CHEM 210 BIOCHEMISTRY MODULE 6 EXAM 2026/2027 |
Lipids, Membranes & Transport | Latest Q&A Verified |
Geneva College | Pass Guaranteed - A+ Graded
Q1: Which structural feature distinguishes phosphoglycerides from triacylglycerols?
A. Presence of glycerol backbone
B. Presence of a phosphate group esterified to the third carbon of glycerol [CORRECT]
C. Saturation of fatty acid chains
D. Number of fatty acid chains attached
Correct Answer: B
Rationale: Both phosphoglycerides (glycerophospholipids) and triacylglycerols share a
glycerol backbone with fatty acid ester linkages at carbons 1 and 2. The defining
difference is that phosphoglycerides have a phosphate group esterified to carbon 3
(forming phosphatidic acid, the parent compound), which is further linked to polar head
groups (choline, ethanolamine, serine, inositol). Triacylglycerols have a third fatty acid
esterified to carbon 3, making them nonpolar storage lipids. Option A is incorrect
because both contain glycerol. Option C is incorrect because both can contain saturated
or unsaturated fatty acids. Option D is incorrect because both typically have two fatty
acid chains at positions 1 and 2; the difference is at position 3 (phosphate vs. fatty
acid).
,Q2: A membrane lipid sample isolated from a psychrophilic (cold-loving) bacterium
grown at 4°C is analyzed. Compared to lipids from a mesophilic bacterium grown at
37°C, which compositional difference would be expected?
A. Higher proportion of saturated fatty acid chains
B. Higher proportion of cis-unsaturated fatty acid chains [CORRECT]
C. Higher cholesterol content
D. Shorter phospholipid head groups
Correct Answer: B
Rationale: Membrane fluidity must be maintained across temperatures. Cold-adapted
organisms increase membrane fluidity by incorporating more unsaturated fatty acids
(specifically cis-unsaturated with kinks that disrupt packing). This prevents excessive
ordering and maintains function at low temperatures. Saturated fatty acids (Option A)
increase packing and would cause rigidification in cold, which is disadvantageous.
Cholesterol (Option C) is typically absent in prokaryotes; even in eukaryotes, it would
decrease fluidity at low temperatures. Head group length (Option D) has minimal impact
on fluidity compared to acyl chain composition.
Q3: Which lipoprotein is responsible for reverse cholesterol transport, moving
cholesterol from peripheral tissues back to the liver?
A. Chylomicrons
B. Very-low-density lipoprotein (VLDL)
C. Low-density lipoprotein (LDL)
, D. High-density lipoprotein (HDL) [CORRECT]
Correct Answer: D
Rationale: HDL functions in reverse cholesterol transport, accepting cholesterol from
peripheral cells (via ABCA1 transporters) and transporting it to the liver for excretion
(via SR-B1 receptors) or conversion to bile acids. This anti-atherogenic process is
central to HDL's protective role. Chylomicrons (Option A) transport dietary triglycerides
from intestine to tissues. VLDL (Option B) transports endogenous triglycerides from
liver to tissues. LDL (Option C) delivers cholesterol to peripheral tissues (forward
transport) and is the primary atherogenic lipoprotein.
Q4: In the fluid mosaic model of membrane structure, which component is primarily
responsible for the "fluid" characteristic?
A. Covalent bonds between lipids and proteins
B. Non-covalent interactions allowing lateral diffusion of lipid and protein components
[CORRECT]
C. Hydrogen bonding between adjacent phospholipid head groups
D. Disulfide bridges linking membrane proteins
Correct Answer: B
Rationale: The fluid mosaic model (Singer & Nicolson, 1972) describes biological
membranes as dynamic structures where lipids and proteins can diffuse laterally within
the bilayer plane due to non-covalent hydrophobic interactions. This fluidity is essential
for membrane function, signaling, and protein mobility. Covalent bonds (Option A) and
disulfide bridges (Option D) would restrict movement. Hydrogen bonding between head
Lipids, Membranes & Transport | Latest Q&A Verified |
Geneva College | Pass Guaranteed - A+ Graded
Q1: Which structural feature distinguishes phosphoglycerides from triacylglycerols?
A. Presence of glycerol backbone
B. Presence of a phosphate group esterified to the third carbon of glycerol [CORRECT]
C. Saturation of fatty acid chains
D. Number of fatty acid chains attached
Correct Answer: B
Rationale: Both phosphoglycerides (glycerophospholipids) and triacylglycerols share a
glycerol backbone with fatty acid ester linkages at carbons 1 and 2. The defining
difference is that phosphoglycerides have a phosphate group esterified to carbon 3
(forming phosphatidic acid, the parent compound), which is further linked to polar head
groups (choline, ethanolamine, serine, inositol). Triacylglycerols have a third fatty acid
esterified to carbon 3, making them nonpolar storage lipids. Option A is incorrect
because both contain glycerol. Option C is incorrect because both can contain saturated
or unsaturated fatty acids. Option D is incorrect because both typically have two fatty
acid chains at positions 1 and 2; the difference is at position 3 (phosphate vs. fatty
acid).
,Q2: A membrane lipid sample isolated from a psychrophilic (cold-loving) bacterium
grown at 4°C is analyzed. Compared to lipids from a mesophilic bacterium grown at
37°C, which compositional difference would be expected?
A. Higher proportion of saturated fatty acid chains
B. Higher proportion of cis-unsaturated fatty acid chains [CORRECT]
C. Higher cholesterol content
D. Shorter phospholipid head groups
Correct Answer: B
Rationale: Membrane fluidity must be maintained across temperatures. Cold-adapted
organisms increase membrane fluidity by incorporating more unsaturated fatty acids
(specifically cis-unsaturated with kinks that disrupt packing). This prevents excessive
ordering and maintains function at low temperatures. Saturated fatty acids (Option A)
increase packing and would cause rigidification in cold, which is disadvantageous.
Cholesterol (Option C) is typically absent in prokaryotes; even in eukaryotes, it would
decrease fluidity at low temperatures. Head group length (Option D) has minimal impact
on fluidity compared to acyl chain composition.
Q3: Which lipoprotein is responsible for reverse cholesterol transport, moving
cholesterol from peripheral tissues back to the liver?
A. Chylomicrons
B. Very-low-density lipoprotein (VLDL)
C. Low-density lipoprotein (LDL)
, D. High-density lipoprotein (HDL) [CORRECT]
Correct Answer: D
Rationale: HDL functions in reverse cholesterol transport, accepting cholesterol from
peripheral cells (via ABCA1 transporters) and transporting it to the liver for excretion
(via SR-B1 receptors) or conversion to bile acids. This anti-atherogenic process is
central to HDL's protective role. Chylomicrons (Option A) transport dietary triglycerides
from intestine to tissues. VLDL (Option B) transports endogenous triglycerides from
liver to tissues. LDL (Option C) delivers cholesterol to peripheral tissues (forward
transport) and is the primary atherogenic lipoprotein.
Q4: In the fluid mosaic model of membrane structure, which component is primarily
responsible for the "fluid" characteristic?
A. Covalent bonds between lipids and proteins
B. Non-covalent interactions allowing lateral diffusion of lipid and protein components
[CORRECT]
C. Hydrogen bonding between adjacent phospholipid head groups
D. Disulfide bridges linking membrane proteins
Correct Answer: B
Rationale: The fluid mosaic model (Singer & Nicolson, 1972) describes biological
membranes as dynamic structures where lipids and proteins can diffuse laterally within
the bilayer plane due to non-covalent hydrophobic interactions. This fluidity is essential
for membrane function, signaling, and protein mobility. Covalent bonds (Option A) and
disulfide bridges (Option D) would restrict movement. Hydrogen bonding between head
