Signal sequences target proteins for secretion FIGURE 9-24 Proteins destined to be secreted from the cell have an amino-terminal sequence that is rich in hydrophobic residues. This signal sequence binds to proteins in the endoplasmic reticulum (ER) membrane that draw the remainder of the protein through the lipid bilayer. The signal sequence is cleaved from the protein in this process by an enzyme called signal peptidase (not shown). Once inside the endoplasmic reticulum, the protein is directed to the cell membrane, from which it will be secreted. ER lumen Signal sequence- Cytosol ER membrane
Proteins
We generally tend to think of proteins only from a dietary lens, as a component of what we eat. However, they are among the most important and abundant organic macromolecules in the human body, with diverse structures and functions. Every cell contains thousands and thousands of proteins, each with specific functions. Some help in the formation of cellular membrane or walls, some help the cell to move, others act as messages or signals and flow seamlessly from one cell to another, carrying information.
Protein Expression
The method by which living organisms synthesize proteins and further modify and regulate them is called protein expression. Protein expression plays a significant role in several types of research and is highly utilized in molecular biology, biochemistry, and protein research laboratories.
Based on Figure 9-24, can you predict the position of a
mutation that would produce an active protein that was
not directed to the correct location?
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