Amino Acid coo Peptide Bond PROTEINS Proteins are polypeptides. They are linear chains of amino acids linked by peptide bonds
H2O H H O H H O peptide bond
* Each protein is a polymer of amino acids .. As there are 20 types of amino acids (e.g., alanine, cysteine, proline, tryptophan, lysine, etc.), a protein is a heteropolymer and not a homopolymer. A homopolymer has only one type of monomer repeating 'n' number of times. This information about the amino acid content is important as later in your nutrition lessons, you will learn that certain amino acids are essential for our health and they have to be supplied through our diet. Hence, dietary proteins are the source of essential amino acids. . Therefore, amino acids can be essential or non-essential. The latter are those which our body can make, while we get essential amino acids through our diet/food. Proteins carry out many functions in living organisms, some transport nutrients across cell membrane, some fight infectious organisms, some are hormones, some are enzymes, etc. Collagen is the most abundant protein in animal world and (RuBisCO) Ribulose bisphosphate Carboxylase-Oxygenase is the most abundant protein in the whole of the biosphere.
Protein Functions Collagen Intercellular ground substance Trypsin Enzyme Insulin Hormone AntibodyFights infectious agents Receptor Sensory reception (smell, taste, hormone, etc.) GLUT-4Enables glucose transport into cells
The acid insoluble pellet also has polysaccharides (carbohydrates) as another class of macromolecules. Polysaccharides are long chains of sugars. They are threads (literally a cotton thread) containing different monosaccharides as building blocks. For example, cellulose is a polymeric polysaccharide consisting of only one type of monosaccharide i.e., glucose. Cellulose is a homopolymer . Starch is a variant of this but present as a store house of energy in plant tissues. Animals have another variant called glycogen. . Inulin is a polymer of fructose.
* In a polysaccharide chain (say glycogen), the right end is called the reducing end and the left end is called the non-reducing end. It has branches as shown in the form of a cartoon .Starch forms helical secondary structures. In fact, starch can hold 12 molecules in the helical portion. The starch- 12 is blue in colour. Cellulose does not contain complex helices and hence cannot hold 12
CH2OH CH OH 6 CH20H CH2OH o 1 CH2OH OH OH CH2OH H CH2OH OH Glucose Fructose Galactose Glucose Fructose (a) Hexoses CH2OH CH2OH OH HOCH2 OH CH2OH Deoxyribose Ribose crose Glycosidic Bond (b) Pentoses
. Plant cell walls are made of cellulose. Paper made from plant pulp and cotton fibre is cellulosic. There are more complex polysaccharides in nature They have as building blocks, amino-sugars and chemically modified sugars (e.g., glucosamine, N-acetyl galactosamine, etc) . Exoskeletons of arthropods, for example, have a complex polysaccharide called chitin. . These complex polysaccharides are mostly homopolymers.
H O CH2OH CH2OH OH HO-CH OH H HO HO H OH H OFH H-C OH CONFIGURATION CONFIGURATION H C- OH (a) and glucose ring structures CH2OH CH2OH CH2OH CH2OH HO OH OH OH OH OH (b) Starch: 1-4 linkage of glucose CH2OH OH CH2OH OH HO OH OH CH2OH OH CH2OH (c) Cellulose: 1-4 linkage of glucose
Nonreducing end (no potential for free at anomeric position) C-O Reducing end (ring can open to yield free C-O at anomeric carbon) CH20H CH3OH OH OH
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