CHEM210 Biochemistry
Final Assessment Review
Module 5 (Questions & Solutions)
2025
©2025
, 1. Case Study – Fatty Acid Structure and Membrane Fluidity
A researcher compares the melting temperatures of lipid bilayers
prepared from saturated versus unsaturated fatty acids. The bilayer
composed of unsaturated fatty acids demonstrates a lower melting
temperature.
Question: What is the primary reason for the lower melting
temperature in the unsaturated lipid bilayer?
A. Increased molecular weight of unsaturated fatty acids
B. Cis double bonds introduce kinks, reducing van der Waals interactions
C. The polar head groups of unsaturated lipids are larger
D. Unsaturated fatty acids form tighter lateral packing
ANS: B. Cis double bonds introduce kinks, reducing van der Waals
interactions
Rationale: Unsaturated fatty acids contain cis double bonds that create
bends ("kinks") in the hydrocarbon chains, which disrupt tight packing
and weaken van der Waals forces, thereby lowering the melting
temperature and increasing membrane fluidity.
---
2. Case Study – Cholesterol’s Role in Membrane Fluidity
In a study of animal cell membranes, a biochemist observes that adding
cholesterol to a phospholipid bilayer at low temperatures increases its
fluidity.
Question: How does cholesterol increase fluidity at low temperatures?
A. It disrupts hydrogen bonding among water molecules.
B. It creates kinks in phospholipid tails.
C. It prevents tight packing by intercalating between phospholipids.
D. It forms micelles with lipids.
ANS: C. It prevents tight packing by intercalating between
phospholipids.
©2025
, Rationale: Cholesterol inserts between phospholipid molecules; at low
temperatures, it disrupts close packing and reduces the crystallinity of
the bilayer, thereby increasing fluidity. Conversely, at high temperatures,
it can reduce fluidity by restraining phospholipid movement.
---
3. Case Study – Phospholipid Head Groups and Membrane Structure
A student comparing different membrane preparations finds that a
bilayer composed primarily of phosphatidylcholine (PC) is more fluid than
one composed primarily of phosphatidylserine (PS).
Question: Which factor most likely contributes to this difference?
A. Size and charge of the head groups
B. Length of the acyl chains
C. Degree of unsaturation only
D. Presence of cholesterol exclusively
ANS: A. Size and charge of the head groups
Rationale: The head group characteristics (steric bulk and charge)
influence the degree of repulsion and hydration among lipids.
Phosphatidylcholine has bulky, zwitterionic head groups that favor
fluidity, whereas phosphatidylserine carries a net negative charge that
may lead to stronger inter-lipid interactions and less fluidity.
---
4. Case Study – Lipid Rafts and Membrane Microdomains
In an investigation of cell signaling, a researcher isolates cholesterol- and
sphingolipid-rich microdomains from plasma membranes.
Question: What is the significance of these lipid rafts?
A. They are regions of low receptor localization.
B. They serve primarily as scaffolds for protein sorting and signal
transduction.
C. They cause membrane destabilization.
D. They are artifacts of detergent extraction only.
©2025
, ANS: B. They serve primarily as scaffolds for protein sorting and
signal transduction.
Rationale: Lipid rafts are membrane microdomains enriched in
cholesterol and sphingolipids that organize protein clusters and facilitate
signal transduction by providing specialized environments for receptor
and signaling molecule interactions.
---
5. Case Study – Sphingolipid Structure and Function
A researcher studying neural membranes notes that sphingomyelin is
abundant in the myelin sheath.
Question: What structural feature distinguishes sphingolipids like
sphingomyelin from glycerophospholipids?
A. They are composed of a glycerol backbone.
B. They use sphingosine as a backbone instead of glycerol.
C. They lack fatty acid tails.
D. They contain a ribose sugar.
ANS: B. They use sphingosine as a backbone instead of glycerol.
Rationale: Sphingolipids are based on a sphingosine backbone rather
than glycerol, which imparts distinct biophysical properties and is critical
in forming specialized membrane domains such as myelin in neural
tissue.
---
6. Case Study – Fluid Mosaic Model and Membrane Proteins
A cell biologist uses fluorescence recovery after photobleaching (FRAP) to
study the lateral mobility of membrane proteins.
Question: The observed rapid recovery of fluorescence suggests what
about the membrane structure?
A. The membrane is a rigid, static structure.
B. Membrane proteins are permanently fixed in one location.
©2025
Final Assessment Review
Module 5 (Questions & Solutions)
2025
©2025
, 1. Case Study – Fatty Acid Structure and Membrane Fluidity
A researcher compares the melting temperatures of lipid bilayers
prepared from saturated versus unsaturated fatty acids. The bilayer
composed of unsaturated fatty acids demonstrates a lower melting
temperature.
Question: What is the primary reason for the lower melting
temperature in the unsaturated lipid bilayer?
A. Increased molecular weight of unsaturated fatty acids
B. Cis double bonds introduce kinks, reducing van der Waals interactions
C. The polar head groups of unsaturated lipids are larger
D. Unsaturated fatty acids form tighter lateral packing
ANS: B. Cis double bonds introduce kinks, reducing van der Waals
interactions
Rationale: Unsaturated fatty acids contain cis double bonds that create
bends ("kinks") in the hydrocarbon chains, which disrupt tight packing
and weaken van der Waals forces, thereby lowering the melting
temperature and increasing membrane fluidity.
---
2. Case Study – Cholesterol’s Role in Membrane Fluidity
In a study of animal cell membranes, a biochemist observes that adding
cholesterol to a phospholipid bilayer at low temperatures increases its
fluidity.
Question: How does cholesterol increase fluidity at low temperatures?
A. It disrupts hydrogen bonding among water molecules.
B. It creates kinks in phospholipid tails.
C. It prevents tight packing by intercalating between phospholipids.
D. It forms micelles with lipids.
ANS: C. It prevents tight packing by intercalating between
phospholipids.
©2025
, Rationale: Cholesterol inserts between phospholipid molecules; at low
temperatures, it disrupts close packing and reduces the crystallinity of
the bilayer, thereby increasing fluidity. Conversely, at high temperatures,
it can reduce fluidity by restraining phospholipid movement.
---
3. Case Study – Phospholipid Head Groups and Membrane Structure
A student comparing different membrane preparations finds that a
bilayer composed primarily of phosphatidylcholine (PC) is more fluid than
one composed primarily of phosphatidylserine (PS).
Question: Which factor most likely contributes to this difference?
A. Size and charge of the head groups
B. Length of the acyl chains
C. Degree of unsaturation only
D. Presence of cholesterol exclusively
ANS: A. Size and charge of the head groups
Rationale: The head group characteristics (steric bulk and charge)
influence the degree of repulsion and hydration among lipids.
Phosphatidylcholine has bulky, zwitterionic head groups that favor
fluidity, whereas phosphatidylserine carries a net negative charge that
may lead to stronger inter-lipid interactions and less fluidity.
---
4. Case Study – Lipid Rafts and Membrane Microdomains
In an investigation of cell signaling, a researcher isolates cholesterol- and
sphingolipid-rich microdomains from plasma membranes.
Question: What is the significance of these lipid rafts?
A. They are regions of low receptor localization.
B. They serve primarily as scaffolds for protein sorting and signal
transduction.
C. They cause membrane destabilization.
D. They are artifacts of detergent extraction only.
©2025
, ANS: B. They serve primarily as scaffolds for protein sorting and
signal transduction.
Rationale: Lipid rafts are membrane microdomains enriched in
cholesterol and sphingolipids that organize protein clusters and facilitate
signal transduction by providing specialized environments for receptor
and signaling molecule interactions.
---
5. Case Study – Sphingolipid Structure and Function
A researcher studying neural membranes notes that sphingomyelin is
abundant in the myelin sheath.
Question: What structural feature distinguishes sphingolipids like
sphingomyelin from glycerophospholipids?
A. They are composed of a glycerol backbone.
B. They use sphingosine as a backbone instead of glycerol.
C. They lack fatty acid tails.
D. They contain a ribose sugar.
ANS: B. They use sphingosine as a backbone instead of glycerol.
Rationale: Sphingolipids are based on a sphingosine backbone rather
than glycerol, which imparts distinct biophysical properties and is critical
in forming specialized membrane domains such as myelin in neural
tissue.
---
6. Case Study – Fluid Mosaic Model and Membrane Proteins
A cell biologist uses fluorescence recovery after photobleaching (FRAP) to
study the lateral mobility of membrane proteins.
Question: The observed rapid recovery of fluorescence suggests what
about the membrane structure?
A. The membrane is a rigid, static structure.
B. Membrane proteins are permanently fixed in one location.
©2025
