Biomolecules
The complex organic molecules which form the basis of life i.e. which build up living organisms and are also required for their growth and maintenance are called biomolecules. For example : carbohydrates, proteins, nucleic acid, vitamins, etc.
Carbohydrates
Carbohydrates are the polyhydroxy aldehydes, polyhydroxy ketones or large polymeric molecules which on hydrolysis produce polyhydroxy aldehydes or ketones. Eg. glucose, fructose, sucrose, etc.
The carbohydrates which contain aldehyde group are called aldoses while those containing ketonic group are called ketoses.
Classification of carbohydrates :
Carbohydrates can be classified as :
Monosaccharide, Oligosaccharide and Polysaccharide :
Monosaccharides : The simplest carbohydrates which can not be hydrolysed further into any smaller molecules are called monosaccharides. These carbohydrates usually contain 3 to 7 carbon atoms in their molecules. Eg. glucose ( C6H12O6), fructose ( C6H12O6) , ribose (C5H10O5), etc.
Oligosaccharides : The carbohydrates which on hydrolysis give two to nine units of monosaccharides of same type or different types are called oligosaccharides. Oligosaccharides are further classified as di-, tri- and tetrasaccharides.
Disaccharides : Carbohydrates which on hydrolysis produce two molecules of monosaccharides of same or different types are called disaccharides. For example : sucrose, maltose, lactose, etc.
Trisaccharides : Carbohydrates which on hydrolysis produce three molecules of monosaccharides of same or different types are called trisaccharides. For example : raffinose.
Polysaccharides :
These are the polymeric molecules of carbohydrates which on hydrolysis give large number of monosaccharide molecules. For example : starch, cellulose, etc.
The general formula of starch is (C6H10O5)n where n = 100 – 3000.
Sugar and non – sugar :
Sugar : The carbohydrates which are sweet in taste and dissolve in water are called sugars. They are generally crystalline in nature. Eg. glucose, fructose sugar, lactose, etc.
Non – sugar : The carbohydrates which are not sweet in taste and are insoluble in water are called non – sugar. They are generally amorphous in nature. Eg. starch, cellulose, etc.
Note : All monosaccharides and disaccharides are sugar and polysaccharides are generally non-sugar.
Degree of sweetness of sugars :
Fructose > Sucrose > Glucose > Galactose > Maltose > Lactose
Besides carbohydrates some other compounds are far more sweet . eg. saccharine is about 500 times sweet than sucrose. Aspartame, a peptide is about 160 times sweet than sucrose. Monalleine, a protein is about 2000 times sweeter than sucrose.
Reducing and non – reducing sugar
Reducing sugar : Carbohydrates which have ability to reduce Fehling’s solution and Tollen’s reagent are called reducing sugar. Eg. glucose.
Non- reducing sugar : Carbohydrates which do not reduce Fehling’s solution and Tollen’s reagent are called non-reducing sugar. Eg. fructose.
Note : Carbohydrates having aldehyde functional group can reduce Fehling’s solution and Tollen’s reagent.
Q) What are disaccharides ? What happens when they get hydrolysed ?
When disaccharide is hydrolysed then monosaccharides are produced. Eg.
Q) How would you obtain glucose from cane sugar? What is meant by invert sugar ?
Glucose is formed by the hydrolysis of cane sugar with an enzyme i.e. invertase.
Invert sugar : A mixture of equal portion of glucose and fructose obtained by inversion (hydrolysis) of sucrose is called invert sugar. It is found naturally in fruits and honey and produced artificially for use in food industries.
Q) How would you obtain ethanol from cane sugar ? Write reaction only.
Structure of glucose and fructose :
- Glucose has 6 carbon atoms and aldehyde functional group therefore it is also called aldohexose.
- Fructose has 6 carbon atoms and ketone functional group therefore it is also called ketohexose.
Functions of carbohydrates :
- It acts as the major source of energy for animals and human beings.
- It stores chemical energy in plants in the form of sugar and starch.
- It acts as energy storage in animals in the form of glycogen.
- Carbohydrates like cellulose support plant structure.
- Carbohydrates form part of the structural framework of DNA and RNA molecules.
- Carbohydrates add flavor and sweetness to diet.
Protein
The complex nitrogenous organic compounds which are essential for the growth and maintenance of life are called proteins. Proteins are macromolecules in which large number of α – amino acid molecules are linked together by peptide bond ( -CONH- ). Thus proteins are polymers of α – amino acids.
Functions of protein :
Proteins are building blocks of the various tissues. Proteins perform many biological functions such as :
- Catalyze a large number of biological reactions in the form of enzymes. Eg. invertase, maltase, etc.
- Acts as chemical regulators in the form of hormones . Eg. insulin, glucogon, etc.
- Provides natural defense to the body against the entry of antigens into the body system in the form of antibody protein.
- Acts as food reserve in the form of food reserve protein. Eg. egg white .
- Acts as the major structural material of animal tissues in the form of structural protein. Eg. collagen in tendon; keratin in skin, hair, silk, nails and feathers.
Amino acids :
Carboxylic acids containing amino (-NH2) group attached to any carbon atom other than the carboxylic carbon are called amino acids. Their general formula is:
The naturally found amino acids contain amino group (-NH2) attached to only α – carbon atom.
Essential and Non – essential amino acids :
- 20 amino acids are required for our body. Human body can synthesize 11 amino acids and 9 must be supplied through diet.
- The amino acids which can be synthesized by our body ( i.e. not necessary in diet) are known as non – essential amino acids. Eg. Glycine, Alanine, ect.
- The amino acids which are not able to synthesize by the body and must be supplied to our body through our diet are known as essential amino acids. Eg. Valine, Phenylalanine, etc.
Zwitter ions :
Amino acids contain both acidic carboxylic (-COOH) group and basic amino (-NH2) group in the same molecule. In aqueous solution, the –COOH group donates its proton to –NH2 group of same amino acid forming a dipolar ion. Such dipolar ion of an amino acid is called zwitter ion.
Q) Why are amino acids amphoteric ?
Amino acids contain both acidic carboxylic acid functional group and basic amino group. Due to the presence of both acidic and basic functional group in the same molecule, amino acid is amphoteric in nature.
Peptide linkage ( bond) :
Compound formed by the condensation of two or more same or different amino acids is known as peptide.
During the formation of peptide, – COOH group of one α – amino acid gets condensed with –NH2 group of other molecule of same or different α – amino acids with the elimination of H2O molecule. The resulting –CONH2– linkage is called peptide linkage or peptide bond.
- A peptide formed by the condensation of two molecules of the same or different α – amino acids is called dipeptide.
Q) Explain how amino acids are combined to form a protein molecule.
Proteins are formed by the combination of a number of α – amino acids with the peptide linkage. The -NH2 group of one α – amino acid condenses with the –COOH group of another molecule of same or different amino acid with the liberation of H2O molecule.
Hydrolysis of protein :
Proteins on hydrolysis give different types of α – amino acids.
Denaturation of protein :
The process that brings about changes in physical as well as biological properties of the protein without effecting its chemical composition is called denaturation of protein. It is caused by following factors :
- Change in pH
- Change in temperature
- Presence of chemicals (acids, alkalies)
Examples :
- Coagulation of albumin present in white of egg upon heating.
- Coagulation of milk in the presence of lemon juice (acid) to make cheese.
Enzymes :
- Enzymes are biological catalyst produced by living cells which catalyze many biochemical reactions in living systems (i.e. animals and plants).
- Enzymes are also used in huge amount in industrial processes besides the biological reactions. For example: invertase, maltase and amylase enzymes which are present in the yeast are used in breweries and food processing industries.
Note : Some enzymes are associated with some non – protein components called prosthetic group. If the prosthetic group is metal ion it is called a ‘co-factor’ . When the prosthetic group is a small organic molecule it is called a ‘coenzyme’.
Co- enzyme : The non – protein substance associated with enzyme which enhances the catalytic activity of enzyme is called co – enzyme.
Nucleic acid
Nucleic acids are long thread like water soluble macromolecules present in high concentration in the nuclei of all living cells. They are responsible for the transmission of hereditary characters from parents to their off springs and for the biosynthesis of protein.
Nucleic acid are of two types :
- DNA (Deoxyribonucleic acid)
- RNA (Ribonucleic acid)
Basic components of nucleic acid :
- Pentose sugar : ribose gugar and deoxyribose sugar.
- Nitrogenous bases :
Purines – Adenine(A) and Guanine(G)
Pyrimidines – Cytosine(C), Thymine(T) and Uracil(U)
- Phosphate group
Differences between RNA and DNA :
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Q) What is the role of hydrogen bonding in the structure of DNA ?
The role of hydrogen bond between two strands (helix) of DNA is to bind them together. Adanine(A) pairs with thymine(T) through two hydrogen bonds and cytosine(C) pairs with guanine(G) through three hydrogen bonds.
Lipids
Waxy or oily substances which are present in all living organism as a main constituent of all cell membrane are called lipids. Actually lipids are the esters of long chain fatty acids and alcohols. Eg. triglyceride of fatty acid.
Note : Fatty acid : Long chain monocarboxylic acids mainly obtained by the hydrolysis of animal fats or vegetable oil. Eg. Palmitic acid (C16) i.e. CH3(CH2)14COOH obtained by hydrolysis of palm oil.
Most natural fats and oils are made of one or more mixed glycerides.
| Fat | Oil |
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Conversion of oils into fats : Hydrogenation or hardening of oil
When oil is hydrogenated unsaturated triglycerides are converted to saturated triglycerides i.e. oil changes to vegetable ghee (vanaspati ghee).
Saponification :
Q) What is soap? How is soap obtained from fat?
Q) What happens when fat (lipid) gets hydrolyzed?
When triglycerides (oil or fat) are hydrolyzed in the presence of sodium or potassium hydroxides glycerol and sodium or potassium salts of fatty acids are formed. The sodium or potassium salts of long chain fatty acids are called soap. This process of formation of soap is called saponification.
See how does soap kills Corona virus……
References:
- Sthapit, M.K., Pradhananga, R.R., Foundations of Chemistry, Vol 1 and 2, Fourth edition, Taleju Prakashan, 2005.
- https://www.britannica.com/science/glucose
- https://www.betterhealth.vic.gov.au/health/healthyliving/protein#:~:text=Protein%20is%20an%20important%20part,used%20as%20an%20energy%20source.
- http://amrita.olabs.edu.in/?sub=73&brch=3&sim=119&cnt=1
- https://courses.lumenlearning.com/introchem/chapter/dna-and-rna/#:~:text=The%20two%20main%20types%20of,to%20carry%20out%20cellular%20functions.