Ribosomes Read the Genetic Code

This introductory section will summarize protein synthesis as it occurs in bacteria. It should be noted that the details of protein synthesis differ between bacteria and higher organisms (see Ch. 8). The bacterial ribosome, as described in more detail below, consists of two subunits, small (30S) and large (50S). S-values tell how fast a particle amino acid Monomer from which the polypeptide chains of proteins are built polypeptide chain A polymer that consists of amino acids protein Polymer made from amino acids; may consist of several polypeptide chains ribosome The cell's machinery for making proteins

S-value The sedimentation coefficient is the velocity of sedimentation divided by the centrifugal field. It is dependent on mass and is measured in Svedberg units transcription Conversion of information from DNA into its RNA equivalent translation Making a protein using the information provided by messenger RNA

Prokaryote

Eukaryote

Gene Gene Gene

Gene Gene Gene

Protein

FIGURE 3.18 Differing Patterns of Transcription

Protein

FIGURE 3.18 Differing Patterns of Transcription

In eukaryotes, each gene is transcribed to give a separate mRNA that encodes only a single protein. In prokaryotes, an mRNA molecule may carry information from a single gene or from several genes that are next to each other on the chromosome.

FIGURE 3.19 Structural Components of a Ribosome

The bacterial ribosome can be broken down into two smaller subunits and finally into RNA molecules and proteins.

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