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6. Cellular Energetics
Some of the more important organic molecules were discussed in Chapter 4.
All three of the energy-rich substances are sugars.
The energy is packed with chemical bonds.
To carry out the processes necessary for life, cells must find a way to release the energy in bonds when they need it and store it away when they don't.
The study of how cells work is called bioenergetics.
The study of how energy from the sun is transformed into energy in living things is called bioenergetics.
The bonds are broken or formed during chemical reactions.
No matter which direction we go, this process involves energy.
A change in energy is involved in every chemical reaction.
In nature, the same holds true.
It is not possible to create or destroy energy.
The sum of energy in the universe is constant.
The first law of thermodynamics is this rule.
The cell can't take energy out of thin air.
The law states that energy transfer leads to less organization.
The universe tends to be disorder.
The products have less energy than the reactants.
Energy is given off during a reaction.
An example can be looked at.
An energy diagram shows the course of a reaction.
An exergonic reaction has an energy diagram.
The y - axis shows energy.
The diagram shows that our reaction released energy.
An example of an exergonic reaction is the release of energy from the chemical bonds in the mitochondria of cells.
Endergonic reactions require an input of energy.
The products have more energy than the reactants.
Plants use carbon dioxide and water to make sugars.
Even though exergonic reactions release energy, they might not occur naturally without a little bit of energy to get things going.
The transition state is where the reactants must first turn into a high energy molecule.
The transition state is difficult to achieve.
A certain amount of energy is required to reach this transition state.
The activation energy is what this is called.
A transition state is not the same as a reaction intermediate.
Transition states occur between the reactant and the product.
There are intermediates between the steps of a multistep reaction.
We needed some energy to get going.
Chemical bonds must be broken before new bonds can be formed.
The hump in the graph is called the activation energy.
The rest of the reaction is downhill once a set of reactants has reached their activation energy.
It is difficult to reach the transition state.
A catalyst speeds something up.
There are biological catalysts that speed up reactions.
They help the transition state to form by lowering the activation energy.
The transition state is not as difficult to overcome as the reaction would suggest.
The starting and ending points of the reaction are unaffected.
The activation energy is lowered by them.
Most of the important reactions occur in the cell.
Each of the enzymes can only do one kind of reaction.
This is known as specificity.
Because of this, the molecule they target is usually named after the enzymes.
The targeted molecule is known as substrates.
The disaccharide maltose can be broken down into two sugars.
The maltose gives the name to the enzyme that makes this reaction happen.
The suffix of the substrate is replaced by the -ase.
When using this terminology, malt ose becomes malt ase.
There is a unique way in which enzymes help reactions along.
The reactants in the reaction are called substrates.
The transition state is brought about by the help of the enzyme.
The active site is a special region on the enzyme.
One or more of the substrates is temporarily bound to the active site by the enzyme.
Once the product is formed, the enzyme is released from the complex and restored to its original state.
The enzyme is free to react with more than one bunch of substrates.
The cell can release much-needed energy by speeding up the reaction by binding and releasing substrates over and over again.
There is a quick review on the function of enzymes.
Scientists have found that the two components don't fit together well.
The shape of the substrates makes it necessary to change the shape of the enzyme.
This is called a fit.
Sometimes certain factors are involved in making the enzyme binding.
Under strict biological conditions, the fit between the enzyme and the substrate must be perfect.
Sometimes a little help is needed in catalyzing a reaction.
Cofactors are factors.
Cofactors can be either organic or non-organic.
Metal ion are the inorganic cofactors.
Vitamins are examples of organic coenzymes.
Your daily dose of vitamins is important because vitamins are active and necessary participants in chemical reactions.
Enzymatic reactions can be influenced by a number of factors.
The speed of the reaction will be determined by the concentrations of the two substances.
The rate of a reaction increases when the temperature of the reaction increases.
Too much heat can damage an enzyme.
If a reaction is conducted at a high temperature, the enzyme becomes inactive and loses its three-dimensional shape.
Denatured enzymes are those that have been damaged by heat and are not able to make reactions.
To change something's nature is one way to denature.
Proper and special folding is needed to keep aProtein's nature.
All of the enzymes operate at an ideal temperature.
This temperature is the body temperature for most humans.
Some organisms have a constant body temperature.
ectotherms depend on the environment to control their body temperatures.
A measure of temperature sensitivity is called Q 10.
The AP Biology Equations and Formulas sheet has an equation for Q 10.
The same temperature unit must be used for both T 1 and T 2.
The two reaction rates must have the same unit.
The factor by which the rate of a reaction increases due to a temperature increase is called Q 10.
The higher Q 10 will be if the reaction is temperature dependent.
The reactions with Q 10 are temperature independent.
The pH is the best place for the function of Enzymes.
The structure of the enzyme can be altered if the pH is incorrect.
The optimal pH is between 7 and 7.
There are other enzymes that operate at a low pH.
pepsin is most effective at an acidic pH of 2.
We know that the rates of chemical reactions are controlled by enzymes.
The cell can regulate the conditions that affect the shape of the enzyme.
Things that bind to them can turn on/off the enzymes.
Sometimes these things can bind at the active site, and sometimes they can bind at other sites called allosteric sites.
If the substance has a shape similar to the transition state, it can compete with the other substance and block the other substance from entering the active site.
It's called competitive inhibition.
The reaction would occur if there was enough substrate available.
When you flood the system with lots of substrate, you can always identify a competitive inhibitor.
If it binding to an allosteric site, it is an allosteric inhibitor.
The shape of the enzyme can be distorted by a noncompetitive inhibitor.
The active site is still able to bind the substrates, but the reaction won't happen.
Some of the molecules that bind to the allosteric site are not inhibitors.
Allosteric regulators are activated by some enzymes.
Everything an animal does requires energy.
Thankfully, it's through the use of adenosine triphosphate.
A molecule of adenosine is bonding to three phosphates.
An enormous amount of energy is packed into those bonds.
It is possible for the body to perform difficult endergonic reactions.
When a cell needs energy, it takes one of these potential-packed molecules of ATP and splits off the thirdphosphate, forming adenosine diphosphate and one loosephosphate.
Whatever use the cell pleases, the energy released from this reaction can be put to use.
This doesn't mean that the cell is above the laws of nature.
Within those constraints, the best source of energy for the cell is ATP.
It is relatively easy to form and only one bond needs to be broken to release the energy.
Organisms can use exergonic processes to increase energy and power reactions.
The majority of it comes from a process called cellular respiration.
A process of breaking down sugar is called cellular respiration.
The sugar is made in autotrophs.
In Heterotrophs, the food we eat is the main source of glucose.
We will start by going over the process of photosynthesis.
Plants are producers.
The earliest photosynthesis was done by prokaryotic cyanobacteria.
The only thing they do is bask in the sun.
We'll look at how plants conduct photosynthesis.
A diverse group of aquatic organisms can perform photosynthesis.
Most of the algae are protists.
Some examples are seaweed, pond scum, or blooms in lakes.
The process by which light energy is converted to chemical energy is called photosynthesis.
There is an overview of photosynthesis.
The raw materials used to make sugars are carbon dioxide and water.
There's more to photosynthesis than the simple reaction shown above.
The light reactions and the dark reactions are part of the photosynthesis process.
The whole process begins when a photon strikes a leaf.
The excited electrons are passed down to a series of electron carriers by the activated chlorophyll molecule.
Both of these products and carbon dioxide are used in the dark to make sugars.
Oxygen is released along the way.
We will soon see that this beautifully orchestrated process occurs thanks to a whole host of special enzymes and pigments.
Let's talk about where photosynthesis occurs first.
The leaves of plants have a lot of chloroplasts.
Let's look at an individual.
The stroma is a fluid filled region if you split the chloroplast.
The structures inside the stroma look like stacks of coins.
The structures are called grana.
The structures that make up grana are called thylakoids.
They have a light- absorbing pigment that drives the process of photosynthesis.
The inside of a tylakoid is called the tylakoid lumen.
The light-absorbing pigments are involved in the process of photosynthesis.
Some of the more important ones are chlorophyll a, chlorophyll b, and carotenoids.
The antenna complexes are clusters of the pigments.
All of the pigments within a unit are able to gather light, but they can't "excite" electrons.
The only molecule that can transform light energy to chemical energy is located in the reaction center.
In other words, the antenna pigments gather light and bounce it to the reaction center.
There are two types of reaction centers.
The main difference between the two is that each reaction center has a specific type of chlorophyll that absorbs a particular wavelength of light.
The reaction center of photosystem II has a maximum absorption wavelength of 680 nanometers.
When light energy is used to make something, it's called photophosphorylation.
The photo shows light and ADP andphosphates being used by autotrophs to produce ATP.
The absorption spectrum shows how well a certain color absorbs radiation.
The light absorbed is plotted.
This spectrum is different from an emission spectrum in that it gives information on which wavelength a pigment emits.
On the next page is the absorption spectrum for chlorophyll a, chlorophyll b, and carotenoids.
The green part of the spectrum does not absorb blue and red light as well as the blue and red part.
Many plants are green because light in the green range is reflected.
Plants with yellow, orange, or red are rich in carotenoids.
The reaction center for photosystem II is sent the energy when a leaf captures sunlight.
The activated electrons are trapped by P680 and passed to a molecule called the primary acceptor, and then they are passed down to carriers in the electron transport chain.
Water is split into oxygen, hydrogen ion, and electrons to replenish the electrons in the thylakoid.
That process is called photolysis.
The missing electrons are replaced by electrons from photolysis.
When the electrons from photosystem II travel down the electron transport chain, they pump hydrogen ion into the thylakoid lumen.
A gradient of protons has been established.
The hydrogen ion moves back into the stroma.
The first and second photosystems were numbered in order of their discovery.
The electrons go to photosystem I after leaving photosystem II.
The electrons are passed through a second electron transport chain until they reach the final electron acceptor.
The photosystem II captures light and passes excited electrons.
I pass excited electrons down an electron transport chain to produce NADPH.
electrons, hydrogen, and free O2 are released from a molecule of water.
The light-dependent reactions occur in the grana of the chloroplasts.
The light- absorbing pigments and the light- dependent reactions are found in the thylakoids.
The linear or noncyclic electron flow is what most plants follow.
Some plants, such as C 4 plants discussed below, perform cyclic electron flow instead.
Cyclic photophosphorylation is similar to noncyclic.
Once an electron is displaced from the photosystem, it is passed down electron acceptor molecule and returns to where it was emitted.
Let's move on to the dark side.
The dark reactions use light reactions to make sugar.
Carbon fixation is a term you've probably heard of.
This means that CO 2 from the air is converted into food.
The leaf has a stroma.
The Calvin-Benson cycle is also called the dark reactions.
The Calvin cycle takes place in the stroma.
The light reactions are needed for carbon fixation.
The CO2 is fixed to form a liquid.
The light-dependent and light-independent reactions can't be done alone.
The light- dependent reactions use water and light to produce water and light to produce light.
CO 2 can enter the leaf and O 2 and water can leave the leaf.
Plants close their stomata on hot, dry days to prevent transpiration.
This limits access to CO 2 and reduces the yield of plants.
Plants start performing photorespiration when there is less CO 2 available.
The wasteful process of photorespiration uses O 2 and ATP, produces more CO 2 and doesn't produce any sugars.
Plants that live in hot climates have evolved two different ways to deal with this problem.
CO 2 is incorporated into organic acids at night.
During the day, they close their stomata and release CO 2 from the organic acids.
C4 plants have a slightly different leaf structure that allows them to perform CO 2 fixation in a different part of the leaf from the rest of the Calvin cycle.
This makes photorespiration impossible.
The first product of carbon fixation is a four-carbon molecule produced by C 4 plants.
The shorthand version of cellular respiration looks like this.
Cell respiration is a conserved pathway across all currently recognized domains of life.
We've taken a sugar, perhaps a molecule ofglucose, and combined it with oxygen to produce carbon dioxide, water, and energy.
The picture of what really happens is more complicated than you might think.
We can break down cellular respiration into two different approaches.
Aerobic respiration is the act of breathing in oxygen.
Anaerobic respiration is when oxygen isn't present.
Let's start with aerobic respiration.
In the first three stages, energy is made.
Special electron carriers called NADH and FADH 2 are some of these.
The electrons are unloaded in the fourth stage and the energy is used to make moreATP.
The splitting of glucose is the first stage.
There are two three-carbon compounds called pyruvic acid that are broken into the six-carbon molecule of Glucose.
Pyruvic acid is corrosive.
It's called pyruvate because it's usually lost in your cells.
The process of glycolysis doesn't happen in one step.
It requires a sequence of reactions.
The process of Glycolysis begins with one glucose and ends with two pyruvates.
There is a net production of 2.
If you take a good look at the reactions, you'll see that two ATPs are needed to produce four.
In biology, you have to invest ATP to make it, and our investment yielded four, for a net gain of two.
The ATP molecule is created by combining the two elements with the help of anidase.
To carry energy is to carry electrons.
The NADH is created by the transfer of electrons to the carrier.
As electrons are being carried and then unloaded, NAD + and NADH are being turned into each other.
Pyruvic acid is taken to thechondrion.
Each pyruvic acid is converted to acetyl-coenzyme A and CO 2 is released.
We've gone from two three-carbons to two two-carbons.
CO 2 is left in the cell by the extra carbons.
Again, two molecules of NADH are produced for each of the different types of sugar.
The process of turning pyruvic acid into acetyl-CoA is catalyzed by the pyruvate dehydrogenase complex.
If you add up the number of calories and the number of grams of sugar, you will see that pyruvate is turned into acetyl-CoA and 1 NADH.
The citric acid cycle is the next stage.
All the carbons will be converted to CO 2 when the two acetyl-coenzyme A molecules enter the Krebs cycle one at a time.
The matrix of the mitochondria contains this stage.
The Krebs cycle begins with each molecule of acetyl-CoA produced from the second stage of aerobic respiration combining with oxaloacetate, a four-carbon molecule, to form a six-carbon molecule.
The cycle begins with a four-carbon molecule, oxaloacetate, and it eventually gets turned back into oxaloacetate to maintain it.
The Krebs cycle takes place in the matrix.
It begins with acetyl-CoA joining with oxaloacetate to make citric acid and ends with oxaloacetate, 1 ATP, 3 NADH, and 1 FADH 2.
We're about to tally up the number of produced.
We've only made four ATP, two from the Krebs cycle and two from the glycolysis.
We have also produced hydrogen carriers in the form of 10 NADH and 2 FADH 2.
The next stage of cellular respiration will be produced by these molecules.
When electrons and hydrogen atoms are removed from a molecule of glucose, they carry with them much of the energy that was originally stored in their chemical bonds.
The electrons and their accompanying energy are transferred to hydrogen carrier molecules.
The charged carriers for cellular respiration are NADH and FADH 2.
Let's see how many loaded electron carriers we've produced.
We have a total of 12 energy carriers.
The resulting NAD + and FADH can be recycled to be used as carriers again, and the hydrogen atoms can be split into hydrogen ion and electrons.
The electron transport chain is similar to the one in photosynthesis.
They have different final electron acceptors: NADP + and O 2.
There are two interesting things that happen.
The high-energy electrons from NADH and FADH 2 are passed down a series of carrier molecules that are embedded in the cristae.
The electron transport chain has some carrier molecules.
Oxygen is the final stop in the electron transport chain.
The next molecule in the chain carries the electrons.
The electrons travel down the transport chain until they reach the final electron acceptor.
Oxygen and electrons form water.
This explains how aerobic respiration works.
If oxygen wasn't available to accept the electrons, they wouldn't move down the chain at all.
Oxygen is the terminal electron acceptor in cellular respiration.
There is another mechanism working at the same time as electrons are being passed down the transport chain.
The hydrogen ion is pumped from the matrix into the intermembrane space by releasing the electron transport chain's energy.
The intermembrane space is created by the pumping of hydrogen ion into it.
The hydrogen ion wants to go back into the matrix.
The potential energy in this area is responsible for the production of ATP.
The pumping of ion and diffusion of ion into the air is called chemiosmosis.
Brown fat, which is found in newborns and mammals, can be used to generate heat.
This happens when they decouple the two.
The hydrogen ion can only diffuse through the channels called ATP synthase.
Both P and ADP are on the other side of the channels.
The flow of protons through these channels leads to the creation of ATP by combining P and P i on the matrix side of the channel.
When electrons are given up, it is called "oxidation" and then theADP isphosphorylated to make the molecule ATP.
Every NADH molecule has a yield of 1.5 ATP.
In both cases, the electron transport chain creates the proton gradient.
In respiration, protons are pumped from the mitochondrial matrix to the intermembrane space, and they return to the matrix through an ATP synthase.
In photosynthesis, protons are pumped from the stroma into the thylakoids compartment, and they return to the stroma through an ATP synthase.
The Calvin cycle and the Krebs cycle have a series of reactions that regenerate their starting product.
Although they don't use it directly, both cycles have an indirect need for a particular substance.
Oxygen is the substance for the Krebs cycle and light for the Calvin cycle.
The goals of the two cycles are different, the Calvin cycle seeks to reduce CO 2 to carbohydrates while the Krebs cycle seeks to oxidize it.
Anaerobic respiration occurs when oxygen is not available.
The electron transport chain stops working.
Glycolysis can continue to run.
This means that it is possible to break down the sugar into two parts.
Two pyruvates and two NADH are given by lysis.
The pyruvate and NADH make a deal with each other, and pyruvate helps NADH get recycled back into NAD + and takes its electrons.
Lactic acid is produced in the muscles of the pyruvate.
The process of ferment is only done in emergencies since these two things are toxic.
A better option is aerobic respiration.
There are yeast cells that make carbon dioxide.
Lactic acid is produced by otherbacteria.
Human beings can ferment in their muscle cells.
If that was the case, it could be the result of anaerobic respiration.
Your muscles need a lot of energy when you exercise.
They convert enormous amounts of sugar to energy.
Your body doesn't get enough oxygen to keep up with the demands of your muscles as you continue to exercise.
This causes an oxygen debt.
They switch to aerobic respiration.
Pyruvic acid can be converted to lactic acid.
Lactic acid causes your muscles to ache.
It is not possible to create or destroy energy.
Endergonic reactions and exergonic reactions exist.
The change in free energy indicates whether the reaction requires energy or not.
The study of how cells accomplish biological processes is called bioenergetics.
The active site is where the reactant is binding to the proteins.
The highest rate of reaction can be found in the narrow range of temperature and pH.
They are no longer active outside of this range.
Allosteric/noncompetitive inhibitors, competitive inhibitors, and activators can be used to regulate or alter the activity of the enzymes.
Coenzymes or cofactors may be required to help with reactions.
The energy molecule in cells is called ATP.
It is created through cellular respiration.
The process by which plants use sunlight to make sugar is called photosynthesis.
Sugar is made in the Calvin-Benson cycle by using the energy from the carbon from CO2 and the hydrogen from water.
NADH and FADH2 are used as electron carriers in cellular respiration.
Anaerobic respiration occurs when cells lack oxygen to act as a final electron acceptor.
In this process, the pyruvates generated by glycolysis are broken down by fermentation to produce lactic acid or ethanol and NAD+, which allows the process to continue and provide the 2ATP it makes.
Chapter 15 contains answers and explanations.
The Mitochondrion is involved in cellular respiration.
There is a schematic of the structure of achondrion.
The binding of Inhibitor Y causes a structural change.
A single-step chemical reaction is catalyzed.
Nearly all forms of life use the critical pathway of lysis.
The process of converting 1 molecule of sugar into 2 molecule of pyruvic acid takes place in the cell's cytoplasm.
Oxygen does not need to be present in cells.
Under anaphylactic conditions, fermentation pathways are required to continue to produce ATP.
In the laboratory, Taq polymerase is used to make the polymerase chain reactions.
Taq is similar to how it would be in a bacterium.
Two groups of cells were grown.
Half of the Mitochondria from each group were isolated and placed in a neutral or low pH, and the other half in a neutral or high pH.
Small Molecules were allowed to diffuse across the outer barrier.
Oxygen bubbles were visible through the growth media.
The second law of thermodynamics states that disorder is increasing in the universe.
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