Transcript Membrane structure, I

Grade breakdowns—Period 5
A=4
B=5
C=13
F=3 (Mandatory
tutoring)
Build a cell membrane
Aka lipid bilayer
Aka plasma membrane
LABEL 5 components
Label outside and inside cell
Pick up 2 different scripts from
demo table (1 per 2 people)
Practice with a partner
What is the role of:
-nucleus
-RNA
-ribosomes
-rough ER
-Golgi
-transport vessicles
Draw diagram
Danish
Review
 Make 4
higher level
questions
from
1)
2)
3)
4)
Ecology
Evolution
Chemistry
Cells
how does ... compare/contrast with ...?
what evidence can you list for ...?
SYNTHESIS
creating a unique, original product that may be in
verbal form or may be a physical object
combination of ideas to form a new whole
what would you predict/infer from ...?
what ideas can you add to ...?
how would you create/design a new ...?
what might happen if you combined ...?
what solutions would you suggest for ...?
EVALUATION
making value decisions about issues
resolving controversies or differences of opinion
development of opinions, judgements or decisions
do you agree that ...?
what do you think about ...?
what is the most important ...?
place the following in order of priority ...
how would you decide about ...?
what criteria would you use to assess ...?
Announcements
Cells test moved to Thursday, Dec 1
Lab report due tomorrow
Keep your Chapters 8 + 9 notes
Answer a flashcard for 0.5 points
Ch.7~MembraneStructure&Function
Fluid mosaic model
Exit Quiz: Membrane
1) Draw a membrane and label 5
components
2) Describe the role of 6 of the 6
membrane proteins
Bonus: Explain the 4 levels of a protein
Membrane structure, I
 Selective permeability
 Amphipathic~
hydrophobic & hydrophilic
regions
 1935 Davson Danielli
sandwich model
 Singer-Nicolson: 1972
fluid mosaic
model
Cell membrane must be more than lipids…
In 1972, S.J. Singer & G. Nicolson proposed
that membrane proteins are inserted into the
phospholipid bilayer
It’s like a fluid…
It’s like a mosaic…
It’s the
Fluid Mosaic Model!
Membrane is a collage of proteins & other molecules
embedded in the fluid matrix of the lipid bilayer
Glycoprotein
Extracellular fluid
Glycolipid
Phospholipids
Cholesterol
Peripheral
protein
Transmembrane
proteins
Cytoplasm
Filaments of
cytoskeleton
1972, S.J. Singer & G. Nicolson proposed Fluid Mosaic Model
Phosphate
Phospholipids
Phosphate head

hydrophilic
Fatty acid tails

“attracted to water”
Fatty acid
hydrophobic
Arranged as a bilayer
“repelled by water”
Aaaah,
one of those
structure–function
examples
Arranged as a Phospholipid bilayer
Serves as a cellular barrier / border
sugar
H2 O
salt
polar
hydrophilic
heads
nonpolar
hydrophobic
tails
impermeable to polar molecules
polar
hydrophilic
heads
waste
lipids
Cell membrane defines cell
Cell membrane separates living cell from
aqueous environment

thin barrier = 8nm thick
Controls traffic in & out of the cell

allows some substances to cross more easily than
others
• hydrophobic (nonpolar) vs. hydrophilic (polar)
Permeability to polar molecules?
Membrane becomes semi-permeable via
protein channels

specific channels allow specific material across
cell membrane
inside cell
NH3
H2 O
salt
aa
sugar
outside cell
Cell membrane is more than lipids…
Transmembrane proteins embedded in
phospholipid bilayer

create semi-permeabe channels
lipid bilayer
membrane
protein channels
in lipid bilyer membrane
Why are
proteins the perfect
molecule to build structures
in the cell membrane?
2007-2008
Proteins domains anchor molecule
Within membrane

Polar areas
of protein
nonpolar amino acids
• hydrophobic
• anchors protein
into membrane
On outer surfaces of
membrane in fluid

polar amino acids
• hydrophilic
• extend into extracellular
fluid & into cytosol
Nonpolar areas of protein
+
H
H+
Retinal
chromophore
Examples
NH2
aquaporin =
water channel in bacteria
H2 O
Porin monomer
b-pleated sheets
Bacterial
outer
membrane
Nonpolar
(hydrophobic)
a-helices in the
cell membrane
COOH
H+ +
H
Cytoplasm
proton pump channel
in photosynthetic bacteria
H2 O
function through
conformational change =
protein changes shape
Many Functions
of Membrane Proteins
“Channel”
Outside
Plasma
membrane
Inside
Transporter
Enzyme
activity
Cell surface
receptor
Cell surface
identity marker
Cell adhesion
Attachment to the
cytoskeleton
“Antigen”
Membrane Proteins
Proteins determine membrane’s specific functions

cell membrane & organelle membranes each have unique
collections of proteins
Classes of membrane proteins:

peripheral proteins
• loosely bound to surface of membrane
• ex: cell surface identity marker (antigens)

integral proteins
• penetrate lipid bilayer, usually across whole membrane
• transmembrane protein
• ex: transport proteins
– channels, permeases (pumps)
Membrane carbohydrates
Play a key role in cell-cell recognition

ability of a cell to distinguish one cell from
another
• antigens


important in organ &
tissue development
basis for rejection of
foreign cells by
immune system