2.1 – Energy and ATP

What is energy and what is ATP?

Learning Objectives

• To learn what energy is and why organisms need it.

• To understand how the molecule ATP stores energy.

• To learn how ATP is synthesised.

• To understand the role of ATP in biological processes.

ENERGY

What is energy?• Energy is something that allows ‘work to be done’ on

something else – i.e. move an object or heat it up.• Energy can exist in different forms:

• Energy can be changed from one form to another:

• This leads us on to the point that energy cannot be created or destroyed.

• Energy is measured in joules (j).• With respect to biology, most of the energy used by

organisms, is stored in chemical bonds in molecules.

Light Heat Sound Electrical Magnetic Chemical

ChemicalElectrical

How is energy related to living organisms?• In order to remain alive, energy is required to ‘power’ the

biological processes occurring within all life forms.• This energy initially comes from the Sun.

• Plants harness this solar energy, using it to combine water and CO2 into glucose – in a process called photosynthesis.

Light Chemical

• Therefore, photosynthesis is responsible for locking solar energy into molecules such as glucose.

• Both plants and animals can then break down these molecules, releasing energy, which can be used in processes essential to life.

What do organisms do with energy?• Organisms are highly ordered, so without the constant input of

energy, these organisms will eventually breakdown into disarray.

Energy is needed for:

Movement

Molecular Synthesis

Thermoregulation

Cell Maintenance/Repair

Active Transport

Metabolism

ATP

So what’s ATP??• Now that we know plants are responsible for trapping solar

energy into molecules such as glucose, we need to know how animals (and plants themselves) benefit from this energy.

• For example:Building a chain of amino acids (into a protein) requires energy. The

bonds between each amino acid do not form spontaneously, but require energy input.

• Do you think this energy comes directly from the breakdown of glucose?

Amino Acid 1 Amino Acid 2

Bond

NO! It doesn’t.• Although glucose stores a lot of energy, it takes time to release, via a

complicated series of reactions.• This means that it is not a good source of immediate energy.

• What actually happens, is that during cellular respiration, molecules such as glucose, are broken down, which releases free energy.

• This free energy, is used to form chemical bonds in a molecule called ATP.

• Aerobic cell respiration produces about 30 ATP molecules per glucose.

• If a reaction only requires one ATP molecule, why use a whole glucose molecule to power it?

ATP is therefore, an energy ‘carrier’.

ENTER: ATP!!

Understanding why ATP is important• As explained on the previous slide, reactions need energy to occur,

and the amount of energy required by a reaction is quite specific.• It’s usually way less than the amount of energy stored in a glucose

molecule – so if you used glucose directly, you’d be wasting the excess energy released.

• This is why we ‘convert’ the energy in one glucose molecule, to energy stored in many ATP molecules.

glucoseATP

ATP

ATP

ATP

ATP

ATP

ATP

ATP

ATP

ATPATP

ATP ATP

ATPATP

ATP

ATP

ATP

ATPATP

ATP

Why would you ‘spend’ a whole glucose, when you can spend a single

ATP?

Think of glucose as your life-savings If you wanted to go out and

buy a phone, you wouldn’t take your life-savings with

you

Instead you’d go to a cash machine and

withdraw the correct amount of

money

Think of the money as ATP, of which the

correct amount can be used to buy your phone

STRUCTURE AND SYNTHESIS OF ATP

Structure of ATP• The full name of this molecule is Adenosine Triphosphate, which as

suggested by the name, has three phosphate groups.

THREE PHOSPHATESRIBOSE

ADENINE

This bond, is the one that can be broken to release energy for reactions

to occur.The bond is formed in cellular

respiration, using energy released during the breakdown of glucose.

Releasing energy from ATP• So when a reaction requires energy, ATP is broken down:

• This hydrolysis reaction releases energy to drive other reactions.• When the terminal phosphate is removed from ATP, the leftover

molecule only has TWO phosphates left, so is now called adenosine diphosphate.

• The phosphate that is removed, is called an inorganic phosphate.

• Yep, you guessed it. ATP can be reformed by adding Pi to ADP!

• Notice how this is a condensation reaction, that requires energy!

ATP + (H2O) ADP + Pi + Eadenosine

triphosphatewater (for hydrolysis)

adenosine diphosphate

inorganic phosphate

energy

ADP + Pi + E ATP + H2O

The conversion of ATP into ADP is a reversible reaction.

When this happens, energy is released,

which can be used to do all kinds of useful

biological processes

When this happens, energy is being used to

reform ATP, which is then ready to drive yet another reaction.

Remember, that in the case of respiration, that energy comes from the complex breakdown of glucose

How and Where is ATP synthesised?• Remember that forming ATP involves adding an inorganic phosphate

(Pi) to an ADP molecule.• This can happen in three ways:

In photosynthesis, ATP is produced in a process called PHOTOPHOSPHORYLATION.

This is essentially where light is used to add the inorganic phosphate to

ADP!

In respiration, ATP is produced in a process called

OXIDATIVE PHOSPHORYLATION.

Within mitochondria electrons are transported, releasing energy to add Pi

1. 2.

3. SUBSTRATE-LEVEL PHOSPHORYLATIONThis is when a reaction has occurred, releasing

enough energy, to combine any nearby Pi and ADP together!

SUMMARY QUESTIONS

1. Name at least 5 ‘forms’ in which energy can exist.2. State the First Law of Thermodynamics.3. What is the unit energy is measured in?4. To biologists, where is energy stored within molecules?5. State the ‘ultimate’ source of energy in organisms, and

explain how it is harnessed.6. Give the 6 main functions that energy is needed for.7. Explain why glucose is not a good source of immediate

energy.8. Draw and label an ATP molecule.9. Write two equations to show the break down and

reformation of ATP.10. State the three methods of synthesising ATP.