Chapter 11 – membrane structure - The most abundant lipids in a cell membrane are phospholipids
- Phospholipids have a phosphate containing hydrophilic head linked
- Plasma membrane – a protein studded fatty film
to a pair of hydrophobic tails
- All cells have plasma membrane to protect their chemical
components from the outside environment
- Structure of plasma membranes are simple, there’s two ply-sheet of
lipid molecules about 5 nm/50 atoms thick
- Plasma membrane does more than just acting as a barrier - Phosphatidylcholine, for example, has the small molecule choline
- There are protein channels and transporter that allow specific attached to a phosphate group as its hydrophilic head
molecules and ions to move in and out of the cells; but membranes - the tails are long hydrocarbon chains typically 14 carbons long
are permeable regardless of channel or transporter proteins - unsaturated (not bonded with hydrogens, double bonded with
- There are other way movement in and out of the cell can take place another carbon) tails are bent
- Other proteins act as sensors and receptors that allow the cell to - Molecules with both hydrophobic and hydrophilic parts are called
receive signals amphipathic
- Plasma membrane also grows with cell size, it can also change shape - Cholesterol, found in animal cell membranes and glycolipids, which
- It can also reseal if broken have sugars as part of their hydrophilic heads are amphipathic
- All cell membranes are composed of lipids and proteins - Hydrophilic molecules are highly soluble because their have charged
- Membranes are permeable or uncharged polar groups that can form electrostatic attractions
- The lipids form a lipid bilayer; acts as a permeability barrier to water or hydrogen bonds with water
soluble molecules - Hydrophobic molecules are not soluble as they do not have charged
- The proteins gave other functions in the membrane and give the atoms and they are nonpolar
membranes their characteristics - Water forms a cage like structure around hydrophobic molecules,
- Animals have extracellular matrixes that help with structure and this is a very ordered structure of water and thus requires free
protection, but they don’t have a cell wall energy
- Endoplasmic reticulum have a single membrane surrounding it. The - To reduce the need of free energy, hydrophobic molecules like fats
inside is hollow, the empty hollow space is called the lumen form a single large drop when dispersed in water
- Amphipathic molecules form a lipid bilayer that allows both the
THE LIPID BILAYER
hydrophobic tail and hydrophilic tail to coexist in the most
- Cells are surrounded and filled by water, so the structure of cell energetically favoured position
membranes are determined by the way the lipids behave in that - The hydrophilic heads are on the outer surface on both sides of a
environment bilayer and the hydrophobic tails are inside
- Bilayers are self sealing
Membrane Lipids Form Bilayers in
Water
- Each lipid has a hydrophobic tail
(water fearing) and a hydrophilic
head (water loving)
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