biological membranes

• all cell and organelle membranes are composed of a phospholipid bilayer
• Cell membranes provide a partially permeable membrane, they are also the site of chemical reactions and have a role in cell communications.
• the phospholipids in a phospholipid bilayer align as such because the hydrophillic heads are attracted to water and the hydrophobic tails are repelled by water.
• Proteins within the cell surface membrane can be extrinsic and intrinsic
• what does it mean if a protein is intrinsic?

  It passes through the whole membrane
• What does is mean if a protein is extrinsic?

  The protein only exists on a half of the membrane
• extrinsic proteins provide mechanical support,or they make glycoproteins and glycolipids. The functions of these is cell recognition like receptor
• The intrinsic proteins are called carrier or channel proteins- they are involved in the transport of molecules across the membrane
• Protein channels form tubes that fill with water to allow water soluble ions to diffuse whereas the carrier proteins will bind with other ions and larger molecules such as glucose and amino acids and change shape to transport them to the other side of the membrane.
• Cholesterol is present in some membranes which restricts the lateral movement of other molecules in the membrane. this is useful as it make sthe membrane less fluid at high temperatures and prevents water and other dissolved ions from leaking out out of the cells.
• high temperatures increase the kinetic energy of the phospholipids so that they can move even more. This increases the fluidity ofthe memrbane which increases the permeability and the strucutre cans tart to break. This makes it easier for particles to move across the membrane. Additionally, high temperatures can denature carrier and channel proteins in the membrane
• Organic solvents, like alcohols, dissolve the phospholipid bilayers in membranes. This damage causes the fluidity of the membrane to increase and become more permeable.
• What is simple diffusion?

  The net movement of molecules from an area of High concentration to an area of low concentration until an equilibrium is reached- no ATP is needed. In order for molecules to diffuse across a membrane they must be small and membrane soluble.
• what is facilitated diffusion?

  A passive process down the concentration gradient through proteins. The movement of ions and polar molecules which cant simply diffuse use protein channels and carrier proteins to be transported across the membrane.
• what is osmosis?

  The movement of water from an area of high water potential to an area of lower water potential across a partially permeable membrane.
• what does it mean if a solution has a low water potential?

  it is more concentrated in terms of the amount of solute that is in there.
• what is an isotonic solution?

  Where the water potential of the solution is the same in the solution and the cell within the solution
• what is a hypotonic solution?

  When the water potential of a solution is more positive, closer to zero, than the cell.
• What is a hypertonic solution?

  when the water potential of a solution is more negative than the cell
• what is active transport?

  The movement of molecules and ions from an area of lower concentration to an area of higher concentration, against a concentration gradient, using ATP and carrier protiens
• Why is active transport described as selective?

  As only certain molecules can bind to the receptor site on carrier proteins. ATP will only bind to the protein on the inside of the membrane and will be hydrolysed into ADP and Pi.
• When a molecule binds to the receptor site of a carrier protein, it changes shape and opens towards the inside of the protein- this allows the molecule to be released on the other side of the membrane
• Describe endocytosis?

  It is a type of active transport, the bulk transport of molecules into a cell. The cell surface membrane bends inwards around the molecule surrounding it to form a vesicle. The vesicle pinches off and moves within the cytoplasm. This requires ATP for the cell to engulf and change shape around the material
• What can endocytosis be classified as?

  Phagocytosis and Pinocytosis
• When is endocytosis described as phagocytosis?

  When a solid particle is being taken in
• When is endocytosis described as pinocytosis?

  When a liquid is being taken in
• describe the process of exocytosis?

  This is the bulk transport of molecules out of a cell. Vesicles move towards the cell surface membrane, they fuse with the membrane and the contents of the vesicles is released outside of the cell. This processes requires energy because ATP is needed to move the vesicle along the cytoskeleton