Hii FriendsToday I am going to give you information about Biomolecules in cell.Biology and its subfields of biochemistry and molecular biology study biomolecules and their reactions. Most biomolecules are organic compounds, and just four elements—oxygen, carbon, hydrogen, and nitrogen—make up 96% of the human body’s mass. But many other elements, such as the various biomolecules, are present in small amounts.Let me explain some information about Biomolecules.

Biomolecules in the cell

A. Carbohydrates :
         The word carbohydrates ‘hydrates of carbon’. They are also called saccharides. They are biomolecules made from just three elements: carbon, hydrogen and oxygen with the general formula (CH,O),. They contain hydrogen and oxygen in the same ratio as in water (2:1). Carbohydrates can be broken down (oxidized) to release energy. The means Based on number of sugar units, carbohydrates are classified into three types namely, monosaccharides, disaccharides and polysaccharides.

1. Monosaccharides:
         These are the simplest sugars having crystalline structure, sweet taste and soluble in water. They cannot be further hydrolysed into smaller molecules. They are the building blocks or monomers of complex carbohydrates. They have the general molecular formula (CH,O), where n can be 3, 4, 5, 6 and 7. They can be classified as triose, tetrose, pentose, etc.
       Monosaccharides  containing the aldehyde (-CHO) group are classified as aldoses e.g. glucose, xylose, and those with a ketone (-C=O) group are classified as ketoses. eg .ribulose, fructose.

Structure of Glucose :-

a. Glucose : It is the most important fuel in living cells. Its concentration in the human blood is about 90mg per 100ml of blood. The small size and solubility in water of glucose molecules allows them to pass through the cell membrane into the cell. Energy is released when the molecules are metabolised by cellular respiration.

b. Galactose : It looks very similar to glucose molecules. They can also exist in a and B forms. Galactose react with glucose to form the dissacharide lactose. However, glucose and galactose cannot be easily converted into one another. Galactose cannot play the same role in respiration as glucose.

c. Fructose : It is the fruit sugar and chemically it is ketohexose but it has a five-atom ring rather than a six-atom ring. Fructose reacts with glucose to form the sucrose, a disaccharide.

2. Disaccharides :
      Monosaccharides are rare in nature.Most sugars found in nature are disaccharides. Disaccharides is formed when two monosaccharides react by condensation reaction releasing a water molecule. This process requires enegy. A glycosidic bond forms and holds the two monosaccharide units together.
       Sucrose, lactose and maltose are examples of disaccharides. Sucrose is a non- reducing sugar since it lacks free aldehyde or ketone group. Lactose and maltose are reducing sugars. Lactose also exists in beta form, which is made from B-galactose and B-glucose. Disaccharides are soluble in water, but they are too big to pass through the cell membrane by diffusion. They are broken down in the small intestine during digestion. Thus formed monosaccharides then pass into the blood and through cell membranes into the cells.

Structure of Maltose :-

Monosaccharides are used very quickly by cells but if a cell is not in need of all the energy released immediately then it may get stored. Monosaccharides are converted into disaccharides in the cell by condensation reactions, which result in the formation of polysaccharides as macromolecules. These are too big to escape from the cell.

  1. Polysaccharides : Monosaccharidescan undergo a series of condensation reactions, adding one unit after the other to the chain till a very large molecule (polysaccharide) is formed. This is called polymerization. Polysaccharides down by hydrolysis are broken into monosaccharides. The properties of a polysaccharide molecule depend on its length, branching, folding and coiling.

a. Starch : Starch is a stored food in the plants. It exists in two forms: amylose and amylopectin. Both are made from a-glucose. Amylose is an unbranched polymer of a-glucose. The molecules coil into a helical structure. It forms a colloidal suspension in hot water. Amylopectin is a branched polymer of a-glucose. It is completely insoluble in water.

Structure of Starch

b. Glycogen : It is amylopectin with very short distances between the branching side-chains. Glycogen is stored in animal body particularly in liver and muscles from where it is hydrolysed as per need to produce glucose.

c. Cellulose : It is a polymer made from B-glucose molecules and the polymer molecules are ‘straight’. Cellulose serves to form the cell walls in plant cells. These are much tougher than cell membranes. This toughness is due to the arrangement of glucose units in the polymer chain and the hydrogen-bonding between neighbouring chains.

Biological significance of Carbohydrates:
              It supplies energy for metabolism. Glucose is the main substrate for ATP synthesis. Lactose, a disaccharide is present in milk provides energy to lactating babies. Polysaccharide serves as structural component of cell membrane, cell wall and reserved food as starch and glycogen.

B. Lipids:

        These are group of substances with greasy consistency with long hydrocarbon chain containing carbon, hydrogen and oxygen. In lipids, hydrogen to oxygen ratio is greater than 2:1 (in carbohydrates it is always 2:1). Lipid is a broader term used for fatty acids and their derivatives. They are soluble in organic solvents (non-polar solvents). Let’s understand what fatty acids are. Fatty acids are organic acids which are composed of hydrocarbon chain ending in carboxyl group (-COOH). They can be saturated fatty acids with no double bonds between the carbon atoms of the hydrocarbon chain. Palmitic and stearic acids found in all animal and plant fats are examples of saturated fatty acids.

          Unsaturated fatty acids are with one or more double bonds between the carbon atoms of the hydrocarbon chain. Oleic acid found in nearly all fats and linoleic acid found in many seed oils are examples of unsaturated fatty acids.
         These fatty acids are basic molecules which form different kinds of lipids. Lipids may be classified as simple, compound and derived lipids.

Simple Lipids :
            These are esters of fatty acids with various alcohols. Fats and waxes are simple lipids. Fats are esters of fatty acids with glycerol (CH,OH-CHOH-CH,OH). Triglycerides are three molecules of fatty acids and one molecule of glycerol. Generally, unsaturated fats are liquid at room temperature and are called oils. Unsaturated fatty acids are hydrogenated to produce fats e.g. Vanaspati ghee.
         Fats are a nutritional source with high calorific value. Fats act as reserved food materials. In plants it is stored in seeds to nourish embryo during germination. In animals fat is stored in the adipocytes of the adipose tissue. Fats deposited in subcutaneous tissue act as an insulator and minimise loss of body heat. Fats deposited around the internal organs act as cushions to absorb mechanical shocks.            
           Wax is another example of simple lipid. They are esters of long chain fatty acids with long chain alcohols. They are most abundant in the blood, the gonads and the sebaceous glands of the skin. Waxes are not as readily hydrolysed as fats. They are solid at ordinary temperature.   
      Waxes from water insoluble coating on hair and skin in animals , waxes from an outer coating on stems , leaves and fruits.


Compound lipids : 
         These are ester of fatty acids containing other groups like phosphate (Phospholipids), sugar (glycolipids), etc. They contain a molecule of glycerol, two molecules of fatty acids and a phosphate group or simple sugar. Some phospholipids such as lecithin also have a nitrogenous compound attached to the phosphate group. Phospholipids have both hydrophilic polar groups (phosphate and nitrogenous group) and hydrophobic non-polar groups (hydrocarbon chains of fatty acids). Phospholipids contribute in the formation of cell membrane. Glycolipids contain glycerol, fatty acids, simple sugars such as galactose and nitrogenous base. They are also called cerebrosides. Large amounts of them have been found in the brain white matter and myelin sheath.

Derived lipids :
            They are composed of fused hydrocarbon rings (steroid nucleus) and a long hydrocarbon side chain. One of the most common sterol is cholesterol. It is widely distributed in all cells of the animal body, but particularly in nervous tissue. Cholesterol exists either free or as cholesterol ester.
       Adrenocorticoids, sex hormones (progesterone, testosterone) and vitamin D are synthesised from cholesterol. Cholesterol is not found in plants. In plants, sterols exist chiefly as Phytosterols. Yam Plant (Dioscorea) produces a steroid compound called diosgenin. It is used in the manufacture of antifertility pills. i.e. birth control pills.

C .Proteins :

           Protein is a macronutrient that is essential to building muscle mass. It is commonly found in animal products, though is also present in other sources, such as nuts and legumes. 
Structure of Protein

Classification of Proteins:
        On the basis of structure , Proteins are classified into three categories :

Simple proteins:
            Simple proteins on hydrolysis yield only amino acids. These are soluble one or more solvents. Simple proteins may be soluble in water. Histones of nuclcoproteins histones are not coagulated by heat. Albumins are also soluble in water but they get coagulated are soluble in water. Globular molecules of on heating. Albumins are widely distributed c.g. egg albumin, serum albumin and legumelin of pulses are albumins.

Conjugated proteins :
          Conjugated proteins consist of a simple protein united with some non-protein substance. The non-protein group is called prosthetic group c.g. haemoglobin. Globin is the protein and the iron containing pigment haem is the prosthetic group. Similarly, nucleoproteins have nucleic acids as prosthetic group. On this basis, proteins are classified as glycoproteins and mucoproteins. Mucoproteins are carbohydrate-protein complexes e.g. mucin of saliva and heparin of blood. Lipopoteins are lipid-protein complexes e.g. conjugate protein found in brain, plasma membrane, milk etc.

   Derived Proteins :
             These proteins are not found in nature as such. These proteins are derived from native protein molecules on hydrolysis. Metaproteins, peptones are derived proteins. Derived proteins.


D. Nucleic Acids :

          Swiss biochemist, Friederich Miescher (1869) discovered and isolated nucleic acids from the pus cells. By 1938, it became evident that nucleic acids are of two types- deoxyribose nucleic acid (DNA) and ribose nucleic acid (RNA). DNA is found in chloroplasts and mitochondria. DNA is the hereditary material in most of the organisms. The nucleic acids are among the largest of all molecules found in living beings. They contain three types of molecules a) 5 carbon sugar, b) Phosphoric acid and c) Nitrogen containing bases. Three join together to form a nucleotide of nucleic acid.
Structure of Nucleic Acids

1.Structure of DNA :
          DNA has a double-helix structure.The sugar and phosphate lie on the outside of the helix, forming the backbone of the DNA. The nitrogenous bases are stacked in the interior, like the steps of a staircase, in pairs; the pairs are bound to each other by hydrogen bonds. Every base pair in the double helix is separated from the next base pair by 0.34 nm.
           The two strands of the helix run in opposite directions, meaning that the 5′ carbon end of one strand will face the 3′ carbon end of its matching strand.
           Only certain types of base pairing are allowed. For example, a certain purine can only pair with a certain pyrimidine. This means A can pair with T, and G can pair with C. This is known as the base complementary rule. In other words, the DNA strands are complementary to each other. If the sequence of one strand is AATTGGCC, the complementary strand would have the sequence TTAACCGG. During DNA replication, each strand is copied, resulting in a daughter DNA double helix containing one parental DNA strand and a newly synthesized strand.

2. Structure of Ribonucleic Acid (RNA):
             Another nucleic acid found in the living organisms is Ribose nucleic acid. In most of the organisms it is not found to be hereditary material but in certain organisms like tobacco mosaic virus, it is the hereditary material. Like DNA, ribose nucleic acid also consists of polynucleotide chain with the difference that it consists of single strand. In some cases e.g. Reovirus and wound tumour virus, RNA is double stranded. The nucleotides of RNA have ribose sugar instead of the deoxyribose sugar as in the case of DNA. Three types of cellular RNAs have been distinguished : (a) messenger RNA (b) ribosomal RNA (c) transfer RNA
        mRNA carries genetic information for arranging amino acids in definite sequence. It  is  linear polynucleotide. It accounts 3% of cellular RNA. Its molecular weight is several million. mRNA molecule carrying information to form a complete polypeptide chain is called cistron. Size of mRNA is related to the size of message it contains. Synthesis of mRNA begins at 5′ end of DNA strand and terminates at 3′ end.
             rRNA form 50-60% part of ribosomes. It accounts 80-90% of the cellular RNA. It is synthesized in nucleus. Kurland (1960) discovered it. It gets coiled here and there due to intrachain complementary base pairing. 
           tRNA molecules are much smaller consisting of 70-80 nucleotides. It is also single stranded but to number of complementary base sequences after pairing, it is shaped like clover-leaf (Holley, 1965). Each tRNA can pick up particular amino acid. Following four parts can be recognized on tRNA 1) DHU arm (Dihydroxyuracil loop / amino acid recognition site 2) Amino acid binding site 3) Anticodon loop / codon recognition site site. 4) Ribosome recognition In the anticodon loop of tRNA, three unpaired nucleotides are present called as anticodon which pair with codon present on mRNA. The specific amino acids is attached at the 3′ end in acceptor stem of clover leaf of tRNA.

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