Types of Transport Across Cell Membranes copyright cmassengale

Types of Transport Across Cell Membranes copyright cmassengale 1

Simple Diffusion • Requires NO energy • Molecules move from area of HIGH to LOW concentration copyright cmassengale 2

DIFFUSION Diffusion is a PASSIVE process which means no energy is used to make the molecules move, they have a natural ENERGY copyright cmassengale 3

Diffusion of Liquids copyright cmassengale 4

Diffusion through a Membrane Cell membrane Solute moves DOWN concentration gradient (HIGH to copyright cmassengale 5 LOW)

Concentration Gradient 6

Osmosis • Diffusion of water across a membrane • Moves from HIGH water potential (low solute) to LOW water potential (high solute) Diffusion across a membrane copyright cmassengale Semipermeable membrane 7

Diffusion of H 2 O Across A Membrane High H 2 O potential Low solute concentration copyright cmassengale 8 High solute concentration

Cell in Isotonic Solution 10% Na. CL 90% H 2 O ENVIRONMENT CELL 10% Na. CL 90% H 2 O NO NET MOVEMENT What is the direction of water movement? equilibrium The cell is at ________. copyright cmassengale 9

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

Cell in Hypertonic Solution 15% Na. CL 85% H 2 O ENVIRONMENT CELL 5% Na. CL 95% H 2 O What is the direction of water movement? copyright cmassengale 11

Cells in Solutions copyright cmassengale 12

Osmosis in Red Blood Cells Isotonic Hypotonic copyright cmassengale Hypertonic 13

What Happens to Blood Cells? copyright cmassengale 14

Three Forms of Transport Across the Membrane copyright cmassengale 15

Passive Transport Simple Diffusion v Doesn’t require energy v Moves high to low concentration v Example: Oxygen or water diffusing into a cell and carbon dioxide diffusing out. copyright cmassengale 16

Passive Transport Facilitated diffusion v. Doesn’t require energy v. Uses transport proteins to move high to low concentration Examples: Glucose or amino acids moving from blood into a cell. copyright cmassengale 17

Proteins Are Critical to Membrane Function copyright cmassengale 18

Types of Transport Proteins • Channel proteins are embedded in the cell membrane & have a pore for materials to cross • Carrier proteins can change shape to move material from one side of the membrane to the other copyright cmassengale 19

Facilitated Diffusion Molecules will randomly move through the pores in Channel Proteins. copyright cmassengale 20

Facilitated Diffusion • Some Carrier proteins do not extend through the membrane. • They bond and drag molecules through the lipid bilayer and release them on the opposite side. 21

Carrier Proteins • Other carrier proteins change shape to move materials across the cell membrane copyright cmassengale 22

Active Transport v. Requires energy or ATP v. Moves materials from LOW to HIGH concentration v. AGAINST concentration gradient copyright cmassengale 23

Active transport v. Examples: Pumping Na+ (sodium ions) out and K+ (potassium ions) in against strong concentration gradients. v. Called Na+-K+ Pump copyright cmassengale 24

Sodium-Potassium Pump 3 Na+ pumped in for every 2 K+ pumped copyright cmassengale 25 out; creates a membrane potential

Moving the “Big Stuff” Exocytosis - moving things out. Molecules are moved out of the cell by vesicles that fuse with the plasma membrane. This is how many hormones are secreted and how nerve copyright cmassengale 26 cells communicate with one another

Exocytosis Exocytic vesicle immediately after fusion with plasma membrane. copyright cmassengale 27

Moving the “Big Stuff” Large molecules move materials into the cell by one of three forms of endocytosis copyright cmassengale 28

Pinocytosis Most common form of endocytosis Takes in dissolved molecules as a vesicle copyright cmassengale 29.

Pinocytosis • Cell forms an invagination • Materials dissolve in water to be brought into cell • Called “Cell Drinking” copyright cmassengale 30

Example of Pinocytosis mature transport vesicle pinocytic vesicles forming copyright cmassengale Transport across a capillary cell (blue). 31

Receptor-Mediated Endocytosis Some integral proteins have receptors on their surface to recognize & take in hormones, cholesterol , etc. copyright cmassengale 32

Receptor-Mediated Endocytosis copyright cmassengale 33

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Endocytosis – Phagocytosis Used to engulf large particles such as food, bacteria, etc. into vesicles Called “Cell Eating” copyright cmassengale 35

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Phagocytosis About to Occur copyright cmassengale 37

Phagocytosis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue) copyright cmassengale 38

Exocytosis The opposite of endocytosis is exocytosis. Large molecules that are manufactured in the cell are released through the cell membrane. Inside Cell copyright cmassengale Cell environment 39

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