Discovered by Robert Hook in the year 1665, cells are the structural and functional unit of life. Some cells are bound by membrane organelles while some are not. Depending on the internal structure of the cells and whether they are bound by a membrane or not, cells in organisms are of two types- Prokaryotic and Eukaryotic.
Prokaryotic cells are the most primitive kind and do not have a defined nucleus with bacteria or cyanobacteria. The cytoplasm of the cells contains scattered chromatin bodies. Prokaryotic cells are smaller than eukaryotic cells and asexual division in the form of binary fission is noted in them.
Eukaryotic cells are believed to have evolved from prokaryotic cells and have a characteristic membrane nucleus. The cytoplasm of these cells contains mitochondria that are bound by membranes, a defined nucleus and chromatin bodies contained within a nuclear membrane as well. Eukaryotic cells are subject to both asexual and sexual divisions. Much larger in size as compared to prokaryotes, these show a more structured organisation.
The most distinguished difference between prokaryotes and eukaryotes are their cellular features. However, these are highly similar in terms of the presence of plasma membranes and the fact that for genetic information, both make use of DNA.
Examples of prokaryotes include microorganisms like bacteria while examples of eukaryotes include various fungi and algae.
Definition of Prokaryotic Cells
Known to be the very earliest in the world, prokaryotic cells are single-celled microorganisms, and include archaea and bacteria. These cells usually live freely by themselves or can be found in the gut of other organisms. The cells have a single membrane and consist of cytoplasm. Certain prokaryotic cells perform photosynthesis with the help of the cyanobacteria inside them.
Main Components of Prokaryotic Cells:
Prokaryotic Cells are Made up of the Following Components:
- Cytoplasm – Present inside the cell and resembling a jelly-like structure, all cell organelles are suspended inside the cytoplasm. The cytoplasm also contains salts and enzymes.
- Plasma Membrane – This is the outer protective covering that consists of phospholipid molecules that act as a barrier between the surrounding environment and the cell.
- DNA – This is a cell’s genetic material. Circular in form, the DNA directs the proteins created by a cell and also regulates its actions.
- Ribosomes – This is the place where the protein synthesis of a cell occurs.
Additional Structure of Prokaryotic Cells
While prokaryotic cells do not consist of nuclear membranes, mitochondria or Golgi bodies, there are several other components that add to their structure. They are:
- Nucleoid – Spherical, spiral or shaped like a rod, the nucleoid is the genetic material inside the cytoplasm of a cell.
- Cell Wall – The outermost layer of prokaryotic cells, this lends shape and structure.
- Capsule – In addition to the cell wall, a capsule protects bacterial cells, retains moisture and helps cells attach themselves to various surfaces or nutrients.
- Flagella – Certain prokaryotic cells have long tail-like structures that help them go from one surface to another. These are called flagella.
- Pili – These are outgrowths of a cell that bear resemblance to fine, tiny hair and attach to the surface of other prokaryotic cells.
Common Characteristics of Prokaryotic Cells
Various Characteristic Features of Prokaryotic Cells are as Follows:
- There is no presence of a nuclear membrane.
- Prokaryotic cells do not consist of mitochondria, Golgi bodies, chloroplast or lysosomes.
- Their cells walls comprise of amino acids and carbohydrates.
- A single chromosome consists of the genetic material.
- Prokaryotic cells use the method of binary fission to divide asexually or recombine as a sexual method of reproduction.
- The plasma membrane carries respiratory enzymes.
Definition of Eukaryotic Cells
Eukaryotic cells form more complex and larger organisms. They have a nuclear membrane that comprises of a nucleus. Eukaryotic cells can thrive in and maintain multiple environments as part of a single cell- a characteristic that helps them grow larger as compared to prokaryotic cells and also facilitates metabolic reactions.
Animals, plants, fungi and protozoa have eukaryotic cells and are classified under the Eukaryota kingdom.
Main components of Eukaryotic Cells:
Eukaryotic Cells Consist of the Following Components that Make up their Structure:
- Plasma Membrane – This acts as a barrier between the cell and the external environment. It is built of embedded proteins that facilitate the exchange of substances to and from the cell.
- Cell Wall – Composed of proteins, cellulose and pectins, this is present only in plant cells and completely absent in animal cells. The cell wall provides shape and structure while also acting as a layer of protection for the cell.
- Nucleus – This is where ribosomes are produced. The nucleus consists of a nucleoplasm that further contains proteins and DNA.
- Cytoskeleton – Located inside the cytoplasm, the cytoskeleton consists of microtubules, fibres and microfilaments, all of which lend shape to the cell, help in cell movement, and also acts as an anchor for organelles.
- Endoplasmic Reticulum – Usually of two types- rough and smooth, the endoplasmic reticulum is a network of structures that are small and tubular in nature.
- Golgi Apparatus – These are not present in plant sieve cells and human red blood cells. Made of disc-shaped, flat structures, these are placed close to the nucleus.
- Ribosomes – They are made of ribonucleic acids, proteins and are where the protein synthesis for a cell occurs.
- Mitochondria – This is the energy-producing powerhouse of the cell, and helps in maintaining cell metabolism as well.
- Lysosomes – Lysosomes consist of hydrolytic enzymes that help digest nucleic acids, carbohydrates, lipids and other proteins.
- Plastids – Only found in plant cells, plastids are double membraned structures often involved in the process of photosynthesis.
Common Characteristics of Eukaryotic Cells
Some of the Most Common Features of Eukaryotic Cells are:
- The nucleus is protected by a nuclear membrane.
- Mitochondria is a component of all eukaryotic cells.
- The outermost layer of eukaryotic cells is a cell wall.
- These cells divide by the process of mitosis.
- Eukaryotic cells comprise of a cytoskeletal structure.
- All genetic information of the cell is within the nucleus that consists of a single and linear DNA.
Difference Between Prokaryotic and Eukaryotic Cells
|Prokaryotic Cells||Eukaryotic Cells|
|Absence of nucleus||Presence of nucleus|
|Presence of a single chromosome, however, the chromosome is not true||Presence of multiple chromosomes|
|Unicellular in nature||Multicellular in nature|
|No microtubules||Presence of microtubules|
|Absence of mitochondria||Presence of mitochondria|
|Smaller ribosomes||Bigger ribosomes|
|No cytoskeleton||Presence of cytoskeleton|
|No Golgi apparatus||Golgi apparatus present|
|Asexual reproduction||Sexual and asexual reproduction|
|Often has fimbriae and pili||Does not have fimbriae and pili|
|The cytoplasm where transcription takes place||The nucleus is where transcription takes place|
|Size is sub-microscopic||Size is microscopic, though enclosed in membranes|
|No presence of chloroplasts||Chloroplasts are present in plants|
|DNA arrangement is circular||DNA arrangement is linear|
|Cell division occurs through binary fission||Cell division occurs through mitosis|
|Examples include bacteria and archaea||Examples include plant and animal cells|