Translation in Prokaryotes vs Eukaryotes
There are several meanings for the term translation, but when it comes as either prokaryotic or eukaryotic translation, its contextual meaning refers to one of the processes in gene expression and protein synthesis. There are differences in the process of translation between prokaryotes and eukaryotes, which are described concisely in this article.
Prokaryotic Translation
When the mRNA strand is being processed to translate into protein at the ribosomes, the prokaryotic translation is said to be in action. There is no nuclear envelope in prokaryotes, and the non-coding nucleotides are also absent. Therefore, the RNA splicing does not take place, and the ribosomal subunits can directly start translation as the mRNA formation takes place in prokaryotes. The tRNA molecules carry amino acids that are specific with the anticodon.
As the transcription takes place, the two ribosomal subunits [50S and 30S units] along with the initial tRNA molecule assemble together at the mRNA strand. The next tRNA molecule [based on the codon sequence in the mRNA strand] comes to the large ribosomal subunit, and the two amino acids attached to the tRNA molecules are attached with a peptide bond. The peptide bonding is continued as per the codon sequence of the mRNA strand and a protein called release factor stops the translation process. In prokaryotic translation, there can be few proteins synthesized in one step. Additionally, few translations can take place simultaneously in prokaryotes though polysomes. It would be important to state that tRNA molecules are not dissolved after peptide bond is completed, but can carry additional amino acids to contribute for translation in prokaryotes.
Eukaryotic Translation
Conversion of information in the transcribed mRNA strand into proteins in eukaryotic organisms is the eukaryotic translation. However, with the presence of both coding and non-coding nucleotides in eukaryotes, the splicing of those from the RNA strand has to take place before the mRNA strand is ready for translation. Additionally, the presence of nuclear envelope does not allow the ribosomes to get close to the genetic material in the nucleus. Therefore, the translation process takes place outside the nucleus or in the cytoplasm.
There are two main ways of initiation in eukaryotic translation known as the cap-dependant and cap-independent. There is a special protein with a tag attached to the 5’ end of the mRNA strand, which binds to the small ribosomal subunit [40S unit]. The translation continues with the assemblage of large ribosomal subunit [80S unit], small subunit with mRNA strand, and tRNA with amino acids. The peptide bonding takes place after that and the eukaryotic release factors terminate the process after the protein is synthesized.
What is the difference between Prokaryotic and Eukaryotic Translation?
• As there is no nuclear envelope, prokaryotic translation takes place close to the genetic material. However, eukaryotic translation takes place in the cytoplasm and never inside the nucleus due to the presence of nuclear envelope.
• Protein capping and RNA splicing take place before translation in eukaryotes, but there are no such steps in prokaryotic translation.
• Translation starts as the dismantling of the DNA and synthesizing of mRNA strand take place in prokaryotes, but eukaryotic translation starts after completion of mRNA synthesis and protein capping with splicing.
• Involved ribosomal subunits in prokaryotic translation are 30S and 50S while eukaryotes have 40S and 80S ribosomal subunits in translation.
• Initiation and elongation are more complex factor-aided processes in eukaryotic translation than in prokaryotic translation. However, the terminations are almost the same in both organisms.
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Every living organism falls into one of two groups: eukaryotes or prokaryotes. Cellular structure determines which group an organism belongs to. In this article, we will explain in detail what prokaryotes and eukaryotes are and outline the differences between the two.
Prokaryote definition
Prokaryotes are unicellular organisms that lack membrane-bound structures, the most noteworthy of which is the nucleus. Prokaryotic cells tend to be small, simple cells, measuring around 0.1-5 μm in diameter.
The key structures present in a prokaryote cell
While prokaryotic cells do not have membrane-bound structures, they do have distinct cellular regions. In prokaryotic cells, DNA bundles together in a region called the nucleoid. Prokaryotes
can be split into two domains, bacteria and archaea. In prokaryotes, molecules of protein, DNA and metabolites are all found together, floating in the cytoplasm. Primitive organelles, found in bacteria, do act as micro-compartments to bring some sense of organisation to the arrangement.
Prokaryotic cell features
Here is a breakdown of what you might find in a prokaryotic bacterial cell.
- Nucleoid: A central region of the cell that contains its DNA.
- Ribosome: Ribosomes are responsible for protein synthesis.
- Cell wall: The cell wall provides structure and protection from the outside environment. Most bacteria have a rigid cell wall made from carbohydrates and proteins called peptidoglycans.
- Cell membrane: Every prokaryote has a cell membrane, also known as the plasma membrane, that separates the cell from the outside environment.
- Capsule: Some bacteria have a layer of carbohydrates that surrounds the cell wall called the capsule. The capsule helps the bacterium attach to surfaces.
- Fimbriae: Fimbriae are thin, hair-like structures that help with cellular attachment.
- Pili: Pili are rod-shaped structures involved in multiple roles, including attachment and DNA transfer.
- Flagella: Flagella are thin, tail-like structures that assist in movement.
Examples of prokaryotes
Bacteria and archaea are the two types of prokaryotes.
Do prokaryotes have a nucleus?
Prokaryotes do not have a nucleus. Instead prokaryote DNA can be found, bundled but free-floating, in a central region called the nucleoid. Prokaryote DNA is usually found as a single chromosome of circular DNA. These organisms also lack other membrane-bound structures such as the endoplasmic reticulum.
Do prokaryotes have mitochondria?
No, prokaryotes do not have mitochondria. Mitochondria are only found in eukaryotic cells. This is also true of other membrane-bound structures like the nucleus and the Golgi apparatus [more on these later].
One theory for eukaryotic evolution hypothesizes that mitochondria were first prokaryotic cells that lived inside other cells. Over time, evolution led to these separate organisms functioning as a single organism in the form of a eukaryote.
Eukaryote definition
Eukaryotes are organisms whose cells have a nucleus and other organelles enclosed by a plasma membrane. Organelles are internal structures responsible for a variety of functions, such as energy production and protein synthesis.
The key structures present in a eukaryote cell.
Eukaryotic cells are large [around 10-100 μm] and complex. While most eukaryotes are multicellular organisms, there are some single-cell eukaryotes.
Eukaryotic cell features
Within a eukaryotic cell, each membrane-bound structure carries out specific cellular functions. Here is an overview of many of the primary components of eukaryotic cells.
- Nucleus: The nucleus stores the genetic information in chromatin form.
- Nucleolus: Found inside of the nucleus, the nucleolus is the part of eukaryotic cells where ribosomal RNA is produced.
- Plasma membrane: The plasma membrane is a phospholipid bilayer that surrounds the entire cell and encompasses the organelles within.
- Cytoskeleton or cell wall: The cytoskeleton or cell wall provides structure, allows for cell movement, and plays a role in cell division.
- Ribosomes: Ribosomes are responsible for protein synthesis.
- Mitochondria: Mitochondria, also known as the powerhouses of the cell, are responsible for energy production.
- Cytoplasm: The cytoplasm is the region of the cell between the nuclear envelope and plasma membrane.
- Cytosol: Cytosol is a gel-like substance within the cell that contains the organelles.
- Endoplasmic reticulum: The endoplasmic reticulum is an organelle dedicated to protein maturation and transportation.
- Vesicles and vacuoles: Vesicles and vacuoles are membrane-bound sacs involved in transportation and storage.
Other common organelles found in many, but not all, eukaryotes include the Golgi apparatus, chloroplasts and lysosomes.
Examples of eukaryotes
Animals, plants, fungi, algae and protozoans are all eukaryotes.
Comparing prokaryotes and eukaryotes
All life on Earth consists of either eukaryotic cells or prokaryotic cells. Prokaryotes were the first form of life. Scientists believe that eukaryotes evolved from prokaryotes around 2.7 billion years ago.
The primary distinction between these two types of organisms is that eukaryotic cells have a membrane-bound nucleus and prokaryotic cells do not. The nucleus is where eukaryotes store their genetic information. In prokaryotes, DNA is bundled together in the nucleoid region, but it is not stored within a membrane-bound nucleus.
The nucleus is only one of many membrane-bound organelles in eukaryotes. Prokaryotes, on the other hand, have no membrane-bound organelles. Another important difference is the DNA structure. Eukaryote DNA consists of multiple molecules of double-stranded linear DNA, while that of prokaryotes is double-stranded and circular.
Key similarities between prokaryotes and eukaryotes
A comparison showing the shared and unique features of prokaryotes and eukaryotes
All cells, whether prokaryotic or eukaryotic, share these four features:
1. DNA
2. Plasma membrane
3. Cytoplasm
4. Ribosomes
Transcription and translation in prokaryotes vs eukaryotes
In prokaryotic cells, transcription and translation are coupled, meaning translation begins during mRNA synthesis.
In eukaryotic cells, transcription and translation are not coupled. Transcription occurs in the nucleus, producing mRNA. The mRNA then exits the nucleus, and translation occurs in the cell’s cytoplasm.
What are the key differences between prokaryotes and eukaryotes?
Prokaryotes and eukaryotes vary in several important ways - these differences include structural variation - whether a nucleus is present or absent, and whether the cell has membrane-bound organelles, and molecular variation, including whether the DNA is in a circular or linear form. The differences are summarized in the table below.
| Prokaryote | Eukaryote | |
| Nucleus | Absent | Present |
| Membrane-bound organelles | Absent | Present |
| Cell structure | Unicellular | Mostly multicellular; some unicellular |
| Cell size | Smaller [0.1-5 μm] | Larger [10-100 μm] |
| Complexity | Simpler | More complex |
| DNA Form | Circular | Linear |
| Examples | Bacteria, archaea | Animals, plants, fungi, protists |