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Carbohydrates 101

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Angel Cruz

on 1 December 2015

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Transcript of Carbohydrates 101

Otherwise known as
, these molecules consist of carbon, hydrogen and oxygen atoms.

A major food source and a key form of energy for most organisms.

When combined together to form polymers, carbohydrates can function as:

Long term food storage molecules
Protective membranes
Structural support for plants
Constituents of cell contents
And so forth
Identification methods
Benedict’s Test:  

Any carbohydrate with a potentially free carbonyl group (C=O) will reduce Benedict’s solution and is therefore called a reducing sugar.  The carbonyl group of carbohydrates such as sucrose, starch, and cellulose are engaged in bonding and will not reduce Benedict’s solution.

Place 2 mL of Benedict’s solution in a small test tube and heat in a gently boiling water bath for 2/3 minutes. 
Add 10 drops of the carbohydrate solution to be tested, mix thoroughly, and place back in the boiling water bath for an additional 5 minutes. 
A color change from blue to green to yellow and finally brick red (CuO2) indicates that the carbohydrate is a reducing sugar. 
The rate of reaction is very important.  Fructose reacts very rapidly, glucose and galactose more slowly.  Even starch and cellulose will give weak results if the solution is heated extensively.

(Identifying Carbohydrates 1996)
Relevance at biological scale
Main source of fuel.

Tissues and cells in our body use glucose for energy.

Essential for the central nervous system, the kidneys, the brain, the muscles (including the heart) in order to function properly.

They can be stored in the muscles and liver, for later use.
Definition & features
As insoluble fiber, it is important for health since it promotes gut motility and satiety (intestinal health and waste elimination).

Structural component of plants and arthropods.

Molecular backbone of numerous enzymes and RNA.

It aids other bio-molecules along their roles in processes such as: Immune system, fertilization, preventing pathogenesis, blood clotting, and corporeal development
are sugars which are composed by only one polyhydroxy aldehydeidic or ketonic unit.

, formed by two monosaccharides. Particularly in the human diet, the most important are sucrose, lactose and maltose.

are formed by short chains of monosaccharidic units (from 2 to 20) linked one to the next by chemical bounds, called glycosidic bounds.

are polymers consisting of 20 to 107 monosaccharidic units.

They differ from each other for the recurring monosaccharides within the structure, for the length and the degree of branching of chains or for the type of links between units.

Note: the term “saccharide” derives from the greek word “sakcharon”, which means sugar.
Wrapping Up
Energy source, digestive, & also helps other bio-molecules.

Basically, an aldehyde or ketone with many hydroxyl groups added.

We store them as Glycogen.

Mono-, Di-, Oligo-, & Poli-.

Come from fruits, vegetables, milk, syrups, and flours.

We have various methods to identify them.

jolly ole' carbs ye' mateys
Yep, this is how we store carbohydrates.
Seliwanoff Test 
When a ketose is heated with a strong mineral acid, hydroxymethylfurfural is formed.  

This compound forms a red complex with the organic compound, resorcinol.  The aldoses will give the red color more slowly.   
To 5 mL of freshly prepared Seliwanoff reagent, add 10 drops of the unknown solution, mix and place in a boiling water bath.  (BE CAREFUL!!  Hot acidic solution is obviously more hazardous than cool acidic solution.) 
A red color within 20 to 30 seconds is indicative of a ketohexose (fructose.  If the red color develops after this time, it would indicate the presence of an alohexose (glucose). " 

 (Identifying Carbohydrates 1996)
Iodine Test

Starch forms a dark blue complex when treated with iodine. Cellulose and the simple sugars produce no color change at all.  A few drops of the iodine solution give an unmistakable positive result for starch. In a small test tube, add 2 mL of the solution to be tested.  Add 2 drops of iodine solution. Mix and observe.

(Identifying Carbohydrates 1996)
Samuel Legorreta Ascencio
// A01372802

Mariana Ramírez Mejía
// A01372739

Ángel Farid Rojas Cruz
// A01373019
Class: PC5028.1

Teacher: Lucila Giammatteo
- Anonymous. (2014). The Importance of Carbohydrates: Functions & Impact of Deficiency. 2015, from study.com. Website:

- Anonymous. (2015). The Nutrition Source – Carbohydrates. 2015, from Harvard School of Public Health. Website:

- Human Sciences. (2013). Carbohydrate. 2015, from Iowa State University. Website:

- Identifying Carbohydrates. (1996). Retrieved August 29, 2015, from:

- McKinley Health Center. (2014). Macronutrients: the Importance of Carbohydrate, Protein, and Fat. 29/08/2015, from University of Illinois. Website:

- Oxford University press. (2015). Carbohydrate. 2015, from Oxford dictionaries Website:

- Venkateswarlu, K. (2014). International Journal o Pharmaceutica. 2015, from:
Gas chromatography exists likewise, nevertheless, it is quite expensive.
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