structure and functions of ribosomes

Question 1

What is the structure of a ribosome?

Answer 1

• Small subunit: Binds to mRNA
• Large subunit: Contains three binding sites for tRNA, catalyzes peptide bond formation, and has an exit tunnel for the growing polypeptide chain.

Question 2

How big are ribosomes in eukaryotic cells?

Answer 2

Eukaryotic ribosomes are about 30 nm in diameter.

Question 3

What are the main functions of the small and large subunits of a ribosome?

Answer 3

Small subunit: Binds to mRNA to guide the translation process.

Large subunit:
- Contains three tRNA binding sites for amino acid attachment.

• Catalyzes the formation of peptide bonds between amino acids.
• Has an exit tunnel through which the growing polypeptide chain exits.

Question 4

What is the difference between free ribosomes and ribosomes attached to the rough endoplasmic reticulum (RER)?

Answer 4

• Free ribosomes:
  Are not attached to any membrane and produce polypeptides that stay in the cytoplasm or enter the nucleus.
• Ribosomes attached to RER:
  Synthesize polypeptides that are transported into the RER lumen and are often sent via vesicles to the Golgi apparatus for further processing or secretion.

Question 5

What happens to polypeptides produced by free ribosomes?

Answer 5

Polypeptides made by free ribosomes are released into the cytoplasm and either stay there or may be transported into the nucleus.

Question 6

What happens to polypeptides produced by ribosomes attached to the RER?

Answer 6

Polypeptides synthesized by ribosomes on the RER are transported into the lumen of the RER. These proteins are then often packaged into vesicles and transported to the Golgi apparatus for further processing or secretion.