Carbohydrates as
Biomolecules
Carbohydrates are biomolecules that always contain carbon, hydrogen, and oxygen. Polysaccharides
are built from monosaccharides.
The monomers of large carbohydrate molecules are the monosaccharide simple sugar carbohydrates,
most notably glucose. Dextrose is the term used for glucose in the purified form administered in IVs
or other medical settings. The two other main 6 carbon monosaccharides are fructose and galactose.
Disaccharides are two simple sugar monosaccharides put together. Sucrose is one glucose and one
fructose. Lactose and maltose are the two other well-known disaccharides.
Polysaccharides, the very large biomolecules that are built with many many simple sugars. Plant
starch is digestible by the enzyme amylase. Amylase breaks down complex carbohydrates such as
starch into many many individual molecules of glucose.
, Animals store their carbohydrates as long branching chains called glycogen. We can store limited
quantities of glycogen in our liver and our muscle cells.
Plant cellulose is highly structured polysaccharide, and it makes up all plant cell walls. This is
completely indigestible for us. Cellulose provides us with insoluble dietary fiber.
Peptidoglycan, which is actually a combination of carbohydrate and proteins - makes up bacterial cell
walls. Protein cross-links hold together many layers of simple sugars.
Glucose is what we measure when we test for blood glucose or blood sugar. The ideal range in the
blood remains quite steady, even between meals. As people lose metabolic flexibility or become pre-
diabetic, they may vary more and more widely from the ideal range of between 70 - 120mg/dL.
Hyperglycemia literally means too much sugar in the blood. It is most commonly seen when people
damage their metabolism and begin to develop Type II diabetes. Hypoglycemia is the opposite
problem, not enough sugar in the blood. It is most commonly seen in diabetics that inject more
insulin than they needed. As we’ll see in a moment, insulin lowers blood sugar. Normoglycemia
means normal amounts of sugar in the blood.
Now, in order for the polar glucose molecules to pass through the cell membranes and enter cells,
the protein hormone insulin binds to insulin receptors on cells. These receptors then stimulate
glucose channels to be inserted into the cell membrane; the polar glucose molecules can then
passively enter the cells through these glucose channels, moving down their concentration gradient.
Insulin allows glucose to enter cells. Thus, insulin decreases blood sugar.
Once inside the cell, glucose is broken down in the cytoplasm in the process of glycolysis, into 2 3-
carbon molecules called pyruvate. Pyruvate enters the mitochondria, where complete breakdown of
the carbon molecules is finished with many enzymatic reactions of the Citric Acid Cycle. The electron
transport chain, on this inner mitochondrial membrane, then generates ATP energy for cellular
activities. Glucose is a key source of ATP production for many cells.
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