Transport Across Membranes SBI4U

Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking passage of harmful substances

Passive Transport the movement of materials across the cell membrane without the use of chemical energy (ATP) occurs because of diffusion

Diffusion the net movement of a substance from an area of higher concentration to an area of lower dynamic equilibrium

Simple Diffusion substances move across membrane unassisted small non-polar molecules (O 2, CO 2, steroid hormones, some drugs) and small polar molecules (H 2 O, glycerol) larger molecules and ions can not pass through membranes unassisted

Facilitated Diffusion diffusion across membrane assisted by integral membrane proteins called transport proteins channel proteins vs. carrier proteins ions, water, amino acids, sugars, etc.

Osmosis the diffusion of water across a membrane water follows concentration gradient until equilibrium

Osmosis direction of osmosis changes depending on type of solution surrounding the cell: isotonic solution hypotonic solution hypertonic solution

10 Cell in Isotonic Solution CELL 10% NaCL 90% H 2 O 10% NaCL 90% H 2 O What is the direction of water movement? The cell is at _______________. equilibrium ENVIRONMENT NO NET MOVEMENT copyright cmassengale

11 Cell in Hypotonic Solution CELL 10% NaCL 90% H 2 O 20% NaCL 80% H 2 O What is the direction of water movement? copyright cmassengale

12 Cell in Hypertonic Solution CELL 15% NaCL 85% H 2 O 5% NaCL 95% H 2 O What is the direction of water movement? ENVIRONMENT copyright cmassengale

Cells and Tonicity

Red Blood Cells

15 hypotonichypertonic isotonic hypertonicisotonic hypotonic copyright cmassengale

Answer the following: How does osmosis impact… …a single-celled organism living in a freshwater environment? …a single-celled organism living in a salt-water environment? …the roots of a plant in the spring after salt has been sprinkled during the winter?

More applications… Why can’t you water a plant with salt water? Why do vegetables in the grocery store get sprayed with water periodically? (What would happen if they were sprayed with salt water?)

Active Transport

the movement of materials against the concentration gradient –From low to high concentration requires cellular energy (ATP) Requires a transport protein: pump ATP induces a conformational change in the protein pump that allows specific molecules to enter/exit the cell against its concentration gradient.

Types of Pumps Often function like carrier proteins but against the gradient so they need energy Often transport ions eg. Na +, K +, Ca 2+, H + Pumps can be coupled to save energy and move 2 molecules at the same time across the concentration gradient

Example: The Na + /K + Pump Active transport Antiport Pump oscillates between 2 conformational states: 3 Na + out of the cell 2 K + into the cell

Example: The Na + /K + Pump

Example of Na-K pump in nerve impulse conduction

Bulk Transport movement of larger or very polar substances across the cell membrane requires energy (ATP) Involves a folding of the cell membrane to form a vesicle

Types of Bulk Membrane Transport Endocytosis –Entry into the cell Eg. Phagocytosis, pinocytosis, receptor- mediated endocytosis Exocytosis –Exiting the cell

Endocytosis

Phagocytosis “cellular eating” Process where living cells ingest other cells or large particles Single cellular organisms use it to feed (eg. Amoeba) Used in multi-cellular organisms as a defense mechanism against invasion by foreign particles –Phagocyte: a white blood cell specialized for protecting the body by ingesting foreign substances.

Pinocytosis “Cellular Drinking” Ingestion of dissolved materials Occurs in most cell types Cell folds inwards to take in the fluid containing the desired substance Process is unspecific in terms of what is being ingested

Receptor-Mediated Endocytosis Intake of molecules that bind specifically to a receptor on the surface of the cell Ligand: a molecule that binds to a receptor Receptor proteins are usually clustered in regions of the membrane called coated pits which contain coat proteins that help form vesicles for endocytosis

Exocytosis Movement of materials from the cell to the cell surface within membrane bound vesicles Vesicles formed off Golgi Body or from endocytosis Reverse of endocytosis

Exocytosis Function Secretion: release wastes, toxins Restoring the cell membrane –Need to balance endocytosis in order to keep the surface area of the cell membrane constant

HW Questions 1.An integral protein changes conformation to transport substances from one side of the membrane to the other. It is also able to move 2 different molecules in the same direction. Classify this type of transport and the protein involved. [K-3] 2.Provide a real-life everyday example of when you have encountered a hypotonic or hypertonic environment. Describe what affect it had and the reason for the observed phenomena. [I-2] 3.How does the function of phagocytosis differ in the human body compared to single cellular organisms? Provide an example of each. [A-2]

Credits Slides #10, 11, 12, and 15 taken from Powerpoint presentations created by Cheryl Massengale, educator extraordinaire & creator of