Nutrient Compartmentalization Cellular Distribution

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The distribution of carbohydrates, lip-ids, proteins, vitamins, and other elements and molecules in animal cells resembles that of human cells (A) while plant cells differ considerably (B). In animal cells, carbohydrate reserves are stored as glycogen, and they can't store much of it. Their role as an energy reserve is of lesser importance since energy stored as fat uses space much more efficiently. Plants, except in seeds, don't have such problems of space and efficiency. They can, therefore, afford the uneconomic luxury of storing energy as large amounts of starch. Plant cell walls usually consist of polysaccha-rides, indigestible to humans, which are also called fiber or roughage. Lipids are always found in fat droplets made of triglycerides or vitamin A esters. They are also found in all biological membranes, which consist mostly of phospho- and sphingolipids. Human and animal cell membranes also contain cholesterol. Plant cell membranes do not.

Proteins are found in all cells and throughout all compartments, as well as all extracellular fluids. This reflects their importance in the structure and function of all living things. Most vitamins, minerals, and trace elements are associated with proteins and hence also found in all cell compartments. Plants contain intracellular organelles known as chloroplasts, not found in animal and human cells, which are the sites of photosynthesis. The structure of chlorophyll—the light absorbing molecule—resembles that of hemoglobin; however, whereas hemoglobin contains iron, chlorophyll has a magnesium ion in its center.

Even though nearly all nutrient types are present in all plant cells, their distribution varies greatly, depending on cell types. In a cereal grain, most vitamins and minerals (C) are found in the aleu-ron layer. This layer makes up just a few percent of the grain's weight. The largest compartment of a grain, the endosperm, consists nearly exclusively of carbohydrate in the form of starch. The germ, on the other hand, is rich in vitamin B1, vitamin E, and lipids. Usually, the germ is removed during the milling process to increase the shelf life of flour since hydrolysis or oxidation of the lip-ids contained in it would affect taste over time.

The aleuron layer and the germ are theoretically the nutritionally most valuable components of a cereal grain. In reality, though, most people prefer the vitamin- and mineral-deficient white flour.

Animal cells have similarly diverse distribution patterns. Muscle cells contain a high percentage of protein, whereas liver cells are rich in vitamins A, D, B12, and folate. Fatty tissues consist mostly of lipids, with which vitamin E and carotenoids are associated.

r A. Animal Cell

Fat droplets

Golgi body


Endoplasmic reticulum

Mitochondrion p B. Plant Cell-

Cell membranes

Triglycerides, phospholipids, protein, vitamin E, carotenes


Soluble and insoluble enzymes, "transporters" Chloroplast

Mg2+, Cu2+, Fe2+, protein, triglycerides, phospholipids

Cytoplasm hpo42-, H2PO4-, S04-,

K+, Mg4+, Ca4+, glucose, fructose, sucrose, amino acids, metabolites

Cell membranes

Triglycerides, phospholipids, cholesterol, vitamin E



Blood plasma

Na+, CI-, HCO3-, Ca2+, proteins, amino acids, glucose

Stored Ca2 Animal Cell

Fat droplets

Cytoplasm hpo42-, H2PO4-, S04-,

K+, Mg4+, Ca4+, glucose, fructose, sucrose, amino acids, metabolites

Stored Ca2 Animal Cell

r C. Structure of a Grain -

Pericarp Seed coat Aleuron layer Polyglucose (a -1.4), polysaccharides, proteins, trace elements



Proteins, vitamins, essential fatty acids, trace elements

Scutellum -


Proteins, vitamins, essential fatty acids, trace elements

Scutellum -


Nutrient distribution (% of total content in grain)








6 12 61

Pantothenic acid 43 9 41

9 12 34

y, +-1 = e

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  • reiss clark
    How compartmentalization affects human nutrition?
    6 years ago

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