Cell membrane

• Give the parts of a cell surface membrane


  Phospholipid bilayer, intrinsic proteins, extrinsic proteins, cholesterol, glycolipids, glycoproteins.
• where is a membrane found


  The cell surface membrane has a single membrane. A double membrane surrounds the nucleus, chloroplasts and mitochondria. The Golgi apparatus, endoplasmic reticulum and vesicles all have a single membrane.
• why do phospholids form a bilayer


  The phosphate group is polar, and attracts water. It is hydrophilic head. The fatty acid tails turn away from water, but mixes readily with fats, these are the hydrophobic tails. The two sets of hydrophilic heads point to the outside of the cell surface membrane, attracted to the water on both sides. The hydrophobic tails point into the centre of the membrane, repelled by the water, to form a bilayer.
• what are extrinsic and intrinsic proteins 


  Extrinsic proteins are only found on one side of the plasma membrane.

  Intrinsic proteins span from one side to the other.
• What are protein channels 


  Proteins that form water-filled tubes to allow water-soluble ions to diffuse across the membrane by facilitated diffusion.
• what are carrier proteins 


  Proteins that bind to ions or molecules like glucose and amino acids, then change shape in order to move these molecules across the membrane by facilitated diffusion.
• what are the functions of proteins in the plasma membrane


  Provide structural support, act as channel or carrier proteins for facilitated diffusion, allow active transport through carrier proteins, form cell-surface receptors for identifying cells, help cells adhere together, act as receptors for hormones, embedded enzymes, act as antigens for cell recognition.
• what is the function of cholesterol 


  Reduces lateral movement of other molecules, including phospholipids, make the membrane less fluid at high temperatures, hydrophobic so prevents leakage of water and dissolved ions from the cells.
• what is the function of gylcolipids 


  Act as recognition sites, help maintain the stability of the membrane, help cells attach to one another and form tissues.
• what is the function of glycoproteins


  Act as recognition sites, to help cells attach to one another and form tissues, allows cells to recognise each other, for example lymphocytes.
• Why can molecules not move freely across the plasma membrane 


  Act as recognition sites, to help cells attach to one another and form tissues, allows cells to recognise each other, for example lymphocytes.
• why is it called fluid mosaic model 


  Fluid because the individual molecules can move past each other, giving flexibility. Mosaic, because the proteins that are scattered through the bilayer like a mosaic.
• what are the functions of the internal plasma membranes


  Control entry and exit from organelles. Separate organelles from cytoplasm, so metabolic reactions can occur. Provide internal transport. Isolate enzymes, that could cause damage. Provide surfaces for reactions to occur.
• What is meant by membrane fluidity

  How much the components of the membrane (phospholipids, proteins etc)

  move around laterally.
• what factors can affect membrane fluidity 


  Increased temperatures make the membrane more fluid.Decreases cholesterol content makes the membrane more fluid.

  Increased number of unsaturated fatty acids in the phospholipids make the membrane more fluid.