RIBOSOMES & ENDOPLASMIC RETICULUM

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Ribosomes Made of ribosomal RNA

and protein Synthesized by nucleolus of

cell Proteins from cytoplasm are

brought to nucleus and made with rRNA into large and small subunits of ribosomes

Subunits leave the nucleus and assemble into ribosomes

Carry out protein synthesis

Ribosomes Cont. Two Types

Bound ribosomes Most proteins

made here function in the cytosol

Free ribosomes Most proteins

made here are for excretion, insertion into membranes, or packaging in other organelles

Endoplasmic Reticulum (ER) Endoplasmic: “within the

cytoplasm” Reticulum: “little net” An organelle in eukaryotic

cells that is an extensive network of membranes

ER consists of cisternae (network of membranous tubules)

Two types of ER: SMOOTH and ROUGH

SMOOTH ER Tasks: synthesis of

lipids, metabolism of carbohydrates, detoxification of drugs and proteins, and storage of calcium ions

Named “smooth” because of the lack of ribosomes

ROUGH ER Cells that secrete proteins

produced by ribosomes attach to the ER

“rough” because it is studded with ribosomes

Makes secretory proteins, also is a membrane factory for the cell – it grows by adding membrane proteins and phospholipids to its own membrane