Eukaryotic Cell Protein Production

• Eukaryotic cells divide the labor of protein production

Protein Production

• The nucleus contains DNA, which specifies the recipe for proteins
• The nucleus also contains the nucleolus, which synthesizes ribosomes
• Messenger RNA (mRNA) matches the sequence of DNA and carries the protein "recipe" through a nuclear pore and the two-layered nuclear envelope
• RNA moves from the nucleus to a ribosome, where the protein is synthesized.
• Some ribosomes float in the cytosol while others attach to the rough endoplasmic reticulum (rER)
• Free-floating ribosomes synthesize proteins that operate in the cytosol.
• Ribosomes attached to the rER synthesize proteins that function inside organelles or outside of the cell
• Secreted proteins move from ribosomes into the rER, where they are modified and folded into their exact 3D shape
• These proteins exit the rER in bubbles of membrane called transport vesicles.
• The vesicles leaving move to the Golgi apparatus, a stack of membrane sacs that acts as a "processing center"
• Proteins leaving the Golgi in transport vesicles ultimately fusing with the cell membrane
• The contents of the vesicle are then expelled outside of the cell

Protein Localization

• The endomembrane system consists of the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and the cell membrane
• The different parts of the endomembrane system work together to secrete proteins, moving them outside of the cell
• Mammary gland cells produce proteins and secrete them in order to make milk for baby mammals.

Cellular Digestion

• Lysosomes contain hydrolytic enzymes
• Some transport vesicles leaving the Golgi carry enzymes that catalyze hydrolysis reactions
• These vesicles may fuse with lysosomes, where cellular digestion of large molecules occurs