GLYCOLYSIS
Glycos = sugar : lysis = splitting of sugar
a) It
is a reductive process that occurs in cytosol of all
living cells (prokaryotes and
eukaryotes).
b)Common in both aerobic and anaerobic respiration.
c)Basically it is an anaerobic pathway.
d) It is an enzymatic, 10 stepped reductive process .
Respiratory substrates are
reduced to form Pyruvic Acid with the production of ATP
and (NADH2 ).
e) Glycolysis yields only 5% of total ATP in respiration
.
f) Anaerobic glycolysis was the first process to occur
during the origin of life.
g) All the reaction of glycolysis are readily reversible
except (step No. 1) for the
one catalysed by hexokinase.
h) Nearly all glycolytic enzymes require Mg ++
as co-factor for their activity.
i) There is no decarboxylation in Glucolysis.
MECHANISM
OF GLYCOLYSIS
1. All
steps of glycolysis occur in the cytoplasm of a cell.
2. The first half of this pathway activates glucose.
3. The second half actually extracts the energy.
Glucose
activation:
a) First
step of glycolysis is phosphorylation of hexose sugar in
which glucose /
fructose is phosphorylated at 1 and 3 by using two ATP to
form Fructose 1, 6
biphosphate.
b) This compound is split in step 4 by aldolase forming
two compounds of 3-C
c) Dihydroxyacelone phosphate (DHAP) are tautomers and
exist in dynamic
equilibrium. DHAP is isomerised into PGAL.
d) This PGAL acts as connecting link between respiration
and photosynthesis.
Energy
Extraction:
a) Each molecule of PGAL is
oxidised into 1, 3-Biphosphoglyceric Acid by utilising
H3PO4 and H2O .
b) In glycolysis oxidation of PGAL occurs by removal of 2
Hydrogen atoms .
c) No free oxygen is used.
d) These two hydrogen atoms dissociate into 2 protons and
2 electrons.
e) Of these 2 H atoms , one complete hydrogen atom and
one extra electron of
another H atom is picked up by NAD+ and get
reduced to form NADH, remaining
(H+) protons free in cytoplasm.
2H -----> 2H+ + 2e-
NAD+ + 2H+ + 2e-
----> NADH + H+
f) This NADH is a high energy substance and
called REDUCING POWER.
g) Dephosphorylation (step 7) to form 3-phosphoglyceric
acid (PGA) in presence of
phosphoglyceric kinase and cofactors Mg++
h) ATP is produced at step 7 by substrate phosphorylation
i.e. direct synthesis of
ATP without ETS.
i) In step No. 8 intramolecular arrangement of phosphate
group takes place.
j) 2 PGA undergoes dehydration in presence of enolase and
cofactor Mg++ .
k) Finally PEP forms pyruvic acid after donating its
phosphate group to ADP to form
ATP.
SIGNIFICANCE OF GLUCOLYSIS
a) It degrades glucose to generate ATP .
b) It provides building blocks for the synthesis of
cellular compounds.
SUMMARY OF GLYCOLYSIS.
1) In this process one molecule of hexose
sugar is split to form two molecules of
a 3c compound , pyruvic acid.
2) 4 ATP molecules are produced and 2 molecules are
consumed and therefore net gain is 2 ATP .
3) 2 mol. of NADH+2H+ (reducing
power) at step No. 6 when PGAL is oxidised
to 1, 3-biphosphoglyceric acid.
4) 4 mol. of H2O are formed.
5) If oxygen is available, these 2 mol. of NADH+2H+
enter the mitochondria and
oxidised through ETS to form 6 ATP . Thus aerobic
glucolysis can produce,
2+6=8
ATP.
So acrobic glycolysis is four times more
effecient than anaerobic glycolysis
|
