Cellular Transport How molecules move in and out of cells

Phospholipid bilayer Hydrolipid Heads Hydrolipid Heads Next to extracelluar fluid and cytoplasm Next to extracelluar fluid and cytoplasm “likes” water “likes” water Hydrophobic tails Hydrophobic tails Inside bilayer Inside bilayer “dislikes” water “dislikes” water Phospholipds not bonded to one another, therefore the double layer is fluid (moveable) Phospholipds not bonded to one another, therefore the double layer is fluid (moveable) To help cells change shape To help cells change shape

Transport proteins Embedded within phospholipid bilayer Embedded within phospholipid bilayer Regulate the movement of WATER SOLUBLE molecules (which cannot pass directly across the bilayer) Regulate the movement of WATER SOLUBLE molecules (which cannot pass directly across the bilayer) Outer shell: made of HYDROPHOBIC amino acids Outer shell: made of HYDROPHOBIC amino acids Inner channel: made of HYDROPHILIC amino acids Inner channel: made of HYDROPHILIC amino acids

Movement of Molecules Depend on 2 factors 1. Concentration of molecules # molecules / volume # molecules / volume 2. Gradient across the membrane Difference in concentration between 2 regions Difference in concentration between 2 regions Moclecules tend to move from Moclecules tend to move from HIGH concentration  LOW concentration areas HIGH concentration  LOW concentration areas Eg. Concentration gradient, pressure gradient, electrical gradient Eg. Concentration gradient, pressure gradient, electrical gradient

Which direction will the molecules be moving according to the gradient? Plasma membrane Outside the cell Inside the cell Answer: Molecules will move INTO the cell because: more molecules outside the cell, therefore a HIG gradient less molecules inside the cell, therefore a LOW gradient REMEMBER! Moclecules tend to move from HIGH concentration  LOW concentration areas HIGH concentration  LOW concentration areas

Cellular Transport - Overview 1. Passive Transport a. Simple diffusion b. Facilitated diffusion c. Osmosis (passive water transport) 2. Active Transport a. Active transport b. Endocytosis Pinocytosis, Phagocytosis, Receptor-Mediated Endocytosis Pinocytosis, Phagocytosis, Receptor-Mediated Endocytosis c. Exocytosis

1. Passive Transport Due to a gradient (difference in concentration between 2 regions) Due to a gradient (difference in concentration between 2 regions) Requires NO energy from the cell Requires NO energy from the cell Gradient provides potential energy that causes the movement of molecules Gradient provides potential energy that causes the movement of molecules Plasma membrane is semi-permeable (allow some molecules to pass through) Plasma membrane is semi-permeable (allow some molecules to pass through) Direction of movement: HIGH concentration  LOW concentration areas Direction of movement: HIGH concentration  LOW concentration areas

1a. Simple Diffusion Diffusion of gases, water, lipid soluble (Hydrophobic) molecules through the bilipid layer Diffusion of gases, water, lipid soluble (Hydrophobic) molecules through the bilipid layer Speed of diffusion depends on: Speed of diffusion depends on: Gradient Gradient Size of molecules Size of molecules Diffusion continues until the concentration of molecules in both regions are equal (Equilibrium) Diffusion continues until the concentration of molecules in both regions are equal (Equilibrium)

1b. Facilitated Diffusion Molecules diffuse through protein channels in a Transport Protein Molecules diffuse through protein channels in a Transport Protein Molecules bind to Transport protein, it changes shape and transport molecule across the membrane Molecules bind to Transport protein, it changes shape and transport molecule across the membrane Transport proteins are reuseable, and remain in the bilayer Transport proteins are reuseable, and remain in the bilayer

Diffusion of Diffusion of charged ions (K +, Na +, Ca 2+ ) charged ions (K +, Na +, Ca 2+ ) Amino acids (because they are too big) Amino acids (because they are too big) Monosaccharides (simple sugars) Monosaccharides (simple sugars) Direction of movement: HIGH concentration  LOW concentration areas Direction of movement: HIGH concentration  LOW concentration areas Rate of diffusion depends on Rate of diffusion depends on Number of Transport proteins present Number of Transport proteins present Gradient present Gradient present Slower than Simple diffusion Slower than Simple diffusion 1b. Facilitated Diffusion

1c. Osmosis – diffusion of H 2 O Diffusion of WATER across membranes Diffusion of WATER across membranes Water diffuses from area of HIGH concentration  LOW concentration Water diffuses from area of HIGH concentration  LOW concentration osmosis stops when the system has reached EQUILIBRIUM osmosis stops when the system has reached EQUILIBRIUM

2a. Active Transport Moving materials UP the gradient Moving materials UP the gradient Direction of movement: LOW concentration  HIGH concentration areas Direction of movement: LOW concentration  HIGH concentration areas Requires energy from the cell in the form of ATP (adenosinbe triphosphate) Requires energy from the cell in the form of ATP (adenosinbe triphosphate) Requires Transport proteins with 2 active sites, one for the molecule and one for ATP Requires Transport proteins with 2 active sites, one for the molecule and one for ATP

ATP Adenosine triphosphate Adenosine triphosphate An ´energy carrier´molecule An ´energy carrier´molecule When ATP loses a phosphate group it gives off energy to become When ATP loses a phosphate group it gives off energy to become 3 Phospate groups ADP (adenosine diphosphate) ADP (adenosine diphosphate) ATP  ADP + Phosphate (Pi)

Transport proteins for Active Transport ATP binding site always inside the cell because the cell must provide energy for transport ATP binding site always inside the cell because the cell must provide energy for transport Molecule binding site may be inside or outside the cell Molecule binding site may be inside or outside the cell Transport protein changes shape after binding ATP to transport molecules from LOW concentration  HIGH concentration areas Transport protein changes shape after binding ATP to transport molecules from LOW concentration  HIGH concentration areas Transport Protein

2b. Endocytosis 3 different ways cells can actively gather materials (ie. Nutrients and fluids): Pinocytosis (cell drinking) Phagocytosis (cell eating) Receptor Mediated Endocytosis

2a. Pinocytosis (cell drinking) To transport fluid from outside the cell To transport fluid from outside the cell Small dimple form in plasma membrane (#2 in diagram) Small dimple form in plasma membrane (#2 in diagram) Surrounding fluid contained within a tiny vessicle (#4 in diagram) to be used by the cell Surrounding fluid contained within a tiny vessicle (#4 in diagram) to be used by the cell Eg. Cells in your intestine Eg. Cells in your intestine

2a. Phagocytosis process in which cells take in large particles, clumps of food and even other cells! process in which cells take in large particles, clumps of food and even other cells! extensions of cytoplasm surround and engulf the object extensions of cytoplasm surround and engulf the object Ameba (asingle celled organism) uses this process to capture food Ameba (asingle celled organism) uses this process to capture food

2a. Receptor-mediated endocytosis A way for cells to gather specific materials A way for cells to gather specific materials molecules in the extracellular fluid bind to receptors (Clatherin) on the cell surface molecules in the extracellular fluid bind to receptors (Clatherin) on the cell surface Clatherins are usually found in concentrated areas called a Coated Pit Clatherins are usually found in concentrated areas called a Coated Pit Coated Vesicle (because it is coated with clatherin INSIDE) is pinched off the plasma membrane Coated Vesicle (because it is coated with clatherin INSIDE) is pinched off the plasma membrane

3c. Exocytosis A way for cells to eliminate waste A way for cells to eliminate waste Reverse of endocytosis Reverse of endocytosis Vesicle moves to cell surface, fuses with plasma membran and contents diffuse away from the cell Vesicle moves to cell surface, fuses with plasma membran and contents diffuse away from the cell

Some real life pictures!

What is this? Receptor mediated endocytosis: see the coated pit!

What is this? Phagocytosis: the white blood cell is engulfing 2 bacteria cells

Cellular Transport - Summary 1. Passive Transport no energy required no energy required from High  Low concentration from High  Low concentration a. Simple diffusion gases, water, lipid soluble (Hydrophobic) molecules through the bilipid layer gases, water, lipid soluble (Hydrophobic) molecules through the bilipid layer b. Faciltated diffusion Molecules bind to Transport protein, it changes shape and transport molecule across the membrane Molecules bind to Transport protein, it changes shape and transport molecule across the membrane c. Osmosis (passive water transport) Diffusion of WATER across membranes Diffusion of WATER across membranes

2. Active Transport from Low  High concentration from Low  High concentration a. Active transport requires ATP requires ATP Transport protein has 2 binding sites Transport protein has 2 binding sites b. Endocytosis A method for cells to gather non-specific or specific materials from extracellular fluid A method for cells to gather non-specific or specific materials from extracellular fluid Pinocytosis, Phagocytosis, Receptor-Mediated Endocytosis Pinocytosis, Phagocytosis, Receptor-Mediated Endocytosis c. Exocytosis Cells dispose of waste Cells dispose of waste Cellular Transport - Summary