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Ribosome

Ribosome

amino acids are all valuable to suckling young, so casein efficiently provides three essential nutrients. And as we have seen in numerous instances, phosphorylation-dephosphorylation cycles regulate the activity of many enzymes and regulatory proteins.

Extra carboxyl groups may be added to Glu residues of some proteins. For example, the blood-clotting protein prothrombin contains a number of y-carboxygluta-mate residues (Fig. 27-29b) in its amino-terminal region, introduced by an enzyme that requires vitamin K. These carboxyl groups bind Ca2 + , which is required to initiate the clotting mechanism.

FIGURE 27-28 Coupling of transcription and translation in bacteria. The mRNA is translated by ribosomes while it is still being transcribed from DNA by RNA polymerase. This is possible because the mRNA in bacteria does not have to be transported from a nucleus to the cytoplasm before encountering ribosomes. In this schematic diagram the ribosomes are depicted as smaller than the RNA polymerase. In reality the ribosomes (Mr 2.7 X 106) are an order of magnitude larger than the RNA polymerase (Mr 3.9 X 105).

1064 Chapter 27 Protein Metabolism

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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