● Proteins are `color{violet}("polypeptides.")`

● They are `color{violet}("linear chains")` of amino acids linked by `color{brown}("peptide bonds.")`

● Each protein is a polymer of `color{violet}("amino acids.")`

● As there are 21 types of `color{violet}("amino acids")` (e.g., alanine, cysteine, proline, tryptophan, lysine, etc.), a protein is a
`color{brown}("heteropolymer")` and not a `color{brown}("homopolymer.")`

● A `color{violet}("homopolymer")` has only one type of `color{violet}("monomer repeating ‘n’")` number of times.

● This information about the `color{violet}("amino acid")` content is important as certain `color{violet}("amino acids")` are `color{brown}("essential")` for our health and they have to be supplied through our diet.

● Hence, `color{violet}("dietary proteins")` are the source of `color{violet}("essential amino acids.")`

● Therefore, amino acids can be `color{violet}("essential or non-essential.")`

● The latter are those which our body can make, while we get `color{violet}("essential amino acids")` through our diet/food.

● Proteins carry out many functions in `color{violet}("living organisms,")` some transport nutrients across cell membrane, some fight infectious organisms, some are `color{violet}("hormones,")` some are `color{violet}("enzymes,")` etc.

● `color{bron}("Collagen")` is the most abundant protein in animal world and `color{brown}("Ribulose bisphosphate Carboxylase-Oxygenase (RUBISCO)")` is the most abundant protein in the whole of the `color{violet}("biosphere.")`

● The `color{violet}("acid insoluble pellet")` also has `color{brown}("polysaccharides (carbohydrates)")` as another `color{violet}("class of macromolecules.")`

● `color{violet}("Polysaccharides")` are long chains of sugars.

● They are `color{violet}("threads")` (literally a cotton thread) containing different `color{violet}("monosaccharides")` as building blocks.

● For example `color{violet}("cellulose")` is a `color{violet}("polymeric polysaccharide")` consisting of only one type of monosaccharide i.e., `color{violet}("glucose. ")`

● `color{brown}("Cellulose"0` is a `color{violet}("homopolymer. ")`

● `color{brown}("Starch")` is a variant of this but present as a store house of energy in `color{violet}("plant tissues.")`

● Animals have another variant called `color{brown}("glycogen.")`

● `color{brown}("Inulin")` is a `color{violet}("polymer of fructose.")`

● In a `color{violet}("polysaccharide chain")` (say glycogen), the right end is called the `color{brown}("reducing end")` and the left end is called the `color{brown}("non-reducing end.")`

● It has branches as shown in the form of a `color{violet}("cartoon.")`

● `color{violet}("Starch")` forms `color{violet}("helical secondary structures.")`

● In fact, starch can hold `color{brown}(I_2 "molecules")` in the `color{violet}("helical portion.")`

● The `color{brown}("starch-" I_2)` is `color{brown}("blue")` in colour.

● `color{violet}("Cellulose")` does not contain `color{violet}("complex helices")` and hence cannot hold `color{brown}(I_2)`.

● `color{violet}("Plant cell walls")` are made of `color{brown}("cellulose.")`

● Paper made from `color{brown}("plant pulp")` is cellulose.

● Cotton fibre is `color{violet}("cellulose.")`

● There are more `color{violet}("complex polysaccharides")` in nature.

● They have as `color{violet}("building blocks, amino-sugars")` and chemically modified sugars (e.g., `color{brown}("glucosamine, N-acetyl
galactosamine,")` etc.).

● `color{violet}("Exoskeletons of arthropods,")` for example, have a `color{violet}("complex polysaccharide")` called `color{brown}("chitin.")`

● These `color{violet}("complex polysaccharides")` are `color{violet}("heteropolymers.")`

● The other type of `color{violet}("macromolecule")` that one would find in the `color{violet}("acid insoluble fraction"0` of any `color{violet}("living tissue")` is the `color{violet}("nucleic acid.")`

● These are `color{brown}("polynucleotides.")`

● Together with `color{violet}("polysaccharides and polypeptides")` these comprise the true `color{violet}("macromolecular fraction")` of any `color{violet}("living tissue or cell.")`

● For `color{violet}("nucleic acids,")` the building block is a `color{brown}("nucleotide.")`

● A `color{violet}("nucleotide")` has three chemically distinct components.

● One is a `color{brown}("heterocyclic compound")`, the second is a `color{violet}("monosaccharide")` and the third a `color{violet}("phosphoric acid")` or `color{violet}("phosphate.")`

● The `color{violet}("heterocyclic compounds")` in `color{violet}("nucleic acids")` are the `color{brown}("nitrogenous bases")` named `color{violet}("adenine, guanine, uracil, cytosine,")` and `color{violet}("thymine. ")`

● `color{violet}("Adenine and Guanine")` are `color{brown}("substituted purines")` while the rest are substituted pyrimidines.

● The skeletal `color{violet}("heterocyclic ring")` is called as `color{brown}("purine and pyrimidine")` respectively.

● The sugar found in `color{violet}("polynucleotides")` is either `color{brown}("ribose")` (a monosaccharide pentose) or `color{brown}("2 deoxyribose. ")`

● A `color{violet}("nucleic acid ")`containing deoxyribose is called `color{violet}("deoxyribonucleic acid (DNA)")` while that which contains ribose is called `color{violet}("ribonucleic acid (RNA).")`