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Protein Digestion Class Test Solutions at Pomona College – Fall 2022

Below are well-explained solutions for a class test done in fall 2022 at Pomona College. Please revise the solutions for a glimpse of what professional biology test assistance looks like. And, in case you need someone to do your human biology tests, don’t hesitate to contact us for instant help.

Discuss The Human Body’s Food Needs for Good Health

The human being, like any other creature, has a limited range of food-stuffs and a limited power of converting digested materials into actual needs. He or she does not have to eat meat to make the meat of muscle tissue, but he or she does have to eat the right vitamins, for example, and the right kinds of protein to stay alive. Food is the supply of raw materials, but when broken down by digestion these are still partially constructed for our needs. A house-builder requires neither trees nor sawdust to make a house but needs the intermediate plank form. The body requires neither meat nor its elemental constituents of nitrogen, hydrogen, carbon, and oxygen, but the intermediate amino-acid form. As the house- builder needs more than one type of plank to make his house, the body requires some thirty to forty essential nutrients.

These essentials consist of about a dozen vital minerals, about a dozen vitamins, some ten amino-acids, a lot of water, and sufficiency of fats, carbohydrates, and proteins. From these, the countless profusion of different bodily constituents will be manufactured, such as the hemoglobin of blood, with each molecule possessing 64,000 atoms, the nucleic acids possessing even more, and the digestive enzymes that can break down still larger molecules. Yet all this profusion also consists of just a very few elements. If a human body (of 156 lbs./70 kgs.), were analyzed completely in a test-tube, and all its complexities were rendered into their constituent elements, it would be found to consist of oxygen 100 lbs. (45.4 kgs.), carbon 28 lbs. (12-7 kgs.), hydrogen-15 lbs. (6-8 kgs.), nitrogen-4.6 lbs. (2 kgs.), calcium -2-3 lbs. (1 kg.), phosphorus 1-6 lbs. (0-7 kgs.), potassium- 8-5 ozs. (241 gms.), sulphur-6 ozs. (170 gms.), sodium-3.7 ozs. (105 gms.), chlorine-3.7 ozs. (105 gms.), magnesium-1.25 ozs. (35 gms.), iron-0-15 ozs. (4-2 gms.), zinc 1-9 grams, copper 0-2 grams, manganese 0-02 grams, molybdenum 0.015 grams, some cobalt, some selenium, and some still smaller fractions of other elements.

Schoolmasters sometimes comment facetiously that, chemically, the body is worth about £1, and certainly there is nothing exotic about its main constituents, although some of the trace elements might fetch more money these days. Nevertheless, nobody could survive were it to be presented, like a chemical Pygmalion, with a ready supply of its constituent elements in the elemental form: it has to have them as protein, as fat, as carbohydrate, as vitamins, as water, and only to a limited extent can it have them as salts and simple inorganic chemicals.

Discuss Proteins as An Element Needed by The Human Body

Every cell contains proteins, and about 18% of body weight consists of protein. They are the most complex compounds found in nature, and consequently have large molecular weights varying from a few thousand to several million. (A molecular weight is relative to that of an atom to oxygen which is taken to be 16.) However big, the structure is always built up of amino-acids, the small constituent units of every protein. Egg albumin, for example, the ordinary 'white' of egg surrounding the yolk, is a small-sized protein of molecular weight 45,000. It consists of 418 amino-acid units bonded together to form each molecule of albumin. Each amino-acid unit has of course a smaller molecular weight than the large built-up protein, and amino-acid weights vary from 75 (glycine) to 240 (cystine).

The list of amino-acids makes unexciting reading, but their vital role demands that they should be heard. Some are more vital than others, and the ten which have been found to be indispensable in the diet of a young growing rat have been under- lined. Without every one of these ten essential amino-acids the laboratory rats suffered. With sufficient supplies of all ten the young rats were able to make the remaining amino acids necessary for the build-up of their proteins. There are several variants in the list of amino-acids, but the basic types include:

Glycine C2 H2 NO2 

Alanine C3 H7 NO2 

Serine C3 H7 NO3 

Threonine C4 H9 NO3

Valine C5 H11 NO2

Norleucine C6 H13 NO2

Leucine C6 H13 NO2

Isoleucine C6 H13 NO₂

Cystine C6 H12 N2 S2 O2

Methionine C5 H11 SNO2 

Aspartic acid C4 H7 NO4 

Glutamic acid C5 H9 NO4 

Hydroxyglutamic acid C5 H9 NO5

Arginine C6 H14 N4 O2 

Lysine C6 H14 N2 O2 

Phenylalanine C9 H11 NO2

Tyrosine C9 H11 NO3

Tryptophan C11 H₁₂ N2 O2 

Histidine C6 H9 N3 O2 

Proline C5 H9 NO2

Hydroxyproline C5 H9 NO3

Like carbohydrates and fats, proteins consist largely of carbon, hydrogen, and oxygen; but, unlike carbohydrates and unlike fats, proteins are distinguished by the presence of nitrogen. Every single one of the amino-acids contains some nitrogen, and a couple contains sulfur as well. The proteins in the human diet are practically the only source of new nitrogen. Constant replenishment of nitrogen is necessary because the reversibly damaged proteins lead to the loss of nitrogen; it passes out of the body in urine as urea. Proteins are also the chief source of sulfur. The figures listed in parentheses after the chemical formulae are the numbers of each of these amino-acids units present in egg albumin.

This one example of the constituents of one fairly simple protein should give some idea of the hideous complexity of organic chemistry, particularly concerning proteins. Ordinary inorganic chemistry seems infantile when set beside the interactions of such large molecules. Every schoolboy is taught basic inorganic reactions, like sulphuric acid acting upon zinc when H2 SO4 + Zn=ZnSO4 + H2. The production of zinc sulfate and hydrogen is straightforward and entirely elementary compared with the changes that must take place when, for example, egg albumin is merely heated. Everyone knows it changes irreversibly with heat from being transparent and fluid to opaque and stiff (in four minutes if you like your egg done that way), but the chemistry of that change and how heat affects those 418 amino-acid units is formidable. Even writing down the 418 constituent formula units of just one albumin molecule is a major endeavor.

Proteins, in short, are complex. However it is not their complexity that is vital to our diet, but their amino-acids (plus their nitrogen and sulfur). Digestion breaks down the large molecules into these amino-acids, and the body then builds up its vast protein molecules, albumin, its hemoglobin, its nucleoproteins, its enzymes, collagens, and keratins. As might be expected animal proteins are, when broken down, nearer to human requirements than plant proteins, but our normal human diet contains a bit of both.

Which Is the Right Amount of Protein in The Body?

In Britain, the average consumption per person per day is 3 ozs. (85 gms.) of protein, almost 2 oz. (57 gms.) of which are animal proteins. In New Zealand, Canada, the United States, and Australia the consumption is nearer 4 ozs. (113 gms.) daily, with nearly 3 ozs. (85 gms.) of animal protein. Conversely, India eats less than 2 oz. (57 gms.) of protein a day, of which only a fifth of an ounce (6 gms.) is of animal protein. If all these figures, even for North America, seem low it should not be forgotten that water is the main weight of most foods. There is only a quarter of an ounce (7 gms.) of protein in a pint of human milk and 3 oz. (85 gms.) or less protein in every pound of beef.

Anyone's intake of either total or animal protein is a very fair guide, and often an extremely precise one, to his or her income in the world. The United States Food and Nutrition Board recom- mends I gm. of protein daily for adults for each kilogram of their body weight (and therefore 2 ½ oz. a day for a 156 lbs. man). This is less than the average American eats, but probably more than he needs, and decidedly more than most people in the world achieve.

Vegans, the vegetarians who eat no animal products, not even the eggs or cheeses that are entirely acceptable to other groups, have to subsist wholly on plant protein. This can lead to dietary difficulties, but plant proteins can be mixed in such a way that the amino-acid content of the mixture is adequate. Many strict vegetarians have adopted the diet for ideological reasons, but tend to look upon the whole business of eating as a slightly sordid necessity. Consequently, they can be lax about diet, and there can be deficiencies in it. Vitamin B12 is an additional complexity for it is short in a vegan's diet. It can easily be supplemented, but its lack may also encounter a general lack of enthusiasm for caring about the unpleasant demands of mere food.

Where Should We Find Proteins?

All flesh, whether of fish, fowl, or mammal, is rich in protein. Cow's milk can have more than twice as much protein as human milk, the dried or condensed milk have a still greater proportion by weight and the cheeses have even more. Cereals contain some protein, roughly 5%-10% by weight, with rice and rye being less good in this respect than wheat and maize. The sugars have no protein, but nuts, beans, lentils, and all such firm botanical end-products are rich in them. Fruits also contain protein, but only 1% or so by weight as so much of their bulk is water. The same also applies to vegetables although, with their water content usually less predominant, the protein proportion is greater.

Where to acquire more protein? The world is short of it, and this lack is the greatest single cause of malnutrition. Kwashiorkor (which in South Africa means the 'disease of a child when another is born') is a protein deficiency and generally occurs after weaning. Even today, with so much chemistry applied to the food industry, no protein is produced synthetically for food on any major scale. Attempts to short-circuit traditional gastronomic procedures have generally been frustrated by human conservatism. 'The force of habit of millions of people is a terrible force' said Lenin. Bill Pirie, of the Rothamsted Experimental Station, has con- stantly produced new schemes for stepping up protein supplies. His 'mechanical cows' have extracted it from leaves, from grass, from cereal waste; and yet people are still suffering from lack of it. The wealthier countries, with enough protein to eat, are more tolerant of new foods than the poorer countries and are in greater need of supplementary-and novel-foods.

Most traditional methods of protein production are wasteful and lengthy. In twenty-four hours half a ton of bullock will make 1 lb. (0.45 kgs) of protein; in twenty-four hours half a ton of yeast will make fifty tons of protein. One wonders how long the world will permit itself to be semi-carnivorous. It is so much more economical not to process available protein through creatures like the cow, the sheep, and the pig before eating it. Vegetarians have long advocated their policy because the raising and killing of animals for food is thoroughly dis- tasteful. Other arguments are equally strong, such as the inefficiency of the process and the great quantities of land consumed not just by the animals themselves but by food grown specifically for them. England, for example, could easily become self- sufficient in food if it became vegetarian, and had lots left over for the hungrier regions of the world.

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