BIOLOGY: DIFFUSION AND THE CELL MEMBRANE

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BIOLOGY DIFFUSION AND THE CELL MEMBRANE

• I. THE PLASMA MEMBRANE CONTROLS WHAT GOES IN
  AND OUT OF THE CELLS (HOMEOSTASIS) OR IT WILL
  DIE.
• ONLY CERTAIN PARTICLES CAN PASS THROUGH this is
  called being SELECTIVELY PERMEABLE
• DIFFERENT TYPES OF CELLS LET IN DIFFERENT
  SUBSTANCES

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• The fluid mosaic model (above) shows that the
  proteins move and bounce like buoys within the
  fats.
• THE MORE UNSATURATED FATTY ACIDS IN A CELL
  MEMBRANE, THE MORE FLUID IT IS.
• Example Hooves of caribou dont freeze or get
  frost bite because they have more unsaturated
  fatty acids in their membranes.

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• CELL MEMBRANE STRUCTURE BILAYER (2 LAYERS) OF
  PHOSPHOLIPIDS WITH PROTEINS AND CHOLESTEROL
  EMBEDDED
• PHOSPHOLIPIDS 2 FATTY ACIDS (TAILS) WITH A
  GLYCEROL (HEAD)
• HEADS ARE WATER SOLUABLE
• HYDROPHILIC
• TAILS ARE WATER INSOLUABLE HYDROPHOBIC
• So therefore the bottom layer is inverted and the
  tails face each other.

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• 2. CHOLESTEROL IMPORTANT IN MEMBRANE GIVES
  STRENGTH AND RIGIDITY TO MEMBRANE. FOUND BETWEEN
  FATS.
• 3. PROTEINS CARRIES OUT MOST OF THE FUNCTIONS
  OF THE MEMBRANE
• TYPE 1
• INTEGRAL (Carrier) GO ALL THE WAY THROUGH THE
  MEMBRANE
• JOB OF CARRIER PROTEINS DETERMINE WHAT SHOULD
  PASS INTO THE CELL.

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2 types of integral proteins

• 1. Carrier protein Changes shape to allow a
  substance through
• 2. Channel protein Always has an open slide to
  allow small substances with a specific shape in.

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TYPE TWO PERIPHERAL

• LOCATED ONLY HALF WAY THROUGH THE FAT LAYER
• JOB OF PERIPHERAL PROTEINS
• MARKER
• IDENTIFICATION (TYPE OF CELL)

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CELLULAR TRANSPORT

• VOCABULARY

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• CELLULAR TRANSPORT
• DIFFUSION Movement
• of particles from higher
• concentration to lower
• concentration across a
• membrane
• CONTINUOUS MOVEMENT
• UNTIL DYNAMIC EQUILIB-
• RIUM which is equal amounts
• of a substance on either side.

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• OSMOSIS DIFFUSION OF WATER
• Note that diffusion and osmosis are very
  similardiffusion is the movement of ANY
  substance across a membrane while osmosis is the
  movement specifically of WATER across a membrane.
• Reverse Osmosis is a term you have heard of in
  purifying water. The water solution is forced
  through a membrane (filter) to be cleaned of
  particles. The water crossing the membrane gives
  it the osmosis part and the forcing of the
  soltion across the membrane give it the reverse
  as it isnt natural but requires energy.

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TYPES OF SOLUTIONS

• Keep in mind the solution around your cells
  would be your blood.

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3 TYPES OF SOLUTIONS (blood) AROUND A CELL

• 1. ISOTONIC THE CONCENTRATION OF DISSOLVED
  SUBSTANCES AND WATER IS THE SAME ON BOTH SIDES OF
  MEMBRANE
• WATER MOLECULES STILL MOVE, BUT NOT ALL
  IN ONE DIRECTION DYNAMIC EQUILIBRIUM

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2. HYPOTONIC SOLUTION WHERE CONC. OF DISSOLVED
SUBS. LOWER THAN IN THE CELL

• WATER MOVES INTO THE CELL AND CELL SWELLS
  AND INTERNAL PRESSURE (TURGOR PRESSURE) INCREASES
• If turgor pressure increases so much the cell
  could burst. The plant cell uses the cell wall
  to prevent this bursting. For animal cells, we
  have the

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• CONTRACTILE VACUOLES (animal only cells)-
  COLLECT EXCESS WATER AND EXCRETE IT SO CELL
  DOESNT BURST

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3. HYPERTONIC SOLUTION WHERE CONC. OF
DISSOLVED SUBSTANCE IS HIGHER OUTSIDE THAN IN THE
CELL

• THIS HAS THE WATER LEAVING THE CELL SO IT SHRINKS
• This shrinking is called PLASMOLYSIS.
• PLASMOLYSIS is the drop of turgor pressure
  because water is leaving the cell. An example of
  this is wilting of a plant. The cells have less
  water so they are smaller and cannot hold up the
  stem and leaves as usual. Water your plant and
  the wilting (plasmolysis) goes away.

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3 solutions illustrated
Hypotonic Isotonic
Hypertonic
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TYPES OF TRANSPORT

• Compare the three types of cellular
  tranpsportation

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1. PASSIVE TRANSPORT

• THIS REQUIRES NO ENERGY TO MOVE SUBSTANCE ACROSS
  MEMBRANE DIFFUSION (move from high to low
  conc.)
• LIPID BILAYER KEEPS MOST SUBSTANCES OUT BECAUSE
  THEYRE REPELLED OR TOO LARGE
• WATER, OXYGEN, NITROGEN, CARBON DIOXIDE AND A FEW
  OTHER SMALL NONPOLAR MOLECULES CAN DIFFUSE
  DIRECTLY ACROSS THE MEMBRANE

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• FACILITATED DIFFUSION A substance travels from
  HIGH concentration to LOW concentration but goes
  through an integral protein instead of the fats
  due to its size. This is a type of passive
  transport. Uses some energy.

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2. ACTIVE TRANSPORT

• A substance moves from LOW concentration to HIGH
  concentration. This goes AGAINST CONC. GRADIENT
  and uses a great deal of ENERGY.

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Think about it

• There is a hill. Is it easier to roll DOWN the
  hill or roll UP the hill? Rolling DOWN the hill
  is going from high to low concentrationnot
  needing a lot of energy so basically this is
  passive transport. Going UP the hill takes
  energy and you are going from a low point to a
  high pointactive transport.

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2 types of active transport

• 1. ENDOCYTOSIS (phagocytosis) CELL SURROUNDS
  THE PARTICLES - DOESNT PASS THROUGH CELL
  MEMBRANE

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• 2. EXOCYTOSIS RELEASE OF WASTES FROM CELL
  VACUOLE.