1.3 Membrane Structure and Functions

• does a solution of sugar have a water potential less or more than zero?

  it has a water potential of less than zero because the freedom of the water molecules are reduced because they are attracted to the solute molecules
• instead of concentration gradient what do we use instead?

  water potential gradient
• what happens to the water potential of water when you dissolve solute in it?

  the water potential lowers
• Pure water at normal atmospheric pressure is given a water potential of what?

  it is given a water potential of 0
• What determines that a solution has a low water potential

  A solution that has alot of dissolved substances and little water and not under pressure.
• What determines that a solution has a high water potential

  a solution that has alot of water and under pressure
• Define the term water potential..which is concentration..in cape terms


  The water potential of a solution is how much water the solution contains in relation to other substances and how much pressure is being applied.
• What other factor affects the rate of simple diffusion

  The permeability of the plasma membrane
• What three groups can protein channels be classified into ?

  Voltage-gated channels-These open and close in response to tiny changes in the voltage across a membrane

  mechanically gated channels-These respond to pressure

  ligand-gated channels- These respond to the attachment of a small signalling molecule-a ligand-that binds with the channel protein
• Explain how the difference between diffusion and facilitated diffusion affects the rate at which diffusion takes place

  If a cell has a limited amount of sodium ion channels , then there woud reach a point where diffusion cannot speed up even if the concentration of sodium ions were to increase

  Oxygen however can diffuse through any part of the phopholipid bilayer, therefore the rate of diffusion would increase of the concentration gradient increases because it isn't restricted.
• State one difference between diffusion and facilitated diffusion

  Diffusion-The molecules just move through the phospholipid bilayer

  Facilitated diffusion-The molecules or ions have to move through protein carrier molecules
• Can symports and antiports be involved in active transport

  Yes
• what is an antiport

  Transports two solutes in opposite directions (Na-K ATPase pump)
• what is a symport

  both molecules move in the same direction
• how does channel proteins allow ions to pass


  These proteins lie in the membrane stretching from one side to the other forming a hydrophilic channel through which ions can pass by diffusion. This also only happens if the molecules or ions happen to bump into the a channel.
• how does ions get through the plasma membrane

  They use facilitated diffusion. Cells provide for her Passage through the plasma membrane which aloe ions to pass through. They are provided by channel proteins.
• what two features of substance affects its ability to diffuse across a cell membrane

  1- Whether or not there's a charge on its molecule

  2- Its size
• Can molecules with an electric charge slip through the plasma membrane

  No. Only atoms like oxygen and carbon dioxide that has no electrical charge can easily slip through the phospholipid bilayer
• What are some active processes in the cell membrane

  Active transport
• What are some passive processes in the cell membrane

  diffusion,facilitated diffusion and osmosis.
• what is glycocalyx

  Portion of glycolipids and glycoproteins form an extensive sugary coat called glycolayx. Act like a molecular signal that enables cells to recognize on another./ Carbohydrate chains on the outside of proteins
• What are the sugar or carbohydrate chains known as

  Glycocalyx
• How are receptor sites important

  They are important in cell signaling when molecules from outside the cell bind with their specific receptors, bringing about changes within the cell.
• What is the function of the short sugar chains on phospholipids and proteins

  They function as sites where other specific molecules from outside the cell can bind to, hence reacting as receptor sites.
• Many proteins have short chains of _____ attached to their surface and are known as ___________ and ____________

  -Sugar

  -glycolipids and glycoproteins
• Name the 6 roles of protein and glycoproteins in cell membranes

  -Form channels through which hydrophilic substances can pass; the channels can be opened and closed.

  -Act as transporters that can move substances across the membrane up their concentration gradients, with the use of energy from ATP.

  -Act as receptor sites, allowing specific molecules from outside the cell, such as hormones, to bind with them and then set up responses within the cell.

  -Act as recognition sites, because their precise structure may be specific to a particular type of cell or to a particular individual (note: glycolipids also have this role).

  -Bind to proteins in neighbouring cell membranes, holding the cells together.

  -Act as enzymes.
• Name a role of cholesterol in the membrane

  -Helps to maintain the fluidity of the membrane, preventing it from becoming too stiff when temperatures are low, or too fluid when temperatures are high.
• Name 2 roles of phospholipids in the cell membrane

  -forms the bilayer which is the fundamental basis of the membrane in which all other components are embedded.

  -provides a barrier to water-soluble (hydrophilic) substances, such as Ions and molecules that carry a charge.
• Some proteins are attached to protein structures in the cytoplasm and are called what?

  They are called microfilaments and they make up a 'scaffolding' in the cell called the cytoskeleton.
• How do transmembrane protein provide a way for ions and other particles to pass

  They have hydrophilic parts lining a channel that runs right through the bilayer
• Is a transmembrane protein attracted to water

  It is amphipathic meaning that it has both hydrophobic and hydroplilic parts.
• proteins that span the entire membrane, usually reaching from one side to another are called what?

  Transmembrane proteins
• How can integral or Intrinsic proteins be removed? An why?

  This can only be removed by distrupting the membrane because unlike extrinsic proteins, these lie within the bilayer.
• What household item can remove the peripheral/Extrinsic proteins from the phospholipids. Explain why

  detergent. They can be removed because they do not penetrtae the lipid bilayer but simply is associate with the hydrophilic surfaces of the bilayer.
• In the membrane, what are the 2 groups that proteins are classified into

  Peripherial or Extrinsic proteins AND Integral and intrinsic proteins
• Are there protein molecules in cell membranes

  Yes there many different protein molecules and they are much larger than phospholipid molecules
• What causes the forming of the phospholipid bilayer

  water is contained both inside and outside of the cell, thus the hydrophilic parts of the bilayer would be attracted to the surrounding water, thus repelling the hydroplilic parts of the molecule to face inwards and away from the water.
• What is said of the heads and tails of the phospholipid bilayer in terms of their attraction to water

  The heads have a tiny charge which is attracted to water while their tails have no charge/Their heads are hydrophilic while their tails are hydrophobic
• All cell membranes have a double layer of molecules called what

  phospholipids in which many kinds of proteins are situated
• Can organelles inside cells have membranes?

  Yes they can and are usually bounded by a single membrane however there are others are bounded by double membranes like the nucleus, mitocondria and chloroplasts.