This document summarizes the functional roles and activation of protein synthesis in insects. It discusses various types of proteins found in insects and their functions, including structural, interstitial, enzyme, heme, bioluminescence, and peptide hormone proteins. It also describes the key steps in protein synthesis: transcription, post-transcriptional modification, and translation. Protein synthesis is controlled by hormones like juvenile hormone and ecdysteroids in a tissue-specific and stage-specific manner to support various functions during insect development.

1. FUNCTIONAL ROLE AND
ACTIVATION OF PROTEIN
SYNTHESIS IN INSECTS
KARTHIKEYAN, S (2015 800503)
Ph.D., Scholar,
Agricultural Entomology,
TNAU, Coimbatore.

2. Functional role of proteins
 Structural proteins
 Interstitial proteins
 Enzymes
 Hemeproteins
 Bioluminescence
 Peptide hormones
 Heat shock proteins (HSPs)

3. Structural proteins
 Contractile(muscular) proteins
- actin, myosin, actomyosin & tropomyosin
 Fibroins – silk in various arthropods
-▲alanine, ▼glycine and serine in Saturniidae
 Proteins of integument
- sclerotin, arthropodin and resilin
 Collagen – insoluble fibre
- glycine, proline and hydroxy proline
 Chromosomal proteins - histones

5. Interstitial proteins
 Carrier proteins
- JH binding proteins
- Lipid-Binding proteins
- Xenobiotic-Binding proteins
- Hemoglobins
-Large lipid transfer protein (LLTP) - Lipophorins
 Storage proteins – calliphorin and lipovitellin
 Enzymes of hemolymph – Trehalase, JH
esterase, pro phenol and phenol oxidase
 Immunoproteins – sarcotoxin(-) and sapecin (+)

6. Hemeproteins
 Cytochroms are major group.
- electron/hydrogen transport by reversible
valency change of their heme ion.
- cytochrome c
- cytochrome b5
- cytochrome p - 450

7. Bioluminescence
 Luciferin oxidized by the enzyme luciferase
and emits light
 Bioluminescence occurs in Collembola,
Homoptera, Diptera and Coleoptera

9. Peptide hormones
 Brain hormone
 Bursicon
 Diuretic hormone – controls urine formation
 Neurohormone C and D – cardiac activity
 Hyperglycemic, hypoglycemic and adipokinetic
peptides (CC)
- regulation of level of blood sugar(trehalose)
 Sex peptides e.g. ninhydrin-positive male
substance which stimulates egg laying,
inhibition of female receptivity & sperm transfer
 Proctolin – myotropic activity of proctodeal
musce of Periplanata americana

10. HSPs in response to Heat
 Mild heat hardening increased the expression of
mRNA levels of Hsp70 and Hsp20 but affects
the fecundity.
 Which improves thermotolerance of the pea
leafminer, Liriomyza huidobrensis.
 Expression of mRNA may play an important role
in balancing the functional tradeoff of thermal
protection and reproductive impairment.
(Huang et al., 2007)

11. "Rapid heat hardening"
 Pretreating insects with a mild heat stressor
can induce expression of Hsp genes and
result in protection from subsequent stresses
termed as "rapid heat hardening"
 It is apparently due to resolubilization of
proteins that were denatured during the
stressing episode.
Mahadav et al., 2009 and Elekonich 2009

12. HSPs in response to radiation
 Gamma radiation exposure to a tropical
species midge, Chironomus ramosus,
expressed elevated levels of Hsp70 mRNA
and proteins in salivary gland cells of
larvae.
(Datkhile et al., 2011)

13. HSPs in
Drought dehydration and anhydrobiosis
 Some insects are able to survive the loss of
almost all their body water content, entering
a latent state known as anhydrobiosis.
 Hsp genes are important genes for
anhydrobiosis in the sleeping chironomid,
Polypedilum vanderplanki.
(Cornette et al., 2011)

14. Protein synthesis
 Transcription
 Post-transcriptional
modification
 Translation

15. Transcription
 mRNA from DNA double helix in
the genome as a template
 The DNA is "unzipped“ by the enzyme helicase
 single nucleotide chain open to be copied.
 RNA polymerase reads the DNA strand from
the 3-prime (3') end to the 5-prime (5') end
 synthesizes a single strand of messenger RNA
in the 5'-to-3' direction.

17. Post-transcriptional modification
 Primary transcripts leaves the nucleus via
nuclear pores to the cytoplasm.
 Post-transcriptional modification to give hnRNA
(heterophil nuclear RNA)
 hnRNA then undergoes splicing
of introns (noncoding parts of the gene)
via spliceosomes to produce the final mRNA.
 Drosophila 20% and in Aedes 3.3% (Lengyel &
Penman 1975)

18. Translation
 The synthesis of proteins from mRNA is
known as translation
 mRNA is decoded to produce a
specific polypeptide according to the
codes specified by the trinucleotide
genetic code
 mRNA as a template to guide the
synthesis of a chain of amino acids that
form a protein

20. Steps involved in
Translation
 Activation of Amino Acids
 Charging of tRNA
 Activation of Ribosome
 Assembly of Amino Acids (Polypeptide Formation)
 Initiation of Polypeptide Chain
 Elongation of Polypeptide Chain
 Termination and Release of Polypeptide Chain
 Modification of Released Polypeptide
 Polysome Formation

21. Activation of Amino Acids
 AA reacts with ATP to form amino acid AMP
complex and pyrophosphate.
 Catalyzed by a specific AA activating enzyme
called aminoacyl-tRNA synthetase in the
presence of Mg2+.
 There is a separate aminoacyl tRNA
synthetase enzyme for each kind of amino
acid.
 The amino acid AMP enzyme complex is
called an activated amino acid.

22. Charging of tRNA
 The amino acid AMP-enzyme complex joins
with the amino acid binding site of its specific
tRNA, where its COOH group bonds with the
OH group of the terminal base triplet CCA.
 The reaction is catalyzed by the same
enzyme, aminoacyl tRNA synthetase.
 The resulting tRNA-amino acid complex is
called a charged tRNA.

23. Activation of ribosome
 smaller and the larger subunits of
ribosome are joined together.
 This is brought about by mRNA chain.
 Activation of ribosome by mRNA
requires proper concentration of Mg++.

24. Assembly of Amino Acids
(Polypeptide Formation)
It involves 3 events:
1. Initiation,
2. Elongation and
3. Termination of polypeptide chain.

25. Initiation
 The mRNA chain has its 5 end an “initiator” or
“start” codon (AUG or GUG) that signals the
beginning of polypeptide formation.
 This codon lies close to the P site of the
ribosome.
 The amino acid methionine initiates the
process.
 It is carried by tRNA having an anticodon
UAC which bonds with the initiator codon
AUG of mRNA

26.  A. A charged tRNA arriving at the A site, reading its codon on the mRNA.
 B. AA of tRNA at P site is ready to transferred to the amino acid of tRNA at A site.
 C. Amino acids are joined by peptide bond and tRNA is discharged from P site.
 D. Peptide chain-carrying tRNA is translocated to P site, making A site free to receive
another charged tRNA.

27. Termination of polypeptide
chain
 At the terminal end of mRNA chain there
is a stop, or terminator codon (UAA,
UAG or UGA).
 It is not joined by the anticodon of any
tRNA amino acid complex.
 Hence, there can be no further addition
of amino acids to the polypeptide chain.

28. Modification of Released
Polypeptide
 The just released polypeptide is a straight,
linear exhibiting a primary molecule, structure.
 It may lose some amino acids from the end
with the help of a peptidase enzyme, and then
coil and fold on itself to acquire secondary
and tertiary structure.
 It may even combine with other polypeptides,
to have quaternary structure.

29. Polysome Formation
 To synthesize of many molecules of the same
polypeptide simultaneously
 A row of ribosomes joined to the mRNA
molecule, is called a polyribosome, or a
polysome.
 Synthesis of many molecules of the same
polypeptide simultaneously from one mRNA
molecule by a polysome is called
translational amplification.

30. Protein synthesis during
embryogenesis
 Kuthe 1973 discovered that protein synthesis
begins early cleavage stage and continuously
transferred to peripheral region of egg.
 Chen 1971 reported In Bombyx, Drosophila,
Culex and histocerca the overall variation in
the conc. of AA b/w release and utilized
represents protein synthesis during
embryonic differentiation.

31. Yolk proteins
 Major function of fat body in adult female is
the synthesis of yolk proteins.
 Released into hemolymph taken up by
growing oocytes
 Tefler (1954) first identified insect vitellogenin
by immunological methods in Cercopia moth.

32. Hemolymph proteins
 Shigematsu (1958) first discovered that the
hemolymph proteins are synthesized in the fat
body.
 Incubation of Bombyx larval fat body with AA
resulted in the release of proteins.

33. Hormonal control
 Most of the proteins are synthesized by the
- fat body,
- follicle cells and
- the ovarial connective tissue.
 All tissues produce more proteins during
oocyte maturation indicates a possible
stimulatory action of juvenile hormone in all
three tissues.
(Lüscher et al., 1971)

34. Insect tissues cultured in vitro
 β-ecdysone stimulated both evagination and
cuticle deposition of wing discs of
Plodia interpunctella (Hübner).
 Cuticle deposition was obtained under the
following conditions:
-(a) 24-hr pulse of (0.5 - 5.0µg/ml)
- (b) continuous treatment with 0.2µg/ml
-(c) continuous treatment with 0.5-50.0µg/ml
in medium conditioned with larval fat body.
(Oberlander, 1976)

35. Thompson et al., (1971)
 In Calliphora, β-ecdysone shown to activate
protein synthesis in larval fat body.
 Injection of alpha ecdysone in fourth instar
Anthraea pernyi stimulated protein synthesis
 Injection of JH in fifth instar Oncopeltus faciatus
increased rate of protein synthesis.

36. Pan (1971)
 No evidence of hormonal control in Cercopia
moth protein synthesis.
 In Danaus plexipus oogenesis is clearly
hormonal control.

37. Conclusion
 The factors activating protein synthesis is not
known to the science with certainty, although
both juvenile hormone and ecdysteroids are
involved.
 Highly species-specific
 Tissue specific and
 Stage specific