11. Translation

Ribosomal Structure

11. Translation

Ribosomal Structure: Videos & Practice Problems

Topic summary

The ribosome, an RNA-protein complex, translates mRNA into proteins. It consists of a large and small subunit, primarily made of ribosomal RNA (rRNA) with some protein for structural support. Translation occurs at three key sites: the aminoacyl (A) site, where charged tRNA pairs with mRNA codons; the peptidyl (P) site, where amino acids are added to the growing polypeptide chain; and the exit (E) site, where uncharged tRNA is released. The ribosome also features a decoding center for accurate tRNA-codon matching and a peptidyltransferase center for peptide bond formation.

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Ribosome Structure

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Ribosome Structure Video Summary

The ribosome is a crucial RNA-protein complex responsible for translating messenger RNA (mRNA) into proteins. It consists of two main components: a large subunit and a small subunit, which are initially separate in the cytoplasm but come together during the translation process. Notably, the ribosome is predominantly made of ribosomal RNA (rRNA), with proteins providing structural support. The assembly of ribosomes occurs in the nucleolus, a specialized region within the nucleus.

During translation, the ribosome has three key sites where different stages of the process occur: the A site (aminoacyl site), the P site (peptidyl site), and the E site (exit site). The A site is where charged transfer RNA (tRNA) molecules, which carry amino acids, enter and match their anticodon with the corresponding codon on the mRNA. This pairing is essential for ensuring the correct amino acid is added to the growing polypeptide chain.

Once the tRNA is bound to the A site, it moves to the P site, where the amino acid it carries is transferred to the growing peptide chain. This transfer is facilitated by a reaction that forms a peptide bond, catalyzed in a specific region known as the peptidyltransferase center. After donating its amino acid, the tRNA moves to the E site, where it is released from the ribosome, becoming uncharged and ready to be recharged with another amino acid.

Additionally, the ribosome contains a decoding center that ensures the correct tRNA is matched to the appropriate codon, enhancing the fidelity of protein synthesis. Understanding these components and their functions is essential for grasping the intricate process of translation, which will be explored in greater detail in subsequent studies.

Problem

Which of the following is true regarding the ribosome structure?

Ribosomes are made up of only proteins

Ribosomes are made up of only RNA

Ribosomes are made up of both protein and RNA

Ribosomes are made up of neither protein nor RNA

Problem

Which of the following is not a ribosomal position used to add amino acids to a growing polypeptide chain?

A site

C site

P site

E site

Problem

Which of the following ribosomal sites is responsible for adding the amino acid to a growing polypeptide chain?

A site

C site

P site

E site

Problem

Ribosomal assembly occurs where in the cell?

Golgi

Cytoplasm

Endoplasmic Reticulum

Nucleolus

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Here’s what students ask on this topic:

What are the main components of a ribosome?

A ribosome is primarily composed of ribosomal RNA (rRNA) and proteins. It consists of two subunits: a large subunit and a small subunit. The rRNA makes up the majority of the ribosome's mass and is crucial for its catalytic activity, while the proteins provide structural support. The ribosome is assembled in the nucleolus, a specialized compartment within the nucleus. During translation, the two subunits come together to form a functional ribosome that translates mRNA into proteins.

What are the functions of the A, P, and E sites in the ribosome?

The A (aminoacyl) site, P (peptidyl) site, and E (exit) site are key functional regions of the ribosome during translation. The A site is where charged tRNA molecules pair with mRNA codons. The P site is where the amino acid from the tRNA is added to the growing polypeptide chain. Finally, the E site is where the uncharged tRNA is released from the ribosome after it has donated its amino acid. These sites work in a coordinated manner to ensure the accurate synthesis of proteins.

How does the ribosome ensure accurate translation of mRNA?

The ribosome ensures accurate translation of mRNA through its decoding center and peptidyltransferase center. The decoding center verifies that the correct tRNA anticodon pairs with the mRNA codon at the A site. This ensures that the correct amino acid is added to the growing polypeptide chain. The peptidyltransferase center catalyzes the formation of peptide bonds between amino acids, ensuring the proper assembly of the protein. These mechanisms work together to maintain the fidelity of protein synthesis.

Where is the ribosome assembled in the cell?

The ribosome is assembled in the nucleolus, a specialized compartment within the nucleus of the cell. The nucleolus is responsible for producing and assembling the ribosomal RNA (rRNA) and ribosomal proteins into the large and small subunits of the ribosome. Once assembled, these subunits are transported to the cytoplasm, where they come together during translation to form a functional ribosome that synthesizes proteins.

What role does rRNA play in the ribosome?

Ribosomal RNA (rRNA) plays a crucial role in the ribosome's function. It constitutes the majority of the ribosome's mass and is primarily responsible for its catalytic activity. The rRNA forms the core of the ribosome's structure and is involved in the binding of tRNA and mRNA. It also catalyzes the formation of peptide bonds between amino acids during protein synthesis. The proteins in the ribosome mainly provide structural support, while the rRNA carries out the essential catalytic functions.

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