Cell Biology and Structure

Nucleus or nucleus-like structures like nucleoid are required to divide and produce daughter cells. Cells incapable to produce daughter cells lack nucleus

Nucleus was the first organelle to be discovered. It was first noticed by Antonie van Leeuwenhoek.

Assembled ribosomal units are the largest sub-units that can pass through nuclear pores.

Nuclear pores provide aqueous channels through the envelope. These are composed of multiple proteins called nucleoproteins.

Promyelocytic leukemia bodies are found in nucleoplasm. These are non-membrane-delineated bodies. They are involved in assemblage of nuclear bodies.

Perichromatin fibrils are located next to the transcriptionally active chromatin and is hypothesised to be the site of active pre-mRNA processing.

Catalysome refers to an organelle, found in adipose tissue, that functions in lipid metabolism; may represent a specialized type of mitochondrion.

Centrioles are cylindrical organelles composed of microtubules that organize spindle fibers during cell division. They are present in animal cells and play a crucial role in mitosis and meiosis. Most plant cells lack centrioles, using alternative mechanisms to organize their microtubules. Bacteria and viruses do not have centrioles.

Cell walls are extracellular structures found in plant cells, fungi, and some protists, but are absent in animal cells. Animal cells rely on their cytoskeleton and extracellular matrix for structural support instead. Mitochondria, nucleus, and centrosomes are all present in animal cells.

Mature mammalian red blood cells (erythrocytes) lose their nucleus during development to maximize space for hemoglobin, which carries oxygen. This enucleation is unique among human cells. White blood cells, nerve cells, and epithelial cells all maintain their nuclei throughout their lifespan.

The nucleus contains the cell's genetic material (DNA) and controls all cellular activities by regulating gene expression. It is often called the cell's 'control center.' Mitochondria produce energy (ATP), ribosomes synthesize proteins, and endoplasmic reticulum processes proteins and lipids, but none direct overall cellular function like the nucleus.

Mature mammalian RBCs lose their nucleus during development to maximize hemoglobin-carrying capacity, but they originate from nucleated eukaryotic progenitor cells. Being enucleated is a specialized adaptation, not evidence of being prokaryotic.

Cell size is regulated by the nuclear-cytoplasmic ratio (the nucleus can only control a limited volume) and metabolic demands. Oxygen needs affect mitochondrial content, material requirements determine cytoplasmic volume, and nuclear control mechanisms maintain size homeostasis.

Membrane pores and channels typically exhibit negative charge to repel anions while allowing cation passage. This charge selectivity is crucial for regulating ion flow across the membrane and maintaining electrochemical gradients.