C1- The Importance of ATP Flashcards
Why is ATP described as the ‘universal energy currency’?
It is used in all cells to drive their reactions.
When is ATP made?
When energy becomes available e.g. in respiration and the light dependant reactions of photosynthesis.
When is ATP broken down?
When a cell needs energy e.g. in biosynthesis, muscle contraction and powering the membrane Na^+/K^+ pumps.
Hoe is ATP suited to its role?
- is 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
Define Chemiosmosis.
The flow of protons down an electrochemical gradient, through ATP synthetase, coupled with the synthesis of ATP from ADP and a phosphate ion.
Describe the pathway electrons take and how this allows energy to be available for the formation of ATP.
(chemiosmosis)
- electrons from hydrogen atoms are transferred from a donor molecule to a recipient.
- a sequence of relations transfers the electrons from one molecule to the next along a chain
- each transfer is a redox reaction- one molecule loses e^- while the other gains them.
- oxidation reactions make energy available, which is used to synthesise ATP.
Describe the pathway hydrogen atoms take to synthesise ATP.
chemiosmosis
- energy release from oxidation pumps the protons from the hydrogen atoms across a membrane so that they are more concentrate on one side than the other.
- the difference is concentration and charge between the two sides of the membrane create an electrochemical gradient- so is a source of potential energy.
- protons flow back down the gradient in a process called chemiosmosis, through the enzyme ATP synthetase.
- the energy release when they do is converted into ATP.
How do bacteria establish a proton gradient?
- they do not have an internal membrane so use the cell membrane to create a proton gradient.
- They pump protons out into the cell wall
Where is a proton gradient established during respiration?
In the inner membranes of the mitochondria.
Where is the proton gradient established during photosynthesis?
In the thylakoid membranes of the chloroplast.
Why are membranes that are used to create a proton gradient described as ‘sealed membranes’?
- They only let protons through in a highly controlled fashion.
- Protons are very small and easily pass through water molecules so the membranes must also be watertight.
Describe how the ATP is made to allow the light dependant reaction of photosynthesis to occur.
- electrons are exited by energy from light
- the electrons move through a series of carriers in the thylakoid membranes
- their energy pumps protons from the stroma into the spaces between the thylakoid membranes
- the energy is released in chemiosmosis- protons flow back down the electrochemical gradient into the storm through ATP synthetase
- the energy is incorporated into ATP
- ATP drives the light-independent reactions of photosynthesis and energy is incorporated into macromolecules made by the cell
Briefly describe how ATP is made during respiration.
- electrons are excited by the 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 inter-membrane space creating a proton gradient
- energy is released in chemiosmosis, as protons flow back into the matrix through ATP synthetase and is incorporated into ATP
- energy not incorporated into ATP is lost as heat.
What occurs is you disrupt the proton gradient?
death
What is apoptosis?
- programmed cell death
- occurs during embryonic development for example
- operates by preventing proton gradients across cell membranes from forming
What is DNP?
- a mitochondrial poison that allows electron transport, but does not allow ATP synthesis- i.e. they are uncoupled
- when taken it causes the body to oxidise fats and carbohydrates- this leads to weight loss.
- all the energy released from from those molecules is converted into heat so no ATP is made- it can cause the body to overheat which can be fatal
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.
Where are hydrogen atoms derived from in respiration?
The breakdown of glucose.
What enzymes transfer hydrogen atoms derived from the breakdown of glucose to the coenzymes.
dehydrogenases
What coenzymes are hydrogen atoms transferred to?
NAD and FAD
How many protons does NAD deliver and how many molecules of ATP can be synthesised from this?
- two protons
- three molecules of ATP
How many protons does FAD deliver and how many molecules of ATP are synthesised from this?
- two protons
- two molecules of ATP
What is phosphorylation?
The addition of a phosphate group.
What is oxidative phosphorylation and why is it called this?
- the energy for the proton pump and electron transport chain is derived from oxidation reactions
- 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
In photosynthesis what transports the excited electrons to electron acceptors
Groups of pigments and proteins called photosystems transfer excited electrons to electron acceptors.
In photosynthesis after the excited electrons are transferred to the electron acceptors where are they then transferred to?
To a series of protein carriers, all on the thylakoid membranes.
What is photophosphorylation?
This is a method of synthesising ATP, that uses energy from light to power the proton pump and electron transport chain in the chloroplasts of a plant.
Describe how protons and electrons are transferred to the pathway that synthesises carbohydrates in photosynthesis.
- Groups of pigments and proteins called photosystems transfer excited electrons to electron acceptors.
- From there they’re transferred to a series of protein carriers, all on the thylakoid membranes.
- Protons from water and the electrons are transferred to the coenzyme NADP and subsequently to glycerate phosphate, in the pathway that synthesises carbohydrates.
Explain how the ATP synthetase complex forms ATP.
- the protons diffuse down the electrochemical gradient through ATP synthetase releasing energy
- the energy released causes the rotor and stalk to rotate
- the mechanical energy from the ration is converted into chemical energy as a phosphate ion is added to ADP to form ATP in the catalytic head.
- it takes three protons to move the rotor 120degrees, releasing 1 ATP molecule
How many protons does it take to produce 1 molecule of ATP.
three
Describe the similarities between the electron transport systems and ATP synthesis in mitochondria and chloroplasts.
- uses ATP synthetase
- 2 protons provide energy to synthesise 3 ATP
- protons pump across the inner membrane of organelle
- electron transport chain on inner membrane of organelle
Describe the differences between the electron transport systems and ATP synthesis in mitochondria and chloroplasts.
- mitochondria use oxidative phosphorylation and chloroplasts use photophosphorylation
- mitochondria gain their chemical energy from redox reactions, whereas chloroplasts gain theirs from light.
- the electron transport chain is in the cristae of the mitochondria and thylakoid membranes of the chloroplasts.
- the coenzymes used in the mitochondria are NAD and FAD, but in chloroplasts NADP is used
- the proton gradient in mitochondria is between the inter-membrane space and matrix, but in chloroplasts it is created between thylakoid space and stroma.
- The mitochondria have 3 proton pumps with NAD and 2 with FAD, but chloroplasts only have one.
- The final electron acceptor is different for mitochondria and chloroplasts.
What are the final electron acceptors in mitochondria and chloroplasts?
- In mitochondria the final electron acceptor is oxygen and H^+.
- In chloroplasts it is:
cyclic photophosphorylation- chlorophyll^+
non-cyclic photophosphorylation- NADP + H^+
