Questions: Biomolecules

Q1 How would you analyse the chemical composition of a living tissue?

Answer: Grind the tissue in trichloroacetic acid with a mortar and pestle to get a thick slurry, then strain it through cheesecloth or cotton. The liquid that passes through is the acid-soluble pool, holding small molecules, and the solid left behind is the acid-insoluble fraction, holding proteins, nucleic acids, polysaccharides and lipids. The soluble pool roughly represents the cytoplasm, and the two fractions together describe the chemistry of the tissue.

Hinglish: Tissue ko trichloroacetic acid mein peeskar slurry banao aur strain karo. Jo liquid nikle woh acid-soluble pool hai jisme chhote molecules hote hain, aur jo solid bache woh acid-insoluble fraction hai jisme proteins, nucleic acids, polysaccharides aur lipids hote hain.

Q2 What are primary and secondary metabolites?

Answer: Primary metabolites are the compounds of normal physiology that are common to animal tissues: amino acids, sugars, nucleotides and fatty acids, all with clear functions. Secondary metabolites are the extra compounds made mainly by plants, fungi and microbes, such as alkaloids, flavonoids, rubber, essential oils, antibiotics, pigments, gums and spices. Their roles in the organism are not all understood, but many are useful to people and some are ecologically important.

Hinglish: Primary metabolites normal physiology ke compounds hain jo animal tissues mein bhi milte hain, jaise amino acids aur sugars. Secondary metabolites plants, fungi aur microbes ke extra compounds hain, jaise alkaloids, rubber, essential oils aur antibiotics.

Q3 Why do lipids appear in the acid-insoluble fraction although they are small molecules?

Answer: Lipids have masses below 800 daltons, so by size they are not macromolecules. But most lipids sit in membranes, and grinding breaks the membranes into vesicles. Those vesicles are not soluble in water, so they go with the acid-insoluble pool. The lipid class therefore travels with the macromolecular fraction because of its membrane association, not because of its size.

Hinglish: Lipids ka mass 800 dalton se kam hota hai, lekin woh membranes mein hote hain. Tissue grind karne par membranes tootkar vesicles bana deti hain jo water-insoluble hote hain, isliye lipids acid-insoluble fraction mein chale jaate hain.

Q4 Compare starch, glycogen and cellulose.

Answer: All three are polymers of glucose. Starch is the plant store of energy and forms a helical secondary structure that can hold iodine, which is why starch gives a blue colour with iodine. Glycogen is the animal store and is highly branched; the number of ends equals the number of branches plus one. Cellulose is the structural material of plant cell walls, is not branched, has no complex helix and does not give the iodine colour reaction.

Hinglish: Teeno glucose ke polymers hain. Starch plant ka store hai aur iodine ke saath blue colour deta hai; glycogen animal ka branched store hai; cellulose plant cell wall ka structural material hai aur iodine test nahi deta.

Q5 What are the four levels of protein structure?

Answer: Primary structure is the sequence of amino acids from the N-terminal to the C-terminal end. Secondary structure is local folding into a helix or a beta-pleated sheet. Tertiary structure is the folding of the whole chain into a compact three-dimensional shape, and this level is essential for biological activity. Quaternary structure is the arrangement of several folded subunits with respect to one another, as in haemoglobin with its two alpha and two beta subunits.

Hinglish: Primary amino acid sequence hai, secondary helix aur beta-pleated sheet hai, tertiary poora 3-D fold hai jo activity ke liye zaroori hai, aur quaternary kai subunits ka arrangement hai, jaise haemoglobin ke chaar subunits.

Q6 What is a peptide bond and why is a protein a heteropolymer?

Answer: A peptide bond forms when the carboxyl group of one amino acid reacts with the amino group of the next, with the loss of water, and it links the two amino acids in a chain. A protein is a heteropolymer because it is built from twenty different amino acids in a particular order, not from one repeating monomer. A homopolymer would have a single monomer type repeated, which is what cellulose has with glucose.

Hinglish: Peptide bond tab banta hai jab ek amino acid ka carboxyl group doosre ke amino group se water nikal kar judta hai. Protein heteropolymer hai kyunki usme 20 alag amino acids ek order mein lagte hain, ek hi monomer repeat nahi hota.

Q7 What is the difference between a nucleoside and a nucleotide?

Answer: A nucleoside is a nitrogenous base attached to a sugar, such as adenosine or cytidine. A nucleotide is a nucleoside with a phosphate group esterified to the sugar, such as adenylic acid or cytidylic acid. Nucleic acids are polymers of nucleotides, so the nucleotide is the building block and the nucleoside is its base-plus-sugar part.

Hinglish: Nucleoside = base + sugar, jaise adenosine. Nucleotide = nucleoside + phosphate, jaise adenylic acid. Nucleic acids nucleotides ke polymers hain.

Q8 Describe the active site and the catalytic cycle of an enzyme.

Answer: The active site is a crevice or pocket on the folded enzyme into which the substrate fits. In the cycle, the substrate binds to the active site, the binding changes the enzyme shape so that it wraps around the substrate, the active site breaks the substrate bonds and an enzyme-product complex forms, and the products are released while the enzyme returns unchanged for the next cycle.

Hinglish: Active site enzyme ke fold mein bana pocket hai jisme substrate fit hota hai. Cycle mein substrate bind hota hai, enzyme ka shape badalta hai, bonds tootte hain, product ban kar release hota hai aur enzyme wapas free ho jaata hai.

Q9 Why is enzyme activity affected by temperature and pH?

Answer: Both temperature and pH alter the tertiary structure of the protein. Each enzyme has an optimum temperature and an optimum pH, and activity falls on either side of the optimum. Low temperature keeps the enzyme temporarily inactive, while high temperature denatures it and destroys activity. pH works the same way through the ionisable groups of the amino acids at the active site.

Hinglish: Temperature aur pH enzyme ki tertiary structure badalte hain. Har enzyme ka optimum hota hai; kam temperature par enzyme temporarily inactive hota hai aur zyada temperature par denature ho jaata hai. pH bhi active site ke ionisable groups par asar daalta hai.

Q10 What are the six classes of enzymes? Give one example of the reaction each catalyses.

Answer: Oxidoreductases catalyse oxidation-reduction between two substrates. Transferases move a group other than hydrogen between substrates. Hydrolases break bonds such as ester, peptide and glycosidic bonds by hydrolysis. Lyases remove groups without hydrolysis and leave double bonds. Isomerases interconvert isomers. Ligases join two compounds by making new bonds, such as carbon-nitrogen or carbon-oxygen bonds.

Hinglish: Chhe classes hain: oxidoreductases (oxidation-reduction), transferases (group transfer), hydrolases (hydrolysis), lyases (group removal without hydrolysis), isomerases (isomer interconversion) aur ligases (do compounds ko jodna).

That completes the ten written answers. The chapter quiz below checks the tissue fractions, the polysaccharides, protein structure, nucleotides and enzyme action.