The A-site of the ribosome interacts with the charged tRNA which contains the amino acid bound to adenosine monophosphate (AMP).

Aminoacyl site (A-site)

The peptidyl site (P-site) of the ribosome binds the charged tRNA where the amino acid has formed a peptide bond with the growing protein, but has not severed the bond with the tRNA. 

Peptidyl site (P-site)

The exit site (E-site) is where the tRNA dissociates from the ribosome to be charged again.

Exit site (E-site)

The *E. coli* ribosome has been well studied and is the model for prokaryotic transcription. The *E. coli* ribosome has two subunits: the 30S and the 50S. In translation initiation, the 30S recognizes the Shine-Delgarno sequence and then the 50S subunit can interact with the 30S to form the assembled ribosome for translation.

*E. coli* Ribosome

The eukaryotic ribosome is the 80S ribosome. The ribosomes have a 40S small subunit and 60S large subunit. Ribosomes in eukaryotic cells can be found in the membrane or free in the cytoplasm.

Eukaryotic Ribosomes

Ribosomes are made up of RNA and proteins. They are responsible for translating mRNA into proteins. Ribosomes are present in the cytoplasm.

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While eukaryotes and prokaryotes have some differences between their processes of translation, they share many of the same enzymes and terms needed for translation. These are:

- Ribosomes
- tRNA
- rRNA

Key Components in Translation

- Cell Wall
- Plasma Membrane
- Cytoplasm
- Ribosomes
- Mesosomes
- Cytoplasmic Inclusions
- Nucleoid
- Capsule
- Flagella
- Pilus
- Fimbriae
- Plasmid DNA
- Endospore
- Inclusion Bodies

Bacterial Structures

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Translation is very similar for prokaryotes and eukaryotes with a few differences. Importantly, translation can occur simultaneously with transcription in prokaryotes, but this does not happen in eukaryotes because of the nucleus.

Translation in Prokaryotes

Ribosomes

Transfer RNAs or tRNAs translate the mRNA code to the corresponding amino acids by binding to the specific codons. There are many types depending on the species. They are also a product of RNA transcription.

tRNA

Ribosomal RNAs or rRNAs make up about 50% of the ribosome. They are structural or enzymatic and are important in forming the ribosome to be used for translation. They are also a product of transcription.

rRNA

The cell wall in bacterial cells is very rigid and provides a stable shape to the cell. It is essential for bacterial growth and division. It is important in preventing the cell from bursting from osmotic pressure changes.

Cell Wall

The cytoplasm consists of organic and inorganic solutes and free floating ribosomes. Chromosomal DNA and plasmids are located in this region.

Cytoplasm

Mesosomes store respiratory enzymes and aid in cellular reproduction. These vesicles are formed by the invagination of the plasma membrane into the cytoplasm. 

Mesosomes

Inclusions can store nutrients or gas needed for the cells metabolism or buoyancy. Inclusions are important in reducing build up of osmotic pressure as the cell accumulates compounds.

Cytoplasmic Inclusions

The capsule is the extracellular layer of the bacterial cell. Generally, they are composed of polysaccharides and proteins. The capsule may allow a bacteria to be more infectious by making it more difficult to be engulfed by white blood cells. 

Capsule

Flagella are hair like filaments that extend from the cytoplasmic membrane to the external part of the cell. The flagella functions in cell motility. 

Flagella

This structure is found in both gram positive and gram negative bacteria. It is located under the cell wall and acts as a semipermeable barrier, controlling the flow of metabolites, between the cell wall and the cytoplasm. 

Plasma Membrane

Fimbriae are short bristle-like strands that extend from the bacteria by the hundreds. They are important in cell adhesion, infection, and colonization.

Fimbriae

The pilus is a appendage that extends to reach surfaces or other bacteria. The sex pilus is a specific pilus important in transferring DNA between bacterial cells.

Pilus

Prokaryotes do not have a nucleus. DNA and DNA-associated proteins are in the nucleoid region. It is a condensed area of DNA in the cell.

Nucleoid

Plasmids are circular, extrachromosomal DNA. Cells can have hundreds of plasmids. They can carry important genes for antibiotic resistance or conjugation.

Plasmid DNA 

Some bacteria are capable of forming endospores through the process of sporulation. The endospore contains that bacterial genome and keeps the bacterium in a dormant state. It is formed when the vegetative cell forms a septum and divides asymmetrically. This action separates the DNA forespore from the cell to eventually form the endospore. The bacterial forms the endospore when in environment is not suitable for growth. It also allows the bacterium to be dormant when exposed to harsh chemicals, radiation or low nutrients.

Endospores

Some bacteria are capable of forming inclusion bodies which are used for holding excess materials like nutrients or proteins. These cell structures decrease osmotic pressure in the cell by containing these compounds in inclusion bodies. 

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