Difference Between Membranous and Nonmembranous Organelles

The key difference between membranous and nonmembranous organelles is that the membranous organelles are absent in prokaryotic cells while nonmembranous organelles are present in both prokaryotic and eukaryotic cells.

The cell is the basic unit of living organisms. However, there are two types of cellular organizations namely prokaryotic and eukaryotic. One of the key features that distinguish prokaryotes and eukaryotes is the presence and absence of membrane-bound cell organelles. Prokaryotic cells do not possess membrane-bound organelles whereas eukaryotic cells possess membrane-bound organelles. Membrane-bound organelles are enclosed with a plasma membrane like membrane while nonmembranous organelles are not enclosed with membranes. The article aims to discuss the difference between membranous and nonmembranous organelles.

CONTENTS

1. Overview and Key Difference
2. What are Membranous Organelles
3. What are Nonmembranous Organelles
4. Similarities Between Membranous and Nonmembranous Organelles
5. Side by Side Comparison – Membranous vs Nonmembranous Organelles in Tabular Form
6. Summary

What are Membranous Organelles?

Membrane-bound organelles are present only in eukaryotic cells. Examples of membrane-bound organelles are the nucleus, rough endoplasmic reticulum (ER), smooth endoplasmic reticulum, Golgi apparatus, mitochondria, plastids, vacuoles and lysosomes. ER consists of branching membranes that connect with the plasma membrane and nuclear membrane. Depending on the presence of ribosomes on the membrane of the tubules there are two types of ER namely smooth ER (SER) and rough ER (RER). RER contains ribosomes on the surface while SER does not contain ribosomes on the surface.

Mitochondria are the powerhouses of the cells. They are present in the cytoplasm, and they are of different shapes. They may be spherical, oval, or rod-shaped. Structurally, the mitochondrion is a double membrane organelle. It has two membranes; a smooth outer membrane and an inner membrane. In order to increase the surface area of the inner membrane, it forms cristae. Cristae bear many oxysomes.

Moreover, Golgi apparatus is a single membrane-bound organelle. Vesicles are separated from the cytoplasm by a unit membrane. Chloroplasts are double membranous organelles, in which, both the membranes are smooth. Cilia and flagella are also membranous structures. Structure of both cilia and flagella are similar. Flagella are long structures while cilia are short structures. One cell normally contains one flagellum or 2 flagella, but it contains a large number of cilia. Both cilia and flagella enclose by a unit membrane which has 9+2 arrangement with 2 central singlet microtubules and 9 pairs of peripheral microtubules. Prokaryotic cells also contain flagella. Flagella in prokaryotic cells do not have the 9+2 arrangement.

What are Nonmembranous Organelles?

Organelles that generally do not contain membranes are ribosomes, cytoskeletal structures, centrioles, cilia, and flagella. Ribosomes are present in both prokaryotic and eukaryotic cells. They are small granule-like structures. They may be found anywhere in the cytoplasm. Ribosomes are of 2 types, the 70s and 80s. Prokaryotes have 70S ribosomes while eukaryotes have 80S ribosomes.

Cytoskeleton has two types of non-membranous components. Those are microfilaments and microtubules. All the three structures do not have a unit membrane. Microtubules are hollow and cylindrical structures. They are very fine unbranched structures. Microtubules are protein tubes made up of tubulin protein. Microfilaments are unbranched solid rod-like structures. They are protein fibres made up of actin protein.

Centrioles are also nonmembranous organelles composed of triplets of microtubules, which are arranged around a cavity. There are no central microtubules. Hence, they show 9 + 0 arrangement of microtubules. Moreover, only animal cells have centrioles. Plant cells do not have centrioles. Normally two centrioles arrange perpendicular to each other. One such pair of centrioles is called a centrosome.

What are the Similarities Between Membranous and Nonmembranous Organelles?

• Both membranous and nonmembranous organelles are present in the cells.
• Also, both carry out important functions within the cells.
• Besides, both types are present in eukaryotic cells.

What is the Difference Between Membranous and Nonmembranous Organelles?

Membranous and nonmembranous organelles are two types of cell organelles. Membranous organelles are present only in eukaryotic cells. Thus, they are absent in prokaryotic cells. On the other hand, nonmembranous organelles are present in both prokaryotic and eukaryotic cells. Therefore, this is the key difference between membranous and nonmembranous organelles. Membranous organelles have a membrane enclosing them while nonmembranous organelles lack a membrane around them. Hence, it is a structural difference between membranous and nonmembranous organelles.

The below infographic on the difference between membranous and nonmembranous organelles shows these differences comparatively.

Summary – Membranous vs Nonmembranous Organelles

A cell contains different types of organelles. Among them, some are membranous while some are nonmembranous. However, membranous organelles are present only in eukaryotic cells. On the other hand, nonmembranous organelles are present in both prokaryotic and eukaryotic cells. Membranous organelles have a membrane surrounding them while nonmembranous organelles lack a membrane. Hence, this is the summary of the difference between membranous and nonmembranous organelles.

Reference:

1. Study.com, Study.com. Available here
2. “Organelle.” Wikipedia, Wikimedia Foundation, 3 Jan. 2019. Available here

Image Courtesy:

1.”Mitochondrion structure”By Kelvinsong, Sowlos – Own work (CC BY-SA 3.0) via Commons Wikimedia 
2.”Ribosome shape”By Vossman – Own work, (CC BY-SA 3.0) via Commons Wikimedia