IBIO 425 Study Guide - Final Guide: Nuclear Membrane, Polysome, Signal Peptide
Document Summary
~20x30 nm electron-dense particles composed of small (40 s) and large (60 s) subunits. Occur "free" in cytoplasm (polyribosomes) or attached to er (rough er) High concentrations of ribosomes yield cytoplasmic basophilia by lm. Mediate interaction of mrna and trna-bound aa to synthesize proteins. Translate unique mrna nucleotide sequence into primary peptide/protein sequence. Bound ribosomes which produce proteins for secretions, cell membranes, golgi, or lysosomes, attach via signal peptide sequence to the er membrance shortly after produced by free ribosomes from directly in the cytoplasm. Polysomes represent multiple ribosomes attached simultaneously to a single mrna molecule. 3d network of tubular membranes that are equal diameter and are devoid of ribosomes. Stores calcium (sarcoplasmic reticulum in striated muscle cells) Branching network of membrane-bound indicidual tubules or stacks of cisternae. Outer membrane studded with tem dense granules of ribonucleoprotein, the ribosomes. Forms a closed system not open to cell exterior but continuous with outer surgace of nuclear envelope.
