exoskeleton&molting of insects
DESCRIPTION
TRANSCRIPT
EXOSKELETON
ByDarbaz AhmadShakar Ahmad
Insect Integument (Exoskeleton)
Outer epicuticle
Inner epicuticleEpicuticle
Exocuticle
Endocuticle
Schmidt’s layer
Epidermis
Basement membranePore canals
Procuticle
Insect Integument (Exoskeleton)
Outer epicuticle
Inner epicuticleEpicuticle
cement
waxoriented wax
cuticulin
Inner epicuticle
Exocuticle (procuticle)
pore canal
Insect Integument (Exoskeleton)
cement
waxoriented wax
WATER WATER
Wax Layers - Control of Water Movement
WATER IS RETAINED
Insect Integument (Exoskeleton)
NH
O = C - CH2
CH2OH
O
NH
O = C - CH2
O
N - acetylglucosamine polymer
OH H
H
OH
H
H
O
CH2OH
H
H
OH H
n
Insect Integument (Exoskeleton)
CO
NH CO
NH CO
NH CO
NH CO
NH CO
NH
CO
NH CO
NH
CO
NH CO
NH CO
NH CO
NH
hydrogen bonds
NH
O = C - CH2
CH2OH
O
NH
O = C - CH2
OH H
H
OH
H
H
O
CH2OH
H
H
OH H
Insect Integument (Exoskeleton)
N - acetylglucosamine polymer
microfibril
sheets of microfibrils
orientation of microfibrils changes
Insect Integument (Exoskeleton)
Protein Matrix
Insect Integument (Exoskeleton)
Cross linking of protein matrix
Insect Integument (Exoskeleton)
OH
Cross linking of protein matrix
OH
C
CH2
Protein Protein
OH
OH
CH2
CH2
O
O
CH2
CH2
OH
OH
CH2
CH2
Protein Protein
N-acetyl dopamine N-acetyl dopamine quinone
Insect Integument (Exoskeleton)
Tensile strength of sclerotized chitin (sclerotin)
kg/mm2
Molting
Molting
• Arthropods periodically shed exoskeleton to allow for growth and/or metamorphosis
• 7 steps during each molt cycle
1. Apolysis
• Retraction of epidermal cells from endocuticle
• Formation of subcuticular space
• Molting gel secreted
• New cuticle laid down
2. Epicuticle formation
• Epicuticle laid down
• It is extensively wrinkled
3. Procuticle deposition
• Formation of chitin microfibrils
• Endocuticular layers of old cuticle digested
• Enzymes in molting gel initially inactive
4. Ecdysis
• Old cuticle splits along middorsal suture
• Cast skin = epicuticle and exocuticle
• Endocuticle recovered and recycled into new procuticle
5. Expansion
• Insect swallows air
• Insect swells, removes wrinkles in epicuticle
6. Hardening and darkening
• New procuticle
stabilized
• Exocuticle formed
7. Endocuticle deposition
• Depositing chitin and protein takes time
• Some insects deposit one lamina of endocuticle every 24 hours
Note: Ecdysis under hormonal control