Transcript 1.3 Membrane structure

1.3 MEMBRANE
STRUCTURE
PHOSPHOLIPIDS
Phospholipids are both
hydrophilic and
hydrophobic, they are
amphipathic.
Phosphate group = hydrophilic.
Hydrocarbon chains = hydrophobic.
PHOSPHOLIPID BILAYER
MODELS
Gorter & Grendel,
proposed a
bilayer.
Davson & Danielli,
proposed layers of
proteins.
High magnification
electron
microscopes.
Evidence of proteins.
Singer & Nicolson,
peripheral/integral proteins.
Fluid mosaic model.
FLUID MOSAIC MODEL
SKILLS
Analysis of evidence from electron microscopy
that led to the proposal of the Davson-Danielli
model.
Analysis of the falsification of the Davison-Danielli
model that led to the Singer-Nicolson model.
FALSIFICATION OF THEORIES
Who proposed
this model?
Davson & Danielli
Evidence proved this theory
• X-ray diffraction studies
• Electron microscopy etc.
FALSIFICATION OF THEORIES
Who proposed
this model?
Davson & Danielli
In 1950’2/60’s evidence appeared that DID
NOT fit the model.
• Freeze-etched electron microscopy
• Extracting & analysing membrane proteins
• Fluorescent antibody tagging
MEMBRANE PROTEINS
MEMBRANE PROTEINS
Integral
Peripheral
Usually hydrophobic on the Usually hydrophilic.
surface.
Embedded in the
hydrocarbon chains in the
centre of the membrane.
Usually attached to the
surface of the integral
proteins.
If they have hydrophilic
parts, these will appear
outside the membrane
(transmembrane).
Usually have a single, HC
chain which can be
inserted into the
membrane = anchor.
MEMBRANE PROTEINS CONT.
Functions
Hormone binding sites e.g. Insulin.
Immobilized enzymes, active site on the outside of enzymes
(small intestines).
Cell adhesion - form tight junctions between cells.
Communication e.g. neurotransmitter receptors.
Protein channels for passive transport of materials.
Active transport, pumps use ATP to move substances across
the membrane.
WHAT DO THESE HAVE IN COMMON?
CHOLESTEROL
Facts
Type of lipid
Categorised as a steroid
Amphipathic
Hydrophobic HC ‘tails’
Hydrophilic hydroxyl
group (attracted to
phosphate groups on
membrane).
• Up to 30% of lipid in the
membrane can be
cholesterol.
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Functions
Fluidity of the membrane
Cholesterol ‘breaks up’
phospholipid arrangement
 increase in fluidity.
BUT it can restrict
movement.
Help membranes to curve
(due to its shape.
TIE-DYE MILK EXP.
• Record qualitative results in a table.
• Write a short paragraph to explain your
observations.
• Method available on moodle.
• Think: Safety!