What is energy and what is ATP? 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 Electrical Chemical

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. Active Transport Movement Metabolism Energy is needed for: Thermoregulation Cell Maintenance/Repair Molecular Synthesis

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

ATP is therefore, an energy ‘carrier’. 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. ATP ATP ATP ATP ATP ATP ATP ATP ATP glucose ATP ATP ATP ATP ATP ATP ATP ATP Why would you ‘spend’ a whole glucose, when you can spend a single ATP? ATP ATP ATP 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. 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. ADENINE RIBOSE THREE PHOSPHATES

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 + E adenosine triphosphate water (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: 1. In photosynthesis, ATP is produced in a process called PHOTOPHOSPHORYLATION. This is essentially where light is used to add the inorganic phosphate to ADP! 2. In respiration, ATP is produced in a process called OXIDATIVE PHOSPHORYLATION. Within mitochondria electrons are transported, releasing energy to add Pi 3. SUBSTRATE-LEVEL PHOSPHORYLATION This is when a reaction has occurred, releasing enough energy, to combine any nearby Pi and ADP together!

Summary questions

Name at least 5 ‘forms’ in which energy can exist. State the First Law of Thermodynamics. What is the unit energy is measured in? To biologists, where is energy stored within molecules? State the ‘ultimate’ source of energy in organisms, and explain how it is harnessed. Give the 6 main functions that energy is needed for. Explain why glucose is not a good source of immediate energy. Draw and label an ATP molecule. Write two equations to show the break down and reformation of ATP. State the three methods of synthesising ATP.