Why is ATP the universal energy currency of cells, and how is it made and used?
The importance of ATP: its structure; its hydrolysis to ADP and inorganic phosphate; why it is a suitable immediate energy currency; and how it is resynthesised by phosphorylation.
A focused answer to the Eduqas Component 1 statement on ATP. Covers ATP structure, its hydrolysis to ADP and inorganic phosphate, why it is the ideal immediate energy currency, and how it is resynthesised by substrate-level and oxidative phosphorylation.
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What this dot point is asking
Eduqas wants you to describe the structure of ATP, explain its hydrolysis to ADP and inorganic phosphate, justify why it is the ideal immediate energy currency, and explain how it is resynthesised by phosphorylation. ATP links directly to respiration and photosynthesis, so it opens Component 1.
The structure of ATP
ATP is a small, soluble, water-based molecule, so it can move easily around the cell to wherever energy is needed.
Hydrolysis of ATP
ATP releases energy when its terminal phosphate bond is broken by hydrolysis:
The enzyme ATP hydrolase (ATPase) catalyses this reaction, producing ADP (adenosine diphosphate) and an inorganic phosphate ion (). The released energy powers cellular work, and the released phosphate can be transferred to another molecule (phosphorylation) to make it more reactive, for example phosphorylating glucose at the start of respiration.
Why ATP is a suitable energy currency
ATP is used for active transport, muscle contraction, anabolic reactions (building large molecules), the conduction of nerve impulses (running the sodium-potassium pump) and secretion.
Resynthesis by phosphorylation
ATP is rebuilt from ADP and inorganic phosphate by adding a phosphate group (phosphorylation), a reaction that requires energy:
This happens by substrate-level phosphorylation (a phosphate transferred directly from a substrate, as in glycolysis and the Krebs cycle), oxidative phosphorylation (using energy from electrons passing along the electron transport chain in respiration), and photophosphorylation (using light energy in photosynthesis). In all cases, a flow of protons through ATP synthase (chemiosmosis) drives the synthesis in oxidative phosphorylation and photophosphorylation.
Examples in context
Example 1. Why cells with high energy demand have many mitochondria. Cells doing a lot of active transport, such as kidney tubule cells, are packed with mitochondria to resynthesise ATP fast enough, a direct structure-to-demand link examiners reward.
Example 2. ATP in the nerve impulse. Restoring the resting potential after each impulse needs the sodium-potassium pump, an active transport process powered by ATP, which is why nerve and muscle tissue respire rapidly.
Try this
Q1. Name the products formed when ATP is hydrolysed. [2 marks]
- Cue. ADP (adenosine diphosphate) and inorganic phosphate ().
Q2. Give two reasons why ATP is a suitable immediate energy currency. [2 marks]
- Cue. Any two: small manageable energy release; rapid single-step hydrolysis; soluble and mobile; easily resynthesised; universal.
Q3. Name the process that resynthesises ATP using light energy in photosynthesis. [1 mark]
- Cue. Photophosphorylation.
Exam-style practice questions
Practice questions written in the style of WJEC Eduqas exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Eduqas 20194 marksExplain why ATP is described as a suitable immediate energy currency for cells.Show worked answer →
ATP releases a relatively small, useful amount of energy when hydrolysed, so energy is not wasted as heat.
It is hydrolysed in a single, rapid reaction to ADP and inorganic phosphate, so energy is released quickly when needed.
It is soluble and moves easily within the cell, and it can be rapidly resynthesised from ADP and inorganic phosphate.
It is a universal currency, used in the same way in all reactions and organisms.
Markers reward the small manageable energy release, the rapid single-step hydrolysis, easy resynthesis, and being a common universal currency.
Eduqas 20213 marksDescribe the hydrolysis of ATP, naming the products and the enzyme involved, and state one use of the energy released.Show worked answer →
ATP is hydrolysed by the enzyme ATP hydrolase (ATPase), which breaks the bond to the terminal phosphate group.
The products are ADP (adenosine diphosphate) and an inorganic phosphate ion (), and energy is released.
The energy can be used for active transport, muscle contraction, or synthesising large molecules (anabolic reactions); the released phosphate can also phosphorylate another molecule to make it more reactive.
Markers reward ATP hydrolase, the products ADP and inorganic phosphate, and a valid named use of the energy.
Related dot points
- Respiration: glycolysis, the link reaction, the Krebs cycle and oxidative phosphorylation; the role of NAD and FAD; anaerobic respiration; and respiratory substrates.
A focused answer to the Eduqas Component 1 statement on respiration. Covers glycolysis, the link reaction, the Krebs cycle, oxidative phosphorylation and chemiosmosis, the role of NAD and FAD, anaerobic respiration, and respiratory substrates.
- Photosynthesis: chloroplast structure; the light-dependent stage (photolysis of water, photophosphorylation and the reduction of NADP); the light-independent stage (the Calvin cycle); and the effect of limiting factors.
A focused answer to the Eduqas Component 1 statement on photosynthesis. Covers chloroplast structure, the light-dependent stage (photolysis, photophosphorylation and reduced NADP), the light-independent stage (the Calvin cycle with RuBP, GP and TP), and limiting factors.
- Enzymes: their role as biological catalysts; the lock-and-key and induced-fit models; the formation of enzyme-substrate complexes; the effects of temperature, pH, substrate concentration and enzyme concentration; and competitive and non-competitive inhibition.
A focused answer to the Eduqas Biology Core Concepts statement on enzymes. Covers enzymes as catalysts, the lock-and-key and induced-fit models, the four rate factors, denaturation, and competitive and non-competitive inhibition.
- The nervous system: the structure of neurones; the resting and action potentials; the propagation of the nerve impulse; saltatory conduction; synaptic transmission; and the reflex arc.
A focused answer to the Eduqas Component 3 statement on the nervous system. Covers neurone structure, the resting and action potentials, propagation of the impulse, saltatory conduction, synaptic transmission, and the reflex arc.
- Homeostasis and the kidney: the principle of negative feedback; the structure of the nephron; ultrafiltration and selective reabsorption; the role of the loop of Henle; and osmoregulation by ADH.
A focused answer to the Eduqas Component 3 statement on the kidney. Covers negative feedback, the structure of the nephron, ultrafiltration and selective reabsorption, the loop of Henle, and osmoregulation by ADH.
Sources & how we know this
- Eduqas A Level Biology Specification (A400) — Eduqas (2015)