for National Geographic News. A massive new study of human genetic diversity reveals surprising insights into our species' evolution and migrationsâincluding support for the theory that the first modern humans originated in Africaâscientists said today.or National Geographic News. A massive new study of human genetic diversity reveals surprising insights into our species' evolution and migrationsâincluding support for the theory that the first modern humans originated in Africaâscientists said today.
Proteins are too large to move across the phospholipid bilayer of the cell membrane so therefore require help getting into (or out of) the cell. Proteins may be brought across the cell membrane by endocytosis - they may then be broken down into amino acid building blocks (by fusion of the endocytotic vesicles with the proteolytic enzyme containing lysosomes) which can then be used by the cell or moved out of the cell by transmembrane transport proteins.
For example, plasma membrane proteins carry out functions as diverse as ferrying nutrients across the plasma membrane, receiving chemical signals from outside the cell, translating chemical signals into intracellular action, and sometimes anchoring the cell in a particular location (Figure 4).