Plasma membranes and transport - Class notes 5 Flashcards
What are plasma membranes?
> Plasma membranes (e.g., cell membranes) are membranes that surround not only cells but the structures (called organelles) within cells.
Plasma membranes are common to all living things - animals, plants, fungi, bacteria and other single-celled organisms.
What is the basic membrane structure?
see diagram.
what is the plasma membrane structure including the transport systems?
SEE DIAGRAM
What is happening at the number 1 spot on the plasma membrane diagram?
Simple diffusion. This process involves the movement of substances from an area of high concentration to an area of low concentration through the phospholipid layer. Diffusion requires no additional energy. With respect to gases, the movement is from an area of high partial pressure to an area of low partial pressure. Only small (uncharged) molecules (e.g., oxygen and carbon dioxide) or lipid-based molecules (e.g., some hormones like testosterone and oestrogen) can pass across phospholipid region of the membrane via simple diffusion.
What is happening at the number 2 spot on the plasma membrane diagram?
Facillitated diffusion. This process is similar in principle to that of simple diffusion. However, facilitated diffusion involves a protein channel or protein carrier molecule. these proteins assist (i.e., facillitate) with the diffusion process. Facilitated diffusion is required for larger molecules (e.g., glucose and amino acids) or for substances that carry a charge (e.g., Na+, Ca2+ and k+).
What is happening at the number 3 spot on the plasma membrane diagram?
active transport. active transport moves substances against their concentration gradient. in other words, substances are moved from an area of low concentration to an area of high concentration. This process requires energy - in the form of ATP. Active transport can be related to the idea of ‘pumping water uphill’. Active transport typically involves transport of ions, such as Na+, Ca2+ and K+. Active transport is used to maintain high concentrations of ions on one side of a membrane or the other, e.g., necessary for nerve and muscle function.
What is happening at the number 4 spot on the plasma membrane diagram?
Osmosis. Osmosis is really a form of simple or facillitated diffusion But it involves water.
How is water said to move?
Either: ‘Water moves from an area of high free water concentration to an area of low free water concentration’
Or: ‘water moves from a high water potential to a low water potential’
OR: ‘water moves from a low solute concentration to a high solute concentration’.
Know diagram for osmosis and understand it.
See diagram.
What is water potential?
Water potential is defined ad the tendency for water to leave one system in order to enter another. Ahigh water potential, therefore, means a high tendency to leave and go elsewhere. Systems with high water potentials have few or no solutes (hence are dilute solutions) OR are under high pressure (which mostly applies to plant cells).
What is the symbol for water potential?
little trident thing = psi, measured in kPA
what is the water potential scale?
0 kPa = high water potential - zero solutes
-150 onwards kPa = low water potential and high solute concentrations
Where do water molecules move from?
Water molecules move from a less negative water potential to a more negative water potential = water molecules move from a high waterpotential to a low water potential. (know diagram)
What is the function of plasma membranes?
to regulate the movement of substances in and out of cells (or in and out of organelles) however, the membrane serves other functions as will be seen.
What is the function of glycoproteins and glycolipids?
> Receptor sites for chemical messengers (e.g., hormones)
> cell recognition
