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Class 11 Biology: Biomolecules- Carbohydrates

Ravi Singh

27/02/2020 0 0

CARBOHYDRATES
1. Compounds of C, H, O
2. Also called saccharides (sugars)
3. Biomicromolecules- monosaccharides, derived monosaccharides, olgiosaccharides)
4. Biomacromolecues- polysacharadies
MONOSUGARS/MONOSACCHARIDES
1. General formula for monosaccharides where n is the number of C-atoms.
2. Simple sugars, can’t be hydrolyzed further
3. Of 3-7 carbon atoms
4. Monosaccharides are called sugars as these are sweeter in taste.

Types of monosaccharides
1. Based on C-atoms, monosaccharides are divided into following.
  1. Trioses (with-3carbons)
    1. General formula = C₃H₆O₃
    2. e.g. Glyceraldehyde, Dihydroxyacetone.
  2. Tetroses (with 4-carbons)
    1. General formula = C₄H₈O₄
    2. e.g. Erythrose, Threose.
  3. Pentoses (with 5-carbons)
    1. General formula = C₅H₁₀O₅
    2. e.g. Ribose, Deoxyribose, Xylose, Xylulose, Ribulose.
  4. Hexoses (with 6-carbons)
    1. General formula = C₆H₁₂O₆
    2. e.g. Glucose, Mannose, Galactose and Fructose.
  5. Heptoses (with 7-carbons)
    1. General formula = C₇H₁₄O₇
    2. e.eg. Sedoheptulose.
  6. Aldoses.
    1. These monosugars have aldehydic group at C-1’
    2. g. Glucose, Galactose.
  7. Ketoses.
    1. These monosugars have ketonic group at C-2’
    2. g. Fructose.
  8. General formula Cn (H2O) n, H:O in 2:1 ratio
  9. Aldose and ketose group can also react with alcoholic and nitrogen group of another compound forming C-O-C or C-N-C (glycosidic bond)
  10. Glycosidic bond also established during condensation of monosaccharides for formation of oligosaccharides and polysaccharides
  11. A molecule of H2O is usually produced at each condensation, called dehydration synthesis
2. Two cyclic forms of monosaccharides
  1. Furanoses.
    1. All the pentoses (e.g. Ribose, Deoxyribose) and Ketohexoses (e.g. Fructose) occur as a 5-membered ring form which resembles furan so called furanose ring e.g. Ribose and Fructose.
    2. Has pentagon structure with 4 carbons and 1 oxygen
  2. Pyranoses.
    1. Most of aldohexoses (e.g. Glucose, Galactose and Mannose) occur as 6-membered ring form which resembles pyran so called pyranose ring.
    2. Hexagon structure with 5 carbon atoms and one oxygen atom
  3. DEFIVED MONOSACCHARIDES (modified monosaccharides)
    1. DEOXYSUGARS
      1. Deoxyribose
    2. AMINOSUGARS
      1. Monosaccharide has an amino group (-NH2)
      2. g. Glucosamine (forms chitin (NAG), Hyaluronic acid and chondroitin sulphate)
    3. SUGAR ACID
      1. g. Ascorbic Acid, Glucuronic Acid
      2. Glucuronic acid and galacturonic acid occur in mucopolysaccharides

SUGAR ALCOHOL

g. Glycerol, Mannitol (storage alcohol in some fruits)

Functions of monosaccharides
1. As respiratory fuel. Glucose acts as chief respiratory fuel because it is easily oxidizable and is present abundantly in the body fluids. Glucose provides energy for about 60 per cent of energy needs of man. One glucose molecule produces about 38 ATP moleculese., 280 Kcal.
2. Ribose & Deoxyribose for nucleic acids and nucleotides
3. Intermediates of C₃-cycle of photosynthesis e.g. Glyceraldehyde, Xylulose, Ribulose, Sedoheptulose, etc.
4. Galactose is the component of medullary
5. Act as monomers.
6. When excess, monosugars can be changed into amino acids or fats.
7. Ascorbic acid (Vitamin C) is a sugar acid and maintains capillary wall and helps in tyrosine metabolism.

OLIGOSACCHARIDES
1. 2-9 monosaccharides joined by glycosidic bonds
2. Are biomicromolecules
3. Glycosidic bond between aldehyde/ketone group of one monosaccharide and alcohol group of another by dehydration
4. Normally between C-1 and C-4
5. They can be disaccharides (sucrose, maltose, lactose, trehalose)
6. Trehalose ( glu-glu joined by α (1-1)bond, is present in haemolymph of insects
7. trisaccharide (raffinose= glu + gal + fruct, in sugarbeet, cotton seed, and many cereals), tetrasaccharide ( stachyose= glu + fruct + 2 galactoses, in vegetables etc)
8. Larger oligosaccharides have branched or unbranched chains occur attached to cell membrane
Disaccharides

Maltose/Malt Sugar
1. Occur in malted grains of barley, most germinating seeds and tissues where starch is broken down
2. Reducing sugar
3. α (1-4) bond
Lactose/Milk Sugar
1. In milk, reducing sugar
2. Β (1-4) bond of glucose and galactose
3. Souring of milk is conversion of lactose into lactic acid
4. Lactose composed of β-D-glucose and α-D-galactose units interlinked by β (1 → 4) glycosidic bond. It is also called milk sugar
Sucrose
1. Glucose and fructose
2. Non-Reducing sugar
3. It is composed of α-D-glucose and β-D-fructose together by the aldehyde and ketone
4. Carbon by α (1 → 2) glycosidic bond sucrose is not a reducing sugar as compared to maltose and lactose which are reducing ones. Sweetening power of sucrose is considered to be 100. It is common cane or table sugar.

Trisaccharides
1. Raffinose
  1. is a common trisaccharide found in plants. Raffinose is found in sugarbeet, coffee It is non-reducing sugar.
2. REDUCING SUGARS
  1. Sugars which can reduce Cu2+--------Cu+ ions
  2. Basis of benedict’s and Felhling’s test
  3. In all those saccharides having free -CHO and -C=O group
  4. All monosaccharides
  5. Among disaccharides, sucrose is non reducing because both aldehyde and ketone groups participate in glycosidic bond formation
  6. Blue alkaline solution (Cupric Sulphate) changes to reddish precipitate (Cuprous Oxide) on gently heating
3. Functions
  1. Fuel.
    1. Disaccharides can act as fuel to provide energy.
  2. Storage food.
    1. Sucrose is the reserve storage product in sugarbeet and sugarcane.
  3. Recognition point.
    1. Oligosaccharides attached with cell membrane help in recognizing the cells of their own kind.
  4. Sucrose is main transport sugar in the phloem of plants.

POLYSACCHARIDE
1. Called glycans (polymer of glucose), are the polymers of more than 10 monosaccarides, interlinked by glycosidic bonds formed by dehydration synthesis differ in the nature and number of their monosaccharides, and degree of branching
2. Branched or unbranched
3. Right end of polysaccharides is reducing and left non reducing
4. 2 types:
Homopolysaccharides
1. cellulose, starch, glycogen, inulin, agar, xylan, araban, etc.
2. only one type of monomers
3. GLYCOGEN
  1. Found in the muscles and liver cells of animals is also a branched homopolysaccharide formed of about 30,000 α-d-Glucose molecules.
  2. α(1-4) and β(1-6) at branching points
  3. Its molecular weight is about 4 millon and it gives red coloured with iodine.
  4. A polysaccharide chain has two specific ends: right reducing end and left non reducing end.
  5. Chemically non-reactive and is osmotically inactive
4. STARCH
  1. Chemically non-reactive and osmotically inactive
  2. Forms helical secondary structure, into helix
  3. Chemically, the starch is formed of two glucose polymers:
    1. Amylose
      1. α (1-4) glycosidic bonds) between glucose molecules
      2. straight chain of 200-1000 glucose units
      3. it is helical, each turn has 6 glucose units
    2. amylopectin
      1. a branched glucan of about 2,000-200,000 α-Glucose molecules
      2. form straight chains and branches (after 25 glucose units)

branching points have α (1-6) bonds

CELLULOSE (CELLULIN)
1. Structural polysaccharide
2. Paper made from pulp of cellulose
3. Cotton fibre is cellulose
4. Most abundant organic compound/carbohydrate in biosphere
5. 50% of carbon found in plants is cellulose
6. Forms about 25-50% of wood and about 90% of cotton
7. Tunicin (of tunicates) related to cellulose
8. These are unbranched linear chains
9. A chain contains 6000 or more glucose units
10. Glucose joined by β (1-4) linkage
11. Number of chains present in close antiparallel fashion
12. Molecules are held together by intermolecular Hydrogen bonds between OH groups at position 6 or glucose residue on one molecule and glycosidic oxygen between 2 glucose residues of adjacent molecule
13. As cellulose does not contain complex helices so cannot hold iodine and give no colour with Iodine.
14. Artificial fibre Rayon is manufactured by dissolving cellulosic material in alkali and by extruding and coagulating filaments
15. Artificial silk is polysaccharide prepared from Rayon
16. By treatment with other chemicals, cellulose is converted into cellulose acetate (used in fabrics, cellulosic plastics and shatter proof glasses)
17. Cellulose Nitrate is used in propellant explosives
18. Carboxymethyl cellulose, added to ice-creams, cosmetics, medicines to emulsify and give a smooth texture
19. Cellulose can be hydrolyzed to soluble sugars, microbes can then convert these sugars to form like ethanol, butanol, acetone, methane etc.
INULIN
1. A fructan, is storage polysaccharide of roots and tubers of Dahlia
2. Inulin is not metabolized in human body and is readily filtered through the kidney, therefore used in testing of kidney functions (especially glomerular filtration)
CHITIN
1. Second most abundant organic substance
2. Homopolysaccharide of nitrogen containing glucose called N-Acetylglucosamine
3. Exoskeleton of arthropods have chitin
4. Chitin is soft and leather, hence provide strength and elasticity
5. It becomes hard when impregnated with certain proteins and calcium carbonate
6. Chitin is unbranched
7. Monomers joined by 1-4 B-linkage
8. Molecules lie parallel and held by H-bonds

Heteropolysaccharides
1. two or more types of monosaccharides or their derivatives as amino sugars like glucosamine, N-acetyl galactosamine or sugar acids like glucuronic acid, etc.
2. Hyaluronic acids:
  1. Heteropolymer of D-Glucoronic Acid(a carboxylic Acide) & D-N-Acetyl Glucosamine (glucose derivative)
  2. It gives toughness and flexibility of cartilage and tendons
  3. liner acidic hetropolysaccharide found in various lubricating fluids of body e.g. synovial fluid of limb joints, around the ovum, etc.
3. Peptidoglycan:
  1. cell wall of bacteria and cyanobacteria
  2. degraed by Lysozyme
  3. it is made of alternate amino sugars, N-Acetyl Glucosamine and N-Acetyl Muramic Acid
  4. It is formed of a polysaccharide chain linked with tetrapeptide molecules.
  5. It prevents the lysis and osmotic inflow of the cell wall.
4. Agar
  1. In cell wall of red algae, released on boiling
  2. Mucopolysaccharide, repeated units of D-galactose joined by proteins
  3. Used in culture medium
5. function
  1. Reserve food, structure polysaccharides Cellulose, Chitin, Chondroitin, Peptidoglycans, Anticoagulation, Cellulose, Agar, hyaluronic acid, Hormones, Blood antigens

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