Cell Membrane

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Cell Membrane
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Cell Membranes

• Phospholipid
• bi-layer

The main portion of the cell membrane is
constructed of a phospholipid bi-layer. There
are two layers that are mirror images of each
other.
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Phospholipids

• Each phospholipid is made of two parts
• The head is a PHOSPHATE molecule (PO4)
• The Phosphate is polar which makes it
  HYDROPHILLIC (attracted to water).
• The tails are made of FATTY ACIDS.
• The Fatty Acid tails are non-polar which make it
  HYDROPHOBIC (repelled by water)

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Cell Membranes - Proteins
Receptor proteins enables cell to sense
surroundings by binding to substances. Transport
proteins moves substances through the bi-layer
that cannot do so themselves.
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Cell Membranes - Carbs
Surface markers chains of carbohydrates that
identify what type of cell it is.
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Homeostasis

• The Cell Membrane plays an important role in
  homeostasis by managing the amount of water is in
  the cell.

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Selectively Permeable

• The Cell Membrane SELECTIVELY PERMEABLE. This
  means that only some items are able to pass
  through the membrane.

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SELECTIVELY PERMEABLE(Semi-permeable)
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Passive Transport

• Passive transport is when a cell transports
  things across the membrane without energy.
• Things always move from high concentration to low
  concentration when no energy is used.

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Diffusion Across a Space

• Type of passive transport
• Molecules move automatically down the
  concentration gradient from an area of higher
  concentration (more particles) to an area of
  lower concentration (less particles).
• Examples Blue dye in a beaker demo
• someone making popcorn or grilling (smell)
• strong perfume
• bad smell in room

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Concentration Gradient

• A difference in the
• concentration of a
• substance
• across a
• distance

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Diffusion Through a Cell Membrane
The particles move until they are evenly
distributed, which is called equilibrium
semipermeable
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Osmosis

• The diffusion of water molecules across a
  selectively permeable membrane is known as osmosis

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Diffusion of H2O Across A Membrane
High H2O potentialLow solute concentration
Low H2O potentialHigh solute concentration
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Osmosis

• If a cell has more particles (like sugar) inside
  the cell than outside, this means that there is a
  higher concentration of water outside than inside
• Remember that osmosis is the movement of WATER
  across a membrane
• Also remember that in diffusion, particles move
  from areas of HIGHER CONCENTRATION TO LOWER
  CONCENTRATION

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Osmosis

• Therefore the water is going to move INSIDE the
  cell until equilibrium is reached
• This cell is said to be in a hypotonic solution.
  Hypotonic solution has less particles outside
  than inside the cell.
• As water moves in, the cell will get bigger.

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Cell in Hypotonic Solution
10 NaCL90 H2O
CELL
20 NaCL 80 H2O
What is the direction of water movement?
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Osmosis

• If the concentration of particles is higher
  outside of a cell than inside, then the
  concentration of water is higher inside and the
  water will move out of the cell until equilibrium
  is reached.
• This cell is said to be in a hypertonic solution
  where there is more particles outside of the
  cell.
• As water moves out of the cell, the cell will
  shrink.

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Cell in Hypertonic Solution
15 NaCL85 H2O
ENVIRONMENT
CELL
5 NaCL 95 H2O
What is the direction of water movement?
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Osmosis

• If the concentration of particles outside the
  cell are the same as inside of the cell, water
  will not move in or out.
• A cell in this case is said to be in an isotonic
  solution where the concentration of particles is
  the same on both sides of the cell membrane.

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Cell in Isotonic Solution
10 NaCL90 H2O
ENVIRONMENT
CELL
NO NET MOVEMENT
10 NaCL 90 H2O
What is the direction of water movement?
equilibrium
The cell is at _______________.
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Osmosis
Type of Solution Particle concentration in solution Particle concentration in cytoplasm Where is there more water? Which way will water move?
Hypotonic
Hypertonic
Isotonic
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Passive Transport

• Simple Facilitated Diffusion
• Doesnt require energy
• Moves high to low concentration
• Example Simple-O2. H2O, CO2Facilitated- amino
  acids, glucose

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Active Transport

• Requires energy or ATP
• Moves materials from LOW to HIGH concentration
• AGAINST concentration gradient

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Moving the Big Stuff
Exocytosis- moving things out.
Molecules are moved out of the cell by vesicles
that fuse with the plasma membrane.
This is how many hormones are secreted and how
nerve cells communicate with one another.
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Exocytosis
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Moving the Big Stuff
Large molecules move materials into the cell by
one of three forms of endocytosis.
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Moving Ions through pumps

• The Sodium/Potassium Pump