#2- The Teeny-Tiny Organs of Cells: Organelles

You have organs to stay alive, so do the little cells

Staying organised is key to being on top of your game. For instance, you would like to keep your documents in folders that are correctly labelled and organised by date. Sometimes, you might even organise things by putting one folder in another, and those two will be in a third folder and so on because I am that kind of person.

The same goes for all the cells in you and other cool critters around. While observing the inside of a cell with an electron microscope, you will begin to appreciate how organised it looks in there. Every itty-bitty organ called an organelle, are located in specific regions to carry out their required tasks.

It is time to look past the plasma membrane and dive right into the cell!

Introducing the Cell’s Organelles

As described in the main text in bullet points
Figure 1- Typical anatomy of a cell containing the necessary organelles required to function. Source- Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014”. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002–4436

Here are the following organelles from Figure 1 (top to bottom), explained:

  • Cilia (singular: cilium)- Long, slender organelles seen on eukaryotic cells. There are 2 types — Motile and non-motile. Non-motile cilia are involved in sensory, and the former, in movement like pushing dirt and mucus away from the lungs in the human respiratory tract.
  • Microvilli (singular: microvillus)- Tiny microscopic projections of the plasma membrane that increase surface area to perform many functions like absorption of nutrients in our small intestine.
  • Cytosol- The watery inside of all cells which gets compartmentalised by intracellular membranes forming the organelles. Not to be confused with the cytoplasm.

Imagine this: The cell is like a jiggly jello on a plate (the cytoplasm) with small pieces of fruit scattered inside, like the organelles.

  • Golgi Apparatus (GA)- Contains an organised stack of membrane discs known as Golgi cisternae or simply cisternae. They receive, pack, and transport, proteins and lipids manufactured from the endoplasmic reticulum, in vesicles, to many places in and out of the cell.
  • Centrioles- Cylindrical organelles, predominantly made of tubulin protein, are always seen as a pair called the mother centriole and the daughter centriole. The centriole pair is enclosed in a membrane to form the centrosome and have crucial roles to play from cell division to animal development.
  • Endoplasmic Reticulum (ER)- A labyrinth of membranes found close to the nucleus. They come in 2 forms — rough (RER) and smooth (SER). RER has ribosomes studded on its surface to produce soluble and integral proteins which will go to the cell surface or other organelles. SER lacks ribosomes but manufactures lipids and steroids, and more.
  • Lysosomes- Degrades old and worn-out organelles, macromolecules, and particles from outside the cell, with powerful digestive enzymes.
  • Cytoskeleton- Strands of protein that are involved in maintaining the structure of the cell, like the bones in our body.
  • Ribosomes- Microscopic structures responsible for protein synthesis. Found on RER and floating about in the cytosol.
  • Nucleus (plural: nuclei)- The main guy that controls the whole cell! Has an inner and outer membrane that makes up the nuclear envelope, and is riddled with nuclear pores to allow the movement of molecules in and out of it. Contains DNA, and nucleolus, the place where ribosomes are created.
  • Mitochondrion (plural: mitochondria)- You guessed it! This sausage-shaped, double membraned organelle is the powerhouse of the cell that produces most of the energy for the cell in the form of ATP.

Whatever info I gave on each of these organelles is just surface level to get you folks familiar with them. There is a LOT more to know about these organelles, like, PILES of research papers on their functions and even disorders associated with them. It is exciting but can be discussed some other time.

Some Differences Between Plant and Animal Cells

These two cell types (See Fig. 2 and Fig. 3) have almost the same set of organelles doing the same work. However, they have some structural and organelle-level differences which we shall see below.

Use organelle description from main text and some from Glossary
Figure 2- A typical animal cell with its organelles. Source- LadyofHats Mariana Ruiz. Wikipedia link: https://en.wikipedia.org/wiki/Cell_(biology)
Description in main text and Glossary
Figure 3- A typical plant cell with its organelles. Source- LadyofHats Mariana Ruiz. Wikipedia link: https://en.wikipedia.org/wiki/Cell_(biology)

When comparing these cells (See Fig. 2 and Fig. 3), you will notice that the plant cell has a well-defined shape due to a rigid cell wall, which is clearly absent in animal cells. Secondly, the presence of a large, permanent vacuole acting as a storage vessel is seen. In contrast, animal cells do have vacuoles but they are usually small and short-lived. Lastly, additional bits such as the plasmodesmata and chloroplast are unique only to plant cells.

Overall, cells, be it plant, animal, or anything else, are so amazing and sometimes you want to appreciate the beauty of the microscopic world!

Thanks for reading my work; now you know the basics of what a microbiologist typically knows 😄

Comment to let me know what kind of material you want me to simplify in my future posts or any improvements 😊

One last thing! I will be posting every Saturday on Medium so look out 👀

Glossary

Eukaryotic cell or eukaryote- Cells and organisms that have a well-defined nucleus

Intracellular- Literally means ‘within the cell’

Cytoplasm- The inside of a cell which includes both the cytosol and all organelles except the nucleus

Vesicles- Small, round-ish, membrane structures found in cells carrying digestive enzymes or transporting molecules

Macromolecules- Literally means ‘large molecules’

ATP- Adenosine triphosphate, the energy currency needed for every cell to function

Chromatin- A highly condensed form of DNA; imagine taking a file on the computer which is taking a lot of space and you compress it into a zip file

Peroxisome- Vesicles containing enzymes with oxidising abilities

Secretory vesicles- Vesicles carrying molecules needing to be secreted out of the cell

Flagellum- A tail to help cells propel, be it an animal cell or some bacteria; plural: flagella

Plasmodesmata- Pores that extend to form channels to connect with neighbouring plant cells for communication and transport

Chloroplast- A type of plastid responsible for photosynthesis

Sources

  • Part IV: Internal organization of the cell, Chapter 12: Intracellular Compartments and Protein Sorting. From the textbook Molecular Biology of the Cell, by Alberts et al., 6th Edn.
  • Me remembering some of my school and university lecture material

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