Cellular TransportCellular Transport

How molecules move in and out How molecules move in and out of cellsof cells

Phospholipid bilayerPhospholipid bilayer Hydrolipid HeadsHydrolipid Heads

Next to extracelluar fluid and Next to extracelluar fluid and cytoplasmcytoplasm

““likes” waterlikes” water Hydrophobic tailsHydrophobic tails

Inside bilayerInside bilayer ““dislikes” waterdislikes” water

Phospholipds not bonded Phospholipds not bonded to one another, therefore to one another, therefore the double layer is fluid the double layer is fluid (moveable)(moveable) To help cells change shapeTo help cells change shape

Transport proteinsTransport proteins

Embedded within phospholipid bilayerEmbedded within phospholipid bilayer Regulate the movement of WATER Regulate the movement of WATER

SOLUBLE molecules (which cannot pass SOLUBLE molecules (which cannot pass directly across the bilayer)directly across the bilayer)

Outer shell: made of HYDROPHOBIC amino Outer shell: made of HYDROPHOBIC amino acids acids

Inner channel: made of HYDROPHILIC Inner channel: made of HYDROPHILIC amino acidsamino acids

Movement of MoleculesMovement of Molecules

Depend on 2 factorsDepend on 2 factors

1.1. Concentration Concentration of molecules of molecules # molecules / volume # molecules / volume

2.2. Gradient Gradient across the membraneacross the membrane Difference in concentration between 2 regionsDifference in concentration between 2 regions Moclecules tend to move from Moclecules tend to move from

HIGH concentration HIGH concentration LOW concentration areas LOW concentration areas Eg. Concentration gradient, pressure gradient, Eg. Concentration gradient, pressure gradient,

electrical gradientelectrical 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!REMEMBER!Moclecules tend to move from Moclecules tend to move from HIGH concentration HIGH concentration LOW concentration areas LOW concentration areas

Cellular Transport - Cellular Transport - OverviewOverview

1.1. Passive TransportPassive Transporta.a. Simple diffusionSimple diffusionb.b. Facilitated diffusionFacilitated diffusionc.c. Osmosis (passive water transport)Osmosis (passive water transport)

2.2. Active TransportActive Transporta.a. Active transportActive transportb.b. EndocytosisEndocytosis

• Pinocytosis, Phagocytosis, Receptor-Mediated Pinocytosis, Phagocytosis, Receptor-Mediated EndocytosisEndocytosis

c.c. ExocytosisExocytosis

1. Passive Transport1. Passive Transport Due to a gradient (difference in Due to a gradient (difference in

concentration between 2 regions)concentration between 2 regions) Requires NO energyRequires NO energy from the cell from the cell Gradient provides potential energy that Gradient provides potential energy that

causes the movement of moleculescauses the movement of molecules Plasma membrane is semi-permeable Plasma membrane is semi-permeable

(allow (allow somesome molecules to pass through) molecules to pass through) Direction of movement: Direction of movement: HIGH HIGH

concentration concentration LOW concentration areas LOW concentration areas

1a. Simple Diffusion1a. Simple Diffusion Diffusion of Diffusion of gases, gases,

water, lipid soluble water, lipid soluble (Hydrophobic) (Hydrophobic) moleculesmolecules through the through the bilipid layerbilipid layer

Speed of diffusion Speed of diffusion depends on:depends on: GradientGradient Size of moleculesSize of molecules

Diffusion continues Diffusion continues until the concentration until the concentration of molecules in both of molecules in both regions are equal regions are equal ((EquilibriumEquilibrium))

1b. Facilitated Diffusion1b. Facilitated Diffusion Molecules diffuse through protein channels in a Molecules diffuse through protein channels in a

Transport ProteinTransport Protein

Molecules bind to Transport protein, it changes Molecules bind to Transport protein, it changes shape and transport molecule across the membraneshape and transport molecule across the membrane

Transport proteins are reuseable, and remain in the Transport proteins are reuseable, and remain in the bilayerbilayer

Diffusion of Diffusion of charged ions (Kcharged ions (K++, Na, Na++, Ca, Ca2+2+)) Amino acids (because they are too big)Amino acids (because they are too big) Monosaccharides (simple sugars)Monosaccharides (simple sugars)

Direction of movement: Direction of movement: HIGH HIGH concentration concentration LOW concentration areas LOW concentration areas

Rate of diffusion depends on Rate of diffusion depends on Number of Transport proteins presentNumber of Transport proteins present Gradient presentGradient present

Slower than Simple diffusionSlower than Simple diffusion

1b. Facilitated Diffusion1b. Facilitated Diffusion

1c. Osmosis – diffusion of 1c. Osmosis – diffusion of HH22OO

Diffusion of WATER Diffusion of WATER across membranes across membranes

Water diffuses Water diffuses from area of from area of HIGH HIGH concentration concentration LOW concentration LOW concentration

osmosis stops osmosis stops when the system when the system has reached has reached EQUILIBRIUMEQUILIBRIUM

2a. Active Transport2a. Active Transport

Moving materials UP the gradient Moving materials UP the gradient Direction of movement: Direction of movement: LOW LOW

concentration concentration HIGH concentration HIGH concentration areasareas

Requires energy from the cell in the Requires energy from the cell in the form of form of ATP (adenosinbe triphosphate)ATP (adenosinbe triphosphate)

Requires Transport proteins with 2 Requires Transport proteins with 2 active sites, one for the molecule and active sites, one for the molecule and one for ATPone for ATP

ATPATP

Adenosine triphosphateAdenosine triphosphate An ´energy carrierAn ´energy carrier

´molecule´molecule When ATP loses a When ATP loses a

phosphate group it phosphate group it gives off energy to gives off energy to becomebecome

3 Phospate groups

ADP (adenosine ADP (adenosine diphosphate)diphosphate)

ATP ATP ADP + Phosphate ADP + Phosphate (Pi)(Pi)

Transport proteins for Active Transport proteins for Active TransportTransport

ATP binding siteATP binding site always always inside the cell because the inside the cell because the cell must provide energy for transportcell must provide energy for transport

Molecule binding site may be inside or outside the Molecule binding site may be inside or outside the cellcell

Transport protein changes shape after binding ATP Transport protein changes shape after binding ATP to transport molecules from to transport molecules from LOW concentration LOW concentration HIGH concentration areasHIGH concentration areas

Transport Protein

2b. Endocytosis2b. Endocytosis

3 different ways cells can actively 3 different ways cells can actively gather materials (ie. Nutrients and gather materials (ie. Nutrients and fluids):fluids):

Pinocytosis (cell drinking)Pinocytosis (cell drinking)

Phagocytosis (cell eating)Phagocytosis (cell eating)

Receptor Mediated EndocytosisReceptor Mediated Endocytosis

2a. Pinocytosis (cell 2a. Pinocytosis (cell drinking)drinking)

To transport fluid from To transport fluid from outside the celloutside the cell

Small dimple form in Small dimple form in plasma membrane (#2 plasma membrane (#2 in diagram)in diagram)

Surrounding fluid Surrounding fluid contained within a tiny contained within a tiny vessicle (#4 in diagram) vessicle (#4 in diagram) to be used by the cellto be used by the cell

Eg. Cells in your Eg. Cells in your intestineintestine

2a. Phagocytosis2a. Phagocytosis

process in which cells process in which cells take in large particles, take in large particles, clumps of food and clumps of food and even other cells! even other cells!

extensions of extensions of cytoplasm surround cytoplasm surround and engulf the objectand engulf the object

Ameba (asingle celled Ameba (asingle celled organism) uses this organism) uses this process to capture process to capture food food

2a. Receptor-mediated 2a. Receptor-mediated endocytosisendocytosis

A way for cells to gather A way for cells to gather specific materialsspecific materials

molecules in the molecules in the extracellular fluid bind to extracellular fluid bind to receptors (receptors (ClatherinClatherin) on ) on the cell surface the cell surface

Clatherins are usually Clatherins are usually found in concentrated found in concentrated areas called a areas called a Coated PitCoated Pit

Coated VesicleCoated Vesicle (because (because it is coated with clatherin it is coated with clatherin INSIDE) is pinched off INSIDE) is pinched off the plasma membrane the plasma membrane

3c. Exocytosis3c. Exocytosis

A way for cells to A way for cells to eliminate wasteeliminate waste

Reverse of Reverse of endocytosisendocytosis

Vesicle moves to cell Vesicle moves to cell surface, fuses with surface, fuses with plasma membran plasma membran and contents diffuse and contents diffuse away from the cellaway from the cell

Some real life pictures!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 - Cellular Transport - SummarySummary

1.1. Passive TransportPassive Transport no energy requiredno energy required from from High High Low concentration Low concentration

a.a. Simple diffusion Simple diffusion gases, water, lipid soluble (Hydrophobic) gases, water, lipid soluble (Hydrophobic)

molecules through the bilipid layermolecules through the bilipid layer

b.b. Faciltated diffusionFaciltated diffusion Molecules bind to Transport protein, it changes Molecules bind to Transport protein, it changes

shape and transport molecule across the shape and transport molecule across the membranemembrane

c.c. OsmosisOsmosis (passive water transport) (passive water transport) Diffusion of WATER across membranesDiffusion of WATER across membranes

2.2. Active TransportActive Transport from from Low Low High concentration High concentration

a.a. Active transport Active transport requires ATPrequires ATP Transport protein has 2 binding sitesTransport protein has 2 binding sites

b.b. Endocytosis Endocytosis A method for cells to gather non-specific or A method for cells to gather non-specific or

specific materials from extracellular fluidspecific materials from extracellular fluid• Pinocytosis, Phagocytosis, Receptor-Pinocytosis, Phagocytosis, Receptor-

Mediated EndocytosisMediated Endocytosisc.c. ExocytosisExocytosis

Cells dispose of wasteCells dispose of waste

Cellular Transport - Cellular Transport - SummarySummary