A&P Lecture 1.4: Ribosome

This is an in depth  explanation of the Ribosome as a part of the cell. This lecture note is linked to A&P Lecture 1: The Cell

ANATOMY AND PHYSIOLOGY LECTURE 1.4

RIBOSOME

Ribosomes  are the sites of protein synthesis. Each ribosome is composed of a large subunit and a smaller one. The ribosomal subunits, which consist of ribosomal RNA (rRNA) and proteins, are produced separately in the nucleolus of the nucleus. The ribosomal subunits then move through the nuclear pores into the cytoplasm, where the ribosomal subunits assemble with mRNA to form the functional ribosome during protein synthesis. Ribosomes can be found free in the cytoplasm or associated with an intracellular membrane complex called the endoplasmic reticulum. Free ribosomes primarily synthesize proteins used inside the cell, whereas ribosomes attached to the endoplasmic reticulum u

sually produce proteins that are secreted from the cell.

Ribosomes are often called the “protein factories” of the cell because it is here that proteins are produced according to the genetic information contained in messenger RNA. The ribosomes are quite tiny, about

25 nanometers in size, and can be found both free in the cytoplasm and located on the surface of an organelle called the endoplasmic reticulum.

Each ribosome consists of two subunits, which are designated 30S and 50S after their sedimentation rate in

a centrifuge (this is measured in Svedberg units, from which the “S” is derived). Each of the subunits is composed of both ribosomal RNA and proteins. Contrary to earlier expectations of most scientists, it now appears that the ribosomal RNA molecules serve as enzymes (called ribozymes ) for many of the reactions

in the ribosomes that are required for protein synthesis.