Download Cell Membranes

Cell Membranes and Interaction with their
environment
Structure and Functions
Cell Membranes
1. All cells have a cell membrane
2. Functions:
a. Controls what enters and exits the cell to
maintain an internal balance called
homeostasis
b. Provides protection and support for the
cell
Cell Membranes
3. Structure of cell membrane
Lipid Bilayer -2 layers of phospholipids
a. Phosphate head is polar (water loving)
b. Fatty acid tails non-polar (water fearing)
c. Proteins embedded in membrane
Polar heads love
water
Proteins
Non-polar tails hide
from water
.
Cell Membranes
 Cell membranes have pores (holes) in it
a. Selectively permeable (semi-
permeable): Allows some molecules in
and keeps other molecules out
b. Take cell membrane quiz!
a. http://www.wisconline.com/objects/ViewObject.aspx?I
D=AP1101
Types of Cell Transport
1. Passive Transport
2. Active Transport
 Endocytosis
 Exocytosis
Passive Transport
Characteristics
Types of Passive Transport
 No energy required
1. Diffusion
 Move due to gradient
 differences in concentration,
pressure, charge
2. Facilitated diffusion
 Move to equalize gradient
 HIGH  low
3. Osmosis
Vocab
 Concentration gradient is the different amounts of
solutes or substances in one place
 Solute – a SUBSTANCE dissolved in a fluid
 Solvent – the FLUID part of a solution
 Solution – a MIXTURE of two or more substances
(a solute and solvent)
Diffusion
 Diffusion is the movement of any
particles from an area of HIGH
concentration to an area of low
concentration.
 Molecules move to equalize concentration
Equilibrium
 Equilibrium– occurs when the particles that
were diffusing are now equally distributed
Movement Across the Cell
Membrane
 A few molecules diffuse freely
across the membrane:
 Water,
 Carbon dioxide,
 Ammonia,
 Oxygen
Facilitated Diffusion
2. Facilitated Diffusion is diffusion
of specific particles through
transport proteins found in the
membrane
 Channels (are specific) help molecule
or ions enter or leave the cell
 No energy is used
Process of Facilitated Transport
 Protein binds with molecule
 Shape of protein changes
 Molecule moves across membrane
Osmosis
 Osmosis- diffusion of water through a selectively
permeable membrane
 Water is so small and there is so much of it the cell
can’t control its movement through the cell
membrane.
 Equilibrium occurs until water is balanced on
both sides of the membrane.
 ONLY
DIFFUSES IN OSMOSIS!!!
Solute/Solvent/Solution
 This is sugar water.
 What is the solute?
 What is the solvent?
 What is the whole
mixture called?
Solute/Solvent/Solution
 A glass of iced tea.
 What is the solute?
 What is the solvent?
 What is the whole
mixture called?
Solute/Solvent/Solution
 Ex: Propel Energy Drink
 What is the solute?
 What is the solvent?
 What is the whole
mixture called?
Solute/Solvent/Solution
 Ex: Dr. Pepper
 What is the solute(s)?
 What is the solvent?
 What is the whole
mixture called?
Osmosis
 What direction will the water go?

are solutes
Types of Osmosis:
 Hypertonic solutions – more dissolved solutes
 Hypotonic solutions – less dissolved solutes
 Isotonic solutions – the same dissolved
solutes
“Hyper-” means over, above, a lot
“Hypo-” means under, below
“Iso-” means equal or the same
Hypertonic Solution
• More solute outside the cell
• Less water outside the cell
Result: The WATER will move
OUT of the cell, causing the cell to
shrink (or crenate)
Osmosis Animations
for isotonic,
hypertonic, and
hypotonic solutions
Osmosis Animations for
isotonic, hypertonic, and
hypotonic solutions
Hypotonic Solution
 Less solute outside of the cell
 More water outside of the cell
Result: The WATER will move INTO
the cell, causing the cell to swell or
burst (lysis)
Osmosis Animations for
isotonic, hypertonic,
and hypotonic solutions
Isotonic Solution
 Water is the same outside the cell
and the same inside the cell.
 Solutes are the same inside the cell
as outside the cell.
 Result: Water is moving in and
out at the same rate
How Organisms Deal with
Osmotic Pressure
 Paramecium
(protist) removing
excess water video
• Bacteria and plants have cell walls that prevent them from
over-expanding. In plants the pressure exerted on the cell
wall is called tugor pressure.
• A protist like paramecium have contractile vacuoles that
collect water flowing in and pump it out to prevent them
from over-expanding.
• Salt water fish pump salt out of their specialized gills so
they do not dehydrate.
• Animal cells are bathed in blood. Kidneys keep the blood
isotonic by removing excess salt and water.
A study of Tonicity in Cells
Active Transport
Characteristics
Types of Active Transport
 Molecular movement
1.
requires energy/ATP to move
against the concentration
gradient
 LOW  high
 Example is sodiumpotassium pump
Endocytosis
2. Exocytosis
Endocytosis
 Movement of large material
 Particles
 Organisms
 Large molecules
 Movement is into cells
 Types of endocytosis
 bulk-phase (nonspecific)
 receptor-mediated (specific)
Process of Endocytosis
 Plasma membrane surrounds material
 Edges of membrane meet
 Membranes fuse to form vesicle
Forms of Endocytosis
 Phagocytosis – cell eating
 Pinocytosis – cell drinking
Exocytosis
 Reverse of endocytosis
 Cell moves material OUTSIDE the cell
Exocytosis
 Vesicle moves to cell surface
 Membrane of vesicle fuses
 Materials expelled
Active Transport
• cell uses energy (in the form of ATP)
• actively moves molecules to where they are needed
• Movement from an area of low concentration
to an area of high concentration
• (Low  High)
• Three Types
Types of Active Transport
 1. Protein Pumps transport proteins that
require energy to do work
• Example: Sodium /
Potassium Pumps are
important in nerve
responses.
Protein changes shape to
move molecules: this
requires energy!
Types of Active
Transport
2. Endocytosis: taking

bulky material into a cell
•
•
•
•
•
Uses energy
Cell membrane folds in
around food particle
creating a vesicle that is
made of the cell
membrane
“cell eating”
Lysosomes come and digests
food
This is how white blood
cells eat bacteria!
Types of Active Transport
3. Exocytosis: Forces material out of cell in bulk
• membrane surrounding the material fuses with cell
membrane
• Cell changes shape – requires energy
• EX: Hormones or wastes released from cell