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Conjugated molecules

100 questions found

Practice Questions

96. The architectural layout of the myelin membrane shows an unusually high lipid-to-protein ratio (4:1), containing specific glycolipids like galactocerebrosides. A targeted autoimmune response against these nervous system glycolipids causes

A. Duchenne muscular dystrophy
B. Multiple sclerosis or Guillain-Barré syndrome variants
C. Type 1 diabetes mellitus
D. Severe combined immunodeficiency (SCID)

Autoimmune attacks targeting myelin glycolipids or associated proteins disrupt the structural layout of the myelin sheath, impairing nerve signal conduction.

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Jul 3, 2026

97. The chemical structure of lipopolysaccharide (LPS) includes the core polysaccharide, the O-antigen, and Lipid A. If a mutant strain of Salmonella synthesizes an altered Lipid A that lacks three of its normal six fatty acid acyl chains, the physiological result is

A. The total inability of the bacteria to divide
B. A massive reduction in its endotoxic potency and structural toll-like receptor 4 (TLR4) activation
C. Spontaneous transformation of the bacteria into a virus
D. Complete loss of its internal ribosomal nucleoproteins

The host immune receptor TLR4 identifies the specific configuration of Lipid A's six fatty acid chains; altering this number prevents effective receptor binding and signaling.

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Jul 3, 2026

MTP is essential for transferring lipids onto the emerging ApoB-100 polypeptide chain; a deficiency in MTP results in the disorder abetalipoproteinemia.

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Jul 3, 2026

99. The biochemical characterization of advanced glycation end-products (AGEs), which accumulate pathologically in patients with chronic hyperglycemia, shows they are formed via the

A. Template-directed synthesis of proteins on structural ribosomes
B. Non-enzymatic covalent cross-linking of reducing sugars to proteins or lipids
C. Controlled addition of mannose-6-phosphate inside the Golgi
D. Rapid breakdown of nuclear nucleoproteins during cell division

AGEs are formed via glycation, a chaotic, non-enzymatic reaction where excess blood sugars bind randomly to proteins and lipids, disrupting their function.

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Jul 3, 2026

Retinal links to the opsin protein via a carbon-nitrogen double bond called a Schiff base linkage, which is central to proton-pumping mechanisms.

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Jul 3, 2026

Hyaluronic acid is a massive, unsulfated glycosaminoglycan that serves as the central structural spine for large extracellular proteoglycan complexes.

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Jul 3, 2026

94. The human immunodeficiency virus (HIV) utilizes its surface glycoprotein gp120 to bind to host cells. This conjugated molecule exhibits a high degree of structural shielding due to dense N-linked glycosylation, which allows the virus to

A. Directly synthesize ATP inside the viral particle
B. Mask its highly conserved protein epitopes from neutralizing host antibodies
C. Replicate its genome without utilizing an RNA intermediate
D. Form covalent cross-links with the host cell wall

The dense array of host-derived sugar chains on gp120 creates a structural "glycan shield" that hides underlying viral protein epitopes from the host immune system.

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Jul 3, 2026

95. A sample of isolated cellular membranes is treated with an enzyme that selectively cleaves sialic acid (neuraminic acid) residues from the terminals of all surface glycoproteins. The physical consequence of this treatment on the cells will be a significant

A. Increase in the overall positive charge of the cell coat
B. Decrease in the net negative surface charge, causing reduced electrostatic repulsion between cells
C. Sudden breakdown of the internal nuclear envelope
D. Spontaneous alignment of membrane proteins into a double-helix

Sialic acid residues carry a negative charge at physiological pH; removing them lowers the cell's negative charge, altering cell-to-cell spacing and interactions.

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Jul 3, 2026

80. The specialized conjugated molecule found in the photosynthetic membranes of chloroplasts that combines proteins with light-harvesting pigments is the

A. Cytochrome oxidase complex
B. Light-harvesting complex (LHC)
C. Ribosome assembly matrix
D. Nucleosome core filament

LHCs are pigment-protein chromoprotein complexes where chlorophylls and carotenoids are precisely bound to a protein matrix to capture light.

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Jul 3, 2026

81. The component of the bacterial cell wall in Gram-negative organisms that acts as a physical barrier against hydrophobic dangerous toxins and antibiotics is the

A. Cytoplasmic histone protein coat
B. Outer leaflet of the outer membrane made of lipopolysaccharides
C. Matrix of purely non-polar storage fats
D. Layer of nucleoproteins floating in the periplasm

The dense, charged sugar chains of the lipopolysaccharide layer form a hydrophilic shield that resists the entry of hydrophobic toxic compounds.

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Jul 3, 2026

82. The molecular weight of a mature glycoprotein can often be variable and non-uniform compared to a pure protein because

A. Ribosomes synthesize protein chains at random speeds
B. Glycosylation is a non-templated, step-by-step enzymatic process
C. Carbohydrate chains are prone to spontaneous nuclear fission
D. Proteins undergo spontaneous conversion into fatty acids

Unlike template-driven translation, carbohydrate assembly depends on local enzyme concentrations and kinetics, resulting in glycan variations.

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Jul 3, 2026

83. The major lipoprotein particle responsible for removing cholesterol from dying cells and returning it to the liver is

A. Chylomicron remnants
B. High-density lipoprotein (HDL)
C. Very low-density lipoprotein (VLDL)
D. Intermediate-density lipoprotein (IDL)

HDL acts as a vascular scavenger, picking up free cholesterol from peripheral tissues and transporting it back to hepatic tissues.

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Jul 3, 2026

84. The physical property that allows mucins (mucus glycoproteins) to form thick, protective viscoelastic gels is their ability to

A. Dissolve completely into single atoms
B. Form extensive intermolecular disulfide bonds and trap water molecules
C. Condense into solid crystalline structures inside the cell
D. Bind directly to the hydrophobic core of the nuclear membrane

Mucins cross-link via disulfide bonds to form large polymeric networks. Their hydrophilic sugar chains then trap water molecules to form a gel.

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Jul 3, 2026

85. The biochemical feature that protects the protein backbone of lysosomal membrane glycoproteins from being digested by the acidic hydrolases inside the lysosome is

A. A thick protective layer of attached oligosaccharide chains
B. The presence of embedded nuclear DNA markers
C. A continuous coating of non-polar cholesterol molecules
D. The inclusion of heavy metal ions like lead

Heavily glycosylated proteins form a protective sugar shield on the inner lysosomal membrane, protecting the peptide bonds from proteases.

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Jul 3, 2026

86. An experimental cell line exhibits a mutation resulting in a total loss of the enzyme phosphomannose isomerase. Biochemically, this defect leads to the failure of N-linked glycosylation. The immediate pathobiological outcome for the secreted proteins in this cell system will be

A. Their conversion into functional cytoplasmic glycolipids
B. Their retention in the endoplasmic reticulum due to misfolding and accelerated degradation
C. Spontaneous export as highly active structural catalysts
D. Their structural conversion into double-stranded nucleoproteins

Unmodified or poorly glycosylated proteins fail the ER quality control check, remain bound to chaperones, and are targeted for ER-associated degradation (ERAD).

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Jul 3, 2026

87. A researcher isolates a novel lipid-anchored protein from a mammalian cell membrane and determines that it is released from the membrane upon treatment with the enzyme phosphatidylinositol-specific phospholipase C (PI-PLC). This observation proves that the protein is a

A. Lipopolysaccharide variant
B. Glycosylphosphatidylinositol (GPI)-anchored glycoprotein
C. Core histone nucleoprotein complex
D. Chylomicron apolipoprotein component

PI-PLC specifically hydrolyzes the phosphodiester bond within the GPI anchor, releasing the attached glycoprotein from its lipid tail.

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Jul 3, 2026

88. The disease known as I-cell disease (mucolipidosis II) is a severe lysosomal storage disorder caused by a deficiency in the enzyme UDP-GlcNAc phosphotransferase. As a result of this molecular defect, lysosomal enzymes

A. Are synthesized with abnormal lipid tails
B. Lack the mannose-6-phosphate sorting tag and are constitutively secreted out of the cell
C. Are permanently trapped inside the nuclear matrix
D. Undergo spontaneous conversion into structural proteoglycans

Without the phosphotransferase enzyme, lysosomal proteins lack the mannose-6-phosphate tag needed for sorting, causing them to be misdirected and secreted.

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Jul 3, 2026

Dolichol phosphate is a long, polyisoprenoid lipid molecule embedded in the ER membrane that serves as the membrane anchor for building the core glycan.

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Jul 3, 2026

Lipoprotein lipase requires ApoC-II as a co-factor to bind and hydrolyze triacylglycerols within chylomicrons and VLDLs.

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Jul 3, 2026
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