Practice Questions

50. The chemical structure of a cerebroside, a key glycolipid found in myelin tissues, consists of a galactose or glucose unit bound to a

A. Molecule of glycerol and three fatty acids
B. Sphingosine backbone with a fatty acid chain
C. Core histone protein cluster
D. Long polymer of repeating ribonucleotides

Cerebrosides are monoglycosylceramides, meaning they utilize a sphingosine amino alcohol base instead of a glycerol backbone.

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49. The carbohydrate configuration of the glycoprotein hormone erythropoietin (EPO) is highly critical because its removal results in

A. Spontaneous conversion into an active lipid
B. Immediate clearance and loss of biological activity in vivo
C. The conversion of the hormone into an active enzyme
D. Direct entry of the hormone through the nuclear envelope

The oligosaccharide chains on circulating glycoprotein hormones shield them from rapid hepatic filtration and enzymatic degradation.

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48. The protein component of a conjugated molecule, stripped of its non-protein prosthetic group, is technically referred to as the

A. Holoenzyme
B. Apoenzyme / Apoprotein
C. Coenzyme
D. Prosthetic matrix

An apoprotein (or apoenzyme) is the purely proteinaceous part of a conjugated molecule that remains inactive or incomplete without its partner.

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47. The component that gives lipoprotein particles their micelle-like stability in aqueous blood plasma is the alignment of

A. Hydrophobic fats on the very outer surface
B. Amphipathic phospholipids and proteins on the outer monolayer
C. Solid cholesterol crystals forming a hard outer shell
D. Hydrophilic DNA loops surrounding a core of oil

Phospholipids align with their hydrophilic heads facing the watery plasma and their hydrophobic tails pointing inward toward the fat core.

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46. The non-protein portion of a chromoprotein, such as the rhodopsin found in retinal rod cells, is

A. Retinal (Vitamin A derivative)
B. Oligosaccharide chain
C. Palmitic acid
D. Ribose monophosphate

Rhodopsin is a conjugated light-sensitive chromoprotein consisting of the protein opsin covalently bound to the carotenoid retinal.

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45. The cellular process known as O-linked glycosylation typically takes place within the

A. Outer mitochondrial membrane
B. Lumen of the Golgi apparatus cisterna
C. Inner nucleoplasm matrix
D. Hydrophobic layer of the chloroplast stroma

While N-linked glycosylation begins in the rough ER, O-linked sugar modification is localized almost entirely within the Golgi complex.

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44. The modification of chromatin structure via the addition of acetyl groups to histone proteins alters the nucleoprotein affinity, resulting in

A. Permanent destruction of the DNA template
B. Relaxation of chromatin structure to permit transcription
C. Dense packing of DNA into transcriptionally silent heterochromatin
D. The immediate export of histones into the cytoplasm

Acetylation neutralizes the positive charges on histones, weakening their grip on DNA and allowing transcription machinery to bind.

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43. The presence of lipopolysaccharides (LPS) in the outer membrane of Gram-negative bacteria causes them to behave functionally as

A. Vital vitamins for host absorption
B. Endotoxins that trigger severe immune responses
C. Structural channels for glucose diffusion
D. Catalysts for extracellular starch digestion

The Lipid A portion of LPS is an endotoxin that can trigger severe inflammatory pathways, leading to toxic shock in host organisms.

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Silicoproteins are conjugated molecules where silicon or silicate complexes are structurally integrated into a protein backbone.

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41. The architectural arrangement of eukaryotic chromatin reveals that the interaction between DNA and histone proteins is primarily driven by

A. Covalent peptide linkage
B. Electrostatic attraction between opposite charges
C. Hydrophobic exclusion principles
D. Sharing of electrons between aromatic rings

Positively charged basic amino acids (lysine and arginine) on histones bind strongly to the negatively charged phosphates of the DNA molecule.

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