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Lecture Comments (11)

1 answer

Last reply by: Bryan Cardella
Tue Jun 21, 2016 1:18 PM

Post by Scott Pearce on June 21 at 08:15:57 AM

Sorry, at the end of a video I have had touble replaying it again. can I watch it again

0 answers

Post by Hossain Khondaker on June 22, 2015

I like how you teach with examples and stuff

1 answer

Last reply by: Bryan Cardella
Thu Dec 11, 2014 5:23 PM

Post by Alyson Muller on December 11, 2014

why do i keep getting "NETWORK ERROR"

1 answer

Last reply by: Bryan Cardella
Sun Nov 16, 2014 11:22 AM

Post by Anmol Chowdhary on November 15, 2014

Hi! Is there more information about Enzymes and Metabolic Pathways on this site? (The stuff like affecting enzyme speed like temperature, cofactors, enzyme inhibitor, etc.?  Very helpful video too, thanks again!

1 answer

Last reply by: Bryan Cardella
Tue Jun 17, 2014 11:15 AM

Post by Enrique Salinas on June 16, 2014

Have a question about a previous lesson:
Is there a formula as to how bases get paired?; adenine, guanine, thymine, cytosine, uracil. I which pairs with which, however, don't know how to solve a problem on pairing them....tks
Enrique Salinas

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Last reply by: Bryan Cardella
Fri Mar 14, 2014 3:24 PM

Post by Lilian Comparini on March 14, 2014

I love you!!!

Cellular Energy, Part I

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Energy Facts 0:05
    • Law of Thermodynamics
    • Potential Energy
    • Kinetic Energy
    • Chemical Energy
    • Mechanical Energy
    • Solar Energy
  • ATP Structure 4:07
    • Adenosine Triphosphate
    • Common Energy Source
  • ATP Function 6:13
    • How It Works
    • What It Is Used For
    • GTP
  • ATP Cycle 10:35
    • ATP Formation
    • ATP Use
  • Enzyme Basics 13:51
    • Catalysts
    • Protein-Based
    • Reaction Occurs
  • Enzyme Structure 19:14
    • Active Site
    • Induced Fit
  • Enzyme Function 21:22
    • What Enzymes Help With
    • Inhibition
    • Ideal Environment to Function Properly
  • Enzyme Examples 25:26
    • Amylase
    • Catalase
    • DNA Polymerase
    • Rubisco
  • Photosynthesis 28:19
    • Process To Make Glucose
    • Photoauthotrophs
    • Endergonic
    • Reaction
  • Chloroplast Structure 31:55
    • Photosynthesis Factories Found in Plant Cells
    • Thylakoids
    • Stroma
  • Chloroplast Micrograph 34:14
  • Photosystems 34:46
    • Thylakoid Membranes Are Filled with These Reaction Centers
    • Photosystem II and Photosystem I
  • Light Reactions 37:09
    • Light-Dependent Reactions
    • Step 1
    • Step 2
    • Step 3
    • Step 4
    • Step 5
    • Step 6
  • Dark Reactions 43:15
    • Light-Independent Reactions or Calvin Cycle
  • Calvin Cycle 44:54

Transcription: Cellular Energy, Part I

Hi, welcome back to, this is the lesson on cellular energy.0000

Some facts that we should go over before continuing into a lot of the details about energy and cells,0006

is just some kind of laws of physics that have through with energy, the important thing is to keep in mind.0011

The laws of thermodynamics, there are a couple of main things we need to know.0016

First off, energy can neither be created nor destroyed.0020

First off, thermodynamics has a lot to do with heat movement out of organisms and organisms, 0024

but not even with just living things, we are talking about everything in the universe.0031

When we talk about energy, it is not just energy inside of you or me.0035

We are talking energy having to do with work in the car, solar energy, energy in stars, any form of energy.0038

It cannot be created or destroyed.0047

It is all about conversions, it is about taking one form of energy and converting it into something else.0051

That is how the world works, that is how the universe works.0056

How all the energy got here in the first place, that is debatable.0060

But in terms of using energy, we just cannot make it from scratch.0064

It is about transferring from one to the other.0067

We do these things called chemical reactions,0070

involving energy transferring from one form to another and taking sort of different forms.0072

The chemical reactions that happen whether we are breaking something out or building something, 0080

it always contributes to increased entropy.0085

Entropy is basically chaos in the universe, even building up of molecules in cells.0087

Over time, it is a losing battle, in terms of making energy work for you.0096

Overtime, there is just increased chaos.0104

Here is another way to look at it.0109

When you crack an egg, the egg comes out of the shell, spills out on the frying pan.0111

There is no way you can get that egg back into the shell.0118

It is not going to go back to its previous form, you cannot reverse that.0122

Any reaction that happens, you can choose the chaos in the universe.0125

That really comes into play when we talk about physics.0130

In terms of biology, we are going to focus more about different types of energy and how that affects cells.0132

How do you get solar energy being converted to chemical energy, food.0141

We are going to talk about that in this lesson.0144

In terms of the different types of energy, potential energy,0146

if I hold something up a certain distance from the surface of the Earth that has potential energy.0150

It has a certain amount of mass and we calculate how far above the earth it is, 0156

we are going to determine, if I let it go, what is going to happen?0161

Potential energy is me holding it here.0164

When I let it go, that potential energy gets converted to kinetic energy, that is the energy of movement.0167

You do these physics problems quite often in physics classes.0173

In terms of biology, this particular course, chemical energy is a big part of it.0177

The chemical energy is food, in terms of powering a car that could be gasoline.0183

Chemical energy in food, we eat that energy that is stored in chemicals, sugars, lipids, proteins, etc.0189

And that gets converted in our bodies into mechanical energy, the energy of moving parts.0196

Machines have mechanical energy.0203

We are not a machine, we are made of cells.0205

But, our heart beating that is the mechanical energy.0208

It would not happen without the chemical energy from food, us moving our muscles, 0212

that is certainly mechanical energy.0217

Solar energy is another important one.0220

Without energy from the sun, we would not have the ability to have sugars.0222

Plants take solar energy, convert that to chemical energy.0228

All of this, it is just a cycle, the one leads to the other, and so on and so forth.0232

A lot of the lesson in this particular part of the course is about how energy gets transferred from one version to another.0238

When we are talking about energy, you got to know about ATP, adenosine triphosphate.0248

ATP is kind of like energy currency, you can spend it on doing anything in a cell that requires energy.0254

There are other energy molecules but this is definitely the most common energy source 0264

that is readily available for use in cells.0268

How do you get this name adenosine triphosphate?0271

Well, it is made of an adenine, let me color code this.0274

Adenine, right there, it is this.0278

Ribose, here is ribose, this is a sugar ribose and 3 phosphate, that is why you get triphosphate.0284

3 phosphates, here is 1, 2, and 3 adenosine triphosphate.0297

The first part adenosine, they took this word adenine and ribose.0306

Adenosine, they just combine them.0311

It is easier than saying Adenine Ribose Triphosphate, adenosine triphosphate.0314

They have all these labels here in this particular diagram because they are trying to say, just this part, 0321

if we ignore those three, this is the adenosine.0326

If we also include this one phosphate, it is known as AMP, adenosine monophosphate also known as adenolic acid.0329

AMP actually has to do with signaling inside the cells.0339

ADP adenosine diphosphate would be, if we did not have this third one, 0343

if we just had these two phosphates attached here, that is ADP.0349

You will see more about that in the next few slides.0353

And then finally, the whole molecule, this whole thing is ATP.0355

The whole way works is, it is the breaking of this bond.0360

The third phosphate leaving and being put back on, that powers the majority of work in cells.0364

As I mentioned before, ATP function, the way it actually functions, it is kind of like spending money.0374

We will talk about aerobic respiration later on this lesson.0381

When you take a glucose molecule, sugar molecule, in your diet, 0384

it is very common sugar molecule that mostly need every day.0387

Glucose, you cannot just take that sugar and attach it to a membrane protein to be like,0391

I want you to pump that stuff out, sugar.0396

The sugar, you cannot do that.0400

What you have to do is you to take the sugar, break it down, or release the energy to make ATP.0402

And you can take an ATP molecule and have it grab it to a protein, 0408

and cause it to move and actually pump something in and out of the cell.0412

It is like, if you went to another country, men had to trade your version of money whether it is euros or dollars, whatever, 0417

you change it into their currency so you can spend it wherever you want in that country.0425

It is similar, it is just changing from one chemical energy source to another.0429

ATP is really the most common energy molecule in cells.0433

The way it actually works, it phosphorylate substances, changing their form or shape.0438

Phosphorylate is a fancy term that means you are attaching a phosphate to something.0443

Remember, ATP has three phosphates.0449

Typically, that third phosphate is what is coming off, attaching to a protein,0452

attaching to something in a cell that changes its shape, makes it do work.0456

What are the other things you can use it for?0462

One of things is movement, there is these things called motor proteins,0464

that walk along parts of the cytoskeleton and they are carrying little vesicles.0468

They have this funny way of moving that looks like they have legs.0475

They have some kind of container that they are moving possibly to the surface of the cell,0478

to dump out contents whether it is hormones, or waste, or whatever.0485

The way that it actually looks like it is walking, an ATP molecule attaches a phosphate that cause it to shift.0490

Phosphate breaks off, shifts again, another ATP molecule comes and keeps doing that over and over,0497

and that makes it almost walk, in a sense.0503

That is a movement of something inside a cell.0506

Also, muscles, the way that muscles actually relax and contract has to do with moving proteins back and forth across each other.0508

That is certainly movement that is responsible or ATP responsible for doing that.0519

Building molecules, if you want to build up molecules and cells.0524

Let us say you work out, you have muscle soreness.0529

On a microscopic level, what actually happen is you have torn your muscle proteins.0533

These little microscopic tears, we are not talking like major injury.0539

I’m talking about microscopic tears.0542

Your body rebuilds upon them to reinforce and strengthen your muscle, 0544

to get back to how it was, and potentially maybe even stronger.0549

That is why working out does that.0552

Building those molecules requires energy in cells, requires ATP.0555

Active transport, discussed in the cellular transport lesson.0560

Without ATP, active transport is going to happen because that is the type of transport0564

in and out of a cell that requires the use of energy.0568

And there are more things that can ATP do, with the other classic examples.0571

There are other molecules in cells for energy use, one of them is GTP.0575

Instead of it being adenine, that molecule GDP is actually guanine.0579

The funny thing about that is adenine and guanine can actually be parts of DNA and RNA.0585

But in the case of ATP or GTP, they are kind of like place holders for the phosphates.0593

Ribose that is a sugar, you could take the sugar and break it down.0599

In the case of ATP along with adenine or in this case guanine, 0603

they are just place holders for what is going on with the phosphates.0607

This actually is guano, guanosine triphosphate.0610

Let us move on.0631

ATP cycle, how do you actually form ATP? How do you use ATP?0638

Is this back and forth that is happening throughout a cell's life?0643

When it comes to ATP formation, it is an endergonic reaction, meaning input of energy has to happen.0647

Energy needs to be put in to this cycle in a sense, to get the ATP to be formed, to get it come together.0655

We will talk about later on in this lessons about how aerobic respiration is a process,0663

in which you get that energy available to put ATP together, that happens in mitochondria, the powerhouses of the cell.0667

When you use ATP, there is a release of energy.0675

When that bond is broken from the third phosphate and that second phosphate, 0678

that is an exergonic reaction, the release of energy, and that is shown here.0682

What this is saying, what that is saying is, all are saying that adenosine diphosphate ADP plus another phosphate,0687

the third P gives you ATP adenosine triphosphate. 0694

This is the opposite, this ATP having that third phosphate break off.0698

Remember, when there is a reaction, you do not have matter being created nor destroyed.0703

You do not have energy being created nor destroyed.0710

You still have these molecules there, it is just now they are separated.0712

The bond that was keeping these together has been broken, 0716

and energy is been released and applied to something else, that is how ADP works.0721

If we would illustrate this, here is the cycle.0725

ADP phosphate, this is like an uncharged battery, in a sense.0729

You want to recharge the battery, you put them back together.0737

How do you get to here? How you get them attaching to one another?0744

You need an input of energy.0748

That input of energy is thanks to respiration, aerobic respiration.0753

Later on this lesson, we will get into the details of what actually happens.0769

In summary, sugar molecules are broken down, the bonds that keep that sugar together is broken.0774

Energy released from there is encapsulated in molecules that help to make ATP.0781

The energy for aerobic respiration that gives you a lot of ATP.0786

And then, you end up using it, you end up using ATP which brings you back to square one.0793

You got to put back together and it keeps happening.0799

ATP, there is a release of energy.0802

This is the release of energy from ATP being broken down and this releases energy for cellular work.0809

This keeps happening throughout a cell's life, it has to.0828

When it comes to energy, we have to talk about enzymes.0832

These are some facts about enzymes, some basic things you need to know.0835

Catalysts, enzymes are always catalysts.0839

Since, this term catalysts can be used in social situations.0840

You would say, she was a catalyst in helping him and I, in our dispute or our disagreement.0845

In that case, we are calling her a helper, someone that facilitated that to happen.0851

A catalyst is very much like that chemically.0858

Catalysts are molecules that help a reaction happen more quickly or easily.0861

All enzymes are catalysts, but you can have a catalysts that is not an enzyme.0865

The distinction is, if the substance is a catalyst and it is made up of protein, it is an enzyme.0870

Protein based catalysts, that is what an enzyme, they are always made of protein0877

and they always help reactions happen more quickly and more easily.0882

How do they help? How do they physically help a reaction happen more quickly or more easily?0885

What they do is they lower the activation energy required for a reaction to occur.0891

That might seem kind of abstract, what is this activation energy, what was that mean?0896

Here is a little graph that tells us what it means, visually.0901

Here in the Y axis, we have the amount of energy you contained in the molecules, we have participating in this reaction.0905

You could see that at time 0, because time is right here, as we go to the right times,0912

A time 0, we have this amount of energy because in our reactants, this would be glucose.0919

Glucose is a very common sugar on planet earth.0925

There is glucose and oxygen gas, you will see that actually, when we get to our products at the end of a reaction,0931

we have less energy than what we started with because this is an exergonic reaction.0938

There is going to be energy released, thanks to the enzymes helping out with this reaction.0943

But the reaction could happen without enzymes.0948

Here is the distinction, if we look at the red part of the graph.0952

This little energy hump and it is going down here, it tells us the amount of energy 0956

that we would need to be put into this to get from the reactants to the products.0964

This is the activation energy required.0971

Without an enzyme, you need quite a bit of energy supplied here to get from reactants to products.0974

But, when we have the assistance of this catalyst known as an enzyme,0980

this blue part of the graph, this blue curve with the enzyme, look at the difference from there to there.0985

A lot less activation energy required, it is less of a hump to get over, to get to the products.0992

That is what enzymes do, they physically lower the activation energy.0997

You could see the difference, here it is being graphed.1002

The activation energy required with an enzyme, this is the amount required without it.1005

Like I said before, we actually do get energy being released in this reaction because it is exergonic.1011

You can also find some of these enzyme graphs reversed,1018

meaning you start out with reactants that have less energy inside of them than what we get at the end.1022

Because, if by the end we are building bigger molecules, that is endergonic.1029

You actually have to have an input of energy to make those products.1033

Another example would be with something like Hydrogen peroxide H₂O₂.1038

H₂O₂ can be decomposed into water and oxygen gas.1048

We can do the full chemical reaction and balance it out with the coefficients.1054

But in this particular case, let us just keep in mind that hydrogen peroxide can be broken down in water and oxygen gas.1058

It can happen without an enzyme.1067

If you buy hydrogen peroxide in a brown bottle, you put it on a counter, unscrew the cap, and just let it sit there.1069

After couple of weeks, you are actually going to get close to having just pure water.1074

The oxygen gas will be leaving and you get gradual decomposition.1080

The reason why hydrogen peroxide is in that brown bottle is it actually makes it less likely that this is going to happen.1087

If you have hydrogen peroxide in a clear bottle like rubbing alcohol would be,1093

the sunlight heating it overtime would actually decompose the H₂O₂ and cause oxygen gas to leave, leaving you with just water.1097

That is why they have it in that brown or dark bottle, to prevent sunlight from gradually getting it over this hump,1105

from gradually making that reaction happen.1113

If you sit that bottle out and let it be exposed to light and just the elements, you are going to have it eventually happen.1116

You are going to have gradually leaving the oxygen, and eventually what you have is just water.1125

You know what, you can speed up that reaction, make it happen a lot faster, a lot easier,1130

when you have something called catalase.1135

Catalase is an enzyme that is meant to have this reaction happen much more easily.1138

It actually fits H₂O₂, it grabs a hold of it, forces oxygen gas to leave, and it just makes a reaction happen a lot faster.1144

Enzyme structure, when we look at a structure of an enzyme, what is it looks like? What is it shape like?1155

The first important part that I want to tell you about is the active site.1160

It is that specific shape that fits the substrate.1163

The substrate is whatever molecule that the enzyme is acting upon.1166

Here, we have this kind of cartoony version of what an enzyme could look like.1172

The actual protein shape of an enzyme looks much more complicated but nonetheless, this is a good illustration.1176

Here, we have this little that looks like a kind of puzzle cutout piece.1183

That is the active site, it fits in with the substrate.1186

You can see the edge of this, it looks like it is going to fit in there, as it meant to.1190

Chemically, this enzyme is meant to break down the substrate.1195

It could be a sugar molecule, it could be a number of things.1198

What is the substrate? You can notice substrate is that particular molecule of the enzyme,1203

is meant to break down and the active site fits that.1209

Induced fit is kind of like a clamping down on the substrate.1213

Here, we have an example that you could see that, when the substrate comes into contact with the active site,1218

the enzymes grabs a hold of it, that is called an induced fit.1224

It clamps down and holds it.1229

Once this is broken down, it will grab another one.1231

You could see that we have these products at the end.1235

Before it was connected, maybe this was a disaccharide, meaning like a double sugar.1239

Now, it is two individual simple sugars or monosaccharide because the enzyme broke them apart.1245

You can see that, these products a little bit different chemically than what we had before as this substrate and his reactant.1251

Notice, the enzyme is not damaged, it has not been consumed, it has not gone away.1260

Enzymes are not consumed by the reaction.1264

Enzymes will eventually break down, but you can supply thousands and thousands 1267

of the substrate molecules and the enzyme will be just fine.1273

There are things that can damage enzyme and I will tell you more about that in a second.1277

What do the enzymes help with?1284

Two main kinds of reactions, if we would be really general about it, enzymes can help with breaking down molecules,1286

which would cause the release of energy, that is exergonic, or building molecules, an endergonic kind of reaction.1293

You can build a glycogen inside of your body, meaning you take individual sugar molecules of glucoses 1300

and put them together to make a giant storage molecule known as a glycogen, which we store in our liver and muscles.1307

Enzymes can be interfered with the inhibition.1315

If you remember that image from the previous slide, it is a little bit different than the one on the previous slide.1318

Let us say that is the enzyme and here is the active site.1328

It turns out that it is really good at breaking down of this molecule.1332

There is the molecule, it is meant to fit in there.1338

That is what the enzyme is supposed to be working on, here is the substrate, there is the enzyme.1341

But there could be another molecule that is like this.1345

Now, the enzyme is not supposed to break this down, but this could get in the way of the enzyme breaking down what it is meant to.1354

This is an example of an inhibitor, a kind of molecule that gets in the way of the enzyme doing its job.1364

There can be molecules that do not allow the enzyme do what it is supposed to do.1371

Also, enzymes have an ideal environment to function properly.1375

As with many other chemicals and reactions in cells, they have their range of what is acceptable or what is tolerable.1379

The three main things that will damage an enzyme to the point that it cannot work is extreme temperature, PH, and salinity.1390

They can denature the enzymes.1398

Denature is a term used with proteins, in general.1401

If the protein gets unraveled, that is denatured.1404

If it is no longer has its shape and no longer has formal function that allows it to do what it is supposed to do.1408

Let me show you a little graph that kind of illustrates this.1415

On the Y axis, we are going to say here is the percent effectiveness,1420

meaning the higher at we are, the better enzymes are working.1425

There is percent effectiveness, here let us say this is temp.1431

If we were to graph temps, I mean it really depends on the scenario.1439

If we are talking Celsius, maybe this is 20°C.1442

Here is 0, here is 40, and we can graph and look like a bell curve.1450

What this is saying is that for this particular enzyme, it could be any enzyme, 1461

but at some enzyme that actually works really well at 20°C.1466

It is saying, right there, this temperature, enzyme is doing just fine.1471

If we heated up, the enzyme is now effective.1475

That higher temperature, kind of messes with their structure, causes them to ravel.1480

They are not as good at maintain the active site and working on that substrate.1484

Same with when we get it too cold, we can replace this particular label with a PH or salinity.1489

Every enzyme has their kind of range that is acceptable.1497

If you take enzymes out of your stomach, out of your gastric juice, where they are used to a PH of 2 which is really acidic,1500

if you put them in your mouth, your mouth has a PH that is closer to 7 and that is really different.1507

And vice versa, if you take your enzymes like salivary amylase from your mouth and try to have it work in your stomach, 1513

it is outside of the acceptable PH range for that enzyme.1522

Some examples, I have mentioned one of these already but some classic enzymes 1527

that you will find in the human body and other organisms, amylase.1531

Amylase breaks down larger sugars into smaller sugars.1535

Salivary amylase, it is in the saliva but it turns out that amylase has been discovered in1539

virtually every organism on earth, bacteria, plants, fungi, animals, amoebas.1545

Amylase is an enzyme that you need to take larger sugars and get them into tinier ones1552

that you can use for aerobic respiration, which we will go over later on in this lesson.1558

Catalase breaks down hydrogen peroxide.1563

It gets you from H₂O₂ hydrogen and water and oxygen.1569

Now, the next two, they do not break things down, they actually build things up.1574

DNA polymerase attaches the building blocks of DNA to each, they are other called nucleotides.1579

This actually says it all in the name, DNA polymer.1586

A polymer is when we take monomers, little individual building blocks and string them together to make a polymer.1589

DNA polymerase, notice the -ase, typically enzymes end with -ase.1598

A lot of times in this course, if the word ends in ase, it is probably an enzyme.1609

Unless the word is phase, you now like a phase of cell division.1614

ASE typically enzymes end with that particular suffix.1619

Rubisco, wait a second that does not end in ase.1624

Rubisco, it is actually short for a much longer name of Ribolose biphosphate carboxylase.1628

That is a mouthful, it is brainful, it is easier to just call it rubisco.1637

Rubisco is short for RUBP, Ribolose biphosphate carboxylase.1644

What it does is it attaches CO₂ to organic compounds during photosynthesis.1650

It is the enzyme that allows a plant to make sugar.1654

Without it, you would not get gaseous CO₂ getting attached and inbound into molecules inside of plant cells.1659

Some scientists estimate, I have read this in a couple of different books, that rubisco maybe the most abundant protein.1666

Certainly, the most abundant enzyme on planet earth because there are so many plant cells, algae, etc, in the ocean, trees, bushes, etc.1673

It is so incredibly important, you can thank rubisco for all the sugars you get.1683

These two at the bottom, enzymes that help build molecules.1689

These two at the top are enzymes that help break down molecules.1693

Now, I went to photosynthesis, this is how you get sugars, this is how plants make food. 1700

It is the process by which water, carbon dioxide, and some air use to make glucose which is the classic sugar.1707

This process is performed by all photoautotrophs.1713

The term autotrophs means self-energizing.1719

Any cell that does not need to eat, any cell that can make its own organic compounds 1724

and break them down to make ATP will be considered an autotroph.1730

Photoautotrophs says that they are using a light to help get that process going.1735

It is important to have a distinction because there is also chemoautotrophs.1740

At the bottom of the ocean where sunlight would not even penetrate down there, 1745

you have chemoautotrophs because they can take gases and heat from hydrothermal vents,1749

and make organic compounds with those building blocks.1754

Photoautotrophs, plants and their relatives.1758

Of course, this is every tree, bush, every weed, every flowering plant.1762

Algae, single celled or multi cellular, typically in the ocean, you can have it in lakes as well.1769

Cyano bacteria also known as blue green algae, this is a kind of bacteria that has a blue green look, 1775

it does photosynthesis as well.1782

All sugars on earth, every sugar are produced, thanks to this process.1785

The sugar that the humans get from, to make baked goods and all the kinds of sweet goodies,1792

you can get it from sugar cane.1799

You can get it from beets, there is a lot of sources that you can extract sugar from.1801

It is an endergonic process, the fact that it is endergonic means that it is an input of energy.1808

Thanks to the sunlight that is how you really get that input of energy started, to build up this sugar.1815

Here is the reaction, these are the reactants and these are the products.1822

Sometimes, you will see this slightly different meaning, instead of having some lights or just solar energy on the left,1838

sometimes you will see the arrow, you are getting us from reactants to products and you will see light on top of it.1847

Because in this case, light is a catalyst, it is what is getting you from the reactants to products.1856

Putting it on this side is fine, you will soon realize that sunlight does not have matter.1863

It is not made of atoms, it is not a molecule, it is just a form of energy.1869

But the rest of this it is atoms, it is molecules.1874

It is all balanced meaning the amount of carbon, oxygen, hydrogen that you start out with in the reactants,1878

it has to be the same when we get to the products.1885

You are not just making atoms out of thin air or having them disappear.1888

It is all about changing one form of energy into another, by rearranging matter in a sense.1892

For every 6 carbon dioxide and 6 waters with enough sunlight, 1900

you are going to be able to make one molecule of glucose C₆H₁₂O₆.1904

You are going to have a waste product in photosynthesis, 6 oxygen molecules.1909

Chloroplasts are the structures that are really responsible for photosynthesis.1917

All eukaryotes, all plant cells that actually have membrane bound organelles will have chloroplast,1922

they are like photosynthesis powerhouses.1930

Bacteria that do photosynthesis would not have these because they do not have membrane bound organelles.1932

But they can have pigment molecules that also get photosynthesis going,1938

it will be less efficient than if they had chloroplast.1942

These are the photosynthesis factories found plant cells.1946

These little green pancake looking things, they are called thylakoids.1949

There are sites for the light reactions, that is how a photosynthesis begins.1956

It is the photo part of photosynthesis because photo means light.1961

A stack of thylakoids is called a granum.1965

Here you have granums, stack of thylakoids, plural will be grana.1969

You do not say granum, grana is plural.1979

Look at all the lovely grana in this chloroplast.1982

Yes of course, this is a computer generated image.1985

On the next slide, I will show you an actual micrograph, what they really look like.1988

But this is good for zooming in and seeing what is really going on inside of it?1993

Stroma is another important part in this chloroplast.1998

It is the fluid surrounding the thylakoids.2003

All of this kind of light yellowish green, this is the stroma.2005

You can see that it is label here, the aqueous fluid.2010

It is mainly water but there is enzymes and molecules and ions, dissolved inside of it.2013

The other parts of photosynthesis, the dark reactions also known as the light independent reactions.2019

They happen in the stroma and that is the second part of photosynthesis.2027

It is the synthesis part of photosynthesis.2030

On the outside, you have a double membrane, you can see that there is the outer membrane,2034

here is the lower or deeper membrane.2040

Inside of that, you got all your grana and stroma.2044

Chloroplast also have their own DNA and ribosomes, interesting enough.2049

Here, we have a picture of individual plant cells.2056

Here is one plant cell, you can see its boxy cell wall that I just drew a line around,2060

and here are chloroplasts, here is two of them.2068

If we can zoom in even further, we will be able to see thylakoids, the grana.2074

But to get that close, you need an electron microscope.2080

In terms of the details of photosynthesis, we got to start off with photosystems.2089

The thylakoids membranes which are very green of course, are green, thanks to these.2093

A thylakoid membranes are filled with these reaction centers and they are composed of chlorophyll.2098

This is the green pigment molecule, most common pigment molecule on plants.2106

Chlorophyll that is green, there are lots of other pigment molecules that have different names.2113

The other part of the photosystems are proteins.2118

This is a nice computer generated image of what a photo system looks like and how complex it is.2122

All of the green stuff like these little guys here, those are your chlorophyll molecules.2127

The rest of it, these are protein pieces, different shapes and different confirmations,2134

holding all this together and in helping at work as a very large macromolecule.2140

When you look at thylakoid membranes in chloroplasts, there are two main photosystems.2147

Photosystem 2 and photosystem 1, I listed them in that order2151

because photosystem 2 gets things start off and photosystem 1 continues the process.2155

You might think why is it in reverse order, what is the deal with that?2161

I read that actually photosystem 1 was discovered first, and then named it one, 2165

props it away to anticipate numerous other photosystems.2171

We will find number 2, 3, and 4, etc.2176

Then, number 2 was discovered and they realized photosystem 2 2179

actually gets the process started and send something along to photosystem 1.2184

Then, the rest of the thylakoid membrane it is all photosystem 2, photosystem 1. 2189

They kept it that way presumably because there were already papers and research done in photosystem 1, 2195

changing a name or reversing the numbers would have probably cause more problems.2201

Just remember that P2 photosystem - 2 comes first and then photosystem 1.2206

You will see in future slide in this lesson, how the images of those photosystems and how they relate to another.2211

They do get the process of photosynthesis started.2218

Photosystems because certainly light does affect them, that is the photo part of it.2222

We are going to get it started.2231

The light reactions, this is the photo part of photosynthesis.2233

We will get to this synthesis part next.2242

These are also called the light depended reactions because they are dependent on light.2244

They really do depend on light.2249

Heading the photo systems on the balcony to get it started.2251

Step 1, involves this right here light, this thing that looks like a little thunderbolt.2255

It is actually photons, individual electromagnetic radiation, that is really the lightest form of radiation.2263

It is just light heating it, that will get us started.2274

Sunlight absorption by photosystem 2, you will see this PS2 right here.2277

It causes a loss of electron from the chlorophyll.2282

Here, the photosystem image in that previous slide, a bunch of proteins with chlorophyll throughout.2285

Light hits it, chlorophyll molecules, there is an excitation that happens when light hits it.2293

Electrons, the subatomic particles inside the chlorophyll, they get excited.2298

They just swing out of there and they end up getting transported through proteins next to the photosystem.2304

Because you do not want electron loss to gradually make chlorophyll kind of disappear,2312

you do not want all the electrons to keep leaving it, no more chlorophyll, you got to replace the electrons that left.2317

The way that happens is the process of light hitting here also splits water.2324

There is water, water is inside of the thylakoid membranes.2331

Thylakoid lumen just means the space inside of that green pancake, it is filled with water.2335

Water is right underneath the photosystem.2340

It is part of this reaction water get split apart to give you O₂ oxygen and protons and electrons.2343

The electron that came out from that spitting of water, electrons from water replace the loss from chlorophyll.2351

Chlorophyll gets retained as a molecule, it does not gradually get degraded.2359

Also, protons H+ they go somewhere and we will get to that next.2365

Step 3, protons H+, there is H+ see where they are going?2372

They build up and move through ATP synthase to make ATP.2380

ATP synthase, if you remember from the previous slide about -ase, this is an enzyme.2384

It is kind of like a turbine, in a sense.2391

These protons are H+, they get moved through here and there is a spinning reaction that happens.2396

This part of the enzyme spins and moves in a particular way that helps attach ADP adenosine di-phosphates to a phosphate.2401

The reason why I say π, I just mean it is inorganic phosphate.2411

When ATP and P combine, ATP, that is a major part of these reactions making ATP, 2415

and there is a reason for that we will get into a bit.2423

Those are the first few steps.2426

As that is happening, step 4 is also occurring and that is on the next slide.2428

Step 4, as we saw before that electron got excited and left photosystem 2.2435

It gets moved along these proteins and eventually gets to photosystem 1.2440

That was step 4, electrons are passed along the thylakoid membrane proteins.2447

Step 5, when electrons arrive at photosystem 1, P1, the sunlight reenergizes them.2452

Look there is sunlight again, heading that photosystem, photosystem1.2459

Notice, this blue double line goes up.2466

Think of the electron arriving at photosystem 1 and being tired.2469

Electrons do not literally get tired, they do not have personalities.2474

But, there is an energy loss that occurs as it moves through and sunlight hitting it reenergizes that electron.2477

It gets reenergize and moves it a little further along the path, the electron eventually reaches an ADP reductase to form NADPH.2485

Now that is a mouthful, I realized that, NADP reductase.2495

Here is what that means, this is an enzyme because it ends with the -ase.2501

What this does is, its job is attaching electrons to NADP to make NADPH.2506

This is another very important product.2515

NADPH a very long name, the whole point is NADP, when you get electrons, protons, being attached to make NADPH, 2518

it is transporting those particles to what are called the dark reactions.2529

It is going to give up what it gained here to help build sugar.2535

Making NADPH and ATP, that is the main point of the light reactions.2539

The absorption of sunlight, the splitting of water, helps make all this happen, helps build NADPH and ATP.2547

This enzyme literally reduces NADP to make NADPH.2556

The reduction term is just a fancy as saying electrons were added to it.2563

It gained electrons and or protons.2568

We made ATP and NADPH, and those move on to the stroma.2570

They are actually in the stroma right now, because if this is a thylakoid membrane and this is the inside of a thylakoid up here,2575

that is actually the outside of the thylakoid or the grana, the stock of thylakoids.2583

Now they are in the stroma, add some carbon dioxide in the mix, you get dark reactions happening.2589

Dark reactions also known as the light independent reactions meaning they do not need the light to happen.2597

Because, light was needed to do the previous steps.2603

Just let you know, the dark reactions typically do not take place in the dark.2606

They are called the dark reactions because light is not needed.2613

But the thing about this, if you are a plant and you just made ATP and NADPH, 2615

you are going to use those to make sugar, why wait?2620

You just made those products in the light reactions during the daytime because there was light,2623

get it done, make your sugar, make your food.2629

Oftentimes, the light independent reactions actually taking place during the daytime, it just do not need light to happen.2631

The Calvin cycle is a name for the dark reaction as a whole, because , a scientist with last name Calvin actually discovered it.2638

It takes ATP and NADPH from the light reactions and carbon dioxide2649

from the air to build a glucose molecule in the stroma of chloroplasts.2654

Here is an image of what glucose can look like, this is the linear form, 2658

there is also the ring form of glucose that is very common.2662

But here, I like this diagram because they count the number of carbons.2665

There are 6 carbons in glucose 1,2,3,4,5,6 and you have H and OH attached to the carbons.2669

This is why glucose is known as a carbohydrate.2677

Carbohydrate H and OH make H₂O, that is the carbohydrate name.2681

How does the Calvin cycle work? 2691

We have got 6 CO₂ that you really need to make glucose and that make sense.2694

We just looked to the previous slide with glucose and how many carbons it has, glucose has 6 carbons, that C₆H₁₂O₆.2701

6 carbons, where those 6 carbons come from, 6 carbon dioxides.2710

These come into the air, they combine with something else and it is known as RUBP, 6 of them.2715

This is short for Rubolose biphosphate, RUBP for short.2729

Just to keep track of this, we are going to have a little dot next to these molecules to tell us how many carbons in each molecule.2734

With CO₂, there is only 1 carbon right, CO₂, but it is times 6 because there is 6 CO₂, and 1 carbon per molecule.2743

There is a total of 6 carbons there.2755

Every RUBP is actually 5 carbons, 6 x 5 is 30.2756

30 carbons in total combined with 6, you will end up getting 36 carbons, of course.2770

But CO₂ does not just automatically attach to RUBP.2776

It needs something called rubisco.2779

I mentioned this earlier in the enzyme section on this lesson.2793

Rubisco is short for Rubolose biphosphate carboxylase, RUBP carboxylase meaning this enzyme gets carbon attached to this.2796

It facilitates this particular reaction and makes it happen much more easily.2808

Thank you rubisco for helping us to make PGA.2812

Because of these coming together, you will end up making 12 of these2826

phosphoglyceride molecules that is what PGA stands for, not Professional Golfers Association.2828

PGA is made here and it actually gets turned into something else.2835

Each one of them, guess how many carbons they have?2839

Because it is combining, it end up with 36 but there are 12 molecules.2842

How many carbons are in each molecule?2848

There are 3, 12 x 3 is 36, that is PGA.2849

We needed ATP and ADPH to get this going, we made those in the light reactions.2859

Here is how they end up participating.2869

You get 12 ATP that helped change this molecule due to the energy released from ATP, 2876

being turned into ADP by getting rid of that third phosphate on them.2887

They also have 12 NADPH and it has a plus charge, it gets rid of that particular part of it.2892

These two, they just release what they gained from the reactions to the system.2915

The energy from that helps turn the PGA’s into something a little bit different, 2919

it is called G3P Glyceride hydride phosphate is what it actually stands for.2925

The brilliance of G3P is you need two of them, of these 3 carbon molecules.2934

No carbon left, we did not see any carbon leave or any carbon come in here.2944

It is the same amount of carbons as PGA had but they are just arranged differently.2949

The H and O on them, stuff got switched around.2954

The brilliance of GDP is you just need two of them, put them together, you got glucose.2958

You might be thinking, why did we take all 12 of them and make 6 glucoses?2964

You could, but you would not get this back.2971

The last part of the Calvin cycle in addition to making glucose, that is the whole point of it, you have to regenerate this.2976

You got to get back where you started with so it can happen all over again, 2984

as long as you supplies with CO₂, ATP, and ADPH.2987

The other 10 are actually rearranged to get back your 6 RUBP's.2992

We have a kind of fork in the road here.2998

Two G3P's are put together to make glucose sugar.3001

That was the whole point of doing photosynthesis.3015

This is the synthesis part, now that I remember, this is the synthesis part of photosynthesis because we are making a molecule.3018

The other 10 g3p's, remember they still have 3 carbons.3028

10 x 3 that is 30, guess what 6 x 5 = 30.3044

It is just a rearrangement of these 10 molecules to get back your 6 RUBP’s.3049

To do that, few more ATP are needed.3057

There you go, you get back, your RUBP, and it can start all over again, as long as you have carbon dioxide, ATP, and ADPH.3069

Glucose, oftentimes, in a plant, it is just broken down to get energy, just to do what is known as aerobic respiration.3076

Get a bunch of ATP out of this, way more than what was required to build it, that is the brilliance.3082

You get a whole bunch of the ATP after breaking down of glucose.3090

Also, plants will store glucose, they will put it together, hundred thousands of them to make starch and we need starch.3094

Starch is very bountiful, it is something like a potato.3102

It is just a huge package of glucoses, stored for a rainy day, quite literally, it can be stored for rainy day in a plant.3105

You can also modify glucose to build all kinds of other molecules 3113

that a plant would need metabolism working properly inside of itself.3118

The Calvin cycle, the last part of photosynthesis is very important.3123

That is what allows a plant to take what it gained from light reactions and make glucose.3127