2. (6pts) The properties of a lipid bilayer are determined by the structures of
ID: 190958 • Letter: 2
Question
2. (6pts) The properties of a lipid bilayer are determined by the structures of its lipid molecules. I the following were true, would you predict the membrane to be more fluid, less fluid, or the same fluidity as a normal membrane? Provide a briet explanation for each answer. A. The hydrocarbon chains were longer than normal, -24 carbon atoms long B. An extra C-C double bond were introduced to every tailgroup C. Each lipid's molecules two tailgroups were covalently liked to each other D. Each lipid molecule were covalently linked through the end carbon atom of one of its hydrocarbon chains to a lipid molecule in the opposite monolayer 3. (3pts) Please state if you AGREE or DISAGREE with the following, & provide your reasoning: and beta sheets forr In proteins, secondary structure elements because of favorable interactions between sidechains.Explanation / Answer
Biological membranes are mainly composed of lipids and proteins (protein molecules float in the sea of lipids) and provide selective permeability for various molecules into the cell. They are a sheet like, non-covalent assemblies. The lipid molecules of the membrane prevent the free flow of polar molecules whereas proteins serve as receptors for signalling cascades and components of transport systems. Membrane structure and composition is dynamic i.e., it changes according to the environmental conditions. They are asymmetric and fluid in nature i.e., all the lipids and several proteins can easily diffuse rapidly in the plane of the membrane.
The fluidity of the membrane depends on its chemical composition and temperature. Lipids with longer fatty acid chains have more interactions between the hydrophobic fatty acid tails, stabilizing the crystal-like state and making the membrane less fluid. Saturated fatty acids also strengthen membranes and reduce fluidity.
The longer chains would increase the amount of Vander Waals interactions and absence of double bonds reduces the kink in structure, would enhance packing of the fatty acid tails of the phospholipids.
Incorporation of specific lipids, such as sphingomyelin is known reduce the membrane fluidity. So, its synthesis may go up. Cholesterol acts as a positive as well as a negative regulator of membrane fluidity. At high temperatures, it stabilizes the membrane structure, whereas at low temperatures it intercalates between the phospholipids and prevents them from clustering together.
Crosslinking within the monolayer increases fluidity.
Crosslinking between monolayers decreases fluidity.
Answers:
A. More fluid
B. Less fluid
C. More fluid
D. Less fluid
3.
Secondary structures are stabilized by interactions among peptide backbone (-CO-NH-).
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