Download Transport Across the Cell Membrane

Transport Across the Cell
Membrane
Cell Membrane
 The cell membrane is selectively permeable.
 This means that some molecules are able to pass
through more easily.
 The molecules that can easily pass through are
 Lipids (nonpolar)
 Small molecules (glucose, water, amino acid,
carbon dioxide, oxygen and neutral molecules)
 It is very hard for large molecules and charged
molecules.
Structure of the Cell Membrane
 It is made up of lipids, proteins,
carbohydrates and some cholesterol!
 It is a phospholipid bilayer!
 That means it is made up of 2 layers of
phospholipids!
Structure of the Cell Membrane
 Proteins in the membrane!
Proteins can go through the whole membrane (integral)
or just be attached to one side of the membrane
(peripheral)!
 Proteins that go through the membrane acts as channels
or pumps for molecules to move through.
 Carbohydrates in the membrane!
 The carbohydrates chains here act as identification cards
 Cholesterol in the membrane!
 This keeps the fluidity of the membrane.

Outside
of cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside
of cell
(cytoplasm)
Protein
channel
Lipid bilayer
“Mosaic”
 The membrane is said to be mosaic because of the
proteins, carbs and lipids that make it up!!!!
Cell Wall
• The main function of the cell wall is to provide
support and protection for the cell.
• Cell walls lie outside the cell membrane and are
porous enough to allow H2O, O2, CO2 and other
substances through
 Plant cell walls are made from
cellulose, a tough carbohydrate fiber.
Movement Through
Cell Boundaries
•EVERY LIVING CELL
EXISTS IN A LIQUID
ENVIRONMENT.
Movement Through Cell Boundaries
 One of the most important functions of a
cell membrane is to
 regulate the movement of dissolved
molecules from the liquid on one side of
the membrane to the liquid on the other
side
Types of Movement
 Passive
Diffusion
Osmosis
Facilitated
Diffusion
 Active Transport
Passive Transport
 No energy is needed for movement across the
membrane
 Molecules of liquids and gases are in constant
motion
 Therefore, the molecules move from where there is a
high concentration to where there is a low
concentration
Passive Transport
 Diffusion
 Movement
of molecules from an area of high
concentration to an area of lower concentration
 Occurs because molecules are in constant motion
 Will eventually reach an equilibrium where the
concentration of the solute is the same
throughout
 So
substances use the concentration gradient to
move across the membrane without using any
energy
 Seen with copper sulfate
Passive Transport
 Facilitated Diffusion
 Uses
transport proteins found in the cell
membrane for diffusion
 So the molecules still move from a higher
concentration to a lower concentration but do so
through a protein.
 Transport protein - a passage for molecules to go
through by diffusion
 Two
types of transport proteins
Channel proteins – pores that certain
ions can pass through
Carrier proteins – molecules bind on one
side and are released onto the other side
of the membrane when the protein
change shape
Passive Transport
 Osmosis
Diffusion of water through a selectively permeable
membrane from a high concentration to a lower
concentration
 Isotonic solution – one that has the same concentration
of dissolved substances as the living cell placed in it. The
two solutions are the same strength.
 Hypertonic solution – “above strength”; solution has a
higher solute concentration than the cell.
 Usually water moves OUT of the cell
 Plasmolysis – shrinking of the cytoplasm

Figure 7-15 Osmosis
Section 7-3
Passive Transport
 Hypotonic
solution – there is a lower
concentration of dissolved substances than in the
cell.
Concentration of water molecules is higher in
the hypotonic solution than in the cell so water
will move INTO the cell.
Turgor pressure in plants – makes the plant
look firm and healthy
 In a solution, particles move constantly and
tend to spread out where there is less of
them.
 When the concentration is the same
throughout the solution the system has
reached…..Equilibrium!!!!!!!
Review - Isotonic, Hypertonic, Hypotonic
 Isotonic: When concentrations are the same
on both sides of a membrane
 Hypertonic: The more concentrated side.
 Hypotonic: The less concentrated or diluted
side.
 http://www.linkpublishing.com/videotransport.htm#Elodea__Hypertonic_Solution
Organisms and Osmotic Pressure
 Osmotic pressure
 Organisms
have to balance osmosis
 Osmotic pressure on the hypertonic side of
the membrane could cause the cell to burst
 Most cells are bathed in an isotonic
solution
 Plants and bacteria have cell walls to help
protect them
Active Transport
 Molecules move against the concentration
gradient
 In order for transport across the membrane,
transport proteins (carrier proteins) or
pumps are needed
 So the pumps use energy to move
molecules across the membrane
 Endocytosis – taking materials into the cell by infoldings of
the cell membrane. Large molecules can be taken in this
way
 Phagocytosis – cell eating - http://www.edumediasciences.com/a82_l2-phagocytosis.html
 Pinocytosis – cell drinking http://student.ccbcmd.edu/~gkaiser/biotutorials/eustru
ct/pinocyt.html
 Receptor
mediated endocytosis
This is seen with cholesterol
Sometimes molecules bind to receptors
on the membrane
Once many molecules have bonded to the
membrane, the membrane than pinches
in and the enters the cell.
Active Transport
Molecule to
be carried
 Exocytosis – the membrane of a food vacuole fuses
with the cell membrane and the contents are
released from the cell.
Energy
Molecule
being carried
Organization of Cells
 Unicellular organisms – one cell that
performs all the functions necessary for life
 Multicellular organisms – made up of more
than 1 cell
 The cells most communicate and work
together with each other
 Cell specialization- cells throughout the
organism can develop in different ways to
perform different tasks
4 Levels of Organization
1) Cells (muscle cells)
2) Tissue (smooth muscle tissue)
3) Organ (stomach)
4) Organ System (digestive system)
Levels of Organization
Section 7-4
Muscle cell
LEVELS OF ORGANIZATION
Smooth muscle tissue
Stomach
Digestive system