The importance of ATP Flashcards
What is ATP sometimes referred to as?
The universal energy currency. This means that it is used in all cells to drive their reactions. ATP is one of the molecules that is characteristic of all living systems and was present in LUCA (Last common ancestor of all living cells)
When is ATP made?
When is ATP broken down?
-It is made when energy becomes available, for example in respiration and in the light-dependent reactions of photosynthesis
- It is broken down when the cell needs energy, such as biosynthesis, muscle contraction and powering the membrane Na+/K+ pumps
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ATP is ideally suited to its role because it:
- Inert
- Can pass out of mitochondria into the cytoplasm
- releases energy efficiently
- Releases energy in useable quantities, so little is wasted as heat
- Is easily hydrolysed to release energy
- Is readily reformed by phosphorylation
In the synthesis of ATP, electrons and protons derived from hydrogen atoms different pathways
- Electrons from hydrogen atoms are transferred from a donor molecule to a recipient. Then, a sequence of reactions transfers the electrons from one molecule to the next along a chain. Each transfer is a redox reaction, in which one molecule is oxidised, i.e. loses electrons, and the next in the sequence is reduced, i.e gains electrons. Oxidation reactions make energy available, and this energy is eventually used to synthesise ATP
- The energy released by oxidation pumps the protons from the hydrogen atoms across a membrane so that they are more concentrated on one side of the membrane than the other. The difference in concentration of protons and the charge on either side of the membrane constitutes an electrochemical gradient and is a source of potential energy. Protons flow back down this gradient, in a process called chemiosmosis, through the enzyme ATP sythetase, sometimes called ATP synthase. The energy they release as they do so is converted into chemical energy in ATP
How does ATP synthetise make ATP?
From the energy associated with protons gradients across membranes
How do bacteria establish a proton gradient?
As they do not have internal membranes they use the cell membrane to establish a proton gradient by pumping protons out into the cell wall
What does respiration use to establish a proton gradient?
What does photosynthesis use to establish a proton gradient?
Respiration uses the inner membranes of the mitochondria
Photosynthesis uses the thylakoid membranes of the chloroplasts
Why are the inner membranes of mitochondria described as ‘sealed membranes’?
These membranes must only let protons though, and in highly controlled fashion. Protons are very small and easily pass through water molecules, so the membranes must also be watertight
Explain proton gradients
Proton gradient occur in non-living systems, such as oceanic alkaline hydrothermal vents. It may be that naturally occurring proton gradients such as these had a significant role in the origin of life, because proton gradients are a fundamental characteristic of all living things
What happens during the light-dependent stage of photosynthesis, with reference to chemiosmosis and ATP?
Electrons are excited by energy derived from food molecules. Their energy is made available as they move through a series of carriers on the inner mitochondrial membrane. The energy pumps protons across the membrane, from the matrix into the into the inter-membrane space, setting up a proton gradient. Energy is released in chemiosmosis, as the proton flow back into the matrix through ATP synthetase, and is incorporated into ATP. Energy that is not incorporated into ATP is lost as heat
Disrupting proton gradients cause death: Apoptosis
Apoptosis is programmed cell death and occurs, for example, during embryonic development. It operates by preventing proton gradients across cell membranes from forming
Disrupting proton gradients cause death: DNP
DNP is a mitochondrial poison that allows electron transport but does not allow ATP synthesis, i.e. they are uncoupled. Some people have used DNP to try to lose weigh. The body oxidises fats and carbohydrates , so weight is lost, but all the energy released from those molecules is converted to heat, as no ATP can be made. The body overheats, sometimes fatally
What is the electron transport chain?
A series of protein carriers on the inner membranes of mitochondria and chloroplasts. It releases energy from electrons and incorporates it into ATP
The electron transport chain: in respiration
- Hydrogen atoms derived from the respiratory breakdown of glucose are transferred by dehydrogenase enzymes to the coenzymes NAD and FAD and carried to the inner membrane of the mitochondrion
- The electrons and protons of the hydrogen atoms have different pathways but because they both move through the electron transport chain, the system is often described as carrying hydrogen atoms
- For every two protons delivered by reduced NAD, enough energy is released to synthesise three molecules ATP
- When reduced FAD delivers two protons, enough energy is released for only two molecules of ATP
Where is the energy for the proton pump and the electron transport chain derived from?
What is phosphorylation?
What is oxidative phosphorylation?
- Oxidation reactions i.e. electron loss
- Phosphorylation is the addition of a phosphate group.
- So synthesising ATP by adding a phosphate ion to ADP using energy derived from oxidation reactions is called oxidative phosphorylation
