Transcript Chapter 4 The Cell and it`s Environment

The cells environment
• 1. All cells live in a fluid environment.
– Fluid = moist or water filled.
• 2. Cells must obtain nutrients from the
outside and release substances into their
moist environment.
Cell membrane and transport
Plasma Membrane
• Plasma membrane- the outer boundary
of a cell.
• Gatekeeper - the plasma membrane
prevents certain materials from entering
the cell and allows certain materials to
pass into the cell.
Selectively permeable membrane
• Selectively permeable membranemembrane allows certain structures to pass
into and out of the cell while keeping others
inside or outside of the cell.
– Ex. Tea bag.
• SPM- maintains the organization of the cell.
Lipid Bilayer
• Lipid Bilayer- makes up the plasma
membrane.
– Made up of two layers of phospholipids.
• Phospholipid - composed of a phosphate
head and a fatty acid tail
Phospholipid bilayer
• Hydrophilic head - the phosphorous head is
attracted to water.
• Hydrophobic tails - the fatty acid tails are
“afraid” of water.
• Results in a two layered (bilayer) membrane
Membrane Proteins
• Proteins are scattered about the plasma
membrane.
• Proteins serve as a door in which large
molecules can pass through the membrane.
• Cholesterol - (lipid) provides rigidity to the
cells membrane.
Fluid Mosaic Model
• Fluid mosaic model - model for the
structure of a plasma membrane in which
the membrane is a phospholipid bilayer
with proteins embedded within it.
– Ex. Tile floor
• fig 4-8
page 95
Membrane function
• Membranes are selectively permeable.
• Random movement - “In nature, there is a
tendency toward randomness. Energy is
required for nonrandomness.”
• Diffusion - random movements of ions and
other particles.
Diffusion
• 1. Results in movement of particles from a
region of greater concentration to a region
of lesser concentration.
• Dynamic equilibrium - condition in which
there is a continuous movement of
molecules but no overall change.
Osmosis
• Osmosis - the diffusion of water into and out of
cells across a selectively permeable membrane.
• Osmotic balance - occurs when the movement of
water into and out of the cell is equal.
– Blood cells
– plant cells
Types of Solutions
• Isotonic Solution – equal concentration of
solution and the cell. (Osmotic balance)
• Hypotonic Solution – Greater water
concentration outside the cell than inside
the cell (The cell bursts)
• Hypertonic Solution – Greater water
concentration inside the cell than outside
the cell (The cell shrinks)
Passive transport
• Passive transport - the cell plays no active
role and does no work in moving the
particles. Requires no Energy
• 1. Water
• 2. Lipids
• 3. Substance soluble in lipids
• 4. very small particles
Types of passive transport
• 1. Osmosis
• 2. Diffusion
• 3. Facilitated Diffusion
Facilitated Diffusion
• Many particles needed by cells must have
some help getting across the cell membrane.
• Facilitated diffusion - the use of transport
proteins to aid the passage of materials
across the plasma membrane
Transport proteins
• 1. Channel proteins - simplest type. These
are simply called pores. These serve as
channels that allow ions to pass through.
– Depend on size and charge.
• Even if an ion is small enough to pass
through the pore, it may be prevented by its
charge.
Transport proteins (continued)
• Carrier proteins or GATE Proteins- more
complex, works like a gate.
• 1. A particle on one side of a membrane attaches
to a protein
• 2. The protein changes shape
• 3. Allows the desired particle to pass into or out of
the cell.
• 4. When the signal molecule is released, the gate
closes
Active Transport
• Active transport - the moving of particles
from a region of lesser concentration to a
region of greater concentration.
– Requires Energy
• Pumps - transport proteins used to move a
particle through a plasma membrane.
– Requires chemical energy to alter the shape of
the protein.
Active Transport (continued)
• Examples of Active Transport
• 1. Marine Fish - actively pump out salt even
though the concentration of salt is more
outside their body.
Other methods of entering and
exiting the cell.
• 1. Endocytosis - the process by which the
mambrane engulfs and takes in a substance.
– Phagocytosis - solid particles are ingested
– Pinocytosis - liquid particles are ingested.
• 2. Exocytosis - cell products or wastes are
released to the surroundings
• see figs 4-17, 18, 19