for van der Waals interactions?
Slightly greater than the length of the covalent bond between two atoms
At this distance, potential energy is minimized.
What is the role of hydrogen-bonded water molecules in proteins?
They can stabilize the three-dimensional protein structure
Water molecules can also form ‘water wires’ aiding in proton pumping.
What are salt bridges?
Ionic interactions in proteins
They are typically weaker than ionic interactions found in NaCl crystals.
What is osmolarity?
The concentration of solute molecules in 1 L of solvent
It affects the colligative properties of the solution.
What are colligative properties?
Properties that depend on the number of solute particles, not their identity
Examples include freezing point depression, boiling point elevation, vapor pressure lowering, and osmotic pressure.
How does a 1 molal solution affect the freezing point of water?
Lowers it by 1.86 °C
This occurs at 1 atm pressure.
How does a 1 molal solution affect the boiling point of water?
Increases it by 0.54 °C
This change is temperature dependent.
What is osmotic pressure?
The pressure required to counteract osmosis across a semipermeable membrane
Osmotic pressure is proportional to solute concentration.
What happens to a cell in a hypotonic solution?
It swells and may burst
This is because water diffuses into the cell.
What happens to a cell in a hypertonic solution?
It shrinks
Water diffuses out of the cell.
What is an isotonic solution?
A solution with the same solute concentration as the cytosol
In an isotonic solution, water diffusion into and out of the cell is balanced.
What are important solutes in human blood?
Glucose and serum albumin
Normal glucose levels are ∼5 mM and albumin is present at ∼0.5 mM.
How do paramecia cope with hypotonic environments?
They use contractile vacuoles to expel excess water
This prevents cell swelling and lysis.
What provides structural support to plant cells?
A rigid cell wall
This protects against osmotic pressure and environmental stress.
What is turgor pressure?
The pressure exerted by the central vacuole in plant cells
It provides stiffness and supports plant structure.
What is the ionization of water?
The process where water molecules form H⁺ and OH− ions
This occurs in a reversible reaction where two water molecules rearrange.
What is the equilibrium constant for the ionization of water at 25 °C?
1.8 × 10−16 M
This helps calculate the concentrations of H⁺ and OH− at equilibrium.
What is Kw?
The water ionization constant, equal to 1.0 × 10−14 M²
It relates the concentrations of H⁺ and OH− ions in a solution.
What is the pH scale?
A logarithmic scale that expresses the concentration of H⁺ ions
pH = -log[H⁺].
What does a change of one pH unit represent?
A 10-fold change in H⁺ concentration
For example, pH 7 corresponds to [H⁺] of 1 × 10−7 M.
What is the relationship between [H⁺] concentration and pH?
[H⁺] of 1 × 10−8 M = pH 8; [H⁺] of 1 × 10−9 M = pH 9
The pH is calculated using the formula pH = -log[H⁺].
What pH values are considered acidic, neutral, and basic?
Acidic: pH < 6.5; Neutral: pH between 6.5 and 7.5; Basic: pH > 7.5
Acidic solutions have [H⁺] > [OH−], while basic solutions have [H⁺] < [OH−].
How is the pH of a solution commonly measured?
Using a pH meter or colorimetric indicators such as litmus paper
These methods provide a way to determine the acidity or basicity of a solution.
What is a weak acid?
An acid that dissociates H⁺ less readily than a strong acid.
Weak acids are only partially ionized in solution.
What does Ka represent in acid-base chemistry?
The acid dissociation constant, indicating the strength of an acid.
A low Ka value corresponds to weak acids, while a high Ka value corresponds to strong acids.
What is pKa?
The negative logarithm of the acid dissociation constant (Ka).
pKa is used to express the strength of an acid in a more manageable form.
What is the Henderson–Hasselbalch equation used for?
To calculate the pKa of a weak acid at a given pH using concentrations of HA and A−.
The equation is pH = pKa + log([A−]/[HA]).
What occurs when pH > pKa?
[A−]/[HA] > 1 and [A−] > [HA].
This indicates that the conjugate base predominates over the acid.
What is a titration curve?
A plot of the pH of a solution as a function of the amount of base added.
Titration curves help determine the pKa of weak acids.
What is the buffering capacity?
The ability of an acid or base to resist changes in pH.
Buffers contain sufficient amounts of an acid-base conjugate pair to stabilize pH.
What is the pH range for acetic acid’s buffering capacity?
3.7–5.7
This range indicates where acetic acid can effectively buffer changes in pH.
What is a polyprotic acid?
A weak acid with more than one dissociable H⁺.
Examples include phosphoric acid, which has three pKa values.
What are the pKa values for phosphoric acid?
Three pKa values corresponding to the dissociation of each proton.
Each pKa is identified by the addition of 0.5, 1.5, and 2.5 equivalents of base.
What is the primary buffering system in blood?
Carbonic acid–bicarbonate buffer system.
It helps maintain blood pH levels at approximately 7.40.
What is the reaction for the carbonic acid–bicarbonate buffering system?
H2CO3 ⇌ H⁺ + HCO3−
This reversible reaction allows for adjustments in serum H⁺ levels.
What is the primary buffering system in blood?
The bicarbonate buffering system
It functions through equilibrium with H2CO3 and HCO3− levels in response to changes in serum H⁺ levels.
What enzyme catalyzes the reversible reaction between H2CO3 and CO2(aq)?
Carbonic anhydrase
This enzyme facilitates the interconversion of carbonic acid (H2CO3) with dissolved carbon dioxide (CO2) and water (H2O).
What happens to blood H⁺ concentration during acidosis?
It is reduced by increasing the breathing rate and decreasing HCO3− excretion
Acidosis occurs when pH levels drop.
How does the bicarbonate buffering system respond to alkalosis?
Increases blood H⁺ concentration by slowing the breathing rate and increasing HCO3− excretion
Alkalosis occurs when pH levels rise.
What principle governs the bicarbonate buffering system?
Le Châtelier’s principle of mass action
This principle states that equilibrium shifts to counteract changes imposed on it.
What is the pH threshold for acidosis?
Below 7.4
Acidosis is characterized by a decrease in pH levels.
True or False: Water can act as both a hydrogen-bond donor and acceptor.
True
This property makes water a universal solvent critical for biochemical reactions.
What is the significance of hydrogen bonding in water?
It explains hydrophobic effects and the structure/function of biomolecules
Nonpolar groups in water lead to the formation of cage-like structures around them.
Fill in the blank: The lower density of ice compared to liquid water is due to its _______.
Open lattice structure
This structure forms when H2O molecules hydrogen bond with maximum donors and acceptors.
Define ‘hydrophobic’.
Nonpolar molecules that tend to pack close together away from water
Hydrophobic interactions are crucial in biological systems.
Define ‘hydrophilic’.
Polar molecules with an attraction for hydrogen bonds to water
Hydrophilic interactions are essential for solubility in biological systems.
What is osmolarity?
The concentration of solute molecules in 1 L of solvent
It is a key concept in understanding solution properties.
What are colligative properties?
Physical properties that depend on the number of solute particles
Examples include freezing-point depression and osmotic pressure.
What is the definition of osmosis?
The diffusion of solvent molecules from a region of lower solute concentration to one of higher solute concentration
This process is essential for cellular function.
What is the function of a contractile vacuole?
Helps regulate osmosis by collecting and expelling water from the cell
This organelle is found in some unicellular organisms.
What does the term ‘weak acid’ refer to?
An acid that is only partially ionized in aqueous solution
Examples include acetic acid.
What is the Henderson–Hasselbalch equation used for?
To relate pH and pKa
It is useful for calculating the ratio of protonated to deprotonated species.
Define ‘buffer’.
An aqueous solution that resists changes in pH
Buffers work through the protonation or deprotonation of an acid-base conjugate pair.
What is a polyprotic acid?
A weak acid with more than one dissociable H⁺
Amino acids like glutamate and aspartate are examples.
What is acidosis?
A metabolic condition of low pH, reducing the body’s ability to buffer H⁺
It usually occurs in the blood.
What is alkalosis?
A metabolic condition of high pH, reducing the body’s ability to buffer H⁺
It usually occurs in the blood.
What is the water ionization constant (Kw)?
Kw = [H⁺][OH−] = 1.0 × 10−14 M²
This constant is essential for understanding water’s dissociation.
What is the acid dissociation constant (Ka)?
The equilibrium constant for the dissociation of an acid
It helps in calculating the strength of an acid.
What does pKa represent?
The acid dissociation constant expressed as a negative logarithm
It is similar to pH.
