Download cell membrane ppt - Valhalla High School

Cell
Membrane
and
Transport
Mechanism
Cell Membrane
• Fluid Mosaic Model - proteins embedded
in a phospholipid bilayer.
Cell Membrane
• Phospholipid: 1 head and 2 tails
– Polar head attract water - hydrophilic
– Non-polar tails repel water -hydrophobic
Cell Membrane
• Bilayer: 2 layers of phospholipids
– The polar heads stay on the outside and the
tails stay on the inside.
Cell Membrane
• Cell surface proteins
– a. Channel proteins - transport food and other
molecules into the cell and transport wastes
out of the cells.
– b. Receptor proteins - gather information
about the cell’s surroundings.
– c. Cell surface markers - identify the type of
cell, important for cell recognition.
Cell Membrane
• Permeability of the cell membrane
– 1. Semi permeable/selectively permeable only certain substances can pass across the
membrane.
– 2. Factors that determine whether a molecule
can pass through a membrane or not:
• a. size
• b. type (polar, non-polar)
Transport Mechanisms
• Transport Mechanisms - moving material in and out
of the cell
• Concentration gradient - the difference in the
amount of a substance inside and outside of the
cell
– 1. Going “with the gradient”-moving from high to low
concentration
– 2. Going “against the gradient”-moving from low to high
concentration
– 3. Equilibrium exists when the concentration of molecules
is the same throughout a space (inside and outside the
cell)
Transport Mechanisms
• Two categories of transport based on
concentration gradient and the need for
energy
– 1. Passive transport that does not require energy,
goes with the gradient.
• Example = diffusion and osmosis
– 2. Active transport requires energy, goes against
the gradient.
Passive Transport Mechanisms
• Diffusion - movement from an area of high
concentration to an area of low
concentration
– Example: smoke across a room, food coloring
dropped into water, oxygen in lungs
Passive Transport Mechanisms
• Diffusion -
Passive Transport Mechanisms
• Osmosis - diffusion of water
– Direction of osmosis-the direction of water
flow depends upon the concentration of solute
and solvent (water)
– Tonicity-term used to compare 2 solutions
(usually the inside and the outside of the cell)
• a. Hypotonic - less solute (more water)
• b. Hypertonic - more solute (less water)
• c. Isotonic - equal amounts of solute and water
Passive Transport Mechanisms
• Osmosis - diffusion of water
– Water will flow from a hypotonic solution to a
hypertonic solution
– Will water move in an isotonic solution? Yes,
but it won’t be noticeable-equilibrium is
established
Passive Transport Mechanisms
• Osmosis - diffusion of water
– Turgor pressure/osmotic pressure-pressure
due to water in cell.
• Analogy: air pressure in a tire.
– When a cell has high turgor pressure, it is bigger
and stiffer. When a cell has low turgor pressure,
it is smaller and flimsy.
Passive Transport Mechanisms
• Click to: See osmosis in action
Passive Transport Mechanisms
• Plasmolysis - wilting of a cell due to loss of
turgor pressure
• Cytolysis - bursting of a cell due to an
increase in turgor pressure.
– How do plant cells avoid cytolysis? Cell walls
– How do unicellular freshwater organisms
avoid bursting? Contractile vacuoles.
Passive Transport Mechanisms
Passive Transport Mechanisms
Passive Transport Mechanisms
• Facilitated diffusion - transport of specific
molecules across a membrane with the
help of a channel protein
– An example of a molecule that is often
transported in this manner is glucose
Passive Transport Mechanisms
• Click to: see facilitated diffusion
Passive Transport Mechanisms
• Click below to:
Go to the passive transport animation!!!
Active Transport Mechanism
• Active Transport Mechanism
(requires energy in the form of ATP)
• Sodium-potassium pump - pumps sodium
ions out and forces potassium ions in.
Important for conducting nerve impulses
and muscle contraction.
Active Transport Mechanism
• Sodium-potassium pump 1.
4.
2.
3.
Active Transport Mechanism
• Click to: Check out the animation of the
Sodium – Potassium Pump
Active Transport Mechanism
• Proton pump-transport protons through
membranes of chloroplasts and
mitochondria
Active Transport Mechanism
• Endocytosis - process of bringing larger
molecules into the cell by engulfing them.
– 1. Pinocytosis – liquids
– 2. Phagocytosis - solids (amoebas eat this
way, white blood cell engulf bacteria
Active Transport Mechanism
• Click to: see phagocytosis
Active Transport Mechanism
• Excocytosis - discharge of wastes,
hormones or other larger molecules out of
the cell (opposite of endocytosis)
Active Transport Mechanism
• Click to: see exocytosis
How Cells Communicate
• Organ system involved in communication
– 1. Endocrine system - releases hormones
(protein) for communication
– 2. Nervous system - releases
neurotransmitters to other nerve cells or to
muscle cells.
How Cells Communicate
• Receptors
– 1. Receptors - are proteins that are or the cell
membrane surface - they send messages to
the inside of the cell when they encounter
certain molecules outside of the cell.
– 2. Chemically gated channels - a chemical
trigger transmits information.
– 3. Voltage gated channel - an electrical signal
transmits information along nerve cells.
Active Transport Mechanisms
• Click below to:
Go to the active transport animation!!!
Unit 4, Part 2 Notes
Cell Membrane and Transport
Mechanisms