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 Cell membrane Inside of cell (cytoplasm) Protein channel Lipid bilayer Proteins Carbohydrate chains

“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 H 2 O, O 2, CO 2 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

Section 7-3 Figure 7-15 Osmosis

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. transport.htm#Elodea_- _Hypertonic_Solution transport.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 - sciences.com/a82_l2-phagocytosis.htmlhttp:// sciences.com/a82_l2-phagocytosis.html  Pinocytosis – cell drinking - ct/pinocyt.html 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 Exocytosis – the membrane of a food vacuole fuses with the cell membrane and the contents are released from the cell. Molecule to be carried Molecule being carried Energy

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)

Muscle cellSmooth muscle tissueStomachDigestive system Section 7-4 Levels of Organization LEVELS OF ORGANIZATION