Proteins
Table of Contents
Definition
- biomolecules that are made up of building blocks of amino acids joined by peptide bonds.
- within the membrane, nonpolar amino acids
- hydrophobic
- anchors protein into membrane
- on outer surfaces of membrane in fluid, polar amino acids
- hydrophilic
- extend into extracellular fluid & into cytosol.
- C-terminus is the top side of the bilayer
- N-terminus is the bottom side of the bilayer
Functions
Transporter
- serves as a channel for materials to go through and out.
Enzyme Activity
Cell surface receptor
Cell surface identity marker
- serves as antigen
Cell adhesion
Attachment to the cytoskeleton
- serves to have the cell a defined structure.
Classes
Peripheral proteins
- loosely bound to surface of membrane
- ex. Cell surface identity marker (antigens)
Integral proteins
- also called integrins
- goes through the Phospholipids Bilayer
- monotropic attached to only one side of the membrane
- Lipid-anchored protein attached to lipids embedded to the lipid bilayer.
- Ex: Glycosylphosphatidylinositol (GPI)
Transmembrane protein
- spans across the membrane
- can be either bitropic or polytropic
- bitropic when the protein only spans once
- polytropic when the protein spans multiple times