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Transport Across Membranes SBI4U

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Page 1: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

Transport Across Membranes

SBI4U

Page 2: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

Importance of Transport

• intake of nutrients

• removal of wastes

• communication with environment & other cells

• blocking passage of harmful substances

Page 3: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

Passive Transport

• the movement of materials across the cell membrane without the use of chemical energy (ATP)

• occurs because of diffusion

Page 4: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

Diffusion

• the net movement of a substance from an area of higher concentration to an area of lower

• dynamic equilibrium

Page 5: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

Simple Diffusion

• substances move across membrane unassisted

• small non-polar molecules (O2, CO2, steroid hormones, some drugs) and small polar molecules (H2O, glycerol)

• larger molecules and ions can not pass through membranes unassisted

Page 6: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking
Page 7: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

Facilitated Diffusion

• diffusion across membrane assisted by integral membrane proteins called transport proteins

• channel proteins vs. carrier proteins

• ions, water, amino acids, sugars, etc.

Page 8: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

Osmosis

• the diffusion of water across a membrane

• water follows concentration gradient until equilibrium

Page 9: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

Osmosis

• direction of osmosis changes depending on type of solution surrounding the cell:

• isotonic solution• hypotonic solution• hypertonic solution

Page 10: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

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Cell in Isotonic SolutionCell in Isotonic Solution

CELLCELL

10% NaCL90% H2O

10% NaCL

90% H2O

What is the direction of water movement?The cell is at _______________.equilibrium

ENVIRONMENTENVIRONMENT

NO NET NO NET MOVEMENMOVEMENTT

copyright cmassengale

Page 11: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

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Cell in Hypotonic SolutionCell in Hypotonic Solution

CELLCELL

10% NaCL90% H2O

20% NaCL

80% H2O

What is the direction of water movement? copyright cmassengale

Page 12: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

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Cell in Hypertonic SolutionCell in Hypertonic Solution

CELLCELL

15% NaCL85% H2O

5% NaCL95% H2O

What is the direction of water movement?

ENVIRONMENTENVIRONMENT

copyright cmassengale

Page 13: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

Cells and Tonicity

Page 14: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

Red Blood Cells

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hypotonic hypertonic isotonic

hypertonic isotonic hypotonic

copyright cmassengale

Page 16: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

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?

Page 17: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

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?)

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Active Transport

Page 19: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

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.

Page 20: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

Types of Pumps

• Often function like carrier proteins but against the gradient so they need energy

• Often transport ions eg. Na+, K+, Ca2+, H+

• Pumps can be coupled to save energy and move 2 molecules at the same time across the concentration gradient

Page 21: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

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

Page 22: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

Example: The Na+/K+ Pump

Page 23: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

Example of Na-K pump in nerve impulse conduction

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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

Page 25: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

Types of Bulk Membrane Transport

• Endocytosis– Entry into the cell

• Eg. Phagocytosis, pinocytosis, receptor-mediated endocytosis

• Exocytosis– Exiting the cell

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Endocytosis

Page 27: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

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.

Page 28: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

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

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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

Page 30: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

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

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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

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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]

Page 33: Transport Across Membranes SBI4U. Importance of Transport intake of nutrients removal of wastes communication with environment & other cells blocking

Credits

• Slides #10, 11, 12, and 15 taken from Powerpoint presentations created by Cheryl Massengale, educator extraordinaire & creator of http://www.biologyjunction.com/