DIGESTION OF CARBOHYDRATE ,LIPID ,PROTEIN...............

1. A PRESENTATION ON DIGESTION IN
INSECTS
SUBMITTED BY
SAROJ SAHOOSUBMITTED TO
Dr.(Mrs).Pushpa Singh
Dr . Manoj Kumar

2. DIGESTION IN INSECT
 Digestion is the process by which food molecules
are broken down into smaller molecules that are
able to be absorbed by the gut tissue.
 Primary digestion is the dispersion and reduction in
molecular size of the polymers and results in
oligomers. During intermediate digestion, these
undergo a further reduction in molecular size to
dimers, which in final digestion form monomers.
 Digestion usually occurs under the action of
digestive enzymes.

3.  Different types of enzymes have been isolated from insect
gut.
 These are (i) carbohydrases acting upon disaccharides
and polysaccharides including starch
 (ii) proteases acting upon proteins and
 (iii) lipases on fats and oils.
 According to the nature of food different types of enzymes
are released.
 Omnivorous insects – protease and lipase
 Phytophagous insects – amylase ,maltase, invertase
 Nector feeding insects- invertase
 Wood feeding insects – cellulase
 Meat eating maggots- collagenase
 Blood sucking fly- protease
 Mallophaga, dermestid, cloth moth-keratinase

4.  Enzymes are released from epithelial cells of the midgut,
gastric caecae and salivary gland.
 Midgut epithelial cells –invertase, protease, lipase
 Gastric caecae- invertase, protease, lipase
 Salivary gland –amylase and maltase
 During the secretory activity the epithelial cells undergo
various changes.
 In some insects. the secretions are poured out from the
free margin of the cell.(merocrine cell)
 while in others, the cells burst to release the
enzyme.(holocrine cells )


5.  For the proper functioning of enzymes PH in the gut is
maintained at optimal levels in different parts of the alimentary
canal.
 Mainy vary from 6-8 in most of the insects.
 Phytophagous - alkaline
 Predacious- weakly acidic
 Wool and wax moth – alkaline.

6. DIGESTION OF CARBOHYDARTE
 Carbohydrates are ingested as polysaccharides and
disaccharides and are broken down in to monosaccharides
for absorption through the gut wall.
 The absorption of monosaccharides generally occurs pasively
through the mid gut wall , diffusion along the concentration
gradient.
 Glucosidases secreted in the mid gut hydrolyse the glucosidic
bonds between the sugar residue
 α-Glucosidase hydrolyse the alpha glucosides of
sucrose,maltose,trehalose,melezitose
 β-Glucosidase break the β - glucosides of cellobiose and
gentiobiose
 Amylase act on the α- glucosidic linkages in starch and
glycogen.
 2 types (endoamylase and exoamylase)
 Most common carbohydrase in insects is trehalase which
hydrolyses trehalose into two glucose molecules.

8.  cellulose is a polymer of beta-1,4 –linked glucopyranosyl
monomers.
 Three classes of enzymes involved in the hydrolysis of
cellulose (produced midgut and salivary gland)
 1.endo- β-1,4 –glucanases(cleave the β-1,4- glucosidic bonds
in the cellulose chain)
 2.Exo - β-1,4 –glucanases (cleave the cellubiose residue
from one end of the chain)
 3. β-1,4 –glucosidase (breakdown the cellobiose to glucose)

9. DIGESTION OF PROTEIN
 Protein are broken down into their amino acid constituents by
proteolytic enzymes and absorbed passively through the midgut
wall when they are present in high concentration .
 2 types of proteases
1. Endopeptidases 2. Exopeptidases
(Cleave the internal peptide bonds) (removal the terminal amino acid )
.Carboxypeptidases
(remove the terminal amino acid from carboxyl end of the chain)
.Aminopeptidases
( remove the terminal amino acid from amino end of the chain
. Serine proteases
. Cysteine protease
.Aspartic proteases

10. Serine protease(serine at the active site)

 trypsin (cleave the peptide bond invoving
carboxyl group of arginine ,lysine.)

 chymotrypsin (cleave the peptide bond invoving
carboxyl group of tyrosine ,phenylanaline,tryptophan)



11. Insects are mainly ingest storage lipids that is found in the seed
and fatty acid in animals and membrane lipid in the cells.
Triacylglycerol is the major storage lipid in the seeds.
Lipases or lypolytic enzymes are mainly produced from gastric
caecae and mid gut wall.
Phospholipases remove the fatty acid portion from
phosphatides.
DIGESTION OF LIPID

12. These are resynthesized by the mid gut cells from digested
components before they are released into the haemolymph.
The major lipid components that appear in the haemolymph are
diacylglycerols. And these are insoluble in the haemolymph
these are bounded by a lipo-protein called lipophorin that
allows them to transported throughout the body.
 Triacylglycerol are hydrolyzed by a Triacylglycerol Lipase that
preferentially removes the outer ester links of the substrate and
acts only on the water-lipid interface.
 Esterases are act on molecule that are completely dissolved in
the water, hydrolyzing carboxyl ester into alcohol and
carboxylate.
 Final component are free fatty acid, glycerol, partial acyl
glycerol, lysophospholipid .