What do you already know? In groups of 3 or 4: What do you know about cell membranes with respect to structure and function? What are some ways

What do you already What do you already know?know?

In groups of 3 or 4:

What do you know about cell membranes with respect to structure and function?

What are some ways ‘things’ can enter and exit the cell? (what would some of these ‘things’ be?)

What do you think the term ‘selectively permeable’ membrane indicates (compared to ‘semi-permeable’)

Discuss the terms OSMOSIS, DIFFUSION, CONCENTRATION GRADIENT. How do you think these relate to cells?

Cellular MembranesCellular Membranes1. Structure1. Structure

*A cell is separated from its environment by a selectively permeable plasma membrane.

*Selectively permeable: selects which substances it allows through.

*Commonly described as a fluid mosaic.

Cellular MembranesCellular Membranes1. Structure Review1. Structure Review

A. Fluid Mosaic

It is a mosaic because diverse protein molecules are embedded in a matrix of phospholipids.

It is fluid because its component proteins and phospholipid molecules are flexible and can move.

Peripheral Proteins: act as receptor sites.

Transmembrane Proteins or Channel Protein: act as protein channels which allow large polar molecules to cross the membrane.

Cellular MembranesCellular Membranes1. Structure1. Structure

A. Fluid Mosaic

Phosopholipids form a two-layer membrane called a phospholipid bilayer. The steroid cholesterol helps stabilize the phospholipids.

Cholesterol is wedged between some of the phospholipids helps to stabilize and restrain the movement of phospholipids.

Not all phospholipids are the same, this gives the membrane different consistencies at different parts.

http://www.youtube.com/watch?NR=1&v=Rl5EmUQdkuIhttp://www.youtube.com/watch?NR=1&v=Rl5EmUQdkuI

Cellular MembranesCellular Membranes 1. Selective 1. Selective

PermeabilityPermeabilityB. Selectively Permeable: lets some materials in and not

others. (Formerly refered to as ‘semi-permeable’.) Why do you think this changed?

The hydrophobic interior of the bilayer is one reason membranes are selectively permeable

Hydrophobic molecules-- those that are soluble in lipids-- can easily pass through the membrane.

Small molecules like water and O2 can sneak between the phospholipids of the membrane.

Cellular MembranesCellular Membranes 1. Selective 1. Selective

Permeability Permeability Large hydrophilic molecules like glucose, and ions such as

sodium ions and hydrogen ions, cannot pass through the membrane on their own.

A note about waterA note about water

Water molecules cross cell membranes by 2 pathways which we can call the lipid pathway & the water channel pathway.

In other words water CAN diffuse across the cell membrane

And Aquaporins are proteins embedded in the cell membrane that regulate the flow of water.

Cellular MembranesCellular Membranes2. Diffusion2. Diffusion

A. Concentration Gradient

Diffusion is the tendency for particles to spread out from where they are more concentrated to where they are less concentrated.

This process is ‘passive’ meaning it does not require energy (ATP)

This process can also be described as molecules moving down their concentration gradient.

DiffusionDiffusion

Take a second and think about how things mix together or ‘diffuse’ What do we do to speed this process up?

Dissolving sugar in your coffee?

Kool-Aid dissolved in water or maple syrup (For the people with really sweet teeth)? Which is faster.

DiffusionDiffusion

DIFFUSION FACTORSDIFFUSION FACTORS

Six factors affect the rate of diffusion (How fast molecules will spread out)

1. Concentration: The greater the concentration difference, the faster the diffusion.

2. Temperature: Higher temp=faster diffusion

3. Size and Shape: Smaller more streamline molecules = faster diffusion.

continuedcontinued

4. Ionic Charge: depends on their charge either attracted or repelled by each other

5. Viscosity: (Means fluid density) water vs. Syrup…water is faster

6. Movement of the medium: currents will aid diffusion.

CTSIVM: Whats your acronym? Take 2 min and create one with a partner.


B. Passive Transport

Diffusion across a biological membrane is called passive transport.

The cell expends no energy to move the molecules.

Oxygen and carbon dioxide molecules move into and out of cells by passive transport.

8.2.2

DefinitionsDefinitions

Solute: A substance dissolved in another substance, the component of a solution present in the lesser amount.

Solvent: A substance in which another substance is dissolved, forming a solution

Solution: the mixture of the solvent and solute.



a. Osmosis

The plasma membrane is permeable to water molecules. Diffusion of water molecules across a selectively permeable membrane is a special kind of passive transport called osmosis. 8.3.1



a. Osmosis

The rate and direction of osmosis into and out of a cell is directly affected by the presence of solutes in the water.



a. Osmosis

i. Hyper-Hypotonic Solutions

Which way will the water flow?

Selectively Permeable Membrane

Hypertonic Solution

Hypotonic Solution



Which way will the water flow?Selectively Permeable Membrane

Hypertonic Solution

Hypotonic Solution


a. Osmosis


Why does H20 move from Hyper to Hypotonic solutions?

The solute molecules (eg. glucose) attract the H20 molecules on their side of the membrane. This means there are less free H20 molecules on the Hypertonic side and the water will move by osmosis from high concentration to low.

8.3.2

Cellular MembranesCellular Membranes2. 2.

DiffusionDiffusiona. Osmosis

ii. Isotonic Solutions

There is an equal concentration of solute (eg. glucose) on either side of the membrane so H20 can move freely back and forth but will not accumulate on one side or the other.

8.3.2

Cellular MembranesCellular Membranes2. 2.

DiffusionDiffusionb. Facillitated Diffusion

Proteins embedded in the membrane play a key role in selective permeability. A transport protein spans the membrane and provides a "doorway“ through which a solute can diffuse 8.4.1

Facilitated diffusion is a type of passive transport, since the molecules are diffusing through the membrane and the cell expends no energy to move them.

Facilitated Diffusion = Passive Facilitated Diffusion = Passive Transport Transport

Cellular MembranesCellular Membranes3. Active Transport3. Active Transport

Sometimes a cell needs to move a solute against its concentration gradient. This process is called active transport, and it requires input of energy from ATP.

For instance, most cells need to expel sodium Na+ and take in potassium K+, both against their concentration gradients.

8.5.1

Cellular MembranesCellular Membranes3. Active 3. Active

TransportTransportSodium ions bind to a transport protein. ATP provides the

energy that causes the protein to change shape and push the ions across the membrane, where they are released.

Potassium now binds to the transport protein, the protein changes its shape again, and potassium is released inside the cell. The transport protein returns to its original shape, ready to repeat the process.

Summary of TransportSummary of Transport

Cellular MembranesCellular Membranes4. Exocytosis4. Exocytosis

Large molecules are transported out of the cell by a process called exocytosis. A membrane-bounded vesicle filled w/ large molecules moves toward the plasma membrane.


Once there, the vesicle fuses with the membrane and the contents spill out. Many cells that secrete proteins export their products by means of exocytosis.

Why is it important that the vesicles be made of the same membrane as the external cellular membrane?


Membranes, membranes, everywhere

Cellular MembranesCellular Membranes5. Endocytosis5. Endocytosis

Materials are ingested by the cell by means of endocytosis, a process that is essentially the opposite of exocytosis.

In endocytosis, a vesicle made of the plasma membrane forms around the substance to be ingested. The vesicle pinches closed, carrying its contents into the cell.

8.6.2

Certain white blood cells ingest harmful bacteria this way.


There are two main types of Endocytosis

• Phagocytosis

A cell engulfs a particle by wrapping psuedopods (false feet) around it and packaging it in a membrane sac large enough to be considered a vacuole. This particle will later be digest by a lysosome.


B. Pinocytosis

The cell “gulps” droplets of fluid from outside the cell into tiny vesicles. Any solutes that are dissolved in the cell are taken in with the fluid.

Pinocytosis is not specific in the substances it transports.

Cellular MembranesCellular Membranes6. Cell Size6. Cell Size

Cell size is limited.

Cell’s must survive by moving their food and required chemicals from the outer membrane throughout the cell.

As the cell grows the centre of the cell becomes further away from the edges.

As the cell grows its surface area does not increase as quickly as the volume.


As a cell grows the volume increases much more quickly than the surface area.

Volume represents cell appetite

Surface area represents the cell’s ability to feed itself

If appetite increases faster than food supply the cell will die so it does not grow past a certain size.


http://www.youtube.comwatchv=kfy92hdaAH0&feature=relatedhttp://www.youtube.com/watchv=1ZFqOvxXg9M

David Bolinsky TED talkhttp://www.youtube.com/watch?v=Id2rZS59xSE&feature=relatedhttp://www.youtube.com/watch?v=hrLPPiVmq2g&feature=relatedInner Life of a cell: HQhttp://www.youtube.com/watch?v=CpTmXz8VQF8&feature=relatedMitochondria:http://multimedia.mcb.harvard.edu/

http://www.navtech3d.com/index.php?page=shop.product_details&product_id=8&flypage=flypage.tpl&pop=0&option=com_virtuemart&Itemid=7

active transport, carrier protein, channel protein, cholesterol, concentration gradient, diffusion, endocytosis, exocytosis, facilitated transport, fluid-mosaic membrane model, glycolipid, glycoprotein, hydrophilic, hydrophobic, hypertonic, hypotonic, isotonic, osmosis, passive transport processes, phagocytosis, phospholipid, phospholipid bilayer, pinocytosis, pressure gradient, selectively permeable, tonicity

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What do you already know? In groups of 3 or 4: What do you know about cell membranes with respect to structure and function? What are some ways