Making ATP Flashcards
What is ATP and how does it provide energy?
ATP consists of adenine, connected to a ribose sugar, which is in turn connected to a triphosphate (3 Phosphates interspersed with oxygen, double bond to oxygen on top, single bond to oxygen anions underneath).
The compound has (and thus releases) so much energy because the anions repel each other, but are held together by the phosphates.
What is substrate-level phosphorylation, and what is its key disadvantage?
Substrate-level phosphorylation is the formation of ATP using a chemical substrate to donate phosphate (as distinct from using the energy of electrons in oxidative phosphorylation). It requires more than 30kJ/mol of ATP to produce ATP in this way.
While it can be used short-term, its key disadvantage is that each substrate needs to be metabolised itself, requiring continuously higher levels of energy. This cannot continue indefinitely.
How is oxidative phosphorylation started? How is the energy captured?
All fuels can be funneled to acetyl-CoA, which enters the TCA cycle. This releases NADH and FADH2, which each have an energetic electron. They can enter the electron transport chain, releasing energy as they travel between one molecule and another with an even greater affinity for them.
Describe the electron transport chain
The electron transport chain is the process used to create ATP from energetic electrons. It involves the movement of electrons between molecules, with the final reaction being the reduction of oxygen to water. It takes place in a series of four MULTIPROTEIN COMPLEXES that span the mitochondrial membrane.
By moving to molecules with greater electrical affinity in complexes I, III, and IV, the electrons release energy. This energy is used to pump H+ across the membrane, creating an electrochemical gradient. (Complex II is a direct link to TCA cycle, converting succinate to fumarate, liberating electrons to enter III). Mobile carriers (ubiquinol and Cytosome C) shuttle electrons between the complexes (Uq 1,2->3, Cyt. C 3-4).
After the final reduction of O2 to H2O, there is a strong electrochemical gradient of H+ outside the membrane, wanting to come in. The energy to create ATP is harnessed as these H+ re-enter matrix through the combined channel/enzyme ATP SYNTHASE.
Describe ATP Synthase
ATP synthase is a combined channel and enzyme that regulates the passage of H+ back into the mitochondrial matrix. As H+ pass through the base (in the membrane), they turn a rotor connected to an ATP synthesis unit (in the matrix). This unit has 3 sites for ATP binding, each of which allows an ATP to be freely converted (Keq=1) from ADP+Pi. The newly-formed ATP are physically removed from the rotor by the central (gamma) subunit.
What is Adenine Nucleotide Translocase (ANT) and why is it necessary?
Adenine Nucleotide Translocase (ANT) is an antiporter that shifts ATP out of the mitochondrial matrix while bringing in ADP. The entry of ADP regulates the rate of ATP synthesis, and the relative charges reduce the H+ electrochemical gradient.
ANT is necessary because ATP is generated in the mitochondria, but used (generating ADP) in the cytoplasm. Both of these molecules need to get from where they are ‘made’ to where they are useful.
What process of ATP production would be used and when?
In light activity/long term - the body converts fuels (FAs, Ketones, Glucose) to Acetyl-CoA (releasing CO2), where they can enter the TCA cycle and ETC, creating ATP.
In heavy activity, the body breaks down glycogen stores in the muscle and the liver, releasing lactate. Glucose from the glycogen is broken down into pyruvate and then acetyl-CoA, where it can enter the TCA cycle and ETC.
Under intense activity, the body uses substrate-level phosphorylation, such as by converting phospho-creatine to creatine and ATP. However, this is not sustainable.
Bottom line - short, intense activity = substrate-level phosphorylation. Anything lighter or long-term = oxidative phosphorylation.
