The glyoxylate cycle allows plants to convert fatty acids from stored seeds into carbohydrates during germination. Glyoxysomes are specialized peroxisomes found in plant cells that contain the enzymes of the glyoxylate cycle, including isocitrate lyase and malate synthase. These enzymes bypass the two decarboxylation steps of the Krebs cycle to ensure acetyl-CoA from fatty acid breakdown is not lost as CO2, but instead can be converted to succinate and further utilized for gluconeogenesis to synthesize carbohydrates from fatty acids when glucose is unavailable. The glyoxylate cycle plays an important role in seedling formation and development until photosynthesis can begin.

2. Role Of Glyoxysome In
Glyoxylate Cyclic
Presented By
Hina Tabassum (7519)
Maryam Riasat (7545)
BS Zoology (5th Semester – Morning)

3. Glyoxysome

4. Introduction:-
 Micro-Bodies
 Specialized form of peroxisome
 Present in plant cells (Germinating seeds)
 Not found in animal cells except some
lower animals (Nematodes )

5.  Contain the enzymes of the Glyoxylate
Cycle
Enzymes
Citrate synthase, isocitrate lyase, malate
synthase etc
They contain all the enzymes necessary
for fatty acid oxidation in Glyoxylate
Cycle and Gluconeogenesis.

7. Discovery:-
 R.W Breidenbach and H. Beevers In
1961
 Microbodies of the fat-storing cells of
germinating seeds contain enzymes
 Enzyme were found in the organelle
other than mitochondria
(Glyoxysomes)

8. Role Of Glyoxysomes In
Glyoxylate Cycle
Main Aim:-
 Convert acetyl CoA into succinate for the
synthesis of carbohydrates.
 Fatty acid → Carbohydrates
 In Microorganisms in the absence of
glucose this cycle allows cells to utilize carbon
compounds as a carbon source.

9. Absent in lipid-poor seed such as the
pea

10. Role In Glyoxylate Cyclic
Present in plants e.g (Oil rich seeds)
Soya beans, Castor beans, Sunflower beans

11.  Present at the time of Germination (Plant
seedling)
 Removed in living plants when they become
able to produce their own food from
photosynthesis
 Energy comes from the stored fatty acids
Fatty acid → Carbohydrates
 Glyoxysomes undergo catabolism &
anabolism of lipids

12.  Catabolism carried by the enzymes present
in glyoxysomes (Glyoxylate Cycle)
Contain material to begin formation of new
plants
Form epicotyl & hypocotyl

13. Temporary structures
• When body sustain itself (roots & shoots are
developed) they are removed
• Seeds → Germination → Plant body

14. Enzymes involve in Glyoxylate Cycle
The glyoxylate cycle utilizes five enzymes that
are following:-
 Citrate synthase
 Aconitase
 Isocitrate lyase
 Malate synthase
 Malate dehydrogenase

15. Glyoxylate Cycle

16. Steps Involved In Glyoxylate Cycle:-
Various steps of this cycle are as follows:-
 Acetyl-CoA produced after the β-oxidation of
fatty acids condenses with oxaloacetic acid to
form Citric Acid.

17.  Citric acid is dehydrated to produce Cis-
aconitic Acid in the presence of Aconitase.

18.  Cis-aconitic acid reacts with one molecule of
H2O to form Iso-citric acid.

19.  Iso-citric acid is broken down into glyoxylic
acid and succinic acid by the enzyme
Isocitratase.

20.  Glyoxylic acid combines with acetyl CoA
(produced after the β-oxidation of fatty acids)
in the presence of Malate synthetase to
produce Malic acid.

21.  Malic acid is oxidised into oxaloacetic acid in
the presence of Malic dehydrogenase and the
coenzyme NAD.
 Oxaloacetic acid thus produced combines
with acetyl-CoA to regenerate citric acid.

23. Role Of Glyoxylate Cycle In
Pathogenic Fungi
Main enzymes Isocitrate Lyase and malate
synthase are increased upon contact with the
human host. Mutant of particular fungi that
lacked Isocitrate Lyase are less virulant.
Glyoxylate Cycle is a significant factor for the
pathogenesis of these microbes.

24. Role Of Glyoxylate Cycle In Gluco-
neo-genesis
Fatty acid from lipids are used as an energy
source.
 Fatty acid is converted into acetate molecule
by beta oxidation.
Acetate +active thiol group (coenzyme A) >
TCA cycle > CO2
This pathway allows cells to obtain energy
from fats.