compendium 5

• Fluid Mosaic Model

  
  

  cell membrane is not a rigid structure but is fluid (constantly moving) in nature and can change its shape and, to some extent, its composition over time.

  For instance, the nature of the phospholipid molecules are influenced by diet and membrane proteins come and go depending on the metabolic state of the cell
• The cell membrane can be described as the 'gate keeper of the cell'. What does this mean?

  The cell membrane is a highly selective membrane.It controls what can pass across in, either into or out of the cell.The cell membrane determines what substances pass, in what amounts and at what time
• Functions of the Fluid Mosaic Model

  · Boundary of cell - encloses and supports cell contents

  · Separates intracellular vs. extracellular materials

  · Allows to control what enters and leaves the cell

  · Attaches cells to other cells and to the surrounding matrix

  · Cells communicate with their environment through their cell membrane

  · Determines what can move into and out of the cell (selectively permeable)

  o intra- and extracellular environment is different

  · Difference in charge across membrane - membrane potential (Compendium 10)

  · Structure - fluid mosaic model
• Structure of phospholipid bilayer

  · Hydrophilic Head - Water loving

  
  

  · Hydrophobic Tail - Water hating

  
  

  · Cholesterol

  
  

  · Proteins:

  o Inserted in the lipid bilayer

  o Peripheral or integral

  o Many involved in transporting molecules across the cell membrane.....Eg, Channel proteins, carrier proteins, ATP powered pumps

  o Proteins in membrane

  - Glycoprotein - Made up of Amino acids and a sugar chain is added to it in the Golgi body.

  - Membrane Channel Protein

  - Integral Protein
• What substances need to move into and out of a typical cell?

  Ions, water, proteins, nutrients, waste products, macromolecules, gases such as oxygen and carbon dioxide, cholesterol
• What are the roles of proteins in the cell membrane?

  The membrane proteins help the cell to "communicate" with its environment. Some of these proteins are enzymes, or ion channels allowing certain ions to move through the cell membrane, or carrier molecules necessary for the transport of molecules across the cell membrane and or essential for cell-to-cell recognition
• List the ways that ions and molecules can pass through the cell membrane.

  Osmosis

  
  

  Diffusion

  
  

  Facilitated Diffusion

  
  

  Active Transport
• Explain how water travels across the cell membrane via osmosis


  Water travels across the cell membrane through an aquaporin.

  A selectively permeable membrane lets water to pass through but any solutes dissolved in the water

  If the beaker contains distilled water (water with no solutes), water molecules will move back and forth across the membrane at the same rate and the water level stays the same on both sides of the membrane
• What is Diffusion and examples of substances that travel via diffusion

  Molecules move from an area of higher concentration to an area of lower concentration

  · Continues until the molecules have evenly distributed themselves throughout the solution

  
  

  Oxygen, CO2 and lipids such as hormones
• How substances diffuse through cell membranes

  1. Certain specific non- lipid soluble molecules or ions diffuse through membrane channels

  a. Moves through a protein (not diffusion), hence, most likely a water-soluble molecule.

  2. Other non-lipid soluble molecules, for which membrane channels are not present, can't enter the cell

  a. Semi permeable membrane = only allows certain molecules to travel across

  3. Lipid soluble molecules diffuse directly though the plasma membrane (miscible with lipid)

  a. Moves from an area of high concentration to an area of low concentration
• What is Facilitated Diffusion and examples of substances that travel via this method

  Carrier proteins buying two substances and move them across the plasma membrane and all ions move through the polls of membrane channels (No ATP used = passive).

  
  

  Eg. Glucose moves by facilitated diffusion into muscle cells and adipocytes.
• What is Active Transport and provide an example

  ATP-powered pumps buying two substances and move them across the plasma membrane and.

  
  

  Eg. Sodium Potassium Pump
• Describe the function of Carrier Proteins

  Also called transporters

  
  

  · Integral proteins that move ions from one side of membrane to the other

  
  

  · Carrier proteins have specific binding sites that are specific to certain molecules. Protein changes shape to transport ions or molecules.

  · When the molecule binds it forms a conformational change = the carrier protein shuts on one side and opens on the other to release the molecule to the other side. The protein will the go back to its original shape.

  o Uniporters, symporters, antiporters

  
  

  Uniporters: Transport 1 molecule.

  
  

  Symporters: Transport 2 molecules in the same direction across the membrane.

  
  

  Antiporter: Carries 2 molecules in opposite directions across the cell membrane.
• Describe function of Channel Proteins

  From passage ways to the plasma membrane, allowing specific items or molecules to enter or exit the cell; maybe leak or gated.

  
  

  Non-gated ion channels

  · Gates are always open allowing for free flow of ions

  
  

  Gated ion channels

  · Opened or closed by certain stimuli

  · The protein will receive messages that cause it to open or close

  · Eg. Sodium and potassium channels in a nerve cell
• Describe the function of ATP Powered Transport/Pumps

  · Requires energy in the form of ATP

  · Transports substances AGAINST their concentration gradient, so the cell can accumulate substances

  o Eg. Sodium potassium pump
• Integral membrane proteins


  Proteins that are at least partially embedded in the plasma membrane
• Peripheral membrane proteins


  Attached to either the inner or outer surfaces of the lipid bilayer.
• Explain the process of osmosis and concentration gradients in controlling the movement of water across the cell membrane.

  Water will generally move from a solution with a high concentration of free water molecules (low concentration of solutes) to a solution with a low concentration of free water molecules (high concentration of solutes). When there is no difference in the concentration of the solutes between the inside and outside of a cell, there is no net movement of water. In this case, the solutions are said to be 'isotonic' with respect to each other.
• Tonicity


  A relative measure (like bigger or smaller), and can only be determined when two fluids are separated by a water-permeable membrane, like a cell membrane.
• Osmolarity


  Measurement of a solutions "pull" on water.

  
  

  Measured in Osmoles/L or mOsmoles/L.

  
  

  Weak solutions will have a *low osmolarity value.

  
  

  More concentrated solutions will have a higher osmolarity value.
• Hypotonic Solution


  A cell in a solution that has a lower osmolarity than inside the cell.

  <290 mOsmol/L.

  
  

  Intracellular solution pulls water into the cell.

  
  

  Cell swells (lysis) and bursts.
• Hypertonic Solution


  A cell in a solution that has a higher osmolarity than inside the cell.

  >290 mOsmol/L.

  
  

  Extracellular solution pulls water out of the cell.

  
  

  Cell loses water and shrinks (crenation).
• Isotonic Solution


  When a cell is placed in a solution that has the same osmolarity as the inside of the cell, the solution is called isotonic

  Approximately 290 mOsmol/L.

  
  

  Water will move between the intracellular and extracellular fluid at equal rates (no net movement of water)
• What is metabolism and describe the 2 types.

  Total of all chemical processes that occur in body.

  
  

  Anabolism

  = Two or more reactants chemically combine to form a new and laoxirger product

  o Chemical bonds made, energy stored in the bonds

  o Responsible for growth, maintenance and repair

  o Produce chemicals characteristic of life: carbohydrates, proteins, lipids, and nucleic acids

  
  

  Catabolism

  = A large reactant is broken down to form smaller products

  o Chemical bonds broken; energy released

  o Energy in carbohydrates, lipids, proteins is used to produce energy which drives anabolic reactions, e.g. active cell membrane transport, muscle contraction, protein synthesis
• Chemical Energy and ATP


  Energy stored in chemical bonds.Breaking chemical bonds releases energy.

  When glucose is broken down, this energy can be used to combine Adenosine diphosphate (ADP) with an inorganic phosphate molecule to make ATP
• Potential energy and ATP

  Little energy stored in each ATP = Easier for cell to access than large energy stored in nutrient molecules.

  
  

  Energy = ATP broken down into ADP.

  
  

  Energy used to:

  - Make new proteins.

  - Repair damaged cell membranes.

  - Power active transport (e.g, sodium-potassium pump).
• Cellular Respiration


  Respiration is the process that breaks chemical bonds in food to produce energy which is stored as ATP

  
  

  Three main stages

  1. Glycolysis (Occurs in the cytoplasm)

  2. Citric acid cycle (Occurs in the mitochondrial matrix)

  3. Electron transport change/oxidative phosphorylation (Occurs in the Inner mitochondrial membrane)
• Describe the main stages of glycolysis and name its products.

  Occurs in the cytoplasm.

  
  

  Uses 2x ATP to convert: 1x Glucose (6 carbon sugar) into 2x Pyruvic Acid (3 carbon molecule), 4x ATP and 2x NADHNet.

  
  

  ATP production: 2x ATP.Anaerobic (does not require O2).

  
  

  Oxygen available: Pyruvic Acidmoves into 2nd stage, the Citric Acid Cycle.

  
  

  Oxygen unavailable: Pyruvic Acid converted to Lactic Acid.
• Glycolysis starting and ending products

  Starting: 1x Glucose.

  
  

  Ending: 2x Pyruvic Acid, 2x ATP, 2x NADH.
• Describe the main stages of the citric acid cycle (Krebs cycle) and name its products.

  Occurs in the mitochondrial matrix.

  
  

  Cycle consists of 2 turns.

  
  

  Acetyl CoA Production (Pre-Cycle)

  - Pyruvic Acid converted to acetyl CoA (2 carbon molecule).

  - Produces 1x acetyl CoA, 1x NADH and 1x CO2.

  - Happens twice for each glucose.

  
  

  Cycle Begins

  - Acetyl CoA joins to 4 carbonmolecule to make Citrate (6 carbonmolecule).

  - Citrate goes through series of reactions, losing 2 carbons as 2x CO2 to end up back as a 4 carbon molecule.

  - Cycle uses this 4 carbon to start again.

  - Each turn produces: 1x ATP, 3x NADH, 1x FADH2, and 2x CO2.

  - Cycle consists of 2 turns for each glucose.

  Producing 2x ATP, 6 NADH, 2x FADH2 and 4x CO2.
• Acetyl CoA Production - Citric Acid Cycle (Krebs Cycle) - Starting and Ending Products.

  Starting: 2x Pyruvic Acid.

  Ending: 2x Acetyl CoA, 2x NADH and 2x CO2.
• Citric Acid Cycle (Krebs Cycle) - Starting and Ending Products.

  Starting: 2x Acetyl CoA

  Ending: 2x ATP, 6x NADH, 2x FADH2 and 4x CO2.
• What are NADH and FADH2?

  Electron carrier molecules.

  NAD+ = Nicotinamide Adenine Dinucleotide.

  FAD+ = Flavin Adenine Dinucleotide.

  
  

  Become NADH and FADH2 after receiving electrons.

  Collect the electrons and transport them to the electron transport chain in the inner mitochondrial membrane, donating them to membrane carriers.
• Briefly explain oxidative phosphorylation (electron transport chain) and how ATP is produced in the process.

  Previously produced NADH and FADH2 travel into inner mitochondrial membrane.

  
  

  NADH and FADH2 then donate their electrons to the first receptor (channel protein) in the inner mitochondrial compartment.

  
  

  The channel proteins use this energy from electron transfer, to pump H+ from the inner, to the outer compartment.

  
  

  The released H+ in the outer compartment, results in a high concentration of H+ in the outer when compared to the inner.

  
  

  The H+ then diffuse through the ATP synthase channel protein, into the lower concentration in the inner mitochondrial compartment.

  
  

  The movement of H+ from the outer to the inner is harnessed by ATP synthase to add a phosphate group to ADP, making it ATP.

  
  

  The H+ and an O2 combine to make H2O.A carrier protein transports ATP out of the cell, exchanging it for a fresh ADP.

  
  

  A different carrier protein transports a phosphate group into the inner membrane, ready for the production of more ATP.
• Oxidative Phosphorylation (electron transport chain) - Net ATP production.

  32-34 ATP
• Adenosine triphosphate (ATP)

  An adenosine molecule with three attached phosphate molecules. When ATP is broken down 'energy' is released and used by cells and tissues to function.
• Citric acid cycle

  A series of chemical reactions occurring inside the mitochondria, which convert pyruvic acid into ATP and electron carrier molecules.
• Diffusion

  The movement of solutes (e.g. salt) from an area of high concentration to an area of low concentration. No ATP is used.
• Facilitated diffusion


  The movement of a solute (e.g. glucose) across a plasma membrane via the use of a carrier/channel protein. No ATP is used.
• Glucose


  A simple sugar molecule (monosaccharide). Glucose is used by the body to make ATP or stored as glycogen for future use.