Molecular Cell Biology 6/e

1
Cell Biology
Chapter 10 (??? ???)
Biomembrane structure
2
(No Transcript)
3

• Lipid composition and structural organization
• ? Three classes of lipids are found in membrane
• ? Most lipids and proteins are mobile
• ? Lipid composition influences the physical
• properties
• Protein composition and basic function
• ? Integral membrane protein
• ? Lipid-anchored protein
• ? peripheral membrane protein

4
Lipid composition and structural organization

• Phospholipid bilayers possess three important
  properties
• Hydrophobic core is an impermeable barrier that
  prevents the
• diffusion of water-soluble solutes across
  membrane
• ?Stability The bilayer structure is maintained
  by hydrophobic and
• van der Waals interactions between the lipid
  chains.
• All phospholipid bilayers can formed sealed
  closed compartments
• where the aqueous space on the inside is
  separated from that on the
• outside.
• two surfaces of a cellular membrane as
• the cytosolic face and exoplasmic face.

5
(No Transcript)
6
(No Transcript)
7
(No Transcript)
8
(No Transcript)
9
Two distinct membranes surround three
organelles Nucleus Mitochondria Chloroplast
Natural membranes from different cell
types exhibit a variety of shapes, which
complement a cells function
10
(No Transcript)
11
(No Transcript)
12
Biomembrane contain three principal classes of
lipids

• Phosphoglyceride (?????)
• the most abundant class of lipids in membranes,
  are derivatives
• of glycerol 3-phosphate
• Phosphatidylcholine (PC)
• ? the most abundant phospholipids in membrane,
  the head group
• consists of choline
• Sphingolipid (???)
• Cholesterol (???)

13
Phosphatidylethanolamine
Phosphatidylcholine
glycerol 3-phosphate
Phosphatidylserine
Phosphatidylinositol
14
Biomembrane contain three principal classes of
lipids

• Phosphoglyceride (?????)
• Sphingolipid (???)
• All of the compounds are derived from
  sphingosine, an amino
• alcohol with a hydrocarbon chain and a long
  chain fatty acid
• attached in an amide linkage to the
  sphingosine.
• Sphingomyelin (SM) the most abundant
  sphingolipid.
• Cholesterol (???)

15
Sphingomyelin
sphingosine
Glucosylcerebroside
Other sphingolipids are amphipathic glycolipids
whose polar head groups are sugars.
16
Biomembrane contain three principal classes of
lipids

• Phosphoglyceride (?????)
• Sphingolipid (???)
• Cholesterol (???)
• Steroids
• The basic structure of steroids is a four-ring
  hydrocarbon.

17
(No Transcript)
18
Most lipids and proteins are mobile
19
Most lipids and proteins are mobile
Fluorescence recovery after photobleaching (
FRAP) experiments
20
Lipid composition influences the physical
properties
21
Lipid composition influences the physical
properties
22
Lipid composition influences the physical
properties
Phosphatidylcholine
Phosphatidylethanolamine
23
Lipid composition influences the physical
properties
24
Lipid composition influences the physical
properties
25
Cholesterol and sphingolipids cluster with
specific proteins in membrane microdomains
Membrane lipids are not randomly distributed in
each leaflet of a bilayer
26
Lipid raft
27
Protein composition and basic function
Proteins interact with membranes in three
different ways
?Integral membrane protein ? Lipid-anchored
protein ? peripheral membrane protein
28
Integral membrane protein

• also called transmembrane proteins
• span a phospholipid bilayer and comprise three
  segments.
• Part I/II the cytocolic and exoplasmic domains
  have
• hydrophilic surfaces
• Part III the membrane spanning segments contain
  many
• hydrophobic amino acids whose
  side chains protrude
• outward and interact with the
  hydrophobic hydrocarbon
• core of the phospholipid bilayer.
• the membrane spanning domains
  consist of one or
• more a helices or of
  multiple b strands.

29
Glycophorin A (????? A)
Dimmer
I
III
II
Van Der Waals interaction
30
Bacteriorhodopsin (??????)
7 hydrophobic a helices
Retinal molecular attached to one helix absorbs
light.
31
Multiple b strands in porins(????) form
membrane-spanning Barrels(????)

• Porins are a class of transmembrane proteins
  whose
• structure differs from that of other integral
  proteins
• based on a-helical transmembrane domain
• In the outer membrane of gram-negative bacteria,
• E.coli, and in the outer membrane of
  mitochondria
• and chloroplasts.
• Porin has a hydrophilic interior and
• a hydrophobic exterior

32
In a porin monomer, the outward facing side
groups on each of the b strands are hydrophobic
and form a nonpolar ribbonlike band that
encircles the outside of the barrel.
The hydrophobic band interacts with the fatty
acyl groups of the membrane lipids or other
porin monomers.
The side facing inside of porin are hydrophilic.
33
Protein composition and basic function
Proteins interact with membranes in three
different ways
?Integral membrane protein ? Lipid-anchored
protein ? peripheral membrane protein
34
Lipid-anchored protein

• bound to one or more lipid molecules.
• the hydrophobic segment of lipid is in one
  leaflet of
• the membrane and anchors the protein to the
• membrane.
• the polypeptide chain dose not enter the lipid
  bilayer.

35
phosphoethanolamine
Sugar units
PI (phosphatidylinositol)
C-terminal
N-terminal
36
Protein composition and basic function
Proteins interact with membranes in three
different ways
?Integral membrane protein ? Lipid-anchored
protein ? peripheral membrane protein
37
Peripheral membrane protein

• do not contact the hydrophobic core of lipid
  bilayer.
• they bound to the membrane either by
  interactions
• with transmembrane protein
• or lipid-anchored membrane proteins
• or by interactions with lipid head groups.

38
(????)
phosphoethanolamine
Sugar units
PI (phosphatidylinositol)
C-terminal
N-terminal
39
Glycoprotein and Glycolipids in blood cell surface

• Three related oligosaccharide components of
• certain glycoprotein and glycolipids are
  expressed
• on the surfaces of human red blood cells.

40
Glycoprotein and Glycolipids in blood cell surface

• All human have the enzymes for synthesizing O
  antigen.
• Persons with type A blood also have a
  glycosyltransferase enzyme
• Persons with type B blood also have a transferase
  enzyme that
• adds galactose to O antigen

N-acetylgalactosamine

• AB blood types
• both A B transferase

41
(No Transcript)
42
Proteins can be removed from membranes by
detergents or high-salt solutions
hydrophilic
hydrophilic
hydrophobic
hydrophilic
hydrophobic
hydrophilic
hydrophobic
hydrophobic
43
Proteins can be removed from membranes by
detergents or high-salt solutions
(???????)