Types of Transport Across Cell Membranes 1 Simple

Types of Transport Across Cell Membranes 1

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

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

Diffusion of Liquids 4

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

Osmosis • Diffusion of water across a membrane • Moves from HIGH water potential (low solute) to LOW water potential (high solute) Diffusion across a membrane Semipermeable membrane 6

Diffusion of H 2 O Across A Membrane High H 2 O potential Low solute concentration Low H 2 O potential 7 High solute concentration

Aquaporins • Water Channels • Protein pores used during OSMOSIS WATER MOLECULES 8

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 ________. 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? 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? 11

Cells in Solutions 12

Isotonic Solution Hypotonic Solution NO NET MOVEMENT OF H 2 O (equal amounts entering & leaving) CYTOLYSIS copyright cmassengale Hypertonic Solution PLASMOLYSIS 13

Cytolysis & Plasmolysis Cytolysis Plasmolysis 14

Osmosis in Red Blood Cells Isotonic Hypertonic 15

What Happens to Blood Cells? 16

hypotonic hypertonic isotonic hypotonic 17

Three Forms of Transport Across the Membrane 18

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. 19

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. 20

Proteins Are Critical to Membrane Function 21

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 22

Facilitated Diffusion Molecules will randomly move through the pores in Channel Proteins. copyright cmassengale 23

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. 24

Carrier Proteins • Other carrier proteins change shape to move materials across the cell membrane 25

Active Transport v. Requires energy or ATP v. Moves materials from LOW to HIGH concentration v. AGAINST concentration gradient 26

Active transport v. Examples: Pumping Na+ (sodium ions) out and K+ (potassium ions) in against strong concentration gradients. v. Called Na+-K+ Pump 27

Sodium-Potassium Pump 3 Na+ pumped in for every 2 K+ pumped 28 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 29 cells communicate with one another

Exocytosis Exocytic vesicle immediately after fusion with plasma membrane. 30

Moving the “Big Stuff” Large molecules move materials into the cell by one of three forms of endocytosis 31

Pinocytosis Most common form of endocytosis Takes in dissolved molecules as a vesicle 32.

Pinocytosis • Cell forms an invagination • Materials dissolve in water to be brought into cell • Called “Cell Drinking” 33

Example of Pinocytosis pinocytic vesicles forming mature transport vesicle Transport across a capillary cell (blue). 34

Receptor-Mediated Endocytosis Some integral proteins have receptors on their surface to recognize & take in hormones, cholesterol, etc. 35

Receptor-Mediated Endocytosis 36

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Endocytosis – Phagocytosis Used to engulf large particles such as food, bacteria, etc. into vesicles Called “Cell Eating” 38

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Phagocytosis About to Occur 40

Phagocytosis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue) 41

Exocytosis The opposite of endocytosis is exocytosis. Large molecules that are manufactured in the cell are released through the cell membrane. Inside Cell environment 42