saccharides (carbohydrates)

Biochemistry for nurses

SACCHARIDES (carbohydrates)A saccharide is a biological molecule consisting of carbon (C), hydrogen (H) and oxygen (O2). The saccharides have the general formula (CH2O)n.Saccharides are divided into 4 chemical groupes: monosaccharides, dissacharides, polysaccharides and glycoconjugates.


MonosaccharidesThe monosaccharides have the general formula CnH2On

Most monosaccharides found in the cell have 5 or 6 carbones:• monosaccharide with 5 carbones (C5H10O5) = PENTOSE• monosaccharide with 6 carbones (C6H12O6) = HEXOSE

The most important pentoses are the RIBOSE and the DEOXYRIBOSE. They are elements of the nucleic acid structures (DNA and RNA)

MonosaccharidesThe most important hexoses are the GLUCOSE, FRUCTOSE and the GALACTOSE. They have the same formula C6H12O6 but they have differents structures: They are ISOMERS

The hexoses are important FUEL MOLECULES!


Disaccharides

A disaccharide is a sugar composed of two monosaccharides. It is formed when two sugars are joined together and a molecule of water is removed.

The most important dissacharides are:


SUCROSE = glucose-fructose LACTOSE = glucose-galactose MALTOSE = glucose-glucose


(Cereal grains, corn…)

(Milk…)

(Fruits, sugarcane, sugar beet…)

PolysaccharidesMost of the polysaccharides are long chains of glucoses (= polymers of glucoses).The most important polysaccharides are:• STARCH• GLYCOGEN• CELLULOSE


StarchThere are 2 types of Starch molecules:• AMYLOSE = Long linear chains of glucoses. • AMYLOPECTIN = Long linear and branched chains of glucoses.Each starch can contain 100 to 20.000 molecules of glucose.


The starch is a sugar coming from vegetables (Cereals: rice, wheat, corn and potatoes)

GlycogenThe Glycogen structure is composed by long linear and branched chains of glucoses.The Glycogen is a sugar coming from animals (Meats)

After a meal, our blood sugar increases. The liver cells and muscular cells transform the extra sugar into molecules of Glycogen which causes a decrease of the blood sugar.


The extra sugar is stored as Glycogen in our body. Our body can store up to 600 g of glycogen

CelluloseThe Cellulose is also composed by long linear chains of glucoses but the glucoses are linked by a different type of chemical bond.


(Main component of Wood)

Glycoconjugate• Glycoconjugates is the general classification for carbohydrates covalently linked

with other chemical species such as proteins, peptides and lipids.

• Most of the Glycoconjugates are GLYCOPROTEINS (= proteins linked with polysaccharides). They are especially found in the cell membrane (the blood type is defined by the type of glycoprotein).



Functions of the Carbohydrates

• Provide energy (ATP) to drive metabolic

processes (GLYCOLYSIS).

• Energy-storage molecules, e.g, GLYCOGEN.

• Structural component of cell wall.

• Component found in coenzyme (FAD) and

Nucleic Acids.

ATP molecule is the source of

ENERGY!

CELL METABOLISM (cell respiration)


ATP (Adenosine Triphosphate)ATP is a molecule composed by an organic base (adenine) and a 3 phosphates group attached

to a sugar (ribose).

ATP is manufactured inside the mitochondria from the transformation

of the energy coming from the absorbed foods into a chemical

energy stored in the chemical bond with the 3rd phosphate group.


ATP

ADP+Pi

Energy

ATP hydrolyse provides energyEach day, you hydrolyse 1025

ATP molecules in your body

HydrolysePhosphorylation

Hydrolyse of ATP provides a big energy (35 KJ)



GLYCOLYSIS:Catabolism of Glucose (or Fructose, Mannose) to provide ATPs molecules. That

process is also called “Cell Respiration”, and it happens inside Mitochondria.

DIGESTION (Metabolism) of the polysaccharidesAfter absorption of the polysaccharides coming from the foods, the digestive system of our body has to transform the long chains of polysaccharides into monosaccharides in order to be absorbed by the blood. That reaction is done by enzymes (Ex: Amylase, Maltase or Saccharase). Enzymes are biological catalysts. The breaking of a bond joining 2 saccharides requires a molecule of water (H20): That reaction is called the « HYDROLYSIS of POLYSACCHARIDES


Reminder: What is an enzyme?

• Enzymes are proteins produced in living cells.• Enzyme are biological catalysts = They speed up the rate of chemical reactions.• Enzyme are specific to a particular substrate (Key-Lock: sucrose-sucrase, maltose-maltase,…).



Digestion and absorption of carbohydrates


Storage of carbohydrates

• Carbohydrates are stored in the form of Glycogen• Glycogen is a multibranched polysaccharide of Glucose.

• Glycogen is stored in the cells of the Liver and the Muscles• During starvation, Glycogen act as primary source of energy by

providing molecules of ATP


Recommended dietary allowances (RDAs)• Definition: Minimum required amount of the nutrient for the

maintenance of health in nearly all people.

• RDAs does not apply to sick people

Source: Food and Nutrition Board, Institute of Medicine, National Academies (USA, CANADA)

http://iom.edu/Activities/Nutrition/SummaryDRIs/~/media/Files/Activity%20Files/Nutrition/DRIs/New%20Material/5DRI%20Values%20SummaryTables%2014.pdf

http://iom.edu/Activities/Nutrition/SummaryDRIs/~/media/Files/Activity%20Files/Nutrition/DRIs/New%20Material/5DRI%20Values%20SummaryTables%2014.pdf


Diseases due to overconsumption of carbohydrates• Obesity

• Diabete (Type 2: Non-Insulin Depedent Diabetes

Mellitus)

• Cardiovascular diseases (Heart disease and stroke)

• Dental caries


Diseases due to deficiency of carbohydrates

• Usage of Fats as Energy Source

(underweight)

• KETOSIS: Accumulation of

Ketones in the body (in absence

of carbohydrates the body starts

using the proteins and converts it

to sugars)

• HYPOGLYCEMIA

saccharides (carbohydrates)

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