IB Biology 1.3 Membrane Structure

1. 1.3 MEMBRANE
STRUCTURE

2. Understandings
Phospholipids form bilayers in water
due to the amphipathic properties
of phospholipid molecules.
Membrane proteins are diverse in
terms of structure, position in the
membrane, and function.
Cholesterol is a component of
animal cell membranes.
Applications and Skills
A: Cholesterol in mammalian
membranes reduces fluidity a
permeability to some solutes.
S: Drawing of the fluid mosaic
model.
S: Analysis of evidence from
electron microscopy that led to the
proposal of the Davson-Danielli
model.
S: Analysis of the falsification of the
Danson-Danielli model that led to
the Singer-Nicolson model.
Guidance
- Amphipathic phospholipids have hydrophilic and hydrophobic properties.
- Drawings of the fluid mosaic model of membrane structure can be two-dimensional rather
than three-dimensional. Individual phospholipid molecules should be shown using the
symbol of a circle with two parallel lines attached. A range of membrane proteins should be

3. THE DAVSON-DANIELLI MODEL
Proposed in 1935
Lipid bilayer model that was covered on
both sides by a layer of globular protein
Intended to explain the surface tension of
observations about surface tension of
membranes (actually caused by
phospholipid heads)
http://2.bp.blogspot.com/-

4. SINGER-NICOLSON MODEL
Proposed that proteins are inserted into
the phospholipid layer in a mosaic pattern
Evidence includes:
 Not all membranes are
identical/symmetrical
 Electron microscopes can detect
membranes with different structures and
functions
 A protein layer would be largely nonpolar
and would interface with the aqueous
extracellular fluid
http://publishing.cdlib.org/ucpressebooks/data/13030/n2/ft796nb4n2/figures/ft796nb4n2_00146.gif

5. FLUID MOSAIC MODEL
Current model
Relatively the same for plasma
membranes and organelle membranes
Membranes composed of a bilayer of
phospholipids with integral proteins,
peripheral proteins, glycoproteins, and
cholesterol
http://www.factmonster.com/images/cig/biology/02fi

6. PHOSPHOLIPIDS
http://upload.wikimedia.org/wikipedia/commons/3/3c/0301_Phospholipid_Structure.jpg
Soap Molecule
https://tse1.mm.bing.net/th?id=OIP.M249d88827275758d92bd781aa3842054H0&pid=15.1&P=0

7. CHOLESTEROL
Embedded in the hydrophobic tails
of the bilayer
Reduces membrane fluidity of
animal cells by allowing
membranes to function in a
broader range of temperatures
Plant cells lack cholesterol
https://s.yimg.com/fz/api/res/1.2/aLBIjabupDBLJoGx4udA7A--/YXBwaWQ9c3JjaGRkO2g9MzU5O3E9OTU7dz01MDk-

8. PROTEINS
Two major types
Integral
Peripheral
http://unexpurgatedme.files.wordpress.com/2011/11/phospholipid-bilay

9. INTEGRAL PROTEINS
Amphipathic
Hydrophobic
region in the
midsection of the
bilayer
Hydrophilic
region exposed
to aqueous
solutions on
outside and
inside of cell http://classconnection.s3.amazonaws.com/410/flashcards/2392410/jpg/picture213549

10. PERIPHERAL PROTEINS
Bound to the
surface of the
membrane
Often anchored to
an integral protein
http://classconnection.s3.amazonaws.com/410/flashcards/2392410/jpg/picture21354924

11. GLYCOPROTEINS
Composed of
carbohydrate chains
attached to
peripheral protein
Involved in cell to
cell recognition and
immune response
http://isite.lps.org/sputnam/Biology/U3Cell/glycoprote

12. MEMBRANE FUNCTIONS
Hormone binding: Proteins that are exposed to the exterior that have
a specific shape to fit the shape of specific hormones; interaction
relays message to interior
Enzymatic action: for chemical reaction on inside or outside of cell;
can be grouped together for a metabolic pathway
Cell adhesion: proteins on exterior that can hook together in form
permanent or temporary connections
Cell-to-cell communication: performed by glycoproteins that have
specific identification labels
Passive transport: material moves through a channel from an area of
high concentration to low concentration
Active transport: protein pump moves material (generally against a
concentration gradient) from one side to the other by changing

13. HOMEWORK
Vocab
Hydrophob
ic
Hydrophilic
Endocytosi
s
Integral
proteins
Peripheral
proteins
Glycoprotei
ns
Other
TOK: pg 27
Exercises 12-15: pg 30
Metabolic
pathway
Junctions
Gap junctions
Tight junctions
Active transport
Passive
transport