This summary consists of a summary of Chapter 8 of Biology A Global Apprach. In it the cell membrane is discussed and transport (both passive and active)
This summary is divided into sections as indicated in the book in.
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⚠ The most abundant lipid in membranes are phospholipids. These are
amphipathic molecules, meaning both hydrophilic and hydrophobic.
Most of the membrane proteins are also amphipathic.
The Fluidity of Membranes
A membrane is held together by hydrophobic interactions, which are
weaker than covalent bonds. Lipids in the membrane can switch with other
lipids.
A membrane remains fluid as temperature decreases until the
phospholipids settle into a packed position. Now the membrane is solid.
A membrane with lots of unsaturated lipids can hold a lower
temperature, because the kinks in the tail cannot pack well together.
Cholesterol sits between phospholipids and makes it harder to pack
together, decreasing the temperature needed to solidify the membrane.
Celbiologie 1
, At higher temperatures, it makes the phospholipids stick, making it less
fluid. Cholesterol is therefore called 'fluidity buffer'.
Membranes must be fluid to function properly. If the membrane becomes
solid, then the proteins and other components may become inactive.
Membranes that are to fluid cannot hold everything in place.
Membrane Proteins and Their Function
There are 2 major populations of membrane proteins: integral proteins and
peripheral proteins.
Integral proteins penetrate the hydrophobic interior of the membrane.
Mostly transmembrane proteins, which span the membrane.
Some only extend partway into the hydrophobic interior.
Peripheral proteins are not embedded in the membrane, they are
loosely bound to the surface and often exposed to integral proteins.
On the cytoplasmic side, the proteins are held in place by attachment to the
cytoskeleton. On the extracellular side, membrane proteins may attach to
materials outside the cell.
Celbiologie 2
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