Chapter 4 The Cell Anatomy and Division

The cell anatomy is a complex organism that serves as the structural and functional unit of all living things. The human body’s cells are extremely diverse, and their distinctions in size, shape, and internal makeup reflect their distinct functions. Cells do, however, share many anatomical traits, and all cells must perform specific jobs in order to survive. All cells, for example, can maintain their boundaries, metabolize, digest nutrients, eliminate waste, grow and reproduce, move, and respond to stimuli. Only the function of cell reproduction is considered in this exercise, which focuses on structural commonalities seen in many cells and depicted by a “composite,” or “generalized,” cell (cell division).

The Composite Cell’s Anatomy

The nucleus, plasma membrane, and cytoplasm are the three major regions or portions of all animal cells that can be easily identified using a light microscope. The nucleus is a circular or oval structure located towards the cell’s center. It is encased in the cytoplasm, which is bordered by the plasma membrane. Even smaller cell structures, known as organelles, have been discovered since the development of the electron microscope.


The nucleus houses the genetic material, DNA, which is divided into genes. The nucleus, often known as the cell’s control center, is required for cell reproduction. A cell’s nucleus has been lost or ejected, and it is programmed to die.

The genetic material is loosely spread throughout the nucleus in a threadlike structure termed chromatin when the cell is not dividing. When a cell divides to generate daughter cells, the chromatin coils and condenses, forming dense, darkly colored rodlike substances known as chromosomes—much like when a stretched spring is released, it gets shorter and thicker. Take note of the nucleus’ appearance; when a cell is healthy, it is rather unremarkable. The presence of a black nucleus and clumped chromatin indicates that the cell is dying and degenerating.

One or more small round entities, known as nucleoli, are found in the nucleus and are mostly made up of proteins and ribonucleic acid (RNA). The nucleoli are ribosomal particle assembly sites, which are particularly common in the cytoplasm. Ribosomes are the “factories” that produce proteins.

The nuclear envelope is a double-layered porous membrane that surrounds the nucleus. The nuclear envelope is similar to other cellular membranes in composition, but it is characterized by enormous nuclear holes. Protein complexes span them, regulating what passes through and allowing protein and RNA molecules to pass freely.

Plasma Membrane

The plasma membrane isolates the contents of the cell from the rest of the environment. Phospholipids (fats) and globular protein molecules are the key structural components. Sugar (carbohydrate) side chains are connected to some externally facing proteins and lipids and are vital in cellular interactions. The membrane is a bilayer of phospholipid molecules in which the protein molecules float, as described by the fluid mosaic model. The bilayer is stabilized by the presence of a few cholesterol molecules distributed across it. The plasma membrane not only serves as a protective barrier for the cell, but it also plays an important function in deciding which substances may enter or leave the cell and in what quantities. The plasma membrane is selective in what passes across it due to its molecular composition. It permits nutrients into the cell but keeps unwanted substances out. Excreta, or wastes, travel to the outside, while vital cell proteins and other chemicals are maintained within the cell. Selective permeability is the name for this characteristic. There are two primary modes of transport through the plasma membrane.

Furthermore, the plasma membrane maintains a resting potential that is necessary for excitable cells like neurons and muscle cells to function normally, as well as playing a key role in cell communication and cell-to-cell interactions. Microvilli are tiny fingerlike projections or folds that appear on the membrane of certain cells. Microvilli dramatically enhance the surface area of the cell available for material absorption or transit, as well as signaling molecule binding.

Organelles and Cytoplasm

Between the nucleus and the plasma membrane is the cytoplasm, which contains the contents of the cell. It is the focal point for the majority of the cell’s activity. Many small structures termed organelles (literally, “little organs”) are suspended in the cytosol, the fluid cytoplasmic substance. Organelles are the cell’s metabolic machinery, and they’re well-organized to perform specialized activities for the complete cell. Ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, mitochondria, cytoskeletal components, and centrioles are among the organelles.

Identifying Organelles


Ribosomes are RNA and protein-containing, highly stained, roughly spherical structures. The act of protein synthesis is what they’re called. They can be seen floating around in the cytoplasm or connected to a membrane. The rough endoplasmic reticulum is the name given to the entire ribosome-membrane complex when it is connected.

Endoplasmic Reticulum ER

The endoplasmic reticulum (ER) is a cytoplasmic system of membranous tubules and cisterns (sacs) with a highly folded structure. The ER and the nuclear envelope are connected, forming a system of channels for transporting biological contents (mainly proteins) from one section of the cell to another. There are two types of ER: rough ER and smooth ER. Depending on its specific tasks, a cell may have both or only one. Ribosomes are strewn throughout the rough ER. Its cisterns change, store, and transport newly produced proteins to other parts of the cell. The smooth ER does not engage in protein synthesis, but it is abundant in cells that create steroid-based hormones, such as testosterone-producing interstitial endocrine cells in the testes. Smooth ER is also common in cells involved in lipid metabolism and drug detoxification—for example, liver cells.

Structure of Generalized Cells

Golgi Apparatus

The Golgi apparatus is a collection of flattened sacs with bulbous ends and accompanying membrane vesicles located around the nucleus. The proteins transported to it by transport vesicles from the rough ER are changed, separated, and packaged into membranous vesicles that are eventually (1) integrated into the plasma membrane, (2) secretory vesicles that discharge their contents from the cell, or (3) lysosomes.


Lysosomes are membrane-bound sacs that contain a variety of potent digesting enzymes. They come in a variety of sizes. Acid hydrolases, enzymes capable of digesting worn-out cell components and foreign compounds that enter the cell via vesicle production through phagocytosis or endocytosis, are found in the lysosomes, which are a consequence of the Golgi apparatus’ packaging operations. The lysosomes are commonly referred to as the cell’s “suicide sacs” because of their ability to destroy the entire cell.


Peroxisomes are enzyme-containing sacs, similar to lysosomes. Their oxidases, on the other hand, have a different function. They detoxify a variety of hazardous chemicals, including free radicals, by using oxygen. Peroxisomes are prevalent in kidney and liver cells, which are important in the detoxification process.


Mitochondria are rod-shaped structures with a double-membrane wall, with the inner membrane folded into cristae folds. The Krebs cycle and the electron transport chain (together known as aerobic cellular respiration) are catalyzed by oxidative enzymes on or inside the mitochondria, which break down the end products of food digestion to produce energy. The released energy is caught in the bonds of ATP molecules, which are subsequently transported out of the mitochondria to offer a ready source of energy for the cell to run on. For its many functions, every live cell requires a continual supply of ATP. The mitochondria are known as the “powerhouses” of the cell since they produce the majority of the ATP.

Cytoskeletal elements

The cytoskeletal is an internal structure that supports and moves substances within the cell. Cytoskeletal components ramify throughout the cytoplasm, generating an internal scaffolding termed the cytoskeleton.
Tubulin proteins form the microtubules, which are slender tubules. Most microtubules emanate from the centrosome, a cytoplasmic area near the nucleus that has the potential to assemble and disaggregate spontaneously. During cell division, microtubules arrange the cytoskeleton and create the spindle. They also help preserve cell form by providing rigidity to the soft cellular substance, transporting chemicals down the length of elongated cells (such as neurons), suspending organelles, and transporting substances down the length of elongated cells (such as neurons).

The proteinaceous cytoskeletal components that act as internal guy wires to withstand mechanically (pulling) forces acting on cells are known as stable intermediate filaments. Microfilaments, often known as ribbons or cords, are made up of contractile proteins, principally actin. These are vital in cell mobility and are highly visible in muscle cells that are specialized to contract because of their capacity to shorten and then relax to assume a more elongated form.
The terminal web is a cross-linked network of microfilaments that braces and strengthens the plasma membrane’s interior face. The cytoskeletal structures are microscopic and changing. They are rarely visible, even in electron micrographs, with the exception of the mitotic spindle’s microtubules, which are quite visible during cell division, and the microfilaments of skeletal muscle cells. Special stains, on the other hand, might demonstrate the abundant supply of these vital structures.


In self-replicating cells, the paired centrioles are located near the nucleus within the centrosome.
They are rod-shaped bodies that are perpendicular to one another. Each centriole is made up of nine microtubule triplets on the inside. The centrosome complex, which contains the centrioles, directs the creation of the mitotic spindle during cell division. Centrioles are also known as basal bodies because they create the cell extensions known as cilia and flagella. Other substances and structures found in the cytoplasm of cells include stored meals (glycogen granules and lipid droplets), pigment granules, different crystals, water vacuoles, and swallowed foreign objects. However, because these are not part of the cell’s active metabolic machinery, they are referred to as inclusions.