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

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)


4. 4. Lipids are a family of compounds Lipids are a family of compounds including including

FatsFats

LardLard

WaxesWaxes

Parafin Parafin waxwax

steroidsteroidss

CholesterCholesterolol


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..



Phosphate Phosphate head head ((hydrophilichydrophilic))

14. 14. HydrophilicHydrophilic means “means “water water lovingloving.”.”


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




Lipid Tails Lipid Tails ((hydrophobihydrophobicc))

16. 16. HydrophobicHydrophobic means “means “water fearingwater fearing.”.”


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..



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.


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


““water loving”water loving”

““water loving”water loving”

““water fearing”water fearing”

AqueouAqueouss

AqueouAqueouss



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..


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..


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.


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.”


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.


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.


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

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

Documents

Transcript of Membranes 0 153. The Plasma Membrane 1. The Plasma membrane is approximately 8-nm thick and is...