Lecture 3 Flashcards
Why is water able to dissolve ionic compounds like salt (NaCl)?
A) Water has a low boiling point
B) Water molecules are nonpolar
C) Water has a high dielectric constant, which weakens ionic attraction
D) Water molecules have no charge
C) Water has a high dielectric constant, which weakens ionic attraction
Explanation: The high dielectric constant allows water to surround and separate ions, making it an excellent solvent.
How does water’s high heat capacity help living organisms?
A) It allows rapid temperature changes
B) It helps regulate body temperature and prevents overheating
C) It makes water a poor conductor of heat
D) It lowers the boiling point of water
✅ B) It helps regulate body temperature and prevents overheating
Explanation: Water absorbs heat slowly and releases it gradually, stabilizing temperatures in cells and ecosystems.
Why does water weaken electrostatic forces between two charged particles?
A) Water increases the charges of the particles
B) Water increases the force between the charges
C) Water has a high dielectric constant, which reduces electrostatic attraction
D) Water removes all electrostatic forces
✅ C) Water has a high dielectric constant, which reduces electrostatic attraction
Explanation: Water’s high dielectric constant (~80.4) significantly weakens electrostatic interactions, allowing ions to separate and dissolve.
Which medium would have the strongest electrostatic interactions between two opposite charges?
A) Vacuum
B) Air
C) Olive oil
D) Water
✅ A) Vacuum
Explanation: The vacuum has a dielectric constant of 1, meaning there is no reduction in electrostatic attraction.
Question 1
Why do non-polar molecules group together in water?
A) They are strongly attracted to each other
B) Water molecules prefer to interact with each other, excluding non-polar molecules
C) Non-polar molecules dissolve easily in water
D) Non-polar molecules increase entropy when dispersed
✅ B) Water molecules prefer to interact with each other, excluding non-polar molecules
Explanation: Water molecules form strong hydrogen bonds with each other, pushing hydrophobic molecules together to minimize disruption.
Question 2
What happens to entropy when a non-polar molecule is placed in water?
A) Entropy increases because the molecule dissolves
B) Entropy decreases because water molecules become more ordered around the non-polar molecule
C) Entropy remains unchanged
D) Entropy increases because hydrogen bonds are broken
✅ B) Entropy decreases because water molecules become more ordered around the non-polar molecule
Explanation: Water forms a structured “cage” around hydrophobic molecules, reducing randomness (entropy loss), making dissolution unfavorable.
Question 1
What happens when amphiphilic molecules like detergents are added to water?
A) They dissolve completely as individual molecules
B) They form structures like micelles to shield hydrophobic regions
C) They become hydrophilic and mix with water
D) They react chemically with water
✅ B) They form structures like micelles to shield hydrophobic regions
Explanation: Amphiphiles arrange themselves so that hydrophobic tails are hidden from water, forming micelles or bilayers.
What happens when an amphiphilic detergent is added to water at a concentration below the CMC?
A) Micelles form immediately
B) The detergent molecules remain as individual monomers in water
C) The detergent molecules become hydrophobic and settle at the bottom
D) The detergent reacts chemically with water
✅ B) The detergent molecules remain as individual monomers in water
Explanation: Below the critical micelle concentration (CMC), amphiphiles stay as individual molecules in water.
Why do micelles form in water?
A) Hydrophilic tails repel water, forming a barrier
B) Hydrophobic heads attract water, pulling molecules together
C) Hydrophobic tails group together to minimize contact with water, while hydrophilic heads interact with water
D) The molecules dissolve individually instead of grouping
✅ C) Hydrophobic tails group together to minimize contact with water, while hydrophilic heads interact with water
Explanation: The hydrophobic effect forces tails inside a micelle, keeping heads in contact with water.
Why do phospholipids form bilayers instead of micelles?
A) They contain only one fatty acid tail
B) Their hydrophilic head is much smaller than their tails
C) Their head and tail are similar in size, leading to a cylindrical shape
D) Their hydrophobic tails are too short to form micelles
✅ C) Their head and tail are similar in size, leading to a cylindrical shape
Explanation: Phospholipids have two tails and a head of similar size, allowing them to form bilayers instead of micelles.
What is the main structural difference between a bilayer and a liposome?
A) A bilayer is a closed vesicle, while a liposome is flat
B) A bilayer is a flat sheet, while a liposome is a closed, spherical vesicle
C) A liposome is made of proteins, while a bilayer is made of lipids
D) Liposomes only form in air, while bilayers form in water
✅ B) A bilayer is a flat sheet, while a liposome is a closed, spherical vesicle
Explanation: Bilayers form the structure of cell membranes, while liposomes are vesicles with an aqueous cavity inside.
Which type of amino acid is most likely found in the transmembrane region of a protein?
A) Hydrophilic (polar) amino acids
B) Charged amino acids
C) Hydrophobic amino acids
D) Aromatic amino acids only
✅ C) Hydrophobic amino acids
Explanation: Hydrophobic amino acids allow transmembrane proteins to be embedded in the lipid bilayer.
What does a high positive hydropathy index indicate?
A) The amino acid is hydrophilic
B) The amino acid prefers to interact with water
C) The amino acid is hydrophobic and likely found in membranes
D) The amino acid has no interaction with water
✅ C) The amino acid is hydrophobic and likely found in membranes
Explanation: A high hydropathy index means the amino acid avoids water and is often found in lipid bilayers.
What does a negative hydropathy index indicate?
A) The amino acid prefers nonpolar environments
B) The amino acid is hydrophobic
C) The amino acid prefers to be in water (hydrophilic)
D) The amino acid is found in membrane proteins
✅ C) The amino acid prefers to be in water (hydrophilic)
Explanation: A negative hydropathy index means the amino acid dissolves easily in water and is hydrophilic.
What does a high peak in a hydropathy plot suggest?
A) The protein is likely globular
B) The region is hydrophilic and exposed to water
C) The region is hydrophobic and likely a transmembrane helix
D) The protein is denatured
✅ C) The region is hydrophobic and likely a transmembrane helix
Explanation: High hydropathy values suggest membrane-spanning regions, often α-helices.
How long is a typical transmembrane helix in a membrane protein?
A) About 10 amino acids
B) About 30 amino acids
C) About 100 amino acids
D) About 3 amino acids
✅ B) About 30 amino acids
Explanation: Most transmembrane helices are around 30 residues long, enough to span the lipid bilayer.
