Question

2. Define trans fatty acid and explain the process of hydrogenation.

3. What is Olestra? What is its chemical composition? Why is it not metabolized by the body?

4. What is the fluid mosaic model? How does the chemical composition of the cell membrane affect transport across the membrane?

please answer questions thoroughly thank you

Answer 1

2.

An unhealthy substance that is made through the chemical process of hydrogenation of oils. Hydrogenation solidifies liquid oils and increases the shelf life and the flavor stability of oils and foods that contain them. Trans fatty acids are found in vegetable shortening and in some margarine, crackers, cookies, and snack foods. Trans fatty acids are also found in abundance in many deep-fried foods. Trans fatty acids both raise the 'bad' (LDL) cholesterol and lower the 'good' (HDL) cholesterol levels in blood, markedly increasing the risk of heart disease. Also known as trans fat.

A major health concern during the hydrogenation process is the production of trans fats. Trans fats are the result of a side reaction with the catalyst of the hydrogenation process. This is the result of an unsaturated fat which is normally found as a cis isomer converts to a trans isomer of the unsaturated fat. Isomers are molecules that have the same molecular formula but are bonded together differently. Focusing on the sp2 double bonded carbons, a cis isomer has the hydrogens on the same side. Due to the added energy from the hydrogenation process, the activation energy is reached to convert the cis isomers of the unsaturated fat to a trans isomer of the unsaturated fat. The effect is putting one of the hydrogens on the opposite side of one of the carbons. This results in a trans configuration of the double bonded carbons. The human body does not recognize trans fats.

Although trans fatty acids are chemically "monounsaturated" or "polyunsaturated," they are considered so different from the cis monounsaturated or polyunsaturated fatty acids that they can not be legally designated as unsaturated for purposes of labeling. Most of the trans fatty acids (although chemically still unsaturated) produced by the partial hydrogenation process are now classified in the same category as saturated fats.

The major negative is that trans fat tends to raise "bad" LDL- cholesterol and lower "good" HDL-cholesterol, although not as much as saturated fat. Trans fat are found in margarine, baked goods such as doughnuts and Danish pastry, deep-fried foods like fried chicken and French-fried potatoes, snack chips, imitation cheese, and confectionery fats.

During hydrogenation, vegetable oils are reacted with hydrogen gas at about 60ºC. A nickel catalyst is used to speed up the reaction. The double bonds are converted to single bonds in the reaction. In this way unsaturated fats can be made into saturated fats – they are hardened.

Hydrogenation would be the process of adding hydrogen to an unsaturated bond. This usually solidifies the said liquid fat due to more induced dipole interactions. The usual purpose is so that they don't spoil as quickly as unsaturated fats. By hydrogenating, it is also easier to store the product.

3.

Olestra is a fat substitute. It is found in a number of snack foods, from potato chips to frozen desserts.

Chemists create olestra by combining two naturally occurring substances, sucrose and vegetable oil, to form a molecule that is not found anywhere in nature. Yet the resulting synthetic molecule tastes just like real fats do! Fat is what makes candy bars and french fries so filling (and fattening). With olestra, you get the taste of the fat without any of the calories of the fat, because your body has no way to digest olestra.

A typical fat molecule is essentially three long molecules made of carbon and hydrogen hooked together . In olestra, there are six to eight chains instead of three. These extra chains make olestra's molecular structure much different from that of the typical fat molecule. The reason that your body cannot digest olestra is similar to the reason that your body cannot digest wood. A cellulose molecule is too long for your stomach to process because your stomach lacks the right enzymes to handle it. Olestra is the same way. Olestra simply passes through your stomach and intestines unchanged. Olestra chips have calories from the potatoes, corn or other foods they contain, but no calories from the olestra (unlike a normal chip that contains 9 calories for every gram of fat).

4.

The fluid mosaic model was first proposed by S.J. Singer and Garth L. Nicolson in 1972 to explain the structure of the plasma membrane. The model has evolved somewhat over time, but it still best accounts for the structure and functions of the plasma membrane as we now understand them. The fluid mosaic model describes the structure of the plasma membrane as a mosaic of components —including phospholipids, cholesterol, proteins, and carbohydrates—that gives the membrane a fluid character. Plasma membranes range from 5 to 10 nm in thickness. For comparison, human red blood cells, visible via light microscopy, are approximately 8 µm wide, or approximately 1,000 times wider than a plasma membrane. The proportions of proteins, lipids, and carbohydrates in the plasma membrane vary with cell type. For example, myelin contains 18% protein and 76% lipid. The mitochondrial inner membrane contains 76% protein and 24% lipid.

The main fabric of the membrane is composed of amphiphilic or dual-loving, phospholipid molecules. The hydrophilic or water-loving areas of these molecules are in contact with the aqueous fluid both inside and outside the cell. Hydrophobic, or water-hating molecules, tend to be non- polar. A phospholipid molecule consists of a three-carbon glycerol backbone with two fatty acid molecules attached to carbons 1 and 2, and a phosphate-containing group attached to the third carbon. This arrangement gives the overall molecule an area described as its head (the phosphate-containing group), which has a polar character or negative charge, and an area called the tail (the fatty acids), which has no charge. They interact with other non-polar molecules in chemical reactions, but generally do not interact with polar molecules. When placed in water, hydrophobic molecules tend to form a ball or cluster. The hydrophilic regions of the phospholipids tend to form hydrogen bonds with water and other polar molecules on both the exterior and interior of the cell. Thus, the membrane surfaces that face the interior and exterior of the cell are hydrophilic. In contrast, the middle of the cell membrane is hydrophobic and will not interact with water. Therefore, phospholipids form an excellent lipid bilayer cell membrane that separates fluid within the cell from the fluid outside of the cell.

Proteins make up the second major component of plasma membranes. Integral proteins (some specialized types are called integrins) are, as their name suggests, integrated completely into the membrane structure, and their hydrophobic membrane-spanning regions interact with the hydrophobic region of the the phospholipid bilayer. Single-pass integral membrane proteins usually have a hydrophobic transmembrane segment that consists of 20–25 amino acids. Some span only part of the membrane—associating with a single layer—while others stretch from one side of the membrane to the other, and are exposed on either side. Some complex proteins are composed of up to 12 segments of a single protein, which are extensively folded and embedded in the membrane. This type of protein has a hydrophilic region or regions, and one or several mildly hydrophobic regions. This arrangement of regions of the protein tends to orient the protein alongside the phospholipids, with the hydrophobic region of the protein adjacent to the tails of the phospholipids and the hydrophilic region or regions of the protein protruding from the membrane and in contact with the cytosol or extracellular fluid.

There are 5 broad categories of molecules found in the cellular environment. Some of these molecules can cross the membrane and some of them need the help of other molecules or processes. One way of distinguishing between these categories of molecules is based on how they react with water. Molecules that are hydrophilic (water loving) are capable of forming bonds with water and other hydrophilic molecules. They are called polar molecules. The opposite can be said for molecules that are hydrophobic (water fearing), they are called nonpolar molecules. Here are the 5 types:

1.            Small, nonpolar molecules (ex: oxygen and carbon dioxide) can pass through the lipid bilayer and do so by squeezing through the phospholipid bilayers. They don't need proteins for transport and can diffuse across quickly.

2.            Small, polar molecules (ex: water): This is a little more difficult than the molecule type above. Recall that the interior of the phospholipid bilayer is made up of the hydrophobic tails. It won’t be easy for the water molecules to cross, but they can cross without the help of proteins. This is a somewhat slower process.

3.            Large, nonpolar molecules (ex: carbon rings): These rings can pass through but it is also slow process.

4.            Large, polar molecules (ex: simple sugar - glucose) and ions: The charge of an ion, and the size and charge of large polar molecules, makes it too difficult to pass through the nonpolar region of the phospholipid membrane without help.