Energy I: Metabolism, ATP, Glycolysis
Why do we eat? We eat because we need energy to carry out the processes of life
including:
-The synthesis of new molecules
-Establishing ion gradients
-Mechanical work
-Keeping warm
Collectively these processes are termed metabolism
Metabolism can generally be split into reactions that break molecules down and
those that build them up.
Catabolism is the breakdown of complex molecules to release energy or carry out
mechanical work – (intake of carb, fat, protein -> lead to generation of energy
+CO2/heat, can be precursors to new molecules)
Anabolism is the synthesis of new molecules from less complex components
(biosynthesis of amino acids, nucleotides, sugars, fats from precursors, for growth,
repair, movement etc.)
Why study metabolism?
-To understand the metabolic basis of disease, for example diabetes, atherosclerosis
and gall stones (most diseases have a metabolic origin)
-The diseased state changes the way the body uses food for instance cancer
-To understand a disease we may need to know how the body normally deals with
nutrients
- We can use changes in metabolites to aid diagnosis and to follow treatment
Some metabolic pathways require rapid generation (secs) like exercise while others
require longer (minutes, hours), these are generally involving storing molecules (can
take months/days).
Energy Provision – ATP is central to a cell and can act as both an acceptor and
donator of energy (is an intermediate of energy) acting as a short-term reservoir of
energy. ATP contains high energy phosphate bonds
, The total amount of energy available from the hydrolysis is 65kj/mol and at rest we
use about 40kg per 24hrs. During exercise 0.5Kg a minute!
However, our body only actually contains 100g of ATP, so to meet the demands of the
body it must re-synthesise ATP from ADP (i.e. that ATP is being recycled again and
again very quickly).
This is largely done through oxidative phosphorylation and takes place in the
mitochondria.
The major oxidative pathways include (important in generating ATP) ->
Glycolysis
Citric acid cycle (TCA/Krebs cycle)
Electron transport chain/oxidative phosphorylation (where most ATP generation
occurs)
Fatty acid oxidation
Glycolysis
Glycolysis will break down 6C glucose into two 3C molecules of pyruvate.
Firstly glucose gets phosphorylated (consuming energy) to become glucose-6-
phosphate (G-6-P) (remember this maintains conc. gradient across membrane)
Then the G6P undergoes a conformational change to become Fructose-6-phosphate
Fructose-6-phosphate is then phosphorylated to form Fructose 1,6 bisphosphate
(C6)
F6BP gets split into two 3C units, each then undergoes the following process.
Firstly it generates NADH from NAD+ and ATP from ADP in its reactions ultimately
generating phosphoenol pyruvate which is then converted to pyruvate during which
ATP is synthesised again.
And as this occurs with both 3C we get double
So at the end of glycolysis we are left with
1 glucose -> 2 pyruvates
2 NAD+ -> 2 NADH
2 ADP -> 2 ATP (net gain)
2Pi
Why do we eat? We eat because we need energy to carry out the processes of life
including:
-The synthesis of new molecules
-Establishing ion gradients
-Mechanical work
-Keeping warm
Collectively these processes are termed metabolism
Metabolism can generally be split into reactions that break molecules down and
those that build them up.
Catabolism is the breakdown of complex molecules to release energy or carry out
mechanical work – (intake of carb, fat, protein -> lead to generation of energy
+CO2/heat, can be precursors to new molecules)
Anabolism is the synthesis of new molecules from less complex components
(biosynthesis of amino acids, nucleotides, sugars, fats from precursors, for growth,
repair, movement etc.)
Why study metabolism?
-To understand the metabolic basis of disease, for example diabetes, atherosclerosis
and gall stones (most diseases have a metabolic origin)
-The diseased state changes the way the body uses food for instance cancer
-To understand a disease we may need to know how the body normally deals with
nutrients
- We can use changes in metabolites to aid diagnosis and to follow treatment
Some metabolic pathways require rapid generation (secs) like exercise while others
require longer (minutes, hours), these are generally involving storing molecules (can
take months/days).
Energy Provision – ATP is central to a cell and can act as both an acceptor and
donator of energy (is an intermediate of energy) acting as a short-term reservoir of
energy. ATP contains high energy phosphate bonds
, The total amount of energy available from the hydrolysis is 65kj/mol and at rest we
use about 40kg per 24hrs. During exercise 0.5Kg a minute!
However, our body only actually contains 100g of ATP, so to meet the demands of the
body it must re-synthesise ATP from ADP (i.e. that ATP is being recycled again and
again very quickly).
This is largely done through oxidative phosphorylation and takes place in the
mitochondria.
The major oxidative pathways include (important in generating ATP) ->
Glycolysis
Citric acid cycle (TCA/Krebs cycle)
Electron transport chain/oxidative phosphorylation (where most ATP generation
occurs)
Fatty acid oxidation
Glycolysis
Glycolysis will break down 6C glucose into two 3C molecules of pyruvate.
Firstly glucose gets phosphorylated (consuming energy) to become glucose-6-
phosphate (G-6-P) (remember this maintains conc. gradient across membrane)
Then the G6P undergoes a conformational change to become Fructose-6-phosphate
Fructose-6-phosphate is then phosphorylated to form Fructose 1,6 bisphosphate
(C6)
F6BP gets split into two 3C units, each then undergoes the following process.
Firstly it generates NADH from NAD+ and ATP from ADP in its reactions ultimately
generating phosphoenol pyruvate which is then converted to pyruvate during which
ATP is synthesised again.
And as this occurs with both 3C we get double
So at the end of glycolysis we are left with
1 glucose -> 2 pyruvates
2 NAD+ -> 2 NADH
2 ADP -> 2 ATP (net gain)
2Pi
