membranes 0 153. the plasma membrane 1. the plasma membrane is approximately 8-nm thick and is...
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MembranesMembranes
0
153
153
The Plasma MembraneThe Plasma Membrane 1. 1. The Plasma membrane is approximately The Plasma membrane is approximately 8-nm8-nm
thick and is thick and is selectivelyselectively permeable. permeable.
Selective Selective MembraneMembrane
PorePore
SubstanceSubstancess
PermeablePermeable
PermeablePermeable
Not Not permeablepermeable
2. 2. Selectively permeable means that the Selectively permeable means that the membranemembrane is selective as to which substances can is selective as to which substances can passpass through it through it
The following example will demonstrate this point:The following example will demonstrate this point:
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.
The Plasma MembraneThe Plasma Membrane
3. 3. Cellular membranes are composed primarily Cellular membranes are composed primarily of…of…
LipidLipidss
(fats(fats))
ProteinProteinss
Carbohydrates Carbohydrates (sugars)(sugars)
The Plasma MembraneThe Plasma Membrane
4. 4. Lipids are a family of compounds Lipids are a family of compounds including including
FatsFats
LardLard
WaxesWaxes
Parafin Parafin waxwax
steroidsteroidss
CholesterCholesterolol
The Plasma MembraneThe Plasma Membrane
5. 5. Lipids are Lipids are insolubleinsoluble in in waterwater
6. 6. Insoluble means that they don’t Insoluble means that they don’t dissolvedissolve in in water.water.
7. 7. In a cell’s plasma membrane, back to back In a cell’s plasma membrane, back to back phospholipidphospholipid molecules form molecules form twotwo distinct layers. distinct layers.
Outer Outer layerlayer
Inner Inner layerlayer
8. 8. WaterWater is the main component inside and outside 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
9. 9. A descriptive word meaning “watery” is the term A descriptive word meaning “watery” is the term aqueousaqueous..
10. 10. The outside of the cell is known as the The outside of the cell is known as the extracellularextracellular side. side.
CytoplasmiCytoplasmic sidec side
ExtracellulExtracellular sidear side
11. 11. The inside of the cell is the The inside of the cell is the cytoplasmiccytoplasmic side.side.
12. 12. The two layers together are The two layers together are known as a phospholipid known as a phospholipid bilayerbilayer..
Extracellular Side Extracellular Side (aqueous)(aqueous)
Cytoplasmic Side Cytoplasmic Side (aqueous)(aqueous)
PhospholipiPhospholipid bilayerd bilayer
13. 13. 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))
14. 14. HydrophilicHydrophilic means “means “water water lovingloving.”.”
Phosphate Phosphate head head ((hydrophilichydrophilic))
15. 15. The two blue colored lipid tails are The two 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))
16. 16. HydrophobicHydrophobic means “means “water fearingwater fearing.”.”
Phosphate Phosphate head head ((hydrophilichydrophilic))
17. 17. 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”
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.
18. 18. PhospholipidsPhospholipids are the most are the most abundantabundant lipids in lipids in most membranes.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
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.
19. 19. Phospholipids move laterally at a distance of about Phospholipids move laterally at a distance of about 2 2 μμm m per second, which is about the length of a typical per second, which is about the length of a typical bacterialbacterial cell. cell.
20. 20. Phospholipids also make Phospholipids also make transmembranetransmembrane flip-flops at a rate of about flip-flops at a rate of about once per monthonce per month..
21. 21. Cell plasma membranes are Cell plasma membranes are usually about as fluid as usually about as fluid as salad salad oiloil..
Extracellular Side Extracellular Side (aqueous)(aqueous)
Cytoplasmic Side Cytoplasmic Side (aqueous)(aqueous)
22. 22. This bilayer also contains many This bilayer also contains many molecules of the steroid molecules of the steroid cholesterolcholesterol..
CholesterolCholesterol
24. 24. At lower At lower temperatures temperatures however, cholesterol however, cholesterol helps to keep the helps to keep the membrane from membrane from solidifying.solidifying.
23. 23. Cholesterol Cholesterol slowsslows the movement the movement of phospholipids in of phospholipids in cell membranes.cell membranes.
27. 27. The fewer the number of The fewer the number of cholesterol molecules, the more cholesterol molecules, the more fluid fluid the membranethe membrane..
25. 25. Unsaturated hydrocarbon Unsaturated hydrocarbon tails cause tails cause kinkskinks in the lipid in the lipid bilayerbilayer
26. 26. Bilayers with kinks have Bilayers with kinks have fewerfewer cholesterol molecules than those cholesterol molecules than those without kinks.without kinks.
29. 29. The greater the number of The greater the number of cholesterol molecules, the more cholesterol molecules, the more viscousviscous (thick-flowing) the (thick-flowing) the membrane.membrane.
28. 28. Saturated Saturated hydrocarbons have hydrocarbons have
straightstraight tails tails
Bilayers without kinks have more Bilayers without kinks have more cholesterol molecules than those with cholesterol molecules than those with kinks.kinks.
An Omega-3 Rich DietAn Omega-3 Rich Diet
ExtracellulExtracellular Sidear Side
CytoplasmiCytoplasmic Sidec Side
30. 30. In addition to cholesterol, the membrane In addition to cholesterol, the membrane bilayer is also studded with bilayer is also studded with proteinsproteins..
31.31.These two These two proteins are proteins are integralintegral (internal) proteins, (internal) proteins, meaning that they meaning that they are embedded in are embedded in the bilayer.the bilayer.
32. 32. This protein This protein is a is a transmembrane transmembrane protein. It spans protein. It spans the entire the entire bilayer.bilayer.
CytoplasmiCytoplasmic Sidec Side
33. 33. Like the bilayer, internal proteins have Like the bilayer, internal proteins have water loving water loving and and water fearing water fearing regions.regions.
HydroHydrophilicphilic regionregion
HydroHydrophilicphilic regionregion
HydroHydrophobicphobic regionregion
ExtracellulExtracellular Sidear Side
““water loving”water loving”
““water loving”water loving”
““water fearing”water fearing”
AqueouAqueouss
AqueouAqueouss
ExtracellulExtracellular Sidear Side
CytoplasmiCytoplasmic Sidec Side
34. 34. Other proteins are Other proteins are ExtrinsicExtrinsic (peripheral) (peripheral) proteins, meaning they are not embedded, but proteins, meaning they are not embedded, but cling to the outside of the membrane. cling to the outside of the membrane.
35. 35. Extrinsic Extrinsic proteins are proteins are hydrophilichydrophilic, or , or water loving.water loving.
36. 36. Proteins are made up of chains of Proteins are made up of chains of amino acidsamino acids
The hydrophobic region of the chain is usually The hydrophobic region of the chain is usually shaped like a shaped like a helixhelix or coil. or coil.
HydroHydrophobic phobic (“water (“water
fearing”) helix fearing”) helix or coil shapeor coil shape
HydroHydrophilicphilic regionregion““water loving”water loving”
““water loving”water loving”HydroHydrophilic philic regionregion
SerinSerineeTyrosinTyrosineeAlaninAlanineeLeucinLeucineeValinValineeLysinLysineeCysteinCysteinee
This protein example is made up of 250 amino acids.This protein example is made up of 250 amino acids.
37. 37. Here are some example names of amino Here are some example names of amino acids and their locations within the protein.acids and their locations within the protein.
38. 38. The amino acids in the helix or coil tend to be The amino acids in the helix or coil tend to be nonpolarnonpolar..
39. 39. The amino acids at the ends tend to be The amino acids at the ends tend to be polarpolar..
SerinSerineeTyrosinTyrosineeAlaninAlanineeLeucinLeucineeValinValineeLysinLysineeCysteinCysteinee
NonpolaNonpolarr
PolarPolar
PolarPolar
40. 40. All amino acids have the following parts:All amino acids have the following parts:
H2N
HH O
C OHCC
R
Carboxyl group
Hydrogen atom
Variable group
Central Carbon atom
Amino group
41. 41. There are only There are only 20 20 different different amino acids used in the making of amino acids used in the making of proteins.proteins.
H2N
HH O
C OHCC
RVariable group
42. 42. It is the It is the RR group that makes all 20 group that makes all 20 amino acids structurally different from amino acids structurally different from one another.one another.
Amino group
Hydrogen atom
Central Carbon atom
Carboxyl group
43. 43. The The RR group also determines the amino acid’s group also determines the amino acid’s polaritypolarity..
SerinSerineeTyrosinTyrosineeAlaninAlanineeLeucinLeucineeValinValineeLysinLysineeCysteinCysteinee
R
H3N
H O
C OHCC
44. 44. For example, the For example, the OHOH at the end of the at the end of the RR group of Serine group of Serine makes it a hydrophilic (water loving) polar molecule.makes it a hydrophilic (water loving) polar molecule.
SerinSerineeTyrosinTyrosineeAlaninAlanineeLeucinLeucineeValinValineeLysinLysineeCysteinCysteinee
R
H3N
H O
C OHCC
OHOH
Serine is well suited to aqueous (watery) Serine is well suited to aqueous (watery) environments.environments.
The same goes for Tyrosine, which also has an The same goes for Tyrosine, which also has an OHOH at the end of its at the end of its RR group that makes it “water loving.”group that makes it “water loving.”
SerinSerineeTyrosinTyrosineeAlaninAlanineeLeucinLeucineeValinValineeLysinLysineeCysteinCysteinee
R
H3N
H O
C OHCC
OHOH
CH2
45. 45. The methyl (The methyl (CHCH33) ) RR group of Alanine makes it group of Alanine makes it nonpolar.nonpolar.
SerinSerineeTyrosinTyrosineeAlaninAlanineeLeucinLeucineeValinValineeLysinLysineeCysteinCysteinee
R
H3N
H O
C OHCC
Alanine is found in the middle hydrophobic (water Alanine is found in the middle hydrophobic (water fearing) region of the plasma membrane.fearing) region of the plasma membrane.
CH3
Leucine and Valine have several terminal methyl Leucine and Valine have several terminal methyl RR groups. Because of groups. Because of this, they are also nonpolar and hydrophobic. this, they are also nonpolar and hydrophobic.
SerinSerineeTyrosinTyrosineeAlaninAlanineeLeucinLeucineeValinValineeLysinLysineeCysteinCysteinee
R
H3N
H O
C OHCC
H3C CH3
C – H
46. 46. The phospholipids, steroids and proteins of the The phospholipids, steroids and proteins of the membrane form a membrane form a mosaicmosaic of substances that float of substances that float about.about.This is known as the This is known as the Fluid Mosaic Fluid Mosaic
ModelModel..
47. 47. The Fluid Mosaic Model was proposed by The Fluid Mosaic Model was proposed by Singer Singer and and NicolsonNicolson in 1972. 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
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
OtherOther 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)
Fluid Mosaic ModelFluid Mosaic Model