Eukaryotic Cell · What Is It, Difference from Prokaryotic Cells, and More

A eukaryotic cell, or a cell that contains membrane-bound structures, is the basis of every multicellular organism (including animals, plants, and humans), as well as some organisms composed of a single cell, which are known as unicellular organisms (e.g., protozoa).

Eukaryotic cells contain several membrane-bound structures, or organelles, which are specialized cellular subunits that carry out specific functions. The nucleus, surrounded by the nuclear membrane, or nuclear envelope, stores and protects the genetic material of the cell. The nuclear membrane contains nuclear pores, which selectively allow only certain substances to pass through. Another membrane-bound organelle is the endoplasmic reticulum (ER). There are two types of ER: rough and smooth. The rough ER extends from the nuclear membrane, is covered with ribosomes, and is the location of protein synthesis. Meanwhile, the smooth ER is the main site of lipid and steroid synthesis. The Golgi apparatus is an organelle typically found near the rough ER and is responsible for modifying and packaging proteins into their final form. Another organelle with an important role is the mitochondrion, which produces most of the energy for the cell. Eukaryotic cells may contain additional organelles, with their type and proportions varying according to the cell’s specialized function.

The primary difference between prokaryotic and eukaryotic cells is that only the latter contain a nucleus and other membrane-bound organelles. Prokaryotic and eukaryotic cells make up prokaryotes and eukaryotes, respectively. Prokaryotes are always unicellular organisms, while eukaryotes are often multicellular organisms. Additionally, eukaryotic cells are more than 10 to 100 times larger than prokaryotic cells and are much more complex.

While eukaryotes store their DNA inside the nucleus, prokaryotes keep it in the cytoplasm. Additionally, DNA in eukaryotic cells is organized into double-stranded chromosomes that are condensed by histones. In contrast, prokaryotic cells contain one primary circular chromosome and may also contain plasmids (small rings of DNA). Eukaryotic cells contain a smaller proportion of coding DNA and a higher proportion of noncoding DNA, compared with prokaryotic cells. The ribosome type in eukaryotic cells is 80S, with 40S and 60S subunits, while prokaryotic cells contain 70S ribosomes with 30S and 50S subunits.

The locomotive structures (i.e., flagellum) also vary between prokaryotic and eukaryotic cells. In eukaryotic cells, flagella are microtubule bundles composed of dynein and a plasma membrane, powered by ATP to make a bending motion. Prokaryotic locomotive structures are instead composed of repeated flagellin, a hook, and a motor complex attached to the cellular membrane, and are powered by protons to make a rotational motion.

The cell types also vary in their mechanisms of cell division. Prokaryotes can undergo binary fission, where one cell duplicates its contents, the cytoplasmic membrane elongates, and cytokinesis (i.e., division of the cytoplasm) separates the duplicated DNA molecules, and two identical cells emerge. All eukaryotes undergo a similar but more complicated process called mitosis. In both binary fission and mitosis, parent cells have the exact same number of chromosomes as their daughter cells. However, in sexually reproducing eukaryotic organisms, another type of cell division called meiosis allows gene reassortment and creates genetically unique reproductive cells called gametes, or sex cells. Gametes are haploid cells, meaning they have half the number of chromosomes as the parent cells.

All prokaryotic and eukaryotic cells share several features, including ribosomes, genetic material, cytoplasm, and plasma membranes. The cytoplasm is made up of cytosol, which is the intracellular fluid in which organic material inside the cell is suspended and most cellular activity occurs. Plasma membranes protect the cell and allow for transport of materials in or out of it.

There are two main types of eukaryotic cells: plant and animal cells. A plant cell is surrounded by a cell wall, which is a rigid outer structure; moreover, it contains a large vacuole, and chloroplasts that undergo photosynthesis by converting light energy into chemical energy for the cell. In contrast, animal cells have only a plasma membrane, typically small vacuoles, and no chloroplasts.

There are many different types of animal cells, many of which are primarily found in the human body. They all originate from a single cell, called a zygote, which continues to replicate and eventually differentiates into the specialized cells in the body. These specialized cells each have unique shapes and proportions of organelles depending on their function. For example, epithelial cells that line the intestines are labile (constantly regenerating), and use microvilli (i.e., tiny cell membrane protrusions) to increase the surface area for nutrient absorption. Meanwhile, nerve cells are permanent cells (i.e., they survive for many years) and have a long, thin axon that allows them to quickly transmit information.

Eukaryotic cells are cells containing membrane-bound organelles and are the basis for both unicellular and multicellular organisms. In contrast, prokaryotic cells do not have any membrane-bound organelles and always form unicellular organisms. Both prokaryotic and eukaryotic cells have similar features, including ribosomes, genetic material, cytoplasm, and plasma membranes. There are two primary types of eukaryotic cells: animal and plant cells. The human body contains various types of eukaryotic cells, including neurons, intestinal epithelial cells, and blood cells.