The details of macromolecules found in plasma membranes were covered in lectures
ID: 151570 • Letter: T
Question
The details of macromolecules found in plasma membranes were covered in lectures 2-4. Which of the following statements is not supported by the fluid mosaic model?
The major structural component of the plasma membrane is a phospholipid bilayer.
Cholesterol is a “mosaic” part of the model because it is found in the interior of the plasma membrane due to its hydrophobicity. .
Peripheral glycoproteins on the extracellular surface play a role in cell-cell recognition.
Membranes with a higher ratio of saturated fatty acids are more fluid.
Some integral proteins have enzymatic activity.
Some integral proteins help connect the ECM to the cell and transmit signals across the membrane.
The major structural component of the plasma membrane is a phospholipid bilayer.
b.Cholesterol is a “mosaic” part of the model because it is found in the interior of the plasma membrane due to its hydrophobicity. .
c.Peripheral glycoproteins on the extracellular surface play a role in cell-cell recognition.
d.Membranes with a higher ratio of saturated fatty acids are more fluid.
e.Some integral proteins have enzymatic activity.
f.Some integral proteins help connect the ECM to the cell and transmit signals across the membrane.
Explanation / Answer
The fluid mosaic model was first proposed by S.J. Singer and Garth L. Nicolson in 1972. It explains the structure of the plasma membrane as a mosaic of phospholipids, cholesterol, proteins, and carbohydrates-giving the membrane a fluid character. It is 5-10nm thick. The proportion of the biomolecules contained in the plasma membrane varies with cell type.
d) Membranes with a higher ratio of saturated fatty acids are more fluid is not supported by the fluid mosaic model because in their saturated form, the fatty acids in phospholipid tails are saturated (no double bonds between adjacent carbon atoms) with bound hydrogen atoms. This results in relatively straight tails. In opposite to this, unsaturated fatty acids contain less number of hydrogen atoms, although they do contain some double bonds between adjacent carbon atoms; which results in a bend of approximately 30 degrees in the string of carbons. So, if saturated fatty acids with straight tails are compressed by decreasing temperatures, they press onto each other, resulting in a dense and fairly rigid membrane. If unsaturated fatty acids are compressed, the kinks in their tails push adjacent phospholipid molecules away, maintaining some space between the phospholipid molecules. This room or space created by the pushing the adjacent phospholipid molecules away helps to maintain fluidity in the membrane at temperatures at which membranes with saturated fatty acid tails in their phospholipids would freeze or solidify. For example a cold environment tends to compress membranes composed largely of saturated fatty acids, making them less fluid and more susceptible to rupturing. Organisms like fish are capable of adapting to cold environments by changing the proportion of unsaturated fatty acids in their membranes in response to the lowering of the temperature.