Prokaryotes Vs Eukaryotes Overview

Prokaryotes Definition

Prokaryotes are primordial single-celled organisms that lack additional organelles and a membrane-bound nucleus, making them primitive in both structure and function. The terms “pro” and “karyon,” which mean “nucleus” in Greek, are combined to form the word “prokaryote.” As the most basic form of life, prokaryotes are regarded as the earliest living things to exist on Earth.

Characteristics of Prokaryotes

• The following is a list of the basic characteristics of prokaryotic cells:
• Prokaryotes typically have a size between 0.1 and 5.0 m, which is much smaller than eukaryotic cells.
• Prokaryotes come in a variety of shapes, including cocci, bacilli, spirilla, and vibrio.
• Prokaryotic cells, however, can also be seen in nature with variations on these morphologies.
• Prokaryotic cells lack a membrane-bound nucleus and other cell organelles, resulting in their rudimentary cellular arrangement.
• A single strand of DNA makes up the genetic material of prokaryotic cells in a single chromosome.
• Prokaryotic cells lack the essential histone protein, which is found bound to the chromosomes of eukaryotes.
• Additionally, lacking are the nucleus and the mitotic machinery in prokaryotic cells.
• Prokaryotic cells have a non-cellulosic cell wall that is composed of lipids and carbohydrates.
• Since prokaryotic cells are asexual, they can multiply without the development of gametes.

Prokaryotes Structure (Components/Parts)

• Prokaryotic cells have simpler cell organelles than eukaryotic cells, so their structures are less complicated. The following elements or parts are present in the majority of prokaryotic cells:

Capsule

• Some prokaryotic cells have an extra outer layer like this one that serves as a defence against outside attackers.
• The polysaccharides that make up the capsule help the cells adhere to different surfaces and keep their internal moisture stable.

Cell wall

• Inside the capsule, bacterial cells form a strong core that makes up the cell wall.
• The majority of prokaryotes have peptidoglycan cell walls, which are polymers of lipids and carbohydrates.
• However, in archaeal cells, a different component known as pseudopeptidoglycan replaces peptidoglycan in the cell wall. Proteins and other polymers make up its composition.
• The cell wall gives the cell form while safeguarding the cell organelles found in the cytoplasm.

Cell membrane/ Plasma membrane/ Cytoplasmic membrane

• A phospholipid-based cell membrane is found underneath the cell wall.
• The phospholipid, which is made up of two hydrophilic fatty acid tails and glycerol connected to a hydrophobic phosphate head, forms a bilayer.
• The phospholipid tails in archaea often link, generating a monolayer rather than a bilayer.
• Prokaryotic cells have a plasma membrane that protects the cell while permitting the movement of vital chemicals into and out of the cell.

Cytoplasm

• The whole area of cells found inside the cell membrane is known as the cytoplasm.
• It includes a water-based solution with minerals and other ions that are crucial for the cell, as well as a gel-like substance called cytosol.
• In addition, the cytoplasm houses other cellular components, including chromosomes and ribosomes.

Ribosomes

• 70S ribosomes are present in all bacterial cells. The 30S and 50S subunits make up the 70S ribosomes.
• Here, the 30S subunit includes 16S rRNA, whereas the 50S subunit contains 23S, 5S, and other rRNAs.
• In prokaryotic cells, the ribosome is the internal structure that is most frequently seen.
• Varied prokaryotic cells have different ribosome sizes and counts.
• Proteins are created from polypeptides, which are created by the ribosome.

Nucleoid region

• In prokaryotic cells, the nucleoid portion of the cytoplasm houses a single circular chromosome as well as little rings of extrachromosomal DNA known as plasmids.
• Unlike eukaryotes, which have two copies of DNA, the single circular chromosome only has one copy of the genetic material.
• Additionally, bacterial genomes are smaller than eukaryotic genomes in size.
• In turn, the plasmids are autonomously copied away from the chromosomes. There may be some non-essential genes on these plasmids.

Appendages

• Flagella, pili, and fimbriae are examples of cell appendages that extend from the cell surface of many prokaryotic cells.
• The prokaryotic cells’ most prevalent appendages are flagella.
• These resemble tail-like features that aid in cell movement.
• Cells to diverse surfaces are attached by thin filamentous structures called fimbriae.
• Longer filaments called “pilli” play various roles in various cell types.
• The sex pilli, which binds two cells together as they transfer DNA molecules through conjugation, is one example of this.

Division of Prokaryotes (Reproduction)

• As was already indicated, prokaryotic cells divide asexually without creating gametes. Prokaryotes have a few asexual reproductive methods, including:

Binary fission

• A kind of asexual reproduction known as binary fission occurs when a single live cell or organelle doubles in size before dividing into two identical daughter cells, each of which has the capacity to expand to the size of the original cell or organelle.
• Many prokaryotes, including archaea, cyanobacteria, and eubacteria, reproduce by binary fission.
• The genetic material of the parent cell is shared evenly between the two daughter cells throughout this procedure. As a result, the freshly generated prokaryotic cells show no genetic variation.

Steps of binary fission

• The cell’s DNA splits into two identical molecules, which are both pushed in the direction of the cell membrane.
• The cell then grows by a factor of two, and the membrane slowly begins to separate, with a copy of the DNA in each new cell.
• The cell wall is created between the two strands of DNA, splitting the parent cell into two identical daughter cells when the division of the cell membrane is completed.

Recombination

• Recombination is another asexual method of reproduction in bacterial organisms.
• In this instance, transduction, transformation, and conjugation are used to insert the genetic material of one cell into the cell of another prokaryote.
• Genes are conveyed by the sex pilli, which connects two cells during conjugation.
• The prokaryotic cell transforms by ingesting genetic material from the surrounding environment and integrating it into the bacterial chromosome.
• Genes are exchanged during transduction by viral infection. The target gene is first taken up by the bacteriophage, which then spreads it to another cell.

Prokaryotes Examples

Bacterial cells

• The only single-celled creatures present in every habitat on Earth are called bacteria.
• The peptidoglycan that makes up the bacterial cell wall gives it strength and thickness.
• Because certain bacteria only produce capsules, other prokaryotic cells might not include capsules.
• Bacteria have chromosomes, which are circular coils of genetic material.
• The bacteria E. coli, Streptomyces spp., Pseudomonas spp., etc. are examples of bacterial cells.

Archaeal cells (Archaea)

• As primordial unicellular creatures, archaeal cells share characteristics with bacterial cells.
• Hot springs, the ocean, and marshes are among the harsh conditions where archaeal cells are most frequently found.
• Archaeal cells lack a capsule, and their cell walls are comprised of proteins called pseudopeptidoglycan.
• Similar to how archaeal cells are shielded from hostile conditions by a monolayer of phospholipid in their cell membrane.
• Halobacterium spp., Thermoplasma spp., Sulfolobus spp., etc., are a few examples of archaeal cells.

FAQs on Prokaryotes

What are three examples of Prokaryotes?

Any three examples of Prokaryotes are blue-green algae, E. coli, and mycoplasma.

Do Prokaryotes have ribosomes?

Yes, Prokaryotes have ribosomes. The ribosome is of 70S type.

Do Prokaryotes have a nucleus?

No, Prokaryotes do not have a membrane-bound nucleus, but they do have a nucleoid region in the cytoplasm that contains the genetic material.

Do Prokaryotes have mitochondria?

No, Prokaryotes do not have mitochondria.

Is DNA found in Prokaryotes?

Yes, DNA is found as genetic material and extrachromosomal plastids in Prokaryotes.

How do Prokaryotes divide?

Prokaryotes divide through asexual methods like binary fission and conjugation.

Eukaryotes Definition

• A clearly-defined nucleus that is membrane-bound as well as other membrane-bound organelles make eukaryotes cells complicated in both structure and function.
• The terms “eu” and “karyon,” which in Greek mean “truth” and “nucleus,” respectively, are the origin of the word “eukaryote.”
• The structural makeup of eukaryotic cells is more complex than that of prokaryotes.
• These developments enable eukaryotic cells to carry out more intricate tasks than prokaryotic cells.

Characteristics of Eukaryotes

• The following is a list of the basic characteristics of eukaryotic cells:
• The size of eukaryotes ranges from 10 to 100 m in diameter, making them substantially bigger than bacterial cells.
• Eukaryotes have a wide range of shapes depending on the kind of cell. While some cells have a fixed structure like plant cells, others are pleiomorphic like amoeba. In addition to other functional adaptations, environmental influences have a significant impact on the morphology of the cells.
• The cellular arrangement of eukaryotic cells is more complex, with several membrane-bound organelles and a clearly defined nucleus.
• DNA is the linear genetic material found in eukaryotes, and it has several replication sources.
• Eukaryotic cells have a sophisticated nuclear membrane covering their nucleus. Instead of the circular chromosomes found in prokaryotes, the chromosomes in the nucleus are complex with the histone protein to create linear chromosomes.
• Some eukaryotes have cell walls that are composed of cellulose or other carbohydrates.
• In contrast to other eukaryotic cells, yeast cells replicate asexually by mitosis or fission.

Eukaryotic Structure (components/parts)

Prokaryotic cells are approximately 10,000 times smaller in volume than eukaryotes, which are substantially larger in size. Eukaryotic cells are made up of a variety of membrane-bound and membrane-less organelles that work in unison to maintain the structure and function of the cell. The following are the common components found in eukaryotic cells:

Cell wall

• Some eukaryotic cells, including those of some protists, fungi, and plants, include a cell wall.
• Cellulose microfibrils and a network of glycans embedded in a matrix of pectin polysaccharides make up the cell wall of plants and some protists.
• In fungal cells, the cell wall is made up of a distinct polymer called chitin, which results in a different cell wall composition.
• However, eukaryotic cells also have a comparable role for the cell wall. The eukaryotic cells are supported and shaped by the cell wall.

Cell membrane/ Plasma membrane/ Cytoplasmic membrane

• In eukaryotic cells, the cell membrane is located inside the cell wall.
• The cell membrane serves as the outermost layer of cells without a cell wall, insulating the inside from the external environment.
• A phospholipid bilayer makes up the plasma membrane, and between the two layers are embedded integral proteins.
• Eukaryotes and prokaryotes both have a similar cell membrane structure.

Cytoplasm

• The eukaryotic cell’s cytoplasm is a fluid-filled cavity that holds all of the internal organelles and other substances.
• A jelly-like substance called cytosol and a water-soluble solution made up of minerals, ions, and other molecules make up the cytoplasm.
• Compared to prokaryotic cells, eukaryotic cells have a larger cell volume, which results in a higher quantity of cytoplasm.

Nucleus

• The nucleus is an organelle found in the cytoplasm of a eukaryotic cell.
• It is more complex than the prokaryotic nucleus because the nuclear membrane that surrounds it is comparable to the plasma membrane in composition.
• A eukaryotic cell’s genome is found inside the nucleus, where it coexists with other proteins like the histone protein.
• The DNA molecules are grouped into linear, more orderly chromosomes inside the nucleus.
• The nucleus also has a protein-containing nucleolus that contains the ribosomes and rRNA but is not encircled by a membrane.

Ribosomes

• The ribosomes in eukaryotic cells are of the 80S type and comprise 60S and 40S subunits.
• Proteins, 5S RNA, 28S RNA, and other components make up the bigger subunit, whereas 18S RNA and 33 proteins make up the smaller subunit.
• Eukaryotic cells have ribosomes that are either free in the cytoplasm or linked to the endoplasmic reticulum.

Mitochondria and Plastids

• Membrane-bound organelles present in the cytoplasm of eukaryotic cells include mitochondria and plastids.
• Extrachromosomal DNA controls the operations of the organelles in both mitochondria and plastids.
• The primary physiological activity of the cell is carried out in the inner layer of the mitochondrial membrane, which is folded into cristae. The outer membrane of the mitochondria is composed of phospholipid bilayer.
• Eukaryotic cells of plants and algae include plastids, which give the cell its colour. The green pigment chlorophyll, which is present in plastids as well, is necessary for photosynthesis.

Cytoskeletal structures

• The movement, nutrition, and sensing of many eukaryotic cells are mediated by cytoplasmic projections like flagella and cilia.
• The tubulin proteins that make up these structures are mostly sustained by microfilaments and microtubules.
• The cytoplasm also contains cytoskeletal elements, which give cells their form and support.

Division of Eukaryotes (Reproduction)

• While some eukaryotic cells can exclusively divide asexually, others can divide both sexually and asexually.

Asexual reproduction

• All eukaryotic cells, with the exception of the reproductive cells that create the male and female gametes, are capable of asexual reproduction.
• Mitosis is the most typical kind of asexual reproduction in which the cell doubles in size before being split into two identical daughter cells.
• Unicellular protists and fungal cells divide via budding, in which new cells form a chain on the surface of dividing cells.
• Primitive eukaryotic cells exhibit processes like binary fission and multiple fission.
• It is also known that some fungi may split and reproduce asexually through sporulation.

Sexual reproduction

• The sexual process divides the reproductive cells in both plants and animals.
• In this procedure, the cell underwent meiosis to divide into four daughter cells, each of which contained half as many chromosomes as the parent cell.
• Different eukaryotic cells differ from one another due to sexual reproduction.

Eukaryotes Examples

Plant cell

• Plant cells are an example of an eukaryote, and they have a thick cellulose-based cell wall that gives them form and structure.
• A bigger vacuole in the cytoplasm of every plant cell regulates the cell’s turgor pressure.
• Additionally, unlike other eukaryotic cells, plant cells feature chloroplasts that contain chlorophyll, which is crucial for the process of photosynthesis.

Animal cell

• Another kind of Eukaryotes without a hard cell wall is animal cells.
• Animal cells lack a cell wall, which permits them to take on diverse forms and facilitates phagocytosis and pinocytosis.
• Animal cells vary from plant cells in that they lack chloroplasts and have a smaller vacuole.
• Animal cells also have the centriole, which produces the mitotic machinery needed for cell division.

Fungal cells

• In that they share a stiff cell wall with plant cells, fungus cells are comparable to plant cells.
• However, chitin, not cellulose, makes up the cell wall.
• Some fungi are unicellular, similar to yeasts, and contain microscopic pores in their cell membranes that permit the exchange of cytoplasm and other organelles between the cells.

Protists

• When compared to plant or animal cells, protists are the unicellular eukaryotes that are most primitive.
• Some protists may have a cell wall, but the majority do not.
• While certain protists are known to have chloroplasts that contain chlorophyll, others may have pigments that are used for photosynthetic processes.
• Cilia and flagella, which help the cells move, are known to exist in protozoa.

 

47 Differences Between Prokaryotes and Eukaryotes
S.N.	Character	Prokaryotes	Eukaryotes
1	Term Origin	Greek for “primitive nucleus”	Greek for “true nucleus”
2	Definition	Organisms are made up of cell(s) that lack a cell nucleus or any membrane-encased organelles.	Organisms are made up of cells that possess a membrane-bound nucleus as well as membrane-bound organelles.
3	Major groups	Bacteria, Archae, and Bluegreen algae	Algae, fungi, protozoa, plants, animals
4	Origin	Around 3.5 billion years ago.	Around 2 billion years ago.
5	Size (approximate)	0.5-3.0 μm	>5 μm
6	Cell Type	Usually unicellular (some cyanobacteria may be multicellular)	Usually multicellular
7	Complexity	Simple	Complex organization.
8	Nucleus Location	Free in the cytoplasm, attached to mesosomes	Contained in membrane-bound structure
9	Nuclear membrane	No nuclear membrane.	Classic membrane present.
10	Nucleolus	Absent	Present
11	Chromosome number	One	More than one
12	Chromosome shape	Circular	Linear
13	Genes	Expressed in groups called operons.	Expressed individually
14	Genome	DNA haploid genome	DNA diploid genome
15	DNA base ratio (G+C %)	28-73	About 40
16	DNA wrapping on proteins	Multiple proteins act together to fold and condense prokaryotic DNA. Folded DNA is then organized into a variety of conformations that are supercoiled and wound around tetramers of the HU protein.	Eukaryotes wrap their DNA around proteins called histones.
17	Genome nature	Efficient and compact with little repetitive DNA.	With large amounts of non-coding repetitive DNA.
18	Membrane-bound organelles	Absent	Present
19	Ribosomes (sedimentation coefficient)	70S (50S + 30S).Smaller.	80S (60S + 40S). Larger.
20	Ribosome’s location	Free in the cytoplasm or bound to the cell membrane	Attached to the rough endoplasmic reticulum
21	Mitochondria	Absent	Present
22	Golgi bodies	Absent	Present
23	Endoplasmic reticulum	Absent	Present
24	Mesosomes	Present. Performs the function of Golgi bodies and mitochondria and also helps in the separation of the chromosome during cell division.	Absent
25	Lysosomes	Absent	Present
26	Peroxisomes	Absent	Present
27	Chloroplasts	Absent; chlorophyll scattered in the cytoplasm	Present (in plants)
28	Fimbriae	Prokaryotes may have pili and fimbriae (appendage that can be found on many Gram-negative and some Gram-positive bacteria).	Absent
29	Microtubules	Absent or rare	Present
30	Centrosome	Absent	Present except in flowering plants.
31	Cytoskeleton	May be absent	Present
32	Glycocalyx	Present	Only in some
33	Cytoplasmic streaming	Absent	Present
34	Cytoplasmic membrane	Does not contain sterols (except Mycoplasma)	Contains sterols
35	Cell wall	Complex structure containing protein, lipids, and peptidoglycans	Present for plant cells and fungi; otherwise absent
36	Muramic acid	Present	Absent
37	Movement	Simple flagellum, if present	Complex flagellum, if present
38	Respiration	Via cytoplasmic membrane	Via mitochondria
39	Energy production site	Electron transport chain located in the cell membrane	Within membrane-bound mitochondria
40	Metabolic rate	Higher due to larger surface area to volume ratio	Comparatively slow
41	Reproduction	Asexual (binary fission)	Sexual and asexual/ Mitotic division
42	Generation time	Shorter	Comparatively longer
43	Genetic Recombination	Partial, unidirectional transfer	Meiosis and fusion of gametes
44	Zygote	Merozygotic (partially diploid)	Diploid
45	Extrachromosomal	Plasmid	Inside the mitochondria
	DNA
46	DNA replication	Occurs in the cytoplasm.	Occurs in the nucleus.
47	Transcription and translation	Occurs simultaneously.	Transcription occurs in the nucleus and then translation occurs in the cytoplasm.

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