Question

18. Circle the fatty acid in each pair that has the higher melting temperature.
(a) 18:1∆9 vs 18:2∆9,12
(b) 18:0 vs 18:1∆9
(c) 18:0 vs 16:0
19. Categorize each of the following as an aldose, a ketose, or neither.
H H H H H
HOH OHOH HOHO
O HOH HOH HOH HOH HOH HOH HOHO HH
H H H H H
(a) (b) (c) (d) (e)


20. What is the most significant chemical difference between triacylglycerols and glycerophospholipids that leads to their different functions?  


21. What is the effect of a double bond on the fatty acid structure?  



22. (a) When relatively high concentrations of fatty acids are suspended in water, they form structures known as ________. (b) When relatively high concentrations of membrane phospholipids are dissolved in water, they form structures known as ________. (c) Why are the structures listed in your answers to (a) and (b) above energetically favored?  


23. What is the role of cholesterol in terms of membrane fluidity?


24. There are two reactions in glycolysis which involve the isomerization of an aldose to a ketose or vice-versa. What enzymes catalyze those two reactions?


25. The simple sugar that is used as the reference for naming D and L states of sugars is:



26. Draw D-glucose and a C-3 epimer of D-glucose.






27. Draw the cyclic forms of D-glucose and indicate the anomeric carbon with a *. Name the forms.




28. Describe the structure of starch. Include the identity of its subunits and the details of the bonds between them.




29. Why can humans not use cellulose as a nutrient?




30. Circle the following fatty acid that would have the lowest melting point. Put a square box around the fatty acid that is unlikely to be a natural product. Lastly, Name the fatty acid that you have not Circled or Boxed.

31. In cells, fatty acids are stored as triacylglycerols for energy reserves. Draw the molecule that fatty acids react with to form these energy storage molecules.

Answer 1

Ans.18) (a) 18:1∆9
(b) 18:0
(c) 18:0

Ans 20. Triacylglycerols are nonpolar hydrophobic molecules that can be stored in specialized nonaqueous cellular compartments. Glycerphospholipids are amphiphatic molcules that can serve as structural components of membranes, which have hydrophilic and hydrophobic regions.

Ans.21) Most double bonds in fatty acid are in the cis configuration. This results in rigid bend in the hydrocarbon chain.

Ans.23) Cholesterol acts as a bidirectional regulator of membrane fluidity because at high temperatures, it stabilizes the membrane and raises its melting point, whereas at low temperatures it intercalates between the phospholipids and prevents them from clustering together and stiffening. Cholesterol Helps Maintain the Fluidity of Cell Membranes. Adds firmness and integrity to the plasma membrane and prevents it from becoming overly fluid.

Ans.25) The simple sugar that is used as the reference for naming D and L states of sugars is:Glyceraldehyde

Ans.29.) . Cellulose is a linear polysaccharide polymer with many glucose monosaccharide units. Humans are unable to digest cellulose because the appropriate enzymes to breakdown the beta acetal linkages are lacking