Biochemistry Lipids and Membranes 1 — Questions and Answers
Question 1: Which type of fatty acid contains one double bond?
- Saturated fatty acid
- Monounsaturated fatty acid (Correct answer)
- Polyunsaturated fatty acid
- Trans fatty acid
Correct answer: Monounsaturated fatty acid
Monounsaturated fatty acids contain exactly one carbon-carbon double bond, such as oleic acid (18:1, Δ9), and are liquid at room temperature.
Question 2: The fluid mosaic model of the cell membrane was proposed by:
- Watson and Crick
- Singer and Nicolson (Correct answer)
- Mitchell and Moyle
- Lipmann and Krebs
Correct answer: Singer and Nicolson
Singer and Nicolson (1972) proposed the fluid mosaic model, describing the membrane as a dynamic lipid bilayer with embedded proteins that can move laterally.
Question 3: Which lipid class forms the structural backbone of the cell membrane bilayer?
- Triglycerides
- Cholesterol
- Phospholipids (Correct answer)
- Sphingomyelin
Correct answer: Phospholipids
Phospholipids are amphipathic molecules with a hydrophilic phosphate head group and hydrophobic fatty acid tails that spontaneously form bilayers in aqueous environments.
Question 4: Cholesterol in animal cell membranes functions to:
- Increase membrane permeability to ions
- Modulate membrane fluidity (Correct answer)
- Serve as the primary energy storage lipid
- Provide receptor sites for hormones only
Correct answer: Modulate membrane fluidity
Cholesterol inserts between phospholipid tails, reducing fluidity at high temperatures and preventing crystallization at low temperatures, thereby buffering membrane fluidity.
Question 5: Eicosanoids (prostaglandins, thromboxanes, leukotrienes) are derived from which fatty acid precursor?
- Palmitic acid (16:0)
- Stearic acid (18:0)
- Arachidonic acid (20:4) (Correct answer)
- Linoleic acid (18:2)
Correct answer: Arachidonic acid (20:4)
Arachidonic acid (20:4, ω-6) is released from membrane phospholipids by phospholipase A2 and serves as the substrate for cyclooxygenases and lipoxygenases to produce eicosanoids.
Question 6: What is the term for the movement of a phospholipid from one leaflet of the bilayer to the other?
- Lateral diffusion
- Rotational diffusion
- Flip-flop (transverse diffusion) (Correct answer)
- Vesicle budding
Correct answer: Flip-flop (transverse diffusion)
Flip-flop (transverse diffusion) is the movement of a lipid across the bilayer, which is thermodynamically unfavorable and requires flippase enzymes to occur rapidly.
Biochemistry Lipids and Membranes 1
Which type of fatty acid contains one double bond?