integral and peripheral proteins Flashcards
What is the primary function of cell membranes?
The primary function of cell membranes is to form a barrier that prevents ions and hydrophilic molecules from passing through easily, which is carried out by the phospholipid bilayer.
What is the role of membrane proteins in the cell membrane?
Membrane proteins perform almost all other functions of the membrane, aside from forming the barrier, and are essential for various activities like transport, signaling, and structure.
How can membrane proteins be classified?
Integral proteins
Peripheral proteins
Where are integral proteins located in the membrane?
Integral proteins are embedded in the hydrophobic centre of the membrane because part of their surface is hydrophobic. They may fit into one or both phospholipid layers and may be transmembrane, spanning across the entire membrane.
What is the structure of transmembrane proteins?
Transmembrane proteins extend across the membrane with hydrophilic parts projecting through the phosphate heads of the phospholipid bilayer on either side.
Where are peripheral proteins located in the membrane?
Peripheral proteins have a hydrophilic surface, so they are not embedded in the membrane. They are typically attached to the surface of integral proteins, and this attachment is often reversible.
How are proteins in membranes orientated to perform their function?
Membrane proteins are orientated according to the membrane’s inner and outer faces to carry out their functions effectively. For example, pump proteins in plant root cells are oriented to pick up K+ from the soil and pump it into the root cell.
How are some peripheral proteins anchored to the membrane?
Some peripheral proteins are anchored to the membrane by a single hydrocarbon chain that is inserted into the membrane’s surface.
How does the protein content of membranes vary?
Cell surface membranes: ~50% protein content.
Mitochondria & chloroplasts: ~75% protein content.
Myelin sheath: ~18% protein content.
