2. Define trans fatty acid and

2.

An unhealthy substance that is made through the chemical processof hydrogenation of oils. Hydrogenation solidifies liquid oils andincreases the shelf life and the flavor stability of oils and foodsthat contain them. Trans fatty acids are found in vegetableshortening and in some margarine, crackers, cookies, and snackfoods. Trans fatty acids are also found in abundance in manydeep-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 transfat.

A major health concern during the hydrogenation process is theproduction of trans fats. Trans fats are the result of a sidereaction with the catalyst of the hydrogenation process. This isthe result of an unsaturated fat which is normally found as a cisisomer converts to a trans isomer of the unsaturated fat. Isomersare molecules that have the same molecular formula but are bondedtogether differently. Focusing on the sp2 double bonded carbons, acis isomer has the hydrogens on the same side. Due to the addedenergy from the hydrogenation process, the activation energy isreached to convert the cis isomers of the unsaturated fat to atrans isomer of the unsaturated fat. The effect is putting one ofthe hydrogens on the opposite side of one of the carbons. Thisresults in a trans configuration of the double bonded carbons. Thehuman body does not recognize trans fats.

Although trans fatty acids are chemically “monounsaturated” or”polyunsaturated,” they are considered so different from the cismonounsaturated or polyunsaturated fatty acids that they can not belegally designated as unsaturated for purposes of labeling. Most ofthe trans fatty acids (although chemically still unsaturated)produced by the partial hydrogenation process are now classified inthe 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 muchas saturated fat. Trans fat are found in margarine, baked goodssuch as doughnuts and Danish pastry, deep-fried foods like friedchicken and French-fried potatoes, snack chips, imitation cheese,and confectionery fats.

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

Hydrogenation would be the process of adding hydrogen to anunsaturated bond. This usually solidifies the said liquid fat dueto more induced dipole interactions. The usual purpose is so thatthey 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 snackfoods, from potato chips to frozen desserts.

Chemists create olestra by combining two naturally occurringsubstances, sucrose and vegetable oil, to form a molecule that isnot found anywhere in nature. Yet the resulting synthetic moleculetastes just like real fats do! Fat is what makes candy bars andfrench fries so filling (and fattening). With olestra, you get thetaste of the fat without any of the calories of the fat, becauseyour body has no way to digest olestra.

A typical fat molecule is essentially three long molecules madeof carbon and hydrogen hooked together . In olestra, there are sixto eight chains instead of three. These extra chains make olestra’smolecular structure much different from that of the typical fatmolecule. The reason that your body cannot digest olestra issimilar to the reason that your body cannot digest wood. Acellulose molecule is too long for your stomach to process becauseyour stomach lacks the right enzymes to handle it. Olestra is thesame way. Olestra simply passes through your stomach and intestinesunchanged. Olestra chips have calories from the potatoes, corn orother foods they contain, but no calories from the olestra (unlikea normal chip that contains 9 calories for every gram of fat).

4.

The fluid mosaic model was first proposed by S.J. Singer andGarth L. Nicolson in 1972 to explain the structure of the plasmamembrane. The model has evolved somewhat over time, but it stillbest accounts for the structure and functions of the plasmamembrane as we now understand them. The fluid mosaic modeldescribes the structure of the plasma membrane as a mosaic ofcomponents —including phospholipids, cholesterol, proteins, andcarbohydrates—that gives the membrane a fluid character. Plasmamembranes range from 5 to 10 nm in thickness. For comparison, humanred blood cells, visible via light microscopy, are approximately 8µm wide, or approximately 1,000 times wider than a plasma membrane.The proportions of proteins, lipids, and carbohydrates in theplasma membrane vary with cell type. For example, myelin contains18% protein and 76% lipid. The mitochondrial inner membranecontains 76% protein and 24% lipid.

The main fabric of the membrane is composed of amphiphilic ordual-loving, phospholipid molecules. The hydrophilic orwater-loving areas of these molecules are in contact with theaqueous fluid both inside and outside the cell. Hydrophobic, orwater-hating molecules, tend to be non- polar. A phospholipidmolecule consists of a three-carbon glycerol backbone with twofatty acid molecules attached to carbons 1 and 2, and aphosphate-containing group attached to the third carbon. Thisarrangement gives the overall molecule an area described as itshead (the phosphate-containing group), which has a polar characteror negative charge, and an area called the tail (the fatty acids),which has no charge. They interact with other non-polar moleculesin chemical reactions, but generally do not interact with polarmolecules. When placed in water, hydrophobic molecules tend to forma ball or cluster. The hydrophilic regions of the phospholipidstend to form hydrogen bonds with water and other polar molecules onboth the exterior and interior of the cell. Thus, the membranesurfaces that face the interior and exterior of the cell arehydrophilic. In contrast, the middle of the cell membrane ishydrophobic and will not interact with water. Therefore,phospholipids form an excellent lipid bilayer cell membrane thatseparates fluid within the cell from the fluid outside of thecell.

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 themembrane structure, and their hydrophobic membrane-spanning regionsinteract with the hydrophobic region of the the phospholipidbilayer. Single-pass integral membrane proteins usually have ahydrophobic transmembrane segment that consists of 20–25 aminoacids. Some span only part of the membrane—associating with asingle layer—while others stretch from one side of the membrane tothe other, and are exposed on either side. Some complex proteinsare composed of up to 12 segments of a single protein, which areextensively folded and embedded in the membrane. This type ofprotein has a hydrophilic region or regions, and one or severalmildly hydrophobic regions. This arrangement of regions of theprotein tends to orient the protein alongside the phospholipids,with the hydrophobic region of the protein adjacent to the tails ofthe phospholipids and the hydrophilic region or regions of theprotein protruding from the membrane and in contact with thecytosol or extracellular fluid.

There are 5 broad categories of molecules found in the cellularenvironment. Some of these molecules can cross the membrane andsome of them need the help of other molecules or processes. One wayof distinguishing between these categories of molecules is based onhow they react with water. Molecules that are hydrophilic (waterloving) are capable of forming bonds with water and otherhydrophilic molecules. They are called polar molecules. Theopposite can be said for molecules that are hydrophobic (waterfearing), they are called nonpolar molecules. Here are the 5types:

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

2.           Small, polar molecules (ex: water): This is a little more difficultthan the molecule type above. Recall that the interior of thephospholipid bilayer is made up of the hydrophobic tails. It won’tbe easy for the water molecules to cross, but they can crosswithout the help of proteins. This is a somewhat slowerprocess.

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

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