Metabolism Part 1: Glycolysis This tutorial will take you through the basics of glycolysis for SC 120 Click this button to move forward

What is the purpose of cellular respiration? To provide Oxygen to the cells To use cell energy Not really. Some cells can perform respiration without Oxygen! Cells use up energy for all sorts of activities. They need respiration for something else To bring Oxygen into the body To get energy from food for the cell to use That’s right! The whole point of cellular respiration is to take the food you eat and make it into energy the cells can use. Since cells are so much smaller than the body, a cell couldn’t accomplish this.

What kind of energy is useful to cells? Food ATP Food is what cells break down to make the form of energy they can use. That’s right! Cells move energy from one part of the cell to another in the form of ATP Water Electricity Sorry, cells can’t get power from electricity! Cells do produce water – but it doesn’t give them energy

In cell respiration: A cell takes a molecule of food and breaks it apart By breaking the bonds inside the food molecule, it releases energy It uses this energy to make ATP molecules Which other parts of the cell can break open to get the energy for their own use

It’s a little like cooking… Not everybody wants to eat these raw But anybody can get energy from these Clip art from Microsoft

It’s a little like cooking… Not all parts of your cell can get energy from the food you ate But when that energy is packaged in ATP, all parts of the cell can use it

If taking energy out of the food molecules you ate and making ATP with it is like cooking, WHO ARE THE COOKS? The cooks are the enzymes that: Break down the food molecules Use the energy to make ATP Get rid of the leftovers

Your cell has many groups of ‘cooks’ In a restaurant kitchen, you would have one area dealing with fish and another area dealing with pastry. Each area would have the expert cooks for that kind of food. Your cell, just like the restaurant, has different areas specialized to deal with different kinds of foods, with ‘expert’ enzymes in that area.

A major fuel for your cells is glucose H H-C-O-H C H- O H-C-O-H H-C-O-H C C H- -O-H C6H12O6 H H-O

Two sets of enzyme ‘cooks’ get energy from glucose The first set is out in the cell cytoplasm. As soon as glucose enters the cell, these enzymes grab it and chop it in half! Clip art from Microsoft

Glycolysis ‘Glyco’ = glucose ‘lysis’ = breaking

Breaking glucose in half takes some energy Breaking glucose in half takes some energy. The ‘chef’ uses 2 ATPs worth of energy to do the chopping. Clip art from Microsoft

It also produces some leftovers – Energy released!! But the chopping then releases enough energy to make 4 molecules of ATP. So there is a net gain of 2 ATPs from glycolysis. It also produces some leftovers – electrons that were removed from the glucose.

Two molecules of pyruvic acid (3 carbons each) One molecule of glucose (6 carbons) Energy released!! Net gain of 2 ATPs AND – 4 electrons are removed

Those electrons are a problem Electrons are dangerous to your cell. They can break other molecules, causing cell damage. So this ‘garbage’ has to be put in a safe place – an electron carrier. Clip art from Microsoft

Where will you put the electrons? Your cell has specialized molecules that act as electron carriers Their names are NAD and FAD Each carrier can carry 2 electrons Clip art from Microsoft

Two molecules of pyruvic acid (3 carbons each) One molecule of glucose (6 carbons) Energy released!! Net gain of 2 ATPs AND – 4 electrons are removed Handed to 2 molecules of NAD

But what will happen when all the NADs are filled? When the NADs are all filled, you will have to stop doing glycolysis. Otherwise, your cell would start to fill up with free electrons, and they would damage it.

What is the process of chopping glucose in half called? Glucogenesis Glycogen Gluco- means glucose But ‘Genesis’ means ‘making’! Sorry – ‘glyco’ means glucose, but ‘gen’ means ‘maker’ Glycolysis ATP generation While breaking glucose can make ATP, there’s a special name for the process that tells what it does. Right! ‘Glyco’ means glucose and ‘lysis’ means ‘breaking’. Restart Quiz

What is the glucose chopped into? Two lamb chops Two pyruvic acids Very funny… Right! One half of a glucose is a pyruvic acid. Two ATP molecules Two pairs of electrons Sorry – the energy released by chopping the glucose gives a net gain of 2 ATP molecules. The electrons were pulled off when the bonds in theglucose were broken – but there was a lot more in the glucose than electrons. Restart Quiz

How many net ATPs did that make again? 2 6 Right! That’s way too high – the process uses 2 ATPs and makes 4. So what’s the net gain? Sorry – the energy released by chopping the glucose makes 4 ATP, but you had to use 2 to do the chopping. 4 8 We wish! This is a lot more than you can get from glycolysis. Restart Quiz

And what were the ‘leftovers’ produced? Two lamb chops Two pyruvic acids Still funny… not right, but funny Pyruvic acid is a byproduct, but it’s not a problem because your cell can eat it. Two ATP molecules Two pairs of electrons Right! These electrons are a potential problem for your cell. Hey! ATP’s what we WANTED to make, isn’t it? Not leftovers at all. Restart Quiz

Where will you put those electrons? They diffuse out of the cell In the nucleus BAD, BAD idea. If you put them in the nucleus, they will damage the DNA and make the cell mutate. Not so much. Remember, the cell membrane is made of lipid. Polar things like electrons can’t diffuse across it. On the electron carriers That’s right! Nowhere, they just pile up That’s going to cause a big problem for your cell… Restart Quiz

Some terminology … When the two pairs of electrons were taken off the glucose, the glucose was OXIDIZED You can remember this by thinking of a lion, LEO: Loss of Electrons is Oxidation. Clip art from Microsoft

Some terminology … When the two pairs of electrons were handed to NAD molecules, the NAD molecules were REDUCED You can remember this by thinking of the lion growling, GER: Gain of Electrons is Reduction. Clip art from Microsoft Sound from Wavsource:Animals

When NAD is reduced, it becomes negatively charged Because electrons are negative, adding more of them to a molecule gives it a negative charge. This will make that molecule very attractive to positive ions like H+.

Hydrogen ions buzz around your cell like flies They follow electrons wherever they go, the way flies follow garbage. Clip art from Microsoft

So when electrons are handed to your NAD molecules, the H+ go too. When your NAD molecules are full of electrons, they are also full of Hydrogen.

NADH + H+ In fact, many books write reduced NAD as to show that the Hydrogen ions are hanging around it.

Now, back to glycolysis! Your enzymes were working away, chopping glucose in half and making 2 ATP for every glucose they chopped. But then, all of the NAD electron carriers got full of electrons. The cell had to stop doing glycolysis, because it had no place to put the electrons.

This could kill your cell. If the cell can’t do glycolysis, it can’t make ATP! This is urgent – someone must TAKE OUT THE GARBAGE.

What can your cell do with all those electrons? Your cell has a very clever way of getting rid of the electrons so it can keep doing glycolysis. It puts them back on the pyruvic acids!

Two pyruvic acids One glucose Energy released!! Net gain of 2 ATPs 2 electrons handed to each pyruvic acid AND – 4 electrons are removed Handed to 2 molecules of NAD, reducing them

When NAD hands its electrons to pyruvic acid, what happens? NAD is reduced NAD is oxidized Remember GER: Gain of Electrons is Reduction. Did the NAD gain electrons? RIGHT! NAD has lost electrons, and Loss of Electrons is Oxidation. Pyruvic acid is oxidized Remember LEO: Loss of Electrons is Oxidation. Did the pyruvic acid lose electrons? Glycolysis stops Nope! The whole point of handing off the electrons was to empty the NADs so glycolysis wouldn’t have to stop. Reset Question

Now the NAD is oxidized and can be used again! Glycolysis can go on! Two pyruvic acids One glucose Energy released!! Net gain of 2 ATPs 2 electrons handed to each pyruvic acid AND – 4 electrons are removed Handed to 2 molecules of NAD, reducing them Now the NAD is oxidized and can be used again! Glycolysis can go on!

What’s happened to the pyruvic acid? It has been reduced Right! Gain of Electrons is Reduction. The pyruvic acid gained 2 electrons and was reduced. It has been made back into glucose To make glucose, you would have to stick those pyruvic acids back together. It has been oxidized Remember LEO: Loss of Electrons is Oxidation. Did the pyruvic acid lose electrons? It has been destroyed Nope! The molecule is still there, it just has two more electrons than it did before. Restart Questions

What will the H+ ions do? Stay with the NAD Go to the pyruvic acid Hydrogen ions follow electrons. Did the NAD gain or lose electrons? RIGHT! Those H+ will follow the electrons wherever they go. Die? How could you kill an ion? Die Diffuse out of the cell H+ are polar, and cannot diffuse across the cell membrane. Restart Questions

Pyruvic acid + 2 electrons + 2 H+ Lactic acid Have you heard of LACTIC ACID? It’s the stuff that makes your muscles burn when you exercise too hard.

Let’s look at the whole picture…

Two pyruvic acids Making 2 LACTIC ACIDS One glucose Energy released!! Net gain of 2 ATPs 2 electrons handed to each pyruvic acid AND – 4 electrons are removed Handed to 2 molecules of NAD, reducing them NAD is re-oxidized

How will you get rid of the lactic acids? You know that after you exercise that hard, you sit down and pant. You’re doing that to get rid of the lactic acids and the electrons – but that’s another story, Metabolism part 2. You’re done with this tutorial – go back to the menu to try another.

References WavSource: Animals. Sound files for educational use. Retrieved April 3, 2007 from http://www.wavsource.com/animals/animals.htm