Membranes and Transport

• Selectively Permeable


  Some substances can pass through the membrane, while other substances cannot
• Substances that can pass through the membrane easily

  • Water
  • Sugar
  • Oxygen
  • Steroid Hormones
  • Substances needed for signalling other cells
  • Hydrophobic molecules
• Passive Transport


  Doesn't require energy for substances like water and oxygen to move through the plasma membrane. Under this transport are movement called Diffusion and Osmosis.
• Diffusion


  When molecules such as oxygen and water gets crowded in spaces they tend to move to less crowded space
• Osmosis


  • Diffusion of solvent molecules (water) through a selectively permeable membrane from high water potential region to low water potential region to equalize solute concentrations
  • it is also how cells regulate water content
• Solvent molecules


  Water or Liquid substance with dissolved materials
• Hypertonic


  If the concentration of a solution inside the cell is higher than the outside of the cell

  
  

  Example:

  the water molecules moves outside of the blood cell causing it to shrink
• Hypotonic


  If the concentration of a solution inside the cell is lower than the outside of the cell

  
  

  Example:

  the water molecules moves inside of the blood cell causing it to explode
• Facilitated Diffusion


  How to permeate the cell membrane without so much effort with the use of transport protein
• Cell membranes


  • Made up of phospholipids with a hydrophilic (water loving) outside and hydrophobic (water hating) inside
• Aquaporins


  Protein channels specifically made for water based solutions, with the ability to pass through 3 billion water molecules per second
• Active Transport


  The movement of molecules or ions across the cell membrane from region of low concentration to a region of high concentration or vice versa (against the concentration gradient)

  
  

  this transport requires energy since the movement of the molecules are against the concentration gradient
• Types of Active Transport

  • Primary Transport
  • Secondary Transport
  • Bulk Transport
• Primary Transport


  Uses ATP also known as Adenosine Tri-phosphate as the energy source, e.g. Sodium-Potassium Pump
• Secondary Transport


  Powered by an established electrochemical gradient of the driving ion.

  
  

  e.g. Na+-Glucose Symporter, H+-Glucose Symporter
• Bulk Transport


  Exocytosis and Endocytosis using Vesicles
• ATP (Adenosine Tri-phosphate)


  The energy currency of the cell, required for Active Transport
• How does the Sodium-Potassium Pump works?

  1. Attachment of 3 sodium ions from the inside of the cell
  2. Hydrolysis of ATP (Converting ATP to ADP)
  3. Burst of excitement from the breakage of Covalent bond of phosphate molecule triggers a change in the shape of the protein pump (like a door) it will open to the extracellular side
  4. It will Release the 3 molecules of sodium ion and will attach 2 of potassium ions in the protein pump
  5. The pump will dephosphorylates it self, thus returning to its original shape
  6. It will Release the 2 potassium ions, and the process will start again
• The Active Transport works against 2 gradients at the same time: the Concentration gradient and the Electrochemical gradient
• Electrochemical gradient


  The difference of electrical charge on either side of the membrane
• Bulk Transport


  Cytosis or vesicular Transport done by using Vesicles
• Exocytosis


  When Vesicles transport substances outside of the cell, the vesicle will merge with the phospholipid bilayer thus releasing the substance outside
• Endocytosis


  When Vesicles transport substances inside of the cell, by engulfing substances into vesicles formed from the cell membrane
• Types of Endocytosis

  
  

  • Phagocytosis (bacterium engulfing food particles)
  • Pinocytosis (cell taking fluid from intestine)
  • Receptor-mediated endocytosis
• Mediated Transport


  Includes 'Carriers' and 'Channels' which are both Integral Membrane Proteins

  • Channels only flow a single type of molecule in one direction
  • Carriers can flow two types of molecules in the opposite or same direction at the same time
• Sodium-Potassium Pump


  most cell have this channel protein but they are more vital to the cells that need lots of energy such as muscle cells and brain cells
• How is the Sodium-Potassium pump discovered?

  it was discovered during the 1950's by Jens Christian Skou, a doctor that studies how anesthetics works on nerve cells. He noticed that there are proteins in the cell membranes that pumps out the sodium out of the cell, he observed this pump by studying 25,000 crabs by boiling them and extracting their neuro-fibers.
• How does the Na+-Glucose works? (Secondary Transport)

  Secondary Active Transport
Substance like Glucose needs to be transported from region of low concentration to a high concentration, this requires energy since the glucose is being transported against the concentrated gradient

  1. The driving ion (Na+) will move down its electrochemical gradient
  2. The driven ion (Glucose) against its gradient
  3. The free energy for secondary transport is from the concentration gradient of the driving ion. This process is similar to hitchhiking

  
• what are the types of Transport Protein that are categorized by the number and direction of molecules being transported

  A) Uniporter

  B) Symporter

  C) antiporter

  
• What is a Channel Protein?

  With the characteristic of the cell membrane water molecules and other substances have a hard time passing through the layer but with the help of Channel Proteins, that are passage ways that allows the water molecules and other ions to pass through. The channel protein has hydrophilic inside that draws the water through.
• The water or solution of concentration is always seeking the Isotonic concentration of solution, when the water concentration is equal on both sides of the cells (inside or outside). When water solutions diffuses and attempts to be isotonic it is called as "moving across the concentration gradient". In this process, water moves from an area of higher concentration to an area of lower concentration until equilibrium is reached.