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A plasma membrane

the organisms on earth, by number, are actually prokaryotic. 

Here are some examples of eukaryotes:

  • Animals
  • Plants
  • Fungi (mushrooms, etc.)
  • Protists (algae, plankton, etc.)

Most plants, animals, and fungi are composed of many cells and are aptly classified as multicellular. Most protists consist of a single cell and are classified as unicellular. Funny how that works. 

All eukaryotic cells have the following:

  • nucleus
  • Genetic material
  • plasma membrane
  • Ribosomes
  • Cytoplasm, including the cytoskeleton

Most eukaryotic cells also have other membrane-bound internal structures called organelles. Organelles include:

  • Mitochondria
  • Golgi bodies
  • Lysosomes
  • Endoplasmic reticulum
  • Vesicles

There are a few major differences between animal, plant, fungal, and protistan cells. And guess what? We’ve got some handy-dandy lists to help you learn those differences. 

All plant cells have the following:

  • cell wall made of cellulose
  • A large central vacuole
  • Chloroplasts

Some animal and protistan cells have:

  • Flagella
  • Cilia

But all animal cells have:

  • Centrioles (Well…that was shorter than we expected.)

All fungal cells have:

  • cell wall made of chitin

Huh, that one was also quite short. Have you had enough lists? Us, too.

Structures Found in All Eukaryotic Cells

The Nucleus and Eukaryotic Genetic Material

The nucleus in the cell is analogous to the brain in the body. It is the control center for a cell.

Presenting—dun, dun, DUN—the nucleus:

The nucleus stores all the information a cell needs to grow, reproduce, and function. This information is contained in long but thin molecules of deoxyribonucleic acid, or DNA. One of the functions of the nucleus is to protect the cell’s DNA from damage, but that is not all it does. The nucleus is basically a large membranous sac. Like your face. Ohhhh, snap! 

(Sorry, that was mean. By way of an apology, have a video of a banana driving a car. It’s on us.)

The nucleus also contains a small, round body called a nucleolus, which is like DNA’s apartment building. It’s where the DNA and all of its attendant proteins hang out all day. 

The nuclear membrane has pores through which the contents of the nucleus communicate with the rest of the cell. The nuclear membrane tightly controls what gets into the nucleus and what gets out. This regulation of communication by the nuclear membrane has a great effect on what a cell looks like and what it does.

Chromosomes are also located in the nucleus and are basically organized structures of DNA and proteins. In eukaryotes, the chromosomal DNA is packaged and organized into a condensed structure called chromatin. Chromosomes are single pieces of DNA along with genes, proteins, and nucleotides, while chromatin is a condensed package of chromosomes that basically allows all the necessary DNA to fit inside the nucleus. 

We will dive deeper into the world of chromosomes in another section, but for now, just remember that eukaryotic and prokaryotic cells each have genomes, the name for the entire set of an organism’s genetic and hereditary information. Genomes are entirely encoded in either the DNA or the RNA. In the case of eukaryotes, multiple linear pieces of DNA comprise its genome.

In eukaryotic organisms, the DNA inside the nucleus is also closely associated with large protein complexes called histones. Along with the nuclear membrane, histones help control which messages get sent from the DNA to the rest of the cell. 

The information stored in DNA gets transferred to the rest of the cell by a very elegant process—a process so common and so important to life that it is called the central dogma of biology. No, really.

In eukaryotic cells, the first stage of this process takes place in the nucleus and consists of specific portions of the DNA, called genes, being copied, or transcribed, into small strands of ribonucleic acid, or RNA. RNA containing a copy, or transcript, of DNA is called messenger RNA, or mRNA. These mRNA molecules are then physically transported out of the nucleus through the pores (holes) in the nuclear membrane and into the cytoplasm, where they are eventually translated into proteins by ribosomes. 

Therefore, the central dogma of biology is simply: 

DNA → RNA → Protein 

And it all starts in the nucleus! (Warning: any discussion of the nucleus excludes prokaryotes. The nucleus is a eukaryotic song and dance number, and don’t you forget it.)

Most eukaryotic cells have a nucleus throughout their entire life cycles, but there are a few notable exceptions. Human red blood cells (the good ol’ RBCs), for example, get rid of their nuclei as they mature. Rebels without a cause. Scratch that: rebels with a cause. With their nuclei removed, red blood cells have more space to carry oxygen throughout the body.

Eukaryotic Plasma Membrane

The plasma membrane in eukaryotic cells is responsible for controlling what gets into and out of the cell. A series of proteins stuck in the membrane help the cell communicate with the surrounding environment. Among other things, this communication can include

  • sending and receiving chemical signals from other eukaryotic cells.
  • interacting with the cells of prokaryotic organisms during the process of infection.

Keep in mind that the plasma membrane is universal to all cells, prokaryotic and eukaryotic. Because this cellular component is so important and so common, it is addressed in greater detail further on in the In Depth section.