Everything You Need To Know About Lysosomes – Types, Morphology, Function, Process, And Microscopy

Lysosomes are important cells that can be described as small cell organelles found in eukaryotic or nuclear-bearing animal cells. They can be located in the cytosol, floating freely in the outer nucleus of the cell. 

They are made up of a simple structure that consists of an outer lysosomal membrane encompassed by acidic interior fluid. Like stomachs, lysosomes superfluous cell fragments and digest waste.

Due to their interesting function, they are also known as the ‘suicide bags’ of the cell. This was a term first referred to by a Belgian biologist, Christian de Duve, who discovered it and received a Nobel Prize in Medicine or Physiology in 1974. 

With this in mind, this article will inform you of everything you need to know about lysosomes, including types, morphology, functions, processes, and microscopy. 

What Are Lysosomes?

Lysosomes are the principal digestive sectors of the cell. As a result, they encompass many different enzymes that are able to deteriorate many different biological materials such as lipids, proteins, nucleic acids, and many others. 

These can be found in animal cells and marginal plant cells (if they do, they occur as vacuoles), and they are able to break down a variety of different macromolecules that are delivered into the cell to deteriorate.

Generally, most of these are damaged or have finished their life cycle; meaning they can no longer be of use. 

In conjunction with these macromolecules, lysosomes also serve the purpose of breaking down cells once they have reached their life cycles.

While they are established in most animal cells (the only exception being red blood cells), they are distinctly rich in organs/ tissue that perform high enzymatic reactions. 

These can include organs/ tissues such as the kidney, pancreas, liver, macrophages, and others. Cells found within these organs/ tissues are abundant in lysosomes. 

Types Of Lysosomes 

There are two principal types of lysosomes, these include:

Primary Lysosomes

Primary lysosomes are established from Golgi apparatus visible as small vesicles. While primary lysosomes are the most popular within the Golgi apparatus, they can also be found as monocytes and granulocytes.

A single layer of phospholipid surrounds these lysosomes, which contain acid hydrolases. 

The pH value of the acid found within these vesicles is particularly important due to its ability to make changes by either activating or deactivating the enzymes.

Consequently, the majority of primary granules combine with phagosomes, and the outcome of this is the emergence of secondary lysosomes. 

Secondary Lysosomes 

As previously mentioned, secondary lysosomes are produced when primary lysosomes merge with pinosome/ phagosomes (also referred to as endosomes).

This merge is also the source allowing the previously inactive enzymes to become activated and able to consume and digest biomolecules such as lipids and nucleic acids, and others. 

When comparing the two lysosomes together, secondary lysosomes can be seen to be larger in size than primary lysosomes.

Additionally, they have the ability to release their matter (enzymes) to the outside of the cells where they deteriorate unknown content. 

Generally, a lot of lysosomal enzymes operate within an acidic environment, this is why they are known as acid hydrolases. 

They contain approximately 45 different enzymes that are categorized into six principal groups. These include:

• Nucleases – These are important enzymes that are able to hydrolyze nucleic acids. They are split up into deoxyribonuclease (which acts on DNA) as well as ribonuclease which can hydrolyze RNA. The result of hydrolysis performance on nucleic acids allows phosphates, the production of sugars, and nitrogen bases. 

• Proteases – These include enzymes such as peptidases and collagenase that tackle proteins by changing them into amino acids. 

• Glycosidases – Beta-galactosidase, for example, tackle the glycosidic bonds of polysaccharides by changing them to monosaccharides. To illustrate, galactosidase functions on these bonds by converting lactose to galactose and glucose. 

• Phosphatases – An example of this is phosphodiesterases. These enzymes are important for acting on organic molecules and releasing phosphates when doing so. Although, a phosphate group is needed in the compound. 

• Lipases – These include phospholipases and esterases that work on lipids in order to create alcohol and acids. 

• Sulfatases – These work on organic compounds in order to exert sulfates.

Morphology/ Structure

Lysosomes are defined as membrane-delimited organelles, meaning they are encompassed within a membrane that doesn’t allow for materials to pass through.

This is especially important considering the unbounded release of acidic fluid and enzymes can sustain harm to the portions of the cell. 

As a result of a pH level that is lower than 5, they also have a high concentration of protons.

The exterior membrane is made up of vacuolar-type H+ ATPase, integral proteins, various transporters, and highly glycosylated proteins.

Depending on the function and type of lysosome, they also vary greatly in size (this is generally between 1 micrometer and several micrometers), as well as shape.

Compared to other varieties of organelles, lysosomes are less defined. When observed, they materialize as dense, cytoplasmic bodies that can be spheric, tubular, or ovoid. 

Function

The ways in which lysosomes perform typically depend on the effect of the contents on the inside and outside of the cell caused by the enzymes. Moreover, there are various different processes by which lysosomes digest content. These include:

Endocytosis

This is one of the more popular phenomena performed by cells. When endocytosis takes place, the invagination of the plasma membrane and the cell creates an endocytic vesicle that inundates various extracellular molecules. 

Meanwhile, in phagocytosis (which is a variation of endocytosis) large microorganisms/ molecules such as bacteria are submerged within a vacuole (phagosome).

On the other hand, within pinosomes (another variation) a small number of the solute molecules and exterior fluid are strained off as pinosomes (e.g. pinocytic vesicles). 

When the vesicles merge with primary lysosomes, it results in secondary lysosomes. This causes the enzymes to become activated and then tackle the molecules. This is a process known as ‘Endosomal Pathway’.

Process

Content uptake – development of endosome – development of the phagolysosome – lysis – distribution of digested content and exocytosis. 

Autophagic Lysosome

Excluding endocytosis, lysosomes are also a part of a procedure known as autophagocytosis. This process allows various cells to be degraded that are either malfunctioning or worn out. 

While this simply breaks down cellular components, this process also helps to recycle these materials. During this process, as soon as a particular cell dies, autophagic lysosomes (secondary) set out enzymes to digest them. This is also known as autolysis.

This also takes place during periods of starvation. As a result of this, lysosomes will begin hydrolyzing organic foods that are set aside in cells in order to produce energy. 

Vacuoles In Plants 

When found in plants, vacuoles perform many different functions, this makes them multifunctional organelles.

Although, the properties found in these cells are comparable to lysosomes found in animal cells. As a result, their nature is acidic and includes many hydraulic enzymes that are able to break down many molecules. 

There are many different variations of vacuoles, each serving different purposes. These include:

• Sap Vacuoles – These store nutrients and minerals.
• Contractile Vacuoles – These concern excretion and osmoregulation. 
• Food Vacuoles – This looks at the digestion of nutrients, where this vacuole embodies enzymes that break down these nutrients/ 
• Air Vacuoles – Store metabolic gasses within prokaryotes. 

Differences And Similarities Found Between Primary And Secondary Lysosomes

Similarities 

• Both contain a single phospholipid membrane encompassing them. 
• Both contain acid hydrolases. 

Differences 

• While primary lysosomes are buds that are created from the Golgi apparatus, secondary lysosomes are created through a merge of pinosomes or phagosomes and primary lysosomes. 

• While primary lysosomes are generally used to store content (such as storage vacuoles), secondary lysosomes’ main principle is digestive vacuoles wherein lysis can take place as a result of hydrolytic enzyme activity. 

• Primary lysosomes do not deploy any of their material, while secondary lysosomes are able to deploy their material (enzymes) into the cell cytoplasm during exocytosis. Exocytosis is a process by which enzymes are deployed into the outside areas of a cell or the cytoplasm where they break down various materials. 

• Predominantly, inactive hydrolases are found in primary lysosomes, while secondary lysosomes contain active lysosomes that are able to act on molecules and differing content. 

Recycling

Another important function of lysosomes is their recycling capabilities. Whenever different varieties of cell components or molecules are deteriorated (for example proteins being broken down into amino acids) these amino acids are then utilized as building blocks for new proteins. This allows some byproducts to be used again within the body. 

Likewise, they also help to recycle content that cannot be easily excreted. An example of this would be iron.

Once iron is deployed from being broken down from cell components or various cells (for example, red blood cells), this iron is then used in recycling to create new organelles. This ensures minimum excretion of these by-products and retention of others to be used within the body again. 

Microscopy 

When using a light microscope, lysosomes are too small to be seen. As a result, you will need an electron microscope in order to view them. On the other hand, lysosomes (vacuole) found in the plant cell are possible to observe. 

Below, you will find a procedure to follow in order to observe plant vacuoles. 

Requirements

• Glycerin
• An onion
• A pair of forceps
• Safranin solution 
• Microscope glass slides
• A dropper
• Distilled water
• A light compound microscope
• Two watch glasses
• Microscope cover slip

Procedure

• Using the watch glass, place a few drops of distilled water onto it. 
• With a pair of forceps, carefully peel off a membrane from the onion skin, then place it onto the droplet of water. 
• Take the empty watch glass and add a few drops of safranin.
• Using the forceps to pick up the onion skin, gently place it onto the watch glass with the safranin; leaving it to sit for 30 seconds. 
• Pick up the membrane once again and place it in the center of the watch glass containing distilled water. 
• Then, add a drop of glycerin to the center of the microscope glass slide. 
• Once complete, place the onion skin onto this droplet, then cover with the coverslip.
• Place this onion slide under the microscope and observe the lysosomes. 

Observation

From this observation, you should be able to identify many irregular cells as well as a cell nucleus. In addition, students will clearly be able to view a large vacuole found in the middle of the cell membrane. 

Frequently Asked Questions

When looking into such a complex topic, it is only natural that you may have some questions about the subject. With this in mind, below, you will find some frequently asked questions in regards to lysosomes.

What Are Lysosomes Defined As?

They are defined as sacs filled with hydrolytic enzymes or sphere-shaped vesicles that are able to break down almost every variety of biomolecules. Essentially, they are used to help recycle and clean up any waste and debris. 

Who Discovered Lysosomes?

Lysosomes were first discovered by Christian de Duve, a Belgian biologist, who received a Nobel Prize in Medicine or Physiology in 1974 for his work. Likewise, he is also known for discovering other cellular organelles called peroxisomes. 

What Type Of Cell Possesses Lysosomes?

Lysosomes are only found within eukaryotic animal cells. Prokaryotic cells, for instance, bacteria, don’t accommodate any other membrane-bound organelle or lysosomes.

Do Plant Cells Have Lysosomes?

While plants do not contain lysosomes, the role that is generally performed by lysosomes is, instead, performed by vacuoles. Some findings even propose that vacuoles possess similar hydrolytic enzymes that can be found within animal cells. 

What Is A Lumen In A Lysosome?

The Lumen is described as the area found inside the membrane-bound exterior of the lysosome. This accommodates cellular debris that is kept in the hydrolytic enzymes. With a pH ranging from 4.0 to 5.0, this also makes it acidic. 

Why Are Lysosomes Known As Suicidal Bags?

The principal purpose of lysosomes is to recycle and break down discarded cellular materials, foreign pathogens, and cellular debris.

However, these digestive enzymes have the ability to potentially burst as a result of the lysosomes, hurting the cells themselves and then causing the cell to die.

Where Are The Enzymes Needed By Lysosomes Made?

The enzymes that are needed by lysosomes are synthesized within the rough endoplasmic reticulum. Once synthesized, these enzymes are taken from the Golgi apparatus within tiny vesicles, which are then merged with the bigger acidic vesicles found in the cells. 

What Are Lysosomal Storage Diseases?

Any mutations that may occur in the nuclear genes could result in over 30 different diverse human genetic ailments. These are collectively known as lysosomal storage diseases (LSD). 

Final Thoughts

Lysosomes can be found in almost all animal-like eukaryotic cells. Their main function is to help with cell metabolism, whereby they ingest and break down any unwanted cell debris, foreign substances, or unwanted parts of the cell.

Hopefully, this guide has informed you on everything you need to know about lysosomes, whereas above; we have looked at types, morphology, function, process, microscopy, and more.

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