Final answer:
True, integral membrane proteins do pass all the way through the membrane. They have stop-transfer sequences that allow them to anchor and span across the membrane. Peripheral membrane proteins, however, associate with only one side and if synthesized in the lumen of the ER, will end up on the outside of the plasma membrane.
Step-by-step explanation:
Understanding Integral Membrane Proteins
True or false, integral membrane proteins pass all the way through the membrane? The answer is true. Integral membrane proteins, are permanently embedded within the plasma membrane and indeed pass all the way through the membrane.
During their synthesis in the rough endoplasmic reticulum (RER), these proteins have stop-transfer sequences that anchor them within the membrane. These sequences are hydrophobic domains that get trapped in the fatty acid interior of the membrane, allowing the protein to span across it. It's also noted that depending on the number of these sequences, a protein can cross the membrane multiple times.
Peripheral membrane proteins, on the other hand, are not the same as integral proteins. If synthesized in the lumen of the ER, they would end up on the outside of the plasma membrane after the vesicle carrying them fuses with the cell membrane. This is because peripheral proteins are associated with the membrane on one side but do not span across it.
Transmembrane proteins, a type of integral proteins, seem to be crucial for many cell functions, including transporting molecules across the membrane, acting as cell receptors, and participating in cell adhesion, often identified by carbohydrate chains. The synthesis and modification of these proteins take place within the RER and the Golgi apparatus before becoming part of the plasma membrane.