1. What is it? Why is it important? How is it made?
ATP
What is it?
Why is it important?
How is it made?
Hodder & Stoughton © 2017

2. What is ATP? Its full name is adenosine triphosphate
Each molecule of ATP contains:
one molecule of the purine base, adenine
one molecule of the pentose, ribose
three phosphate groups triphosphate
adenosine
Philip Allan Publishers © 2017

3. ATP: a phosphorylated nucleotide
adenine
ribose
three phosphate ions
adenosine diphosphate (ADP)
adenosine triphosphate (ATP)
Philip Allan Publishers © 2017

4. A simpler representation of ATP
Philip Allan Publishers © 2017

5. ATP can be hydrolysed
Catalysed by ATP hydrolase (ATPase), the hydrolysis of ATP produces:
adenosine diphosphate (ADP)
a phosphate group (PO43− often represented as Pi)
This hydrolysis can be represented in a number of ways:
Representation 1: ATP + H2O  ADP + PO43−
Representation 2: ATP  ADP + Pi
Philip Allan Publishers © 2017

6. ATP can be hydrolysed
Representation 3:
Philip Allan Publishers © 2017

7. Why is the hydrolysis of ATP so important?
It can be used to phosphorylate other compounds, making them more reactive.
ATP Glucose
ADP Glucose phosphate
It is exergonic, i.e. releases energy that can be used to drive a coupled energy-requiring (endergonic) metabolic reaction.
ATP × amino acids
ADP + Pi dipeptide
This is why ATP is often referred to as the energy currency of cells.
Philip Allan Publishers © 2017

8. How do cells make ATP?
Almost all ATP is made by a condensation reaction catalysed by ATP synthase:
ATP synthase
ADP + Pi ATP H2O
In animals, this occurs during respiration.
In plants, this occurs during respiration and during photosynthesis.
Philip Allan Publishers © 2017

9. This ends the AS content
Ofqual accredited GCE board
AS content regarding ATP
AQA (section 3.1.6)
structure of ATP
hydrolysis of ATP coupled to energy-requiring reactions or to phosphorylation of other compounds
during respiration or photosynthesis, ATP is resynthesised by the condensation of ADP and Pi, catalysed by ATP synthase
Edexcel
Knowledge of ATP is not included in AS specification
Eduqas (sections 5c and 5d)
the central role of ATP as an energy carrier and its use in the liberation of energy for cellular activity
the structure of ATP
OCR (section 2.1.3c)
the structure of ADP and ATP as phosphorylated nucleotides
Philip Allan Publishers © 2017

10. A-level content ATP – all the AS content plus what follows
Philip Allan Publishers © 2017

11. How is ATP made?
All organisms produce ATP from ADP by one of three basic chemical methods:
Substrate-level phosphorylation
Oxidative phosphorylation
Photophosphorylation
Philip Allan Publishers © 2017

12. Substrate-level phosphorylation
ADP SP ATP S
In a chemical reaction, a phosphorylated substrate (S) loses its phosphate group to ADP. In your specification, this occurs in, for example, glycolysis.
Philip Allan Publishers © 2017

13. Substrate-level phosphorylation
During the final reaction of glycolysis, two phosphate groups from each triose phosphate molecule are transferred to two ADP molecules Ignoring the reduction of NAD also involved, we could represent this as: 2 triose phosphate + 4 ADP → 2 pyruvate + 4 ATP
Philip Allan Publishers © 2017

14. Some ATP is made during…
glycolysis
the Krebs cycle
Philip Allan Publishers © 2017

15. Oxidative phosphorylation
Occurs during aerobic respiration.
Electrons from reduced coenzymes (mainly reduced NAD) enter the electron transfer chains in the cristae of mitochondria.
Passage of electrons down the electron transfer chains releases the energy that drives the production of ATP from ADP and inorganic phosphate (ADP + Pi  ATP).
The synthesis of ATP is catalysed by the enzyme ATP synthase, which is embedded in the inner membranes of the cristae.
Philip Allan Publishers © 2017

16. Photophosphorylation
Occurs during the light-dependent reaction of photosynthesis.
Absorption of light by chlorophyll results in electrons leaving chlorophyll molecules and being taken up by molecules of coenzyme, NADP:
NADP e− → reduced NADP
Electrons from reduced NADP enter the electron transfer chain in the thylakoid membranes of chloroplasts.
Passage of electrons down the electron transfer chains releases the energy that drives the production of ATP from ADP and inorganic phosphate (ADP + Pi  ATP).
The synthesis of ATP is catalysed by the enzyme ATP synthase, which is embedded in the membranes of the thylakoids.
Philip Allan Publishers © 2017

17. Oxidative phosphorylation and photophosphorylation compared
Feature
Oxidative phosphorylation
Photophosphorylation
Reaction by which ATP is made
ATP synthase
ADP + Pi ATP
Location of ATP synthase
Embedded in inner membrane of mitochondrial cristae
Embedded in thylakoid membranes of chloroplasts
Coenzyme that provides
electrons
Reduced NAD
Reduced NADP
Notice the similarity between these two processes.
This goes further — both involve chemiosmosis.
Philip Allan Publishers © 2017

18. Chemiosmosis
Energy released as electrons pass down electron transfer chains and enables proteins embedded in membranes of each thylakoid or crista to pump protons (H+) through the membrane:
through inner membrane of crista into space between inner and outer membrane (the intermembrane space)
through thylakoid into space in thylakoid (thylakoid space)
This creates a proton gradient across these membranes.
As a result, protons diffuse down this proton gradient:
from intermembrane space into matrix of mitochondrion
from thylakoid space into stroma of chloroplast
The only place they can diffuse is through ATP synthase — an enzyme embedded in these membranes.
The diffusion of protons through ATP synthase provides it with the energy to produce ATP from ADP and Pi.
Philip Allan Publishers © 2017

19. Chemiosmosis in mitochondria
Philip Allan Publishers © 2017

20. Chemiosmosis in chloroplasts
Philip Allan Publishers © 2017

21. Extension reading for A-level chemistry students
Try the following accounts of respiration and photosynthesis from the Royal Society of Chemistry website:
This resource is part of Biological Sciences Review, a magazine written for A-level students by subject experts. To subscribe to the full magazine go to
Philip Allan Publishers © 2017