Protein production

Which organelles are involved in protein production and secretion?

Nucleus, nucleolus, ribosomes, rough endoplasmic reticulum (RER), Golgi apparatus, vesicles, and the cell surface membrane.

What is the role of the nucleus in protein synthesis?

• Stores DNA (the instructions for proteins).

• Nucleolus manufactures ribosomes.

• Site of transcription: an mRNA copy of DNA is produced, which carries the code out of the nucleus via nuclear pores.

What happens at the ribosomes during protein synthesis?

• mRNA attaches to ribosomes in the cytoplasm or on the RER.

• Translation occurs: ribosomes read the mRNA sequence and assemble amino acids into a polypeptide chain.

What is the role of the rough endoplasmic reticulum (RER) in protein synthesis?

• Ribosomes on the RER surface translate mRNA into polypeptides.

• Polypeptides are folded and processed into functional proteins inside the RER.

What is the role of the Golgi apparatus in protein secretion?

• Further modifies proteins (e.g. adds carbohydrates to make glycoproteins).

• Packages proteins into vesicles for transport inside or outside the cell.

What is the role of vesicles in protein transport and secretion?

• Transport proteins between RER and Golgi apparatus, and from Golgi to the cell surface membrane.

• Vesicles fuse with the cell surface membrane to release proteins (e.g. enzymes, hormones) by exocytosis.

Why do cells in hormone-producing glands or enzyme-producing cells of the digestive system contain large amounts of RER, Golgi and ribosomes?

Because they are specialised for high levels of protein synthesis and secretion, so they require many organelles involved in these processes.