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AP exam free response on cell signalling
Forms of energy
Energy is the capacity to do work
Work is transferring energy to an object causing it to move
-Potential Energy- Stored energy because of location or structure
-Activation energy is the energy needed to release the stored potential energy
-Kinetic Energy- Movement
-Thermal Energy- Transfer of kinetic energy of the random movement of atoms to other atoms
-Chemical Energy- The energy stored in the bonds of macromolecules
1st law of thermodynamics
-Energy cannot be created nor destroyed
-Energy does not disappear it gets converted into non-usable energy
2nd law of thermodynamics
-The transfer of energy increases entropy
-Living things increase the entropy of their surroundings
Chemical reactions
-ATP is an energy carrier molecule
-There are other types of energy carrier molecules like electron carriers
-Chemical energy is stored in the bonds of molecules
-Reactants- What goes in
-Products- What comes out
-Exergonic Reaction- When the products have less energy than the reactants
-Endergonic Reaction- When the products have more energy than the reactants
-Endergonic is making something and exergonic is using something
-When you burn sugar to get energy that is an exergonic process
-When a plant makes sugar that is an endergonic process
-A coupled reaction is when an exergonic reaction provides the energy for an endergonic reaction. This is how most of the metabolic pathways work
Gibbs Free Energy
Gibbs free energy is a method of measuring how much energy was released or stored. If your Delta G is negative then energy was released. If your delta G is positive then energy was stored.
-Exergonic- when energy is released (your delta G is negative)
-Endergonic- When energy is stored (Your delta G is positive)
-A coupled reaction is one that takes the energy released in an exergonic reaction and uses it to store energy in an endergonic reaction. The majority of matabolic pathways use coupled reactions
-Since an exergonic reaction is considered to be spontaneous the body couples an endergonic reaction with an exergonic reaction where the overall free energy has a delta G that is negative. This means it will happen spontaneously.
-What does this coupled reaction using ATP look like?
-For example your body turns Glutamic Acid into the amino acid glutamine. Glutamine is made by adding ammonia (NH3) to glutamic acid. This is an endergonic process that has a delta G of +3.4 kcal/mol which means it will not happen spontaneously.
What ends up happening though is an ATP phosphorylates the glutanic acid (It added a P to it.) The Phosphorylated glutamic acid is known as a phosphorylated intermediate. The phosphorylated glutamic acid is very unstable causing the ammonia to displace the phosphate group creating the glutamine.
-Dehydration synthesis of Glutamic acid and ammonia is delta G +3.4 kcal/mol and the hydrolysis of ATP is delta G -7.3 kcal/mol. Together they have a coupled reaction of delta G -3.9 kcal/mol. This turned an endergonic reaction into an exergonic one, which means it will now happen spontaneously.
-An equilibrium is when your delta G is zero. If a cell reaches equilibrium then it is dead. A cell is constantly doing work. It never stops. This constant work is one of the defining points for living cells.
-Think of free energy as though it is a measure of how much usable energy is left in the universe. If your delta G is negative than that amount is how much less free energy there is in the universe.
C6H12O6 + 6 O2 ------ 6 CO2 + 6 H2O The exergonic reaction of burning glucose has a delta G of -686Kcal/mol
Do you remember how to find out the molar mass of a molecule? How many grams of glucose do you need to acquire 686kcal?
ATP + H2O --------- ADP + P = delta -7.3kcal/mol In your cells however they can get delta G -13kcal/mol
-Three types of work
-Chemical work
-Transport work
-Mechanical work
-ATP is constantly being used and regenerated.
-A muscle cell recycles its entire pool of ATP in under a minute
-A muscle cell uses 10 million molecules of ATP a second
ADP + P----------- ATP + H2O = Delta G +7.3kcal/mol
Video on Using Gibbs Free Energy
Video on Life Requires Free Energy
Hydrolysis
-The breakdown of polymers into monomers by "cutting" them with water
Dehydration Synthesis
-The joining of monomers to make polymers by removing water
Enzymes
-Catalysts- A catalyst speeds up a reaction. Enzymes are a biological catalyst.
-Enzymes speed up biological chemical reactions
-They lower the activation energy
-Exergonic reactions happen spontaneously. Meaning they happen on their own without any input of energy. This does not mean they happen fast. It could take years for a spontaneous reaction to occur.
-For example the hydrolysis of sucrose is an exergonic reaction and happens spontaneously but if you were to leave sucrose in a jar of water it would take years in normal conditions to break down into fructose and glucose
So how is it that we can break down sucrose in a matter of seconds?
-We use an enzyme called sucrase
Activation energy barrier
-In order for potential energy to be released it needs to reach an unstable transition state. Potential energy needs activation energy (free energy of activation) to be released.
Explain how a metabolic pathway works
-Basically be able to explain this diagram
-In your explanation include the difference between a catabolic pathway and an anabolic pathway
-How do enzymes speed up a reaction?
-Enzymes can only speed up a reaction that was going to happen naturally
-Biological molecules have a lot of stored potential energy in their bonds, called chemical energy.
-This energy is ready to be released. It will break down and be released on its own without any help it just takes a long time. Enzymes help this energy release take place in a timely manner
-Biological molecules have an activation energy requirement (Ea)
-All biological molecules are activated by heat. But heat is not a good way for our bodies to activate them because heat will activate all the biological molecules in our body at the same time. It will also denature all the enzymes. So instead of using heat our body uses enzymes to break down molecules.
Enzymes have an active site where the substrate binds
-Substrate- the molecule that binds to the enzyme
-Active site- the location where the substrate binds
Inhibition
Inhibition is when something blocks the activation of an enzyme
-Inhibitor- a molecule that is not the substrate that binds to the enzyme and changes its function
-Competitive inhibition- When an inhibitor binds to the activation site and blocks the substrate from binding.
-Noncompetitive inhibition- When an inhibitor binds to a site on the enzyme other than the activation site. this causes the enzyme to change shape
-Noncompetitive inhibitor site- The location on the enzyme where the noncompetitive inhibitor binds
Allosteric Regulation
-Allosteric regulation is when an enzyme can be slowed down or speed up.
-Allosteric activators- bind to an allosteric site that speeds up the enzyme's production
-Allosteric inhibitors- bind to an allosteric site and stop or slow down the enzyme's productions
-Feedback inhibition- In a metabolic pathway the product is also the inhibitor. Once the pathway has created an optimal amount of the product, the product will inhibit the enzymes in the beginning of the pathway so no more products will be made
Metabolism- The sum of all chemical processes in the body
-Metabolic pathway- The steps involved in a chemical process
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