Different Cell Organelles And Their Functions

Cellular organelles are the most important components of a cell, as they carry out many vital functions for the survival of an organism.

They essentially work as a cell’s internal organs, and with a wide variety of them, they all serve different functions and have their own responsibilities within a living organism.

Each singular cell organelle is extremely important in keeping cell processes running smoothly and ensuring all the components of the body are working as they should, so it is important to know what each one is and what they all do differently to assist a cell in achieving its purpose. 

Nucleus

Perhaps the most well known of the cell organelles, the nucleus functions as the control center of all cellular activities and houses and contains the cell’s DNA.

It also plays a role in regulating gene expression and protein synthesis.

The nucleus is divided into two parts: the nucleolus and the nuclear envelope. The nucleolus is where ribosomes (the part of the ribosome that makes proteins) are made.

The nuclear envelope surrounds the nucleus and has pores which allow certain substances to pass through, some of these substances include RNA, enzymes and hormones.

The primary function of the nucleus is to monitor cellular activities such as growth, division and death. When a cell needs to grow or divide, it will activate genes inside the nucleus. 

Genes are responsible for making proteins, which are then used by the cell to build new cells or repair damaged ones.

If a cell dies, its DNA breaks down and causes the nucleus to shrink, which is called apoptosis.

Mitochondria

Located near the nucleus, mitochondria are involved in energy production and metabolism.

Mitochondria produce adenosine triphosphate (ATP) which allows cells to use chemical energy from food molecules, while also helping fuel other biochemical reactions within the cell.

A healthy mitochondria looks like a small, round ball with two membranes inside; the outer membrane and the inner membrane.

In between these two membranes are found cristae, which look like stacks of coins, and are the sites where oxygen-rich compounds are converted into energy.

When the cell requires more energy than can be produced by the mitochondria, the cell sends signals to the mitochondria notifying it to make more ATP.

When there isn’t enough oxygen available, the mitochondria change shape to create more space for oxygen to enter. 

Plasma Membrane 

The plasma membrane plays a crucial role in regulating the movement of substance in and out of the cell. It is composed of phospholipids and cholesterol.

Phospholipids are fatty acids linked together by phosphate groups, while cholesterol is a waxy lipid that forms a layer on top of the plasma membrane.

A plasma membrane consists of four layers. The first layer is the external leaflet, which faces the outside environment.

The second layer is the cytoplasmic leaflet, which is attached to the cytoskeleton. The third layer is the extracellular leaflet, which faces towards the exterior of the cell.

Finally, the fourth layer is the intraluminal leaflet, which is located inside the cell.

The plasma membrane acts as a barrier between the internal and external environments of the cell and works to regulate the flow of materials into and out of the cell, therefore preventing harmful substances from entering the cell and causing damage.

Endoplasmic Reticulum 

Being enclosed in the membrane, there are two main areas of ER that act slightly differently to each other:

Firstly there is the smooth endoplasmic reticulum, suitably named because it lacks any ribosome on its surface, therefore appearing more smooth on its surface.

The primary function of smooth ER is to assist in transporting vesicles and the contraction of muscle cells.

The other area is the rough endoplasmic reticulum that does have a ribosome visible on its surface.

This area is more involved with production of antibodies, along with helping proteins get delivered to the smooth ER.

Centriole 

Found in most eukaryotic cells, centrioles are cylindrical structures that contain microtubules. 

They are formed when the mother centrosome splits into two daughter centrioles during mitosis.

Centrioles play an important part in cell division, during interphase they form the central pair of microtubule organizing centers.

During prophase and metaphase, the centrioles organize spindle fibers and attach chromosomes to them.

As cells progress through telophase, the centriole pairs separate to become the basal bodies of the two new daughter cells and by this point, the centrioles begin to duplicate and elongate, forming the cilia or flagella needed for motility.

Lysosome 

The conditions inside the lysosome are extremely acidic and function to help it in the several cell processes it is actively involved in.

One of these is the breaking down of worn out cell parts and also the extermination of potentially harmful viruses and bacteria.

They can be described as generally destructive but in a beneficial sense, if a cell is damaged beyond repair and is unable to function efficiently, lysosomes can trigger it to self-destruct therefore freeing up space and removing any cell that is not benefiting to the overall system 

Golgi Apparatus 

First discovered by Italian physician Camillo Golgi in 1898, the golgi apparatus is a network of tubular membranes within the cell.

It is found mainly in the cytoplasm of animal cells and is responsible for producing and transporting proteins throughout the body.

It has three main compartments; cisternae, stacks and vesicles:

Cisternae are the smallest compartment and are where protein synthesis occurs.

Stacks are larger than cisternae and are used to store and transport proteins.

Vesicles are the largest compartment and are used to transport proteins to different locations within the cell.

Ribosome 

A ribosome is an organelle that contains three different sections: the large subunit, the small subunit and the connecting stalk. 

The large subunit is responsible for translating mRNA into protein and works in conjunction with the small subunit, which is responsible for carrying amino acids to the growing polypeptide chain.

The ribosome connects to the endoplasmic reticulum through the connecting stalk.

The smaller subunits of ribosomes are called prokaryotes, which have a single membrane surrounding them and contain only one type of ribosome.

Their bigger subunit counterparts are eukaryotic cells. These have multiple membranes surrounding them and contain multiple types of ribosomes.

Eukaryotes also have nuclei which house DNA.

The three stages of the ribosome process are initiation, elongation and termination. Initiation begins when a tRNA binds to the A site of the large subunit.

During this stage, a smaller subunit attaches itself to the 3’ end of the tRNA.

Elongation then occurs when the amino acid enters the peptidyl transferase center of the small subunit and during this stage, the tRNAs will attach themselves to the growing polypeptide chain.

Lastly, termination occurs when the tRNA detaches itself from the growing polypeptide chain and moves back to the P site of the large subunit, registering the end of production for a particular protein.

The ribosome is incredibly important because it is the main component of the translation machinery, which translates genetic information into proteins, allowing cells to grow and divide.

Vacuoles 

While some vacuoles play a role in maintaining the internal hydrostatic pressure of the cell along with its PH, the majority of them are working to store cellular waste products such as lysosomes, peroxisomes, autophagosomes and phagolysosomes.

Vacuoles can be found in all living organisms, but they are most abundant in plants and animals. 

They are usually spherical or ovoid in shape, however there are exceptions, such as plant vacuoles which are often tubular in shape.

They can essentially be seen as empty spaces within a cell that do not contain cytoplasm and are instead filled with watery fluid.

However, unlike other organelles which are bounded by a single membrane, vacuoles are bounded by two membranes, allowing them to hold more fluids than any other organelle.

In addition to holding fluids, vacuoles also serve as storage areas for many molecules including lipids, carbohydrates, ions, and enzymes.

Their size ranges from 0.1-10 micrometers (0.0003-0.003 inches) in diameter.

Along with lysosomes, there are three other major classes of vacuole based on what they contain:

1) Peroxisomes 

2) Autophagic Vacuoles 

3) Phospholipid-Rich Vacuoles 

Phospholipid-rich vacuoles are the largest, being present in every organism and used for storing fatty acids.  

Autophagic functions much the same as lysosomes, however they are not involved in digestion and are instead involved with recycling damaged parts of the cell. 

Finally, peroxisomes are quite small and contain an acidic environment. They break down long chains of fatty acids, along with breaking down certain types of hormones. 

Cytoskeleton 

The cytoskeleton is composed of microtubules and actin filaments.

Microtubules are hollow tubes made up of repeating units called protofilaments while actin filaments are thin strands of protein that form a meshwork throughout the cytoplasm.

The cytoskeleton provides structure to the cell, helping to maintain its shape and position, however it also assists in transporting materials around the cell.

The cytoskeleton can even be involved in helping anchor and support the nucleus through its own processes. 

Gerontoplast

Gerontoplasts are specialized plastids that store large amounts of starch.

These organelles occur only in the roots of some plants such as sugarcane and potato and are often referred to as amyloplasts because of the high amount of starch they are capable of storing.

They are surrounded by a double membrane and have a highly complex system of thylakoid membranes inside, with the innermost layer containing chlorophyll while the outermost layer contains carotenoids.

These organelles are important because they provide energy to the plant during periods when photosynthesis is not occurring. 

Chloroplasts 

Acting as the main photosynthetic organelles for green plants, chloroplasts are surrounded by a double membrane with an inner surrounding system containing thylakoids.

Chloroplasts contain chlorophylls A and B, which absorb light to produce ATP.

In order to create ATP, chloroplasts use proton pumps to pump hydrogen ions across the inner membrane into the stroma. 

Chloroplasts are found in all plant cells except those of mosses and liverworts and are most abundant in leaves but can also be found in other tissues like stems, flowers, and fruits.

However, because of their primary function in absorbing light energy, they are present in the cells of all green tissues of plants and algae of various kinds. 

Stroma 

The above-mentioned stroma is the space between the two membranes of the chloroplast.

It is filled with water and has many enzymes to help breakdown carbohydrates, while also having a number of pigments that can absorb light and give out the red color we see on some leaves.

Summary

While there are many of them, all cell organelles are extremely important for serving their own particular function.

Without them, organic lifeforms would not only risk being unhealthy, but it would not allow bodily functions to act in the way we need them to survive. 

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