Page 189 - MNU microbiology theoritical 2025

General Microbiology & Immunology (PM 401) Second level Semester 4 2024/2025

The 3D model of the
ribosome with
animation

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Steps of translation

Let’s divide translation into three stages: initiation (starting off), elongation

(adding on to the protein chain), and termination (finishing up).
1- Initiation

• It begins when the small ribosomal subunit attaches directly to certain

sequences in the mRNA (Shine-Dalgarno sequences)

• First, an initiation complex forms. This consists of the 30S ribosomal

subunit, an initiator tRNA that carries N-formylmethionine or f-Met, and

proteins called initiation factors.
• Shortly thereafter, the 50S subunit of the ribosome joins that complex and

the initiation factors leave, forming the 70S ribosome.

General Microbiology & Immunology (PM 401) theoretical handbook Page 178