Breakage of glycosidic bonds that form complex carbohydrates is considered

Both facilitated diffusion and active transport require carrier proteins to move substances across the plasma membrane, but the mechanisms differ. Facilitated diffusion uses carrier or channel proteins to transport molecules down their concentration gradient without energy expenditure. In contrast, active transport also uses carrier proteins but moves substances against their concentration gradient, requiring energy input, usually from ATP hydrolysis. These proteins provide specificity for particular molecules and enable transport that cannot occur through simple diffusion, ensuring that cells can regulate nutrient uptake, ion balance, and waste removal efficiently.

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A. Positive-sense RNA: Positive-sense RNA viruses possess genomes that function directly as messenger RNA (mRNA). After entering the host cell, the viral RNA can immediately bind to host ribosomes and begin translation to produce viral proteins. No transcription step is required before protein synthesis, these viruses can rapidly initiate replication once infection occurs.

B. Negative-sense RNA: Negative-sense RNA viruses have genomes that are complementary to mRNA and therefore cannot be translated directly by host ribosomes. Before protein synthesis can occur, the virus must first use an RNA-dependent RNA polymerase to synthesize a complementary positive-sense RNA strand. Only this newly formed RNA can function as mRNA for protein production.

C. Double-stranded RNA: Double-stranded RNA viruses contain both a positive and a negative RNA strand. However, the host cell cannot directly translate the double-stranded genome. The virus must first use viral RNA polymerase enzymes to transcribe the negative strand into a positive-sense RNA that can serve as mRNA for translation.