Eukaryotic cells
What Is a Cell with a Nucleus?
When you think of your body, consider the ultimate boss of everything. What organ tells your entire body what to do? The answer is, your brain! Your brain tells your lungs to breathe, your heart to speed up or slow down, and your digestive system to break down food.
All these organs are made of cells. Cells are the basic units of life, and even though they are microscopic they each have a brain of their own. This brain is called the nucleus. The nucleus holds the cell's DNA and controls all cell function. Cells with a nucleus are eukaryotic, and are also known as eukaryotes.
However, not all cells have a nucleus. Some cells have their DNA just floating around the cell. This would be analogous to lower organisms, like worms, that don't have a nice thick skull around their brains. These cells are called prokaryotic. The nuclear envelope in eukaryotes is like our skull, covering the nucleus and keeping the DNA safe.
Structure of a nucleus
nucleus structure
Eukaryotic cells also have tiny parts called membrane bound organelles. Organelles, like the name sounds, are tiny organs of the cell.
Eukaryotic cells compared to prokaryotic cells
eukaryote versus prokaryote
Like our body has a stomach to digest food, cells have an organelle that serves a similar purpose. These organelles are all contained in a membrane, keeping them separate from the rest of the cell so they can be the most efficient. Let's take a look at some of the common membrane bound organelles and their jobs inside the cell.
Examples of Membrane Bound Organelles
We now know that the nucleus is the brain of the cell, holding the DNA. But other organelles inside the nucleus are also important, just like the other organs in our body are.
A city is another analogy that works for the cell. The city is the cell itself and each organelle is like a building, or part of the city. There is the endoplasmic reticulum, which surrounds the nucleus. This organelle is involved in protein and lipid synthesis, and it's kind of like a factory making the basic parts for the cell.
Those parts are shipped to the golgi to be distributed to the rest of the cell. The golgi is like the post office of the cell. From the golgi, proteins are shipped through vesicles like trucks on a highway, going where they need to be. The plasma membrane might be one destination for those proteins, since it is the outer covering of the cell. The plasma membrane is like the walls of a city, only letting certain things in and out.
The power plant of the cell, supplying energy for the entire city, is the mitochondria. And our cities also need to get rid of waste, right? An organelle called the lysosome breaks down unwanted or old materials in the cell, recycling them for later use. Finally, peroxisomes are important organelles that also do reactions using oxygen and protect the cell from free radicals, or dangerously reactive compounds.
Organelles in an animal cell
animal cell
Plant cells are a little bit different and have some additional organelles. In plant cells, there is an organelle called a vacuole, which is like a water storage tower in a city. Some animal cells have small vacuoles, but they are not as prominent as they are in plants. This organelle stores water and helps the plant cell hold its shape. Plant cells also have an even more rigid boundary outside the plasma membrane called the cell wall. This thick structure is like reinforcements on our cell wall. They also have chloroplasts, which are used to turn sunlight and carbon dioxide into food.
Organelles inside a plant cell
plant cell
Other organelles don't have a membrane but are still important. Ribosomes are a type of organelle that makes protein and can work with the endoplasmic reticulum. Both prokaryotes and eukaryotes have this organelle.