Transcript Other High Energy Compounds

Other High Energy Compounds
Examples of other high energy compounds
Enol Phosphates:
e.g: Phosphoenol pyruvate (PEP) is high energy
phosphate, but for a completely different reason
than ATP.
- PEP is formed in the glycolytic pathway and is
used to synthesize ATP from ADP.
- The reaction with ADP to form ATP is
essentially irreversible.
Reasons:
Enol form of pyruvic acid is less stable than the keto form
by about 10-12 kcal/mole. In addition an enol phosphate is
less stable than any ordinary phosphate ester by about
3kcal/mole.
The phosphate can only exist as the high energy enol form.
Thus when phosphate group is removed, the pyruvate can
go back to the stable low energy ket form and the surplus
energy is released.
Thiol esters
e. g: Thioesters of coenzyme A as
acetyl~Co A:
- In this compound, there is a diminshed
resonance interaction between electrons
of the sulfur and the carbonyl group
relative to the resonance in an oxygen
ester.
-The sulfur will not form a double bond as
readily as oxygen.
Phosphocreatine
ATP- PC system
PC stored at the muscle
It is one step reaction resulting in getting energy.
The reaction catalyzed by creatine kinase enzyme.
PC restoration only occurs during rest when ATP
stores are high.
Ingestion of creatine has been proven to help in
performance in high intensity short term exercise.
Creatine slows the fatigue process because during the
rest stage there is larger amount of ATP replinshed
compared to a person who is not taking creatine.
Biosynthesis work
as energy requiring process
Biosynthesis is a programmed process
that leads from very simple molecule to
the living cell itself.
The flow sheet of biosynthesis
For the biosynthesis of cell components, two
kinds of ingrediants are required.
1- precursors e.g C,H,N
2- ATP
Degradative and synthetic pthways between two
points given (e.g glucose and pyruvate are not
identical (i.e they are not the simple reverse of
each other).
Degradation of one mole of glucose to pyruvate is
accompanied by formation of 2 ATP whereas
biosynthesis of glucose from pyruvate requires an
input of total 6- high energy phosphate bond (4 ATP
+ 2GTP).
i.e Both pathways vary in their energetics
Both are independently regulated in the cell , while
PFK is activated by AMP and inhibited by ATP,
fructose 1,6 diphosphatase has AMP or ADP as
negative modiulators.
Terminal phosphate group of ATP is transferred
to the building block molecule to be energized.
This is known as orthophosphate cleavage.
But sometimes a pyrophosphate group is used
to activate the building blocks (Pyrophosphate
cleavage, more energy 2x7.3+ 14.6 Kcal/mole.
Channeling of high energy
phosphate of ATP through other
nucleotides
Adenylate Energy Charge
Some enzymes respond to absolute
concentration, but most respond to ratios. Dan
Atkinson introduced the concept of ENERGY
CHARGE in 1968 to summarize the energy
status of a cell. It is a measure of the relative
concentration of high-energy phosphoanhydride bonds available in the adenylate
pool .
Defenition Of AEC
AEC is defined as the effective mole
fraction of ATP in the total adenylate
pool (ATP, ADP, AMP).
The energy charge, or E.C., has the range 0 to 1.0.
If all the adenylate is in the form of ATP, E.C. = 1.0,
and the potential for phosphoryl transfer is maximal.
At the other extreme, if AMP is the only adenylate
form present, E.C. = 0.
Then the relative amounts of the three adenine
nucleotides are fixed by the energy charge. The
following figure shows the relative changes in the
concentrations of the adenylates as energy charge
varies from 0 to 1.0.
Regulatory enzymes in energy-producing
catabolic pathways show greater activity at
low energy charge, but the activity falls off
sharbly as E.C. approaches 1.0.
In contrast, regulatory enzymes of anabolic
sequences are not very active at low energy
charge, but their activities increase as E.C.
nears 1.0 .
These contrasting responses are termed R, for
ATP-regenerating, and U, for ATP-utilizing.
Regulatory enzymes such as PFK and
pyrvuate kinase in glycolysis follow the R
response curve as E.C. is varied.
Note that PFK itself is an ATP-utilizing
enzyme, using ATP to phosphorylate fructose6-phosphate
to
yield
fructose-1,6bisphosphate. Nevertheless, because PFK acts
physiologically as the valve controlling the
flux of carbohydrate down the catabolic
pathways of cellular respiration that lead to
ATP regeneration, it responds as an “R”
enzyme to energy charge.
Regulatory enzymes
in anabolic
pathways,
such
as
acetyl-CoA
carboxylase, which initiates fatty acid
biosynthesis, respond as “U” enzymes.