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Lecture

BIOCH 200 (March 14, 2014) - Biological Membranes

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Department
Biochemistry
Course
BIOCH200
Professor
Walter Dixon
Semester
Winter

Description
BIOCH 200 – Biological Membranes (con’t)  (March 14, 2014) • *Cholesterol helps maintain BOTH fluidity and stability of the lipid bilayer o *Help maintain rigidity: by reducing rotational capabilities of the acyl tails at high temperatures o *Help maintain fluidity: by preventing close chain-packing between acyl chains in cold temperatures • *Transition temperature – temperature at which the lipid membrane turns from a crystalline state to a more fluid state o *Remember, the lipids are held together by hydrophobic interactions… NOT covalent bonding o *Is usually a range o If a cell is exposed to colder temperatures, it’s membrane will have a higher unsaturated lipid content, to counteract crystallizing temperatures (cell synthesizes them in response) o If a cell is exposed to higher temperatures, the cell will synthesize a higher amount of saturated lipids for the lipid membrane to maintain stability. o Membranes must exist ABOVE gel temperature  *At gel temperature, lipid bilayer is too stiff to allow for molecules to pass through efficiently  cell doesn’t get nutrients fast enough  cell dies • Lipids of membrane: o Travel laterally o *Do some transverse diffusion (flip-flopping to other side of membrane) but rarely  Process is catalyzed by flippase enzym
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