MCQs

Histone H1 is distinct from the core octamer proteins; it functions as the linker histone that binds to the entry/exit site of DNA on the nucleosome core particle, facilitating higher-order folding into the 30-nm solenoid fiber.

A nucleosome is the fundamental repeating structural unit of chromatin, consist of approximately 146 base pairs of DNA wrapped around a core octamer of basic histone proteins (two copies each of H2A, H2B, H3, and H4).

Telomeres are highly specialized, non-coding repetitive DNA sequences found at the terminal tips of linear chromosomes that protect them from degradation and end-to-end fusion.

Telocentric chromosomes exhibit a centromere at the absolute terminal end, resulting in a single visible arm. Metacentric has a central centromere, sub-metacentric has a slightly off-center centromere, and acrocentric has a near-terminal centromere.

The centromere represents the primary constriction site of a chromosome. It serves as the assembly platform for the kinetochore complex where mitotic or meiotic spindle fibers attach. Telomeres are terminal ends, and satellite bodies are associated with secondary constrictions.

Eukaryotic chromosomes are biochemically composed of chromatin material, which primarily consists of deoxyribonucleic acid (DNA) complexed with highly basic histone proteins. Other options represent different cellular macromolecules not forming the core structural composition of chromosomes.

Premature electron transfers to oxygen at complexes I and III form superoxide radicals, making the mitochondrion the chief producer of intracellular ROS.

Electron flow drives complexes I, III, and IV to pump protons out of the matrix into the intermembrane space, creating a reservoir of high proton concentration.

Porins render the outer membrane freely permeable to small molecules and metabolic substrates, unlike the highly selective inner membrane.

The conversion of amino acid carbon skeletons into metabolic intermediates like alpha-ketoglutarate requires enzymes located within the mitochondrial matrix.

The TIM23 complex is the primary translocase channel that threads unfolded precursor proteins across the inner mitochondrial membrane into the matrix.

Paternal mitochondria entering the egg are tagged with ubiquitin and selectively destroyed via mitophagy, ensuring that only maternal mitochondrial DNA survives.

Nuclear-encoded mitochondrial proteins use the Translocase of the Outer Membrane (TOM) and Translocase of the Inner Membrane (TIM) to cross both bilayers.

Proton flux through the Fo​ base forces the central gamma asymmetric shaft to spin inside the static α3​β3​ hexamer of the F1​ head, inducing conformational changes that forge ATP.

Proton leaks collapse the electrochemical gradient across the inner membrane, directly short-circuiting ATP synthesis.

Uncouplers dissipate the proton gradient without making ATP. Energy is lost as heat, driving the cell to burn oxygen faster to compensate.

These prokaryotic-like genetic traits strongly confirm that mitochondria evolved from ancient alpha-proteobacteria engulfed by primitive cells.

The electron transport chain complexes (I-IV) are embedded within the inner membrane folds (cristae) to easily interact with the chemical environment.

The soluble enzymes of the Krebs cycle reside inside the fluid matrix, with the sole exception of succinate dehydrogenase (bound to the inner membrane).