Download Cells and Their Environment

Cells and Their Environment
Cell Membrane Structure &
Function
Cell membrane
• Maintains homeostasis
• Controls movement into and
out of the cell
• Support
• Selectively permeable- allows
some materials through but not
others.
• Made of 2 groups of organic
molecules:
• 1. Phospholipids
• 2. Proteins
Phospholipid
• Molecule with a polar head and
a nonpolar tail.
• Polar head attracts water and
nonpolar tails repel water.
• Phospholipids form a bilayer.
• Phospholipid Bilayer
Lipid Bilayer
• Fluid like a soap bubble
• Does not let many molecules
in and out
Cholesterol
• Embedded in lipid bilayer
• Gives bilayer strength
Proteins
• Allow materials
to pass through
membrane
• Called cell
surface proteins
3 types of cell surface proteins
• 1. Channel proteins- proteins that let
sugars, amino acids, ions to pass
through – aka Transport proteins or
carrier proteins
• 2. Receptor proteins- transmit
information from outside to inside
• 3. Cell surface markers- identify the
type of cell
Fluid Mosaic Model of Cell
Membrane
Fluid=flexible from lipid bilayer
Mosaic=Proteins arranged in bilayer
Moving Material In & Out of
Cell
2 ways: Passive and Active
Transport
Passive Transport:
• Movement of substances
across membrane without
using energy
• Equilibrium-when a concentration of a
substance is the same throughout a
space.
• Solute- substance dissolved in
another ex-sugar
• Solvent- substance that dissolves
the solute ex-water
• Solution- mixture of solutes and solvents
Types of Passive Transport
1. Diffusion
• Movement of particles from an area of
high concentration to low
concentration until equilibrium is
reached. Uses no energy.
• Concentration gradient: the
difference of concentration of a
substance through a region. Diffusion
goes with the concentration gradient.
Example of Diffusion
• Open a bottle of ammonia.
Molecules move from high
concentration to low
concentration outside the
bottle until they are spread out
evenly.
Example in cells
• In blood cells in your lungs when you
inhale there is a higher concentration of
oxygen in your lungs than in your blood.
Oxygen diffuses into your blood from a
high concentration to a low concentration.
2. Osmosis
• The movement of WATER
molecules from high
concentration to low
concentration.
• https://www.youtube.com/watch?v=HqKlL
m2MjkI
Hypertonic
• A solution with a higher
concentration of solutes than
the solution across the
membrane.
• Water will move into the high
concentration of solutes.
–Picture on board
Isotonic
• Equal solute concentration on
either side of the membrane.
• Equal amounts of water will
move between membrane
• Picture on board.
Hypotonic
• A solution with a lower
concentration of solutes than
across the membrane
• Water will move out of the low
concentration of solutes.
• Picture on board.
3. Facilitated Diffusion
• When substances move from
high to low concentration
through channel proteins.
• (3rd type of passive transport)
Active Transport
• Use energy to transport material
across membrane
• Uses energy because goes from
region of low concentration to high
concentration.
Types of Active Transport
1. Endocytosis- active transport
that moves large particles into
cell membrane
• 2 types• Phagocytosis- cell eating
• Pinocytosis-cell drinking
2. Exocytosis- active transport
that moves large particles out
of cell
3. Molecule Transport “Pumps”
• Used to transport
sodium, potassium ,
and calcium against
the concentration
gradient.
• Uses lots of energy.
• Occurs in nerve cells
Other cell membrane
functions:
Cell Communication
• Cells communicate by using
receptor proteins.
• The receptor protein receive
messages through hormones,
neurotransmitters, voltage
Immune system
• Cell membranes also help to
recognize foreign antigens
(germs).
• http://www.sciam.com/article.cfm?articleID
=0001998E-5F5A-1C749B81809EC588EF21
• http://www.usd.edu/~bgoodman/Lipidsand
Diffusion.html#Lipids
• http://www.jdaross.mcmail.com/cell2.htm