Eukaryotic Cells

 

What is a eukaryotic cell?

A eukaryotic cell, or a cell that contains membrane-bound structures, is the basis for every multicellular organism, including animals, plants, and humans as well as some unicellular organisms (organisms with a single cell), such as protozoa. 

Eukaryotic cells contain several membrane-bound structures, or organelles, which are specialized cellular subunits that carry out specific cellular functions. The nucleus is surrounded by the nuclear membrane, also called the nuclear envelope, which protects the genetic material stored inside. 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, another organelle, extends from the rough ER and is responsible for modifying and packaging proteins into their final form. Another organelle with an important role is the mitochondria, which is where most of the energy for the cell is produced. There are additional organelles that may be present in various eukaryotic cells. Each eukaryotic cell can specialize and contain a different proportion of each organelle type depending on its function.

   

What is the difference between prokaryotic and eukaryotic cells?

The primary difference between prokaryotic and eukaryotic cells is that a nucleus and other membrane-bound organelles are only present in eukaryotic cells. Prokaryotic and eukaryotic cells make up prokaryotes and eukaryotes, respectively. Prokaryotes are always unicellular, while eukaryotes are often multi-celled organisms. Additionally, eukaryotic cells are more than 100 to 10,000 times larger than prokaryotic cells and are much more complex.

The DNA in eukaryotes is stored within the nucleus, while DNA is stored in the cytoplasm of prokaryotes. Additionally, DNA in eukaryotic cells is stored in double-stranded chromosomes that are condensed by histones. In contrast, prokaryotic cells have one primary circular chromosome and various plasmids, which are small rings of DNA. The DNA of eukaryotic cells has proportionally less coding DNA and high amount of non-coding DNA compared to prokaryotic cells. The ribosomes in eukaryotic cells are 80S, with 40S and 60S subunits, and in prokaryotic cells: 70S with 30 and 50S subunits. 

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

The cell types also vary in their mechanisms of cell division. Prokaryotes can undergo binary fission where one cell multiplies its contents, the cytoplasmic membrane elongates in cytokinesis separating the DNA molecules, and two identical cells emerge. All eukaryotes undergo a similar but more complicated process called mitosis. In both binary fission and mitosis, the parent cells have the exact same number of chromosomes as their daughter cells. However, in sexually reproducing eukaryotic organisms, they can also undergo meiosis during which re-assortment creates genetically unique reproductive cells called gametes or sex cells, which have half the number of chromosomes as the parent cells, so they are known as haploids.

How are prokaryotic and eukaryotic cells similar?

All prokaryotic and eukaryotic cells have some similar features as they both contain ribosomes, genetic material, a cytoplasm, and plasma membranes. The cytoplasm is made up of cytosol, which is the intracellular fluid in which the organic material inside the cell is suspended and the place where most cellular activity occurs. Plasma membranes protect the cell and allow for transportation of materials in or out of the cells.

What are some examples of eukaryotic cells?

There are two main types of eukaryotic cells: plant and animal cells. A plant cell has a cell wall, which is a hard cellular membrane surrounding the cell; a large vacuole; and chloroplasts that undergo photosynthesis by using light as energy for the cell. In contrast, animal cells have only a cellular membrane, typically small vacuoles, and no chloroplasts. 

There are many different types of animal cells, many of which are solely found in the human body. They all begin from a singular stem cell, which continues to replicate and divide 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 have cilia to help absorb nutrients and are labile, meaning they constantly regenerate. Meanwhile nerve cells have a long thin axon to quickly transmit information and survive for many years, so they are permanent cells.

What are the most important facts to know about eukaryotic cells?

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 are always part of unicellular organisms. Both prokaryotic and eukaryotic cells have similar features, like ribosomes, genetic material, a 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 cells, and blood cells.