Prokaryotes vs. Eukaryotes | Differences, Structure and Capsule (2023)

introduction

Living organisms are divided into two groups based on the large differences in cell structure; prokaryotes and eukaryotes. It is believed that prokaryotes were the first organisms to appear on Earth. The rest of the higher organisms evolved from these simple prokaryotic organisms.

They differ in cell structure, body shape, habitat, mode of reproduction, cell metabolism, and more. In this article, we will discuss the main differences between the two cell types.

Organisms

Before going into the differences between prokaryotes and eukaryotes, let's first learn about the organisms that fall into two groups. The latest classification divides all known living organisms into five kingdoms.

• Kingdom Monera includes all prokaryotic organisms, true bacteria and ancient bacteria.
• Kingdom Protista, includes eukaryotes distinct from organisms in the other four kingdoms.
• The other three kingdoms, Fungi, Plantae, and Animalia, include all eukaryotic organisms.

cellular structures

In this title, we will discuss the key cellular distinguishing features of eukaryotes and prokaryotes.

cell wall

The cell wall is found in all prokaryotes except members of Mycoplasma. It is also present in all eukaryotic cells except animal cells and animal-like protists. However, some important differences are found in prokaryotic and eukaryotic cell walls.

prokaryotic cell wall

The bacterial or prokaryotic cell wall consists mainly of peptidoglycan. It consists of two membranes with a space in between called the periplasmic space. Lipoproteins are also present in the walls of prokaryotic cells along with teichoic acid and lipoteichoic acid molecules. Three types of cell walls are seen in prokaryotic cells;

• Gram positive cell wall
• Gram-negative cell wall
• mycobacterial cell wall

eukaryotic cell wall

The eukaryotic cell wall is found in plants, fungi, and some protists. It differs from the prokaryotic cell wall in many ways.

• It consists of a single membrane.
• The periplasmic space is absent.
• Teichoic acid and lipoteichoic acid molecules are absent
• It does not stain differently than gram-positive and gram-negative cell walls.

Eukaryotes have different cell walls in fungal and plant cells. The fungal cell wall is mainly made up of chitin while the plant cell wall is made up of cellulose.

cell capsule

A true capsule is found around some prokaryotic cells. such bacteria are called capsule bacteria. The capsule consists largely of polysaccharides. It is the outermost part of the bacterial cell envelope. It protects the cell from degradation and plays an important role in the virulence of certain bacteria.

Although eukaryotic cells lack a true capsule, a similar structure made up of glycoproteins and glycolipids is called the glycocalyx. It is also found in prokaryotic cells.

genetic material

The genetic material in eukaryotes and prokaryotes consists of DNA. However, there is a difference between the way it is stored in the cell. Eukaryotic cells have a nucleus while prokaryotic cells have a nucleoid at the center of the cell.

eukaryotic nucleus

It is a double-membrane organelle found in all eukaryotic cells. The genetic material is contained in the cell nucleus in the form of chromosomes. Various substances can enter or leave the nucleus by passing through specific pores in the nuclear envelope called nuclear pores.

prokaryotic nucleoid

The genetic material in prokaryotes is in the form of a large central nucleoid. DNA does not condense into chromosomes. Instead, it comes in the form of a large core molecule called a nucleoid. There is no barrier between the genetic material and the cell's cytoplasm.

Ribosomes

Ribosomes are the protein synthesis factories present in eukaryotes and prokaryotes. The function of these organelles is essentially the same in both cell types. However, there is a difference between their size in eukaryotes and prokaryotes.

Eukaryotic Ribosomes

Eukaryotic ribosomes are larger than prokaryotic ribosomes. The largest subunit levels off at 60S while the smallest subunit levels off at 40S. Both subunits come together to form a single particle that sediments in the 80s.

(S stands for Svedberg, a unit that measures the size of particles based on their rate of sedimentation during ultracentrifugation.)

Most eukaryotic ribosomes are found associated with the rough endoplasmic reticulum. Some ribosomes are also scattered in the cytoplasm.

prokaryotic ribosomes

These are the smallest particles. The largest subunit levels off in the 50s while the smallest subunit levels off in the 30s The particle formed by combining two subunits levels off at 70S.

Prokaryotic cells do not have an endoplasmic reticulum. Its ribosomes are scattered throughout the cell's cytoplasm.

cellular processes

Different types of cellular processes arise from the cell membrane of prokaryotic and eukaryotic cells.

scourge

Flagellum is the common cellular process found in both cell types. Its function is to support the cell in its locomotion. It also helps detect certain chemicals that are present in the cell's environment.

Related

These are the tiny cellular appendages found only in prokaryotic cells. They are made up of pilin protein. Its function is to aid in the process of bacterial conjugation, the process by which genetic material is transferred between prokaryotic cells.

eyelash

These are the subtle cellular processes found only in eukaryotic cells. its diameter is smaller than the flagella. Cilia also aid in locomotion and detection of chemicals found in the extracellular environment. The beating of the cilia can also remove particles attached to the cell surface.

fools

These are the cellular appendages found only in eukaryotic cells. They serve to enlarge the cell surface and help absorb various substances.

Zytoskelett

It is a structure of microtubules, microfilaments, and intermediate filaments that provides structural support to cells. It maintains cell shape and supports intracellular transport of various substances. It is only found in eukaryotic cells.

other organelles

Prokaryotic cells lack membrane-bound organelles such as mitochondria, Golgi apparatus, endoplasmic reticulum, etc. All of these organelles are present in eukaryotic cells.

cell division

Prokaryotic and eukaryotic cells also employ different methods of cell division. Prokaryotes divide by binary fission while eukaryotes divide by mitosis or meiosis.

cell division

It is the oldest method of cell division in prokaryotic cells. The genetic material is first duplicated through the process of DNA replication. The cell elongates and then divides in half, creating new cells called daughter cells.

These daughter cells can grow and undergo binary fission again, creating new prokaryotic cells. Two new cells are formed after each cell cycle. It is also known as the duplication process. The doubling time is different for different types of bacteria.

Binary fission is also observed in some unicellular eukaryotes such as amoebas, euglena, and other members of the protist kingdom.

mitosis and meiosis

These are two advanced methods of cell division found only in eukaryotes. Each method consists of two processes; Division of the nucleus, called karyokinesis, and division of the cytoplasm, called cytokinesis.

Nuclear material is first duplicated before cell division begins.

During mitosis, daughter cells are formed with the same number of chromosomes as the parent cells. It is a single cycle of cell division. All somatic cells divide by mitosis.

Meiosis involves two rounds of cell division after DNA replication. As a result, a parent cell gives rise to four daughter cells that have half the chromosomes that were present in the parent cell.

Eukaryotic and prokaryotic cells differ in the various metabolic processes that occur within the cell. Eukaryotic cells have membrane-bound organelles that divide the cell into compartments. Various metabolic processes are restricted to specific cell compartments. However, this is not the case in prokaryotes, which lack membrane-bound organelles.

Here we will discuss how some metabolic processes occur differently in two types of cells.

photosynthesis

It is the process by which organisms can create their food from raw materials using the energy of sunlight. Solar energy is used to excite electrons, which are then passed through the electron transport chain. The energy released by these electrons is used to make glucose from water and carbon dioxide and oxygen as a byproduct.

Chlorophyll, the light-absorbing pigment, plays an important role in photosynthesis. It is contained in the chloroplast of eukaryotic cells. The chloroplast is a membrane-bound organelle found only in eukaryotes. Prokaryotic cells have folds of plasma membrane that serve as sites for photosynthesis. Chlorophyll is attached to these membrane folds.

Zellatmung

It is the process by which food is broken down into simpler substances and energy is released. The released energy is used for various other cellular processes. The different types of food molecules that can be used include glucose, fat, lipids, amino acids, etc.

Mitochondria present in eukaryotic cells contain enzymes for most cellular respiration reactions. They extract energy from various food materials and use it to make ATP. Mitochondria are organelles connected by a double membrane and are absent in prokaryotic cells.

Prokaryotic cells all have enzymes in the cytoplasm of the cells. All reactions of cellular respiration take place in the cytoplasm of prokaryotes.

genetic expression

It is the process by which the information present in DNA is expressed in the form of proteins that perform various functions in the cell. It involves two steps;

• Transcription, synthesis of RNA copies from DNA.
• Translation, protein synthesis using the information copied from the gene into RNA

The DNA of eukaryotic cells is present in the cell nucleus. The transcription process in these cells takes place in the nucleus and then the RNA molecules are transferred to the cytoplasm. Protein synthesis takes place on ribosomes, which are present in the cytoplasm of the cell.

Prokaryotic cells do not have a nucleus. Thus, transcription and translation take place in the cytoplasm of the cell. The two processes are often coupled and go hand in hand in prokaryotes while not in eukaryotes.

cellular organization

Prokaryotes are simple unicellular organisms. Each cell lives its own life, independent of the other cells. they are not organized in higher structures. Prokaryotic cells can form colonies. However, each cell in the colony is responsible for its survival independently of the other cells.

Most eukaryotes are complex multicellular organisms. Eukaryotic cells self-assemble to form tissues, organs, and organ systems. Cells in multicellular complex bodies live in harmony with each other, affecting their function and survival.

Summary

Cells of all known living organisms are divided into eukaryotes or prokaryotes based on their different structural characteristics.

Prokaryotic organisms belong to the Monera kingdom while the rest of the four kingdoms includes eukaryotic organisms.

The main difference between the two cell types is the cell nucleus. DNA in eukaryotic cells is present in the nucleus while in prokaryotic cells it is found as a single circular molecule.

The cell wall of eukaryotes is made of cellulose or chitin while prokaryotes have peptidoglycan in their cell walls.

Some prokaryotic cells are covered by a polysaccharide capsule. Eukaryotes have a glycocalyx that performs a similar function.

Ribosomes in eukaryotic cells sediment in the 1980s, while those in prokaryotic cells sediment in the 1970s.

Cellular processes are also different in the two cell types.

• Flagella are found in both eukaryotes and prokaryotes.
• Pili are found only in prokaryotes.
• Cilia and villi are only present in prokaryotic cells.

Prokaryotic cells divide by binary fission while eukaryotic cells undergo meiosis or mitosis.

Cellular processes take place in membrane-bound organelles in eukaryotes, but in the cytoplasm in prokaryotic cells.

The two steps of gene expression occur simultaneously in prokaryotes, while they occur separately in eukaryotes.

Prokaryotes are unicellular organisms, while most eukaryotes are multicellular organisms with cells organized to form tissues, organs, and organ systems.

Frequently Asked Questions

What are the three differences between prokaryotic and eukaryotic cells?

Eukaryotic cells have a membrane-bound nucleus while prokaryotic cells do not. Membrane-bound organelles are present in eukaryotic cells but not in prokaryotic cells.

What are some examples of prokaryotic cells?

Several bacteria are examples of prokaryotic cells, such as E. coli, S. pneumonia, Salmonella typhi, N. meningitides, etc.

What are some examples of eukaryotic cells?

Examples of eukaryotic cells include animal and plant cells such as human cells, canine cells, cat cells, etc.

Does a prokaryotic cell have DNA?

DNA is present in prokaryotic cells. But unlike eukaryotic cells, it exists as a floating circular molecule in the cell's cytoplasm.

references

1. North Carolina State University.“Prokaryotes: Unicellular”.
2. Campbell, N. "Biology: Concepts and Connections." Pearson's education. San Francisco: 2003.
3. Costa G, De Tullio M (2010)."Beyond Prokaryotes and Eukaryotes: Planctomycetes and Cellular Organization".Nature.
4. https://en.wikipedia.org/wiki/Cell_wall
5. https://simple.wikipedia.org/wiki/File:Flagellum-beating.png