👉👉👉6. Biomolecules - Carbohydrates & Lipids👈👈👈
6. BIOMOLECULES
Can you recall?
1. Which are different cell components?
2. What is the role of each component of cell?
• Our planet is having a wide diversity of living organisms.
• They are classified as -
– unicellular (consisting of a single cell; including bacteria and yeast) or
– multicellular having many cells (e.g. plants and animals).
• They have cell as the basic structural and functional unit.
• The cells have protoplasm containing numerous chemical molecules, the biomolecules .
• Biochemistry is biological chemistry that provides us the idea of
– the chemistry of living organisms and
– molecular basis for changes taking place in plants, animals and microbial cells.
• It develops the foundation for understanding
– all biological processes
– communication within and between cells
– chemical basis of inheritance and
– diseases in animals and plants.
• Chemical analysis of all living organisms indicates presence of the most common elements per unit mass of a living tissue.
• The elements are -
– carbon,
– hydrogen,
– nitrogen,
– oxygen,
– sulphur,
– calcium,
– phosphorus,
– magnesium and
– others with their respective content
• Chemically all living organisms have basic three types of macromolecules .
– Polysaccharides (carbohydrates),
– Polypeptides (proteins) and
– Polynucleotides (nucleic acids)
• They are polymers of simple subunits called monomers .
– They are the polymers of monosaccharides , amino acids and nucleotides respectively.
• Lipids are water insoluble and small molecular weight compounds as compared to macromolecules.
6.2 Biomolecules in the cell:
A. Carbohydrates:
• The word carbohydrates means ‘ hydrates of carbon ’.
• They are also called saccharides . –
(Latin - Saccharum = sugar + ide (Eng.) = combining form)
• They are biomolecules made from just three elements:
– carbon , hydrogen and oxygen with the general formula (CH2O)n .
• They contain hydrogen and oxygen in the same ratio as in water (2:1).
• Carbohydrates can be broken down ( oxidized ) to release energy .
• Based on number of sugar units , carbohydrates are classified into three types namely,
– monosaccharides,
– disaccharides and
– polysaccharides
1. Monosaccharides :
• These are the simplest sugars .
• They have crystalline structure.
• They are sweet to taste and soluble in water .
• They cannot be further hydrolyzed into smaller molecules.
• They are the building blocks or monomers of complex carbohydrates.
• They have the general molecular formula (CH2O)n , where n can be 3,4, 5, 6 and 7.
• They can be classified according to the number of carbon atoms in a molecule as
– triose,
– tetrose,
– pentose, etc..
• Monosaccharides containing the aldehyde (-CHO) group are classified as aldoses –
e.g. glucose ( C6 H12O6 ), xylose ( C5H10O5 ), etc.
• Monosaccharides containing a ketone(-C=O) group are classified as ketoses. – e.g. ribulose ( C5H10O5 ), fructose ( C6H12O6 )
• All monosaccharides are reducing sugars due to presence of free aldehyde or ketone group.
• These sugars reduce the Benedict's reagent (Cu2+ to Cu+ ) since they are capable of transferring hydrogens (protons) to other compounds, a process called reduction .
a. Glucose: (C6 H12O6 )
• 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 metabolized by cellular respiration .
b. Galactose: (C6 H12O6 )
• It looks very similar to glucose molecules.
• They can also exist in α and β forms.
• Galactose react with glucose to form the disaccharide lactose.
• However, glucose and galactose cannot be easily converted into one another. • Galactose cannot play the same role in respiration as glucose .
c. Fructose: (C6 H12O6 )
• It is the fruit sugar.
• 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.
• Disaccharide is formed when two monosaccharide react by condensation reaction releasing a water molecule.
• This process requires energy .
• A glycosidic bond forms and holds the two monosaccharide units together .
– e.g. • Sucrose ( C₁₂H₂₂O₁₁ )
• Lactose ( C₁₂H₂₂O₁₁ )
• Maltose ( C₁₂H₂₂O₁₁ )
• Sucrose is a nonreducing sugar since it lacks free aldehyde or ketone group.
• Lactose and maltose are reducing sugars .
• 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.
• 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.
• It result in the formation of polysaccharides as macromolecules.
• These are too big to escape from the cell.
3. Polysaccharides:
• Monosaccharides can 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 are broken down by hydrolysis 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 (C₆H₁₀O₅) ₙ
– Amylopectin (C₆H₁₀O₅) ₙ
• Both are made from α-glucose .
• Amylose is
– an unbranched polymer of α-glucose.
– The molecules coil into a helical structure.
– It forms a colloidal suspension in hot water.
• Amylopectin is
– a branched polymer of α-glucose.
– It is completely insoluble in water.
b. Glycogen: (C₆H₁₀O₅) ₙ
• 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 hydrolyzed as per need to produce glucose.
c. Cellulose: (C₆H₁₀O₅) ₙ
• It is a polymer made from β-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.
