Understanding Cells: Theory and Types

The presence of a distinct nuclear lamina, composed of lamin-associated proteins and lamins, is a universal characteristic of all cell types, irrespective of their differentiation status or origin.

The cell theory, as originally formulated by Schleiden and Schwann, posits that all organisms are composed of cells, and each cell arises de novo, independent of pre-existing cells.

The exclusive presence of N-acetylmuramic acid in cell walls is definitive evidence that the cell is exclusively a bacterial cell.

Epithelial tissues manifest identical structural polarity across all subtypes, characterized by a uniformly positioned apical membrane and basolateral domain irrespective of function or location.

In the context of cell biology, the glycocalyx—a carbohydrate-rich layer on the cell surface—is exclusively composed of glycosaminoglycans covalently linked to integral membrane proteins.

Lipid rafts, characterized by their dynamic assembly enforced by their compositional heterogeneity, are enriched with sphingolipids, cholesterol, and GPI-anchored proteins but devoid of transmembrane proteins to maintain their structural integrity within the plasma membrane.

The rough endoplasmic reticulum's (RER) exclusive function is protein synthesis and folding, rendering it incapable of participating in lipid metabolism or the detoxification of hydrophobic compounds.

The translocon, a protein-conducting channel in the ER membrane, exhibits unidirectional transport, solely facilitating the movement of polypeptide chains from the cytosol into the ER lumen.

All eukaryotic cells invariably possess a single, centrally located Golgi apparatus that functions as a unified processing and sorting station for newly synthesized proteins and lipids.

The constitutive secretory pathway is exclusively responsible for the regulated release of specialized cellular products, such as hormones or neurotransmitters, in response to specific extracellular signals.

Lysosomal hydrolases, optimally functional at a neutral pH, are indiscriminately targeted to lysosomes irrespective of their glycosylation status or mannose-6-phosphate (M6P) tag.

Autophagy, a catabolic process, exclusively targets fully assembled and functional organelles for degradation, ensuring the preservation of damaged or dysfunctional cellular components.

Mitochondria, characterized by their exclusive dependence on the nuclear genome, completely lack the ability to encode any of their essential protein components, relying solely on import from the cytoplasm.

The primary function of peroxisomes is the synthesis of ribosomal RNA (rRNA), which is then exported to the cytoplasm for ribosome assembly.

Microtubules exhibit dynamic instability due to the exclusive hydrolysis of GTP bound to β-tubulin at the minus end, leading to depolymerization only from the centrosome.

Actin filaments, exclusively dependent on ATP hydrolysis for their polymerization, are completely incapable of undergoing reversible assembly or disassembly in response to cellular signals.

Muscle cells are exclusively striated due to the precise arrangement of actin and myosin filaments into sarcomeres, a characteristic absent in all non-muscle cells.

The only role of the nuclear pore complex (NPC) is to passively permit diffusion of all molecules smaller than 40 kDa, while actively transporting selective macromolecules in a bidirectional manner.

The nucleolus, the site of ribosome biogenesis, exclusively transcribes ribosomal RNA (rRNA) genes but is completely devoid of any involvement in ribosome assembly or quality control.

The main function of epithelial cells is sensation and transportation of nerve impulses.

The plasma membrane, comprised of a uniform lipid composition, maintains consistent fluidity across all cellular regions, ensuring equal permeability to all molecules regardless of size or charge.

The primary function of muscular cells is responsible for sensation and transportation of nerve impulses.

Neurons (nerve cells) are considered modified muscular cells in internal human organs.

Smooth muscle cells are a type of epithelial cell with brush boarders, microvilli, secretory cells and basket cells.

The structural and functional unit of living organisms is the tissue.

Smooth muscles are striated and involuntary.

Smooth muscles are found in external organs as stomach and small intestine.

Sensory cells covert the stimuli into nerve impulses for the brain to process.

One example of sensory cells is photoreceptors in skin.

Neurons contain groups of Nissl's bodies (group of Golgi apparatus and chromosomes), which produce proteins of neurons.