Organelles are specialized structures that perform various jobs inside cells. The term literally means “little organs.” In the same way organs, such as the heart, liver, stomach, and kidneys, serve specific functions to keep an organism alive, organelles serve specific functions to keep a cell alive. Show
Cells are grouped into two different categories, prokaryotic cells and eukaryotic cells, which are primarily differentiated by the presence of one organelle, the nucleus. Prokaryotic cells do not have a nucleus, whereas eukaryotic cells do. A nucleus is a large organelle that stores DNA and serves as the cell’s command center. Single-cell organisms are usually prokaryotic, while multi-cell organisms are usually made of eukaryotic cells. Another large organelle found in eukaryotic cells is the mitochondrion, an organelle responsible for making ATP, a chemical that organisms use for energy. Cells often contain hundreds of mitochondria. These mitochondria have an outer membrane, which encases the organelle, and an inner membrane, which folds over several times to create a multi-layered structure known as cristae. The fluid inside the mitochondria is called the matrix, which is filled with proteins and mitochondrial DNA. Chloroplasts are another organelle that contain a double membrane and retain their own DNA. Unlike mitochondria, however, the inner membrane of chloroplasts is not folded. They do, however have a third, internal membrane called the thylakoid membrane, which is folded. In addition, unlike mitochondria, chloroplasts are only present in plant cells. They are responsible for converting sunlight into energy through a process called photosynthesis. Other organelles like lysosomes are responsible for digesting and recycling toxic substances and waste. They are embedded with proteins called enzymes, which break down macromolecules, including amino acids, carbohydrates, and phospholipids. Lysosomes are produced by a larger organelle called the Golgi complex, which manufactures other cellular machinery as well. Whenever a cell dies, it self-destructs using its own lysosomes. A cell organelle is a tiny cellular structure that performs specific functions within a cell. You can think of cell organelles as a cell’s internal organs. For example, the nucleus is the cell’s brain, and the mitochondria are the cell’s hearts. Cell organelles are often enclosed by their own membranes, which divide the cell into many small compartments for different biochemical reactions. [In this figure] The anatomy of an animal cell with organelles labeled. Cell organelles have a wide range of responsibilities, from generating energy for a cell to controlling its growth and reproduction. From this point of view, you can also think of cell organelles as different teams within the factory. Each team carries out its specific task and coordinates to make sure the entire factory works smoothly. Below is a list of the cell organelles found in animal and plant cells, which we’ll use as our guide for this discussion.
Cell organelles can be divided into three typesIn this article, we are going to divide these cell organelles/structures into three types: 1. General cell organelles: they are present in both animal and plant cells all the time – cell membrane, cytosol, cytoplasm, nucleus, mitochondrion, rough and smooth endoplasmic reticulum, Golgi apparatus, peroxisome, lysosome, and the cytoskeleton. 2. Temporal cell organelles: they are only found at specific stages of the cell’s life cycle – chromosome, centrosome, autophagosome, and endosome. 3. Cell type specific cell organelles: they only exist in the plant cells – chloroplast, central vacuole, and cell wall. Many unique cell organelles/structures only exist in specific cell types. For example, the food vacuoles in amoeba and the trichocysts in paramecia, which cannot be found in human cells. On the other hand, some human cells also have unique organelles that can’t be found anywhere else, like the Weibel–Palade bodies in blood vessel cells. 1. General cell organelles in every cellCell membrane
[In this figure] The cell membrane defines the inside and outside spaces of a cell. There are many proteins on or inserted in the cell membrane. They function as channels (controlling the in and out of molecules) or receptors (receiving signals from the outside world). Cytosol
Cytoplasm
Cytoskeleton
[In this figure] Cytoskeleton consists of three types of filament proteins: microtubules, actins, and intermediate filaments. [In this figure] Fluorescent image of vimentin, an intermediate filament protein (green), in human cells. The nuclei were stained in blue color. [In this figure] Fluorescence image of microtubule (orange), and the nucleus (cyan) inside a cell.Microtubule is one type of cytoskeleton inside the cells, and it shapes cell’s morphology. Magnification, 63x. Photo credit: Jason Kirk, 2020 photomicrograph competition. [In this figure] Fluorescence image of microtubule (yellow) and the nucleus (cyan) inside a cell.Microtubules radiated from a tissue cell culture. Notice that the microtubules extend to the very end of the cell membrane. Magnification, 63x. Photo credit: Jason Kirk, 2020 photomicrograph competition. Nucleus
[In this figure] Cell nucleus is a membrane-bound organelle that stores DNA. Nucleolus
Mitochondrion
[In this figure] Left: the structure of mitochondrion showing many folds of membranes and mtDNA. Right: a mitochondrion surrounded by rough ER under a transmission electron microscope. Endoplasmic reticulum
[In this figure] The anatomy of ER.Left: The relationship between the nucleus, rough, and smooth ER. Right: A 3D view of rough ER. The image was created with BioRender.com. Ribosome
[In this figure] The ribosome works like a machine to translate the code sequence of mRNA into a protein. Golgi apparatus
[In this figure] The journey of protein synthesis and transportation. Peroxisome
[In this figure] Peroxisomes. Lysosomes
[In this figure] Lysosome is the recycling center of the cell. 2. Temporary cell organelles for specific tasksAutophagosome
[In this figure] The process of autophagy. Endosome
[In this figure] Phagocytosis vs. Endocytosis. Chromosome
[In this figure] In order to handle the long DNA molecules, our cells pack DNA threads into many compact structures, called “chromosome”. Sister chromatids
[In this figure] Chromosome replication forms sister chromatids. Centrosomes
[In this figure] Illustration and electron micrography of the centrosome. 3. Unique cell organelles in the plant cells[In this figure] The cell anatomy of animal and plant cells. Cell wall
[In this figure] Cell wall provides additional protective layers outside the cell membrane. Vacuole
[In this figure] Drawing of a plant cell showing a large vacuole. Chloroplast
[In this figure] The structure of chloroplast. Related postsAnimal Cell Model Part I – cell membrane, cytosol, nucleus, and mitochondria. Animal Cell Model Part II – endoplasmic reticulum, ribosome, Golgi apparatus, peroxisome, and lysosomes. Animal Cell Model Part III – two types of temporary organelles involving eating behaviors, autophagosomes, and endosomes. Animal Cell Model Part IV – two types of temporary organelles only appearing during mitosis, centrosomes, and chromosomes. Plant Cell Model Part V – cell wall, vacuole, and chloroplast. |