TBR question ochem

[mcatdestroyer]

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Cell membranes are composed of many molecules, including phospholipids. A
phospholipid is a molecule with a glycerol backbone (HocH2-cH(oH)CH2oH),
plus two fatty acids, and a phosphate attached to the oxygen atoms of glyceroi.
A cell membrane would be most rigid if both of its fatty acids were:
A. completely saturated and short molecules.
B. completely saturated and long molecules.
C. uqsaturated and short molecules.
D. unsaturated and long molecules.
Solution
For the membrane to be rigid, there must be many interactions between the lipid
chains. The maximum degree of interaction occurs with long, saturated fitty
acids. Pick B and feel good yet again.

Isnt it D because unsaturated hydrocarbons are more rigid than saturated ones?😕

 

[Singhp03]

i think you miss read, they ask for a rigid membrane(talking about interaction) as oppose to a ridged molecule. So yea, unsaturation makes molecules ridged but since they are ridged, they do NOT interact well with each other. I think it was in the TBR books, they(the authors) said to think of saturated fatty acids as post-boiled spaghetti, which can wrap around each other and form a ridge layer; and unsaturated fatty acid as pre-boiled spaghetti, which slide and spill all over. Notice the longer and "softer" the spaghetti the more ridge mesh it will create.

 

[sciencebooks]

Cell membranes are composed of many molecules, including phospholipids. A
phospholipid is a molecule with a glycerol backbone (HocH2-cH(oH)CH2oH),
plus two fatty acids, and a phosphate attached to the oxygen atoms of glyceroi.
A cell membrane would be most rigid if both of its fatty acids were:
A. completely saturated and short molecules.
B. completely saturated and long molecules.
C. uqsaturated and short molecules.
D. unsaturated and long molecules.
Solution
For the membrane to be rigid, there must be many interactions between the lipid
chains. The maximum degree of interaction occurs with long, saturated fitty
acids. Pick B and feel good yet again.

Isnt it D because unsaturated hydrocarbons are more rigid than saturated ones?😕

Saturated fats are more rigid in groups because they are more straight (unsaturated = some kinks due to double bonds) and can stack more.

 

[Godric]

i remember the passage for this helped answer the question.

 

[V5RED]

One thing that can help is to think about how cooking fats work.

Saturated fats like lard are solid at room temperature. Unsaturated fats like olive oil are liquid at room temperature. A solid thing is more rigid than a liquid thing.

 

[osprey099]

Cell membranes are composed of many molecules, including phospholipids. A
phospholipid is a molecule with a glycerol backbone (HocH2-cH(oH)CH2oH),
plus two fatty acids, and a phosphate attached to the oxygen atoms of glyceroi.
A cell membrane would be most rigid if both of its fatty acids were:
A. completely saturated and short molecules.
B. completely saturated and long molecules.
C. uqsaturated and short molecules.
D. unsaturated and long molecules.
Solution
For the membrane to be rigid, there must be many interactions between the lipid
chains. The maximum degree of interaction occurs with long, saturated fitty
acids. Pick B and feel good yet again.

Isnt it D because unsaturated hydrocarbons are more rigid than saturated ones?😕

Think of it like this: Unsaturated causes more fluidity because there are double bonds. Short molecules cause more fluidity because they cannot pack as tightly as long molecules (have as many intermolecular attractions). So to get high rigidity, you want saturated and long fatty acids.

 

[johnnybravo19]

Fck everyone's analogies. Take my approach:

When it get's rigid, it gets LONG and HARD. 😉 Saturated with stuff inside
On the other hand, when it's Unsaturated, it's wobbly