Call Now
1800-102-2727Carbohydrates are very popular these days for not being part of the diet of those on the journey of weight loss. You must have heard about the “no carb diet”. Well carbohydrates are an essential part of our diet, as we know that for a healthy lifestyle a balanced diet is a must which very much includes carbohydrates. People do not have a clear idea about carbohydrates, therefore it is vital to remember that eating carbohydrates from nutritious meals is more crucial than adhering to a rigid diet that restricts or counts the amount of carbohydrates taken.The type of carbohydrate you choose to consume is crucial since some sources are healthier than others. The type of carbohydrates in the diet is more significant than their quantity, whether high or low. However, what are these carbohydrates? Let’s find out!
Table of Contents
Carbohydrates include all the sugar and starch you have heard of in your food. When you burn sugar, you get carbon and water. That is how the scientists thought of the name carbohydrates or hydrates of carbon. These are the compounds having carbon, hydrogen and oxygen in the ratio 1:2:1.
Fig: Sources of carbohydrates
Carbohydrates have at least 3 carbon atoms, multiple hydroxyl (-OH) groups and either an aldehyde (-CHO) group or a ketone (C=O) group. If an aldehyde group is present then it is called an aldose and if a ketone group is present then it is called a ketose. For example, glucose is an aldose sugar with six carbons and fructose is a ketose sugar with six carbons. However, both of them have the same molecular formula.
Fig: General structure of carbohydrates
Carbohydrates as you know are defined as hydrates of carbon. Thus, the general formula for carbohydrates is Cn(H2O)n. However there are a few rebels, as in sugars that do not follow the general formula for carbohydrates. For example Rhamnose (C6H12O5) and Deoxyribose (C5H10O4).
Fig: Carbohydrates that do not follow the general formula
Carbohydrates are classified based on the number of monomeric units into the following types:
Fig: Classification of carbohydrates
Mono = Single; Saccharide = Sugar. These are the simplest carbohydrates which are generally sweet in taste. They are the building blocks of larger carbohydrates and cannot be further hydrolysed to smaller sugar units.
Monosaccharides are further classified based on the number of carbon atoms.
Fig: Classification of monosaccharides
Monosaccharides can have a maximum of 10 carbon atoms but the ones with 8 (octose), 9 (nonose) or 10 (decose) carbon atoms are not commonly found.
Trioses are monosaccharides with 3 carbon atoms. Eg: glyceraldehyde (C3H6O3)
Fig: Glyceraldehyde
Tetroses are monosaccharides having 4 carbon atoms. Eg: D-Erythrose (C4H8O4)
Fig: Erythrose
Pentoses have 5 carbon atoms. Eg: D-Ribose (C5H10O5), D-Deoxyribose (C5H10O5)
Fig: D-Deoxyribose Fig: D-Ribose
(no OH at carbon 2) (OH on carbon 2)
Hexoses have 6 carbon atoms. Eg: glucose, fructose, galactose
Fig: Glucose
Fig: Fructose
Monosaccharides have two optically active forms called enantiomers of each other. If the OH on the bottom chiral centre points to the right, it is referred to as D- . If the OH on the bottom chiral centre points to the left, it is referred to as L- .These optically active forms are Non-superimposable mirror images.
Fig: Enantiomers of glyceraldehyde
If light is allowed to pass through some filter like a prism (polariser), then after passing through it, the light waves vibrate only in one plane. This light is called plane polarised light. Dextrorotatory (d) turns the plane polarised light to the right and laevorotatory (l) turns the plane polarised light to the left.
Fig: Plane polarised light
Di = Two; Saccharide = Sugar. Disaccharides consist of two monosaccharide units which are joined with a glycosidic bond. Eg: sucrose, maltose, lactose, etc.
Fig: Formation of Disaccharide
Fig: Sucrose
Fig: Maltose
Fig: Lactose
Oligo’ = Few; ‘Saccharide’ = Sugar. In oligosaccharides 3-9 monosaccharide units are joined by glycosidic linkage. Examples include:
Raffinose can be found in beans, cabbage, brussels sprouts, broccoli, asparagus, other vegetables, and whole grains.Stachyose occurs naturally in numerous vegetables and other plants.
Polysaccharides are polymers of repeating units of monosaccharides and are also called ‘glycans’. They are the macromolecules and have high molecular weight.
They have a non-reducing end where there are no free reactive groups and a reducing end where a free reactive group is present.
Polysaccharides are classified based on whether the monomeric units are of same type or different
Homopolysaccharides have the same type of monomeric units. They are further classified into structural polysaccharides which form the structural part of living organisms. Eg:- cellulose and chitin and storage polysaccharides are used for storage. Eg: starch, glycogen, inulin
Fig: Cellulose
Fig: Structure of chitin
Fig: Amylose and amylopectin
Fig: Structure of glycogen
Heteropolysaccharide consist of different types of monomeric units. Eg: agar and peptidoglycan.
Fig: Unbranched and Branched heteropolysaccharides
Fig: Structure of peptidoglycan
Reducing sugars are those which have a free aldehyde/ketone group present. Eg: All monosaccharides, disaccharides like maltose and lactose are reducing sugars.
Non-reducing sugars are those which do not have a free aldehyde/ketone group. All monosaccharides are reducing sugars and all polysaccharides and disaccharide like sucrose are non-reducing.
Benedict’s test is a test for reducing sugars. Reducing sugars reduces the cupric ions in Benedict’s solution to cuprous, while non-reducing sugars cannot.
When reducing sugar is added to benedict’s reagent and heated it results in the formation of a brick red precipitate.
This principle is applied in testing the presence and amount of glucose in blood and urine.
Fig: Benedict’s test for reducing sugar
Q1. Glucose is produced from inorganic sources by:
Solution: All carbohydrates are derived from glucose via different metabolic pathways and photosynthetic organisms are the only living beings which synthesise glucose via the process of photosynthesis. Thus photosynthetic bacteria, and chlorophyll containing organisms such as algae and green plants are the only organisms which can produce glucose from inorganic substrates such as carbon dioxide and water, in the presence of water, via the process of photosynthesis. Thus, the correct option is a.
Q2.Which one of the following is a non - reducing carbohydrate?
Solution: Carbohydrates that have a free aldehyde or keto group are called reducing sugars. Whereas if there is no free aldehyde or keto group then the carbohydrate is called a non- reducing sugar. Sucrose is an example of a non-reducing sugar. Maltose, lactose and ribose 5- phosphate are reducing sugars. Thus, the correct option is b.
Q3. Chitin is a
Solution: Chitin is a nitrogen-containing polysaccharide that constitutes the cell wall of fungi and exoskeleton of arthropods. Chemically chitin is a polymer of N- acetylglucosamine. Chitin contains neither phosphorus nor sulphur. Chitin is not a simple polysaccharide. Thus, the correct option is d.
Q4. Lactose is composed of
Solution: Lactose is a disaccharide and is made up of glucose and galactose. It is found in milk and milk products. Glucose and galactose are joined together by a beta glycosidic bond to form lactose. Thus, the correct option is c.
Q1. What is the composition of Benedict's reagent?
Answer: Benedict's reagent is an alkaline solution of blue coloured copper(II) sulphate pentahydrate, sodium carbonate, and sodium citrate which is used as a chemical reagent. It is frequently used to find reducing sugars. When a Benedict’s reagent along with a reducing sugar is heated it results in the formation of red coloured insoluble precipitate of copper (I) oxide.
Q2. How can fructose and glucose be distinguished?
Answer: Fructose and glucose can be distinguished by Seliwanoff’s reagent. It is a test which helps in distinguishing between an aldose and a ketose sugar. Fructose is a ketose sugar, whereas glucose is a hexose sugar.
Q3. In maltose, the glycosidic bond forms between which two carbon atoms of the adjacent monosaccharide subunits?
Answer: Maltose is a disaccharide which is formed by two units of glucose molecules linked by a glycosidic bond. The bond is formed between the C1 of one glucose with the C4 of another glucose molecule.
Q4. Which sugar is found in cereales and candies
Answer: Maltose is a sugar found in some cereals and candies. It is a product glucose+glucose and may be purified from barley and other grains. In the manufacture of beer, maltose is liberated by the action of malt (germinating barley) on starch therefore, it is often referred to as malt sugar.
Q5. Why are carbohydrates referred to as “Staff of life”?
Answer: Carbohydrates are referred to as the staff of life as they are the most basic components of food that serve as the primary source of energy to all living organisms.
YOUTUBE LINK: https://youtu.be/ZcDIetuGKEk