Question

1. How would eukaryotic genes that do not have operons ensure simultaneous expression of different genes?

2. Triacylglycerols are considered the major form of lipid considered as energy reservoirs in animals.

(a) What makes this lipid able to give larger amounts of energy when it is catabolized by the cell? Does its structure and components have something to do with it? If yes, how?

(b) TAGs are also considered one of the most abundant type of lipid, but they are not components of biological membranes. Why could be the reason why they cannot?

Answer 1

1. Eukaryotic genomes do not have genes arranged in operons. But eukaryotic genes that are co-regulated tend to have the same DNA regulatory element sequence associated with each gene, even if those genes are located on completely different chromosomes. This means the same transcriptional activator or repressor can regulate transcription of every single gene that has that particular DNA regulatory element associated with it. In eukaryotes heat shock proteins help cells survive and recover from heat shock . But the heat shock protein genes are located on different chromosomes. All heat shock protein genes are transcribed simultaneously in response to heat stress, because they all have a DNA sequence element that binds a heat shock response transcription factor.

2.a. Triglycerides consists of a central glycerol backbone that holds three fatty acid chains. These molecules are found predominantly in specialized storage cells called adipose (fat) cells. Triglycerides coalesce inside the cytoplasm of these cells to form large fat globules that take up the majority of the volume of the cell. Triglycerides are also stored in muscle cells and are used by these cells for ATP generation. Triglycerides are highly concentrated stores of metabolic energy because they are reduced and anhydrous. One gram of anhydrous triglyceride stores more than six times as much energy as one gram of carbohydrate and proteins. The basis of this large difference in caloric yield is that fatty acids are much more reduced. Furthermore, triacylglycerols are nonpolar, and so they are stored in a nearly anhydrous form, whereas much more polar proteins and carbohydrates are more highly hydrated.

2.b. Triglycerides or TAGs are tri-esters consisting of a glycerol bound to three fatty acid molecules. Triglycerols lack a polar headgroup, so they cannot orient themselves to form a bilayer .Inorder to form a bilayer, the non-polar acyl chains of triglycerides would have to be buried in the interior, and the glycerol moiety would have to be at the surface in contact with the water. Triglycerides are completely hydrophobic. For a membrane a lipid bilayer with both hydrophilic and hydrophobic ends are necessary.