Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is...

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Membranes Membranes 0 153 153

Transcript of Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is...

Page 1: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

MembranesMembranes

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Page 2: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

The Plasma MembraneThe Plasma Membrane The Plasma membrane is approximately 8-nm The Plasma membrane is approximately 8-nm

thick and is selectively permeable.thick and is selectively permeable.

Selective Selective MembraneMembrane

PorePore

SubstanceSubstancess

PermeablePermeable

PermeablePermeable

Not Not permeablepermeable

Selectively permeable means that the membrane Selectively permeable means that the membrane is selective as to which substances can pass is selective as to which substances can pass through itthrough it

The following example will demonstrate this point:The following example will demonstrate this point:

Page 3: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

Larger molecules, such as polysaccharides, proteins, Larger molecules, such as polysaccharides, proteins, and lipids cannot fit, because they are too big.and lipids cannot fit, because they are too big.

Page 4: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

The Plasma MembraneThe Plasma Membrane

Cellular membranes are composed primarily of…Cellular membranes are composed primarily of…

LipidLipidss

(fats(fats))

ProteinProteinss

Carbohydrates Carbohydrates (sugars)(sugars)

Page 5: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

In a cell’s plasma membrane, back to back In a cell’s plasma membrane, back to back phospholipid molecules form two distinct layers.phospholipid molecules form two distinct layers.

Outer Outer layerlayer

Inner Inner layerlayer

Page 6: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

Water is the main component inside and outside Water is the main component inside and outside the cellthe cell

AqueousAqueous inside the inside the

cellcell

AqueousAqueous environmenenvironmen

t outside t outside the cellthe cell

A descriptive word meaning “watery” is the term A descriptive word meaning “watery” is the term aqueousaqueous..

Page 7: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

The outside of the cell is known as the extracellular The outside of the cell is known as the extracellular side.side.

CytoplasmiCytoplasmic sidec side

ExtracellulExtracellular sidear side

The inside of the cell is the cytoplasmic side.The inside of the cell is the cytoplasmic side.

Page 8: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

The two layers together are known as a phospholipid The two layers together are known as a phospholipid bilayer.bilayer.

Extracellular Side Extracellular Side (aqueous)(aqueous)

Cytoplasmic Side Cytoplasmic Side (aqueous)(aqueous)

PhospholipiPhospholipid bilayerd bilayer

Page 9: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

The yellow phosphate heads of the lipids are The yellow phosphate heads of the lipids are hydrophilichydrophilic..

Extracellular Side Extracellular Side (aqueous)(aqueous)

Cytoplasmic Side Cytoplasmic Side (aqueous)(aqueous)

Phosphate Phosphate head head ((hydrophilichydrophilic))

HydrophilicHydrophilic means “water means “water loving.”loving.”

Phosphate Phosphate head head ((hydrophilichydrophilic))

Page 10: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

The blue colored lipid tails are The blue colored lipid tails are hydrophobichydrophobic. .

Extracellular Side Extracellular Side (aqueous)(aqueous)

Cytoplasmic Side Cytoplasmic Side (aqueous)(aqueous)

Phosphate Phosphate head head ((hydrophilichydrophilic))

Lipid Tails Lipid Tails ((hydrophobihydrophobicc))

HydrophobicHydrophobic means “water means “water fearing.”fearing.”

Phosphate Phosphate head head ((hydrophilichydrophilic))

Page 11: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

A Phospholipid bilayer is an A Phospholipid bilayer is an amphipathicamphipathic structure, structure, meaning it has both a meaning it has both a hydrophilichydrophilic region and a region and a hydrophobichydrophobic region. region.

HydrophilicHydrophilic““water water loving”loving”

HydrophilicHydrophilic““water water loving”loving”

HydrophobiHydrophobicc““water fearing”water fearing”

Page 12: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

The picture on the right is a tunneling electron The picture on the right is a tunneling electron micrograph of a cell’s plasma membrane.micrograph of a cell’s plasma membrane.

PhospholipidsPhospholipids are the most abundant lipids are the most abundant lipids in most membranes.in most membranes.

The diagram on the left is a model which interprets The diagram on the left is a model which interprets the two lines in the micrograph as a bilayer of the two lines in the micrograph as a bilayer of

phospholipidsphospholipids..Plasma membrane

Page 13: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

Membrane DynamicsMembrane DynamicsPhospholipids are very dynamic. They constantly Phospholipids are very dynamic. They constantly vibrate and make rapid lateral movements many vibrate and make rapid lateral movements many times a second.times a second.

Phospholipids move laterally at a distance of about 2 Phospholipids move laterally at a distance of about 2 μμm per second, which is about the length of a typical m per second, which is about the length of a typical bacterial cell.bacterial cell.

Page 14: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

Phospholipids also make transmembrane Phospholipids also make transmembrane flip-flops at a rate of about once per flip-flops at a rate of about once per month.month.

Cell plasma membranes are Cell plasma membranes are usually about as fluid as salad usually about as fluid as salad oil.oil.

Page 15: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

Extracellular Side Extracellular Side (aqueous)(aqueous)

Cytoplasmic Side Cytoplasmic Side (aqueous)(aqueous)

This bilayer also contains many This bilayer also contains many molecules of the steroid molecules of the steroid cholesterolcholesterol..

CholesterolCholesterol

Cholesterol slows Cholesterol slows the movement of the movement of phospholipids in phospholipids in cell membranes. cell membranes.

At lower temperatures At lower temperatures however, cholesterol however, cholesterol helps to keep the helps to keep the membrane from membrane from solidifying.solidifying.

Page 16: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

The fewer the number of cholesterol The fewer the number of cholesterol molecules, the more fluid the molecules, the more fluid the membrane.membrane.

Unsaturated hydrocarbon tails Unsaturated hydrocarbon tails cause kinks in the lipid bilayercause kinks in the lipid bilayer

Bilayers with kinks have fewer Bilayers with kinks have fewer cholesterol molecules than those cholesterol molecules than those without kinks.without kinks.

Page 17: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

The greater the number of cholesterol The greater the number of cholesterol molecules, the more viscous the molecules, the more viscous the membrane.membrane.

Saturated hydrocarbons Saturated hydrocarbons have straight tailshave straight tails

Bilayers without kinks have more Bilayers without kinks have more cholesterol molecules than those with cholesterol molecules than those with kinks.kinks.

Page 18: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

The phospholipids, steroids and proteins of the The phospholipids, steroids and proteins of the membrane form a mosaic of substances that float membrane form a mosaic of substances that float about.about.

This is known as the This is known as the Fluid Mosaic Fluid Mosaic ModelModel..

Page 19: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

The Fluid Mosaic Model was proposed by Singer The Fluid Mosaic Model was proposed by Singer and Nicolson in 1972.and Nicolson in 1972.

This is a 3-D model of what This is a 3-D model of what the membrane might look the membrane might look like.like.

http://www.goldiesroom.org/Note%20Packets/06%20Transport/00%20Transport--WHOLE.htm

Page 20: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

The website below has an animation The website below has an animation which demonstrates how the which demonstrates how the

phospholipids and proteins move phospholipids and proteins move about in the membrane.about in the membrane.

http://home.earthlink.net/~shalpine/anim/Life/http://home.earthlink.net/~shalpine/anim/Life/memb.htmmemb.htm

Page 21: Membranes 0 153. The Plasma Membrane The Plasma membrane is approximately 8-nm thick and is selectively permeable. The Plasma membrane is approximately.

Parting ShotsParting Shots Lipids have about twice the energy content of Lipids have about twice the energy content of

both proteins and carbohydrates. both proteins and carbohydrates. Some lipid derivatives act as hormones Some lipid derivatives act as hormones

(testosterone, estrogen, and progesterone).(testosterone, estrogen, and progesterone). Fat under the skin insulates the body against Fat under the skin insulates the body against

temperature changes (e.g. seal blubber)temperature changes (e.g. seal blubber) Fat is a hydrophobic storage molecule and thus Fat is a hydrophobic storage molecule and thus

is lightweight.is lightweight. Fat acts as a shock absorbent for some organs Fat acts as a shock absorbent for some organs

of the body (e.g. kidneys)of the body (e.g. kidneys)

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Fluid Mosaic ModelFluid Mosaic Model