Cell Proteins and Membrane Structure Flashcards
Why are R groups important (3 main points)?
1) They determine the structure of the protein.
2) They allow the binding of ligands.
3) They determine the proteins location within the cell - the balance of hydrophilic and hydrophobic R groups on the proteins surface influences the solubility of the protein in the cytoplasm.
How are cytoplasmic proteins such as enzymes and G-protiens soluble?
The surface of these proteins have a greater proportion of hydrophilic R groups so they are able to form weak interactions with water molecules. Also, during post-translational modification, phophate groups or sugars can be added to the surface of the protein to make it more hydrophilic. Their hydrophobic R groups are clustered in the centre of the protein forming a globular structure with a hydrophobic core.
Describe the fluid mosaic-model.
Membranes are made of a phospholipid bilayer with globular proteins penetrating the bilayer or attached to it. Each phopholipid molecule has a hydrophilic head and a hydrophobic tail. They form a bilayer with the heads towards the outside and the tails on the inside.
Why can only hydrophobic molecules pass through the cell membrane?
Hydrophobic molecules such as oxygen and thyroxine are polar and so can pass straight through the membrane to reach their receptors in the cytoplasm. However hydrophilic molecules (non-polar) are repelled by the hydrophobic centre of the membrane and so cannot pass straight through.
What are integral proteins?
Integral proteins are held firmly within the membrane by strong hydrophobic interctions with the interior of the membrane. Some only extend part way through the membrane, whilst others go right through the membrane. The ones that go right through the membrane are called transmembrane proteins.
What are peripheral proteins?
Peripheral proteins are only loosely attached to the membrane by forming weak bonds only to the surface, either to the heads of the phospholipids or to exposed parts of intergral proteins.
