Endocytosis and exocytosis are opposite, energy‑requiring processes that let cells transport macromolecules and particles across the plasma membrane. Endocytosis brings material into the cell by forming a vesicle, while exocytosis expels material by fusing a vesicle with the membrane.
B cells and T cells are the two main lymphocyte families of the adaptive immune system. B cells generate antibodies that neutralize extracellular pathogens, while T cells recognize peptide antigens presented on MHC molecules and carry out cell‑mediated actions such as killing infected cells or helping other immune cells.
Interphase is the preparatory stage of the cell cycle, occupying about 90 % of a cell’s lifetime. It consists of three sequential phases—G1, S, and G2—during which the cell grows, copies its DNA, and readies the machinery needed for mitosis.
Phagocytosis is the process by which specialized immune cells recognize, engulf, and destroy solid particles such as microbes. It proceeds through receptor‑mediated recognition, actin‑driven membrane extension to form a phagosome, and fusion with lysosomes to create a phagolysosome where the target is degraded.
Pyruvate oxidation, also called the link or transition reaction, converts each pyruvate molecule into acetyl‑CoA, producing NADH and CO₂ in the mitochondrial matrix. This single step bridges glycolysis and the Krebs (citric‑acid) cycle, allowing the carbon skeletons from glucose to enter aerobic respiration.
Transduction is the bacteriophage‑mediated transfer of DNA between bacteria. In generalized transduction any part of the donor genome can be moved, while specialized transduction transfers only specific genes located next to the prophage integration site.
Reading a codon table involves breaking an mRNA string into three‑base units (codons), locating each codon in the table by its first, second and third bases, and writing down the corresponding amino‑acid symbols. Following these steps converts the nucleotide sequence into the protein sequence it encodes.
Chemiosmosis is the process by which the energy of an electron‑transport chain creates a proton gradient across a membrane. The resulting proton motive force drives ATP synthase, a rotary enzyme that converts ADP + Pi into ATP. This article explains where the gradient forms, how it is maintained, and how ATP synthase harnesses it.
Bacterial conjugation is a direct, pilus‑mediated transfer of genetic material—usually a plasmid—from a donor (F⁺) cell to a recipient (F⁻) cell. This process spreads traits such as antibiotic resistance and underpins many laboratory tools for genetic engineering.
Simple diffusion and facilitated diffusion are both passive transport processes that move substances down their concentration gradient without using cellular energy. Simple diffusion lets small, non‑polar molecules slip directly through the lipid bilayer, while facilitated diffusion relies on membrane proteins to carry larger or polar molecules across the membrane.