ENERGY METABOLISM IN CESTOIDEA (TAPEWORMS)

1. ENERGY METABOLISM IN
CESTOIDEA(TAPEWORMS)
GROUP MEMBERS:
HADIA KHADIJA
NADIR AKHTER
TALHA KHAN
WAQAR AHMED
BS-Zoology (VII)
QAU Islamabad

2. ACQUISITION OF NUTRITION
 All nutrient molecules must be absorbed across the tegument.
 Mechanisms of absorption include
i. active transport
ii. mediated diffusion
iii. simple diffusion
 Plerocercoids of some species are capable of pinocytosis.
 Adult cestodes are facultative anaerobes.
 Derive energy from catabolism of glucose and glycogen.

3. GLYCOLYSIS IN CYTOPLASM
 Glucose from glycogen or absorbed directly from the host intestine is
degrade into phosphoenolpyruvate (PEP).
 PEP splits into two branches:
i. Lactate is produced by dephosphorylation of PEP and reduction of
pyruvate.
ii. Oxaloacetate is produced by fixation of carbon dioxide in PEP
.
 Oxaloacetate is then reduced to malate.
Both branches are functionally equal because each generates a high-
energy phosphate bond and reoxidizes the NADH formed in glycolysis;
therefore, cytoplasmic redox balance is preserved.

5. GLYCOLYSIS IN MITOCHONDRIA
Additional energy is obtained when malate enters the mitochondria
 A part of the malate is metabolized and excreted as acetate.
 The other half of the malate is metabolized and reduced to succinate.
 Reducing equivalents for reduction of fumarate are provided by
oxidation of malate.
 Oxidative decarboxylation of malate is NADP dependent.
 Fumarate reduction is NAD dependent.

7. KREBS CYCLE
 The tricarboxylic acid cycle is of little or no importance in adult cestodes,
but a substantial amount of glucose carbon may flow through the Krebs
cycle in certain species.
 40% of carbohydrate utilized by Echinococcus multilocularis may be
channeled into the Krebs cycle
 Activity of the Krebs cycle increases in S. solidus when the plerocercoids
are activated by an increase in the ambient temperature.

8. ELECTRON TRANSPORT CHAIN
 Cestodes take up oxygen when it is available, but oxygen probably does
not function as a terminal electron acceptor in an energy-producing
series of reactions.
 A classical mammalian type of electron transport system is present in at
least some cestodes is of minor importance.
 The major cytochrome system is a so-called o-type, similar to that
reported in many bacteria.
 The terminal oxidase can transfer electrons to either fumarate or oxygen,
depending on whether conditions are aerobic or anaerobic, and the
products are either succinate or hydrogen peroxide, respectively.

9. ETC

10. ETC cont…

11. PROTEINS AND LIPIDS
 Tapeworms probably do not derive any energy from degradation of lipids or
proteins.
 Hymenolepis diminuta has only a modest capacity for carrying out transaminations
and can degrade only four amino acids. They can convert cystine to cysteine.
 The function served by much of the lipid in cestodes remains a mystery.
 Lipids in cestodes may represent metabolic end products, since they are relatively
nontoxic to store.
 Nitrogenous end products excreted include considerable quantities of ammonia,
α-amino nitrogen, and urea.

12. SYNTHETIC METABOLISM
 They can absorb amino acids, purines, pyrimidines, and nucleosides from the
host and synthesize their own proteins and nucleic acids.
 The worm can neither synthesize fatty acids de novo from acetyl-CoA nor
introduce double bonds into the fatty acids it absorbs.
 Hymenolepis diminuta rapidly hydrolyzes monoglycerides after absorption,
and it can then resynthesize triglycerides.

13. TREMATODE CESTODE NEMATODE
Type Facultative Anaerobes Facultative Anaerobes Obligate Aerobes
Glycolysis
(end products)
Propionate Acetate
Succinate
Acetate
Succinate
Alanine
Propionate
Methylbutyrate
Methylvalrate
Krebs Cycle Functional Mostly Absent Functional
ETC Present in free living,
larval forms
Absent in adults
Present Absent but present in
some with some
mutation
Electron Acceptor Ubiquinone and
cytochrome c in larvae
Rhodoquinone in
adults
O-type cytochrome
system
Fumarate or oxygen
final electron acceptor
Oxygen
Detoxification of
Hydrogen Peroxide
Enzyme Peroxidase Enzyme Peroxidase Hemoglobin and Nitric
oxide co-substrate
TABLE: COMPARSION OF ENERGY METABOLISM OF TREMATODE,
CESTODE, AND NEMATODE

14. THANK YOU