Chapter 7 Modified

8/4/2019 Chapter 7 Modified

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Chapter 7

Membrane Structureand Function


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Plasma Membrane

The membrane at the

boundary of every cell.Functions as a selective

barrier for the passage of

materials in and out of cells.


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Membrane

CompositionLipids

ProteinsQuestion:

How are the materialsarranged?


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Membrane Models


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Fluid Mosaic Model

1972New model to fit the new

evidence with membranes.Example of

Science as a Process.


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Fluid Mosaic Model

Refers to the way the lipids

and proteins behave in amembrane.


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Fluid

Refers to the lipid bilayer.

Molecules are not bondedtogether, so are free to shift.

Must remain "fluid" formembranes to function.


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Ways to keep the

membrane fluidLipid changes or shifts:

Cold hardening of plants(shift to saturated fatty acids).

Hibernating animals

(Cholesterol increase).


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Mosaic

Proteins: float in a sea of

lipids.Proteins form a collage or

mosaic pattern that shifts

over time.


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Types of Membrane

ProteinsIntegral - inserted into the

lipid bilayer.Peripheral - not embedded in

the lipid bilayer, but are

attached to the membranesurface.


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Hydrophilic

Amino Acids

Hydrophobic

Amino AcidsHydrophilic

Amino Acids


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Question?

How do the integral proteins

stick to the membrane?By the solubility of their

amino acids.


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Protein Function in

MembranesTransport.

Enzymatic activity.

Receptor sites for signals.

Cell adhesion.

Cell-cell recognition.

Attachment to the cytoskeleton.


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Carbohydrates


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Membrane

CarbohydratesBranched oligosaccharides

form glycolipids andglycoproteins on externalsurface.

Function - recognition of"self" vs "other.


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Question

How do materials get acrossa cell's membrane?


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Problems

Lipid bilayer is hydrophobic.Hydrophilic materials don'tcross easily.

Large molecules don't cross

easily. Too big to getthrough the membrane.


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Passive Transport

Movement acrossmembranes that does NOTrequire cellular energy.


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Types of Passive

Transport1. Diffusion

2. Osmosis3. Facilitated Diffusion


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Equilibrium

When the concentration isequal on both sides.

There is no net movement ofmaterials.


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Factors that Effect

Diffusion1. Concentration

2. Temperature3. Pressure

4. Particle size

5. Mixing


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Osmosis

Diffusion of water.

Water moving from an area ofhigh concentration to an areaof low concentration.

No cell energy is used.


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Tonicity

The concentration of waterrelative to a cell.

1. Isotonic (same)

2. Hypotonic (below)

3. Hypertonic (above)


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Isotonic

Isosmotic solution.

Cell and water are equal insolute concentration.

No net movement of water in

or out of the cell.

No change in cell size.


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Hypotonic

Hypoosmotic solution

Cell's water is lower than theoutside water (more solutes).

Water moves into the cell.

Cell swells, may burst or thecell is turgid.


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Hypertonic

Hyperosmotic solution

Cell's water is higher than theoutside water (less solutes)

Water moves out of the cell.

Cell shrinks or plasmolysisoccurs.


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Facilitated Diffusion

Transport protein that helpsmaterials through the cellmembrane.

Doesn't require energy (ATP).

Works on a downhillconcentration gradient.


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Active Transport

Movement acrossmembranes that DOESrequire cellular energy.


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Carrier-Mediated

TransportGeneral term for the active

transport of materials intocells AGAINST theconcentration gradient.

Movement is: low high


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Examples

1. Na+- K+ pump

2. Electrogenic or H+

pumps3. Cotransport


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Na+- K+ pump

Moves Na+ ions out of cellswhile moving K+ ions in.


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Electrogenic or

H+

pumpsAlso called Proton pumps.

Create voltages acrossmembranes for other cellprocesses.


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Endocytosis

Moves bulk materials intocells.

Several types known.


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Types

1. Pinocytosis - liquids

2. Phagocytosis - solids3. Receptor Mediated - uses

receptors to "catch" specific

kinds of molecules.


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Forming vesicles


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Summary

Know membrane structure.

Be able to discuss thevarious methods by whichcells move materials through

membranes.Be able to solve problems in

osmosis.


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Chapter 7 Modified