Question

WINILIT OF the following statements is true about biological membranes? Integral membrane proteins are composed exclusively of alpha-helices Lipid bilayers are easily permeable to various ions Both proteins and lipids readily undergo transverse diffusion ("flip-flopping") from the inside to the outside leaflet of the membrane O Membrane lipids self-assemble via non-covalent interactions to form lipid bilayers O Polar head groups in membrane phospholipids are always negatively charged

Answer 1

Answer: The true statements about the biological membranes are

Membrane lipids self assemble via non-covalent interaction to form lipid bilayers.

Polar head groups in membrane phospholipids are always negatively charged.

Explanation for true statements: Hydrophobic interactions are mainly responsible for the self assembly of the lipid bilayer.The hydrophobic tails of the lipid bilayer exclude water and come together forming the interior part of the phospholipid bilayer.Non covalent interactions like Vanderwaal’s forces bring the hydrophobic tails close to each other. Between the polar head groups there are interactions because of hydrogen bond and electrostatic forces. All these interactions help in self assembly of the lipid bliayer.

The polar head groups of the phospholipid billayer are hydrophilic and negatively charged.

Explanation for the other statements:

Mostly the membrane spanning domain is alpha helices but in porins (special transmembrane proteins,also known as beta barrel proteins) there are beta strands present.

Lipid bilayers are permeable only to small uncharged molecules but they are impermeable to large polar molecules and also impermeable to ions.

Transverse diffusion is movement of molecules from one side of the membrane to the other side.Lipid bilayer can undergo transverse diffusion once in many hours as it is a very slow process but unlike lipid bilayer the membrane proteins can not flip flop because the polar portion of the protein has to pass through the non polar portion core of the membrane and hence it is a high energy barrier.

Lipids and proteins can show lateral diffusion. But only lipids can show the transverse diffusion,proteins can not.