ATP is a particular molecule (adenine+ribose+3 phosphate group) co ming from an exergonic reaction and used to provide energy 4
endergonic reactions. If it hydrolyses, it then becomes ADP, p.25. this process of hydrolysis releases an important amount of energy
that is exploited pairing ATP hydrolysis to phosphorylation, transfer of pho sphate group from ATP to substrate which acquires
necessary energy to work and then it loses a phosphate group which enable ADP to become again ATP, generating the cycle of
energetic coupling.
The energetic metabolism consists of a process of partial oxidation of glucose that starts form glucose, which derives from glycogen
and its metabolism, mainly linked to the production of energy, linked to several metabolic pathway. The global process of oxidation of
glucose, named cellular respiration, is divided in 3 steps: glycolysis, Krebs cycle and oxyidative phosphorylation→a series of redox.
Glycolysis
it’s a process of partial ox idation of glucose that doesn’t require oxygen and starts from Glucose, we need to use ATP to create new
energy (small gain) needed by our body, all cells are involved in synthesizing the ATP and energy, but especially the nervous one and
the muscular one.
Glycolysis pathway includes 10 reactions, each one catalysed by a specific enzyme and can be divided in 2 phases
• preparatory phase is the process that leads to the synthesis of the molecule. There are 5 steps in which we use atp molecule.
The synthesis of atp its related to the use of atp itself, we synthesize atp when we need energy in doing so we use energy.
energy spent by the cell to activate the reaction and break the glucose in 2 glyceraldehyde triphosphates (GP3).
• Payoff phase: we eventually synthesize atp, 2 GP3 are transformed into 2 pyruvate molecules(C3H4O3)→we use 2 molecules,
we produce 4, gaining 2; the energy produced is used to synthesize 4 atp and reduce 2 nad+ to nadH and H+.
Every single molecule is characterized by the presence of a phosphate group that makes our molecule negatively charged→ they can’t
go out inside the cell and molecule are oriented in such a way that you have a negative charge at the outside and one inside. if a protein
synthesis is not correct, we can’t create the right enzyme, hence can’t catalyse reaction and a reaction can’t be stopped, metabolic
pathway wouldn’t work anymore coz all the cell that has to synthesise atp wouldn’t work→ metabolic disease. Glycolysis occurs inside
cytoplasm, since it’s an ancient reaction that occurred also into it bacterias, which have no organelles, so it can’t occur into
mitochondria.
Glycolysis is made of 10 steps:
1) The first one involves use of ATP, the process is gonna need energy to produce energy→to produce energy you need to use it.
The carbohydrate uses the molecule of ATP to obtain Glucose6-phosphate→it means that phosphate has made a bond with
the CH2O→final result is CH2OPO3.
To make this reaction start, we use hexokinase, an enzyme that catalyses the reaction. In the first step, what starts as ATP,
ends as ADP, due to the release of 1 phosphate group to make the molecule stabler and stabler→the less phosphate group you
have, the more is stable the molecule. Atp has 3 phosphate groups, while adp has only 2. Hexokinase: “hexo”: you are acting
on a sugar w/ 6 carbon atoms, this enzyme transfers phosphate group from a place to another with ≠ kind of hexokinase
based on ≠ locations, in
- our liver, gluco-kinase when we refer to those enzyme actin’ here, it controls glycemia (glucose concentration in our blood
mainly), we can control the level w/ insulin, the smallest protein we synthesize which is an hormone (substance that has a
control function) and we can control the amount of glucose to be released.
- our muscles, where we use it to synthesize atp
2) Second step: you transform glucose-6 phosphate in its isomer: fructose-6 phospate thx to the enzyme of isomerase. we
transform a glucose molecule to a glucose that has a phosphate group that has taken the place of an hydrogen atom.
3) from f ructose 6 phosphate to fructose 1,6-bisphosphate ( and ADP) which is a fructose sugar made up of 6 carbon atoms,
phosphorylated on the 1st and the 6th (aren’t inside the pentagon). The enzyme involved here is phosphofructokinase1 (PFK-
1) belonging to the kinesis enzyme and 2to the kinesis group you have phosphate group moving.
It’s a key enzyme, called the life enzyme and coded by gene PFK-1. It’s controlled by the pyruvate concentration that can
inhibit this enzyme and by citrate, an intermediate of pyruvate reduction. It’s one of the most important allosteric enzymes
that act on fructose 6 phosphate, transferring phosphate group in position 1, it’s able to regulate glycolysis trough allosteric
inhibition, and in this way, the cell can increase or decrease the rate of glycolysis in response to the cell’s energy requirements.
Key enzymes are the ones that has to deal with the slowest part of a cascata reaction, since it’s the enzyme that occupies of
the velocity at which we arrive at the final stage of the reaction, in this case phosphofructokinase works into the 3rd step of
glycolysis.
4) In step 4 we move from fructose 1,6-bisphosphate to glyceraldehyde 3-p hosphate (phosphate group in position
3)+dihydroxyacetone 3-phosphate. glyceraldehyde has a phosphate group in position 3, start counting from the 1st C of the
chain closer to the functional group (aldehydes, functional group COH). The other molecule that aldolase (enzyme that occurs)
synthesized starting from fructose molecule is dihydroxyacetone 3-phosphate→our path is doubleGlyceraldehyde: the former
pentagon is broken into 2 straight molecules, one coming from the glucose and the other coming from the cheton which has
the same number of atoms.
Since the total amount of charges in a functional group has to be 0, oxidation number of carbons in glyceraldehyde has to be
+1.
5) Step 5 is made by the passage from glyceraldehyde 3-phosphate+dihydroxyacetone 3-phosphate to glyceraldehyde 3-
phosphate. The enzyme that occurs here is triosephosphate isomerase. it’s been found in nearly every organism, such as
mammals, insect, fungi, plants and bacteria.
6) This is the step where passing from glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate(2). The aldehyde groups of the
triose sugars are oxidised (acquires electron and frees H+), and inorganic phosphate Pi is added to them. The H is used to
reduce 2 molecules of NAD+ to give NADH+H+ for each triose. Charge balance is maintained coz Pi group actually exist in the
form of a hydrogen phosphate anion (PO3-), which dissociates to contribute the extra H+ ion and gives a net charge of -3 on
both sides.
the enzyme that acts here is glyceraldehyde 3-phosphate dehydrogenase, which make inorganic phosphate detach (liberare)
H+ coz dehydrogenases are enzymes whose role is to carry out an hydrogen from one molecule to another. We use this enzyme
to oxidize substances, it takes hydrogens with their charges.
