Click this link for a Cellular Respiration Student Learning Guide

1. ATP is at the center of biology

If there was a prize for the most important biological molecule, you might want to consider nominating ATP, which stands for adenosine triphosphate.

ATP: Adenosine Triphosphate

There is so much about ATP that’s remarkable. It’s a nucleotide monomer. The “A” in “ATP” stands for adenosine, parts “1” and “2” above. “1” is the five carbon sugar ribose (remember that in this type of structural formula there’s a carbon at every angle vertex). Number “2” is the nitrogenous base adenine: one of the letters of the code of life.

When you think of nucleotides,  you might think “information,” since that’s the role that nucleotide polymers like DNA and RNA play in living systems. Genetic instructions are encoded as nucleotide sequences. ATP is one of the nucleotides monomers of RNA. RNA is often neglected in favor of DNA, but RNA has a versatility that DNA lacks. Both RNA and DNA can encode genetic information. Only RNA can transmit that information throughout the cell, and, in its various enzymatic roles, translate that information into action.

So the fact that ATP is one of four letters of the genetic alphabet would be enough. But ATP is also life’s energy carrier. And that’s going to be our focus throughout this entire unit. We’ll start by looking at how, on the shortest timespans, ATP (along with its counterpart, ADP) is how living things store free energy, and then release free energy as they perform the work of life. When you eat, you’re eating for two reasons: 1) to replenish the molecules you’re made of, and 2) to fuel the production of ATP. When you move, you’re doing it through transferring ATP’s third phosphate group (the outermost one in #3, above) to a protein. That transfer enables the protein to grab onto a neighboring fiber and bend. Bending shortens the muscle fiber. When you think, some network of neural impulses is creating a pattern that gets experienced as thought. That neural impulse is only possible because of a membrane pump that uses energy from ATP to pump sodium ions outside of the membrane of nerve cells, and potassium ions into the cytoplasm of these cells. This is an active transport process. It takes energy. And that energy comes from ATP.

So ATP’s roles include transferring energy and encoding biological information. But there’s even more. When cells need to respond to messages received from outside the cell, they do this through a second messenger system that’s based on a modified form of ATP called cyclic AMP. The “M” in “AMP” stands for “mono”, and notice the single phosphate group that’s connected to ribose. 

800px-cyclic-adenosine-monophosphate-2d-skeletal
Cyclic AMP (from Wikipedia)

So, energy, information, and cellular response. As I said above, ATP is quite a good candidate for “most important molecule” of all time. Below, we’ll see how it works as an energy currency. But first, let’s check to see how much you retained from what’s above.

[qwiz random = “true;” style “width = 540px” qrecord_id=”sciencemusicvideosMeister1961-ATP Quiz 1 (M10)”]

[h]ATP is at the center of biology: Quiz

[i]

[q labels = “top”]Let’s try some labeling.

 

[l]adenine (nitrogenous base)

[fx] No. Please try again.

[f*] Great!

[l]three phosphate groups

[fx] No. Please try again.

[f*] Excellent!

[l]ribose sugar

[fx] No. Please try again.

[f*] Great!

[!]question 1 [/!]

[q]In a nucleotide polymer, this part is one of the four letters

[textentry single_char=”true”]

[c*]2

[f]Yes. “2” is adenine, one of the four letters of the genetic alphabet (A, T, C, G in DNA; A, U, C, G in RNA)

[c]*

[f]No. Look for the nitrogenous base. Just think about which part could possibly be described as “nitrogenous.”

[!]question 2 [/!]

[q]Which part is the sugar ribose?

[textentry single_char=”true”]

[c*]1

[f]Yes. “1” is the sugar ribose.

[c]*

[f]No. Sugars typically have a hexagonal (six sided) or pentagonal (5 sided) structure. Which of the numbered parts above looks like a sugar?

[!]question 3[/!]

[q]Which part is involved in energy transfer?

[textentry single_char=”true”]

[c*]3

[f]Yes. The phosphate groups at “3” are where and how ATP stores and releases energy.

[c]*

[f]No. It’s the phosphate groups that play this role. Which is the only part that could possibly be a phosphate group?

[!]question 4[/!]

[q]ATP is a nucleotide __________

[hangman]

[c]monomer

[f]Yes. ATP is a nucleotide monomer.

[!]question 5[/!]

[q]Which molecule below is ATP?

1 2 3

[textentry single_char=”true”]

[c*]3

[f]Yes. The three phosphate groups at “3” make this molecule “ATP,” or adenosine triphosphate.

[c]*

[f]No. Count the number of phosphate groups attached to each molecule. What does the “T” in “ATP” stand for?

[!]question 6[/!]

[q]ATP (in a slightly modified form) also serves as one of the “letters” in which of the following polymers?

[c]DNA

[c*]RNA

[c]protein

[c]polysaccharides

[f]No, but you’re very close. ATP is a monomer of one of the nucleotide polymers, but not DNA (the one you’re possibly most familiar with). What’s the other nucleotide polymer.

[f]Correct! ATP (in a slightly modified form) also serves as one of the letters of RNA.

[f]No. The letters that make up protein are amino acids. It’s one to the two informational nucleotides on the list.

[f]No. Polysaccharides are carbohydrate polymers. They’re made of monomers, but the “letter” notion really doesn’t apply to them. Make another choice when you see this question again.

[x]

[restart]

[/qwiz]

2. Releasing chemical energy through combustion

03_Streichholz
Combustion: “Streichholz” by Heidas – Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons

Before we examine how ATP stores and releases energy, let’s take a look at how chemical energy gets released in some systems that aren’t alive, where what happens is much simpler.

One way to release stored chemical energy is combustion. Combustion is what happens when wood burns:

 WOOD +  oxygen –>  energy (heat and light) + carbon dioxide + water

What this means is that the molecules in the wood combine with oxygen in the air. This releases heat and light energy, along with two waste products: carbon dioxide (CO2) and water (H2O). Carbon dioxide is a colorless and odorless gas. The water released is in the form of water vapor, or steam.

Exhaust from a car’s tailpipe. What you see is mostly water vapor. The carbon dioxide is invisible. Source: “Automobile exhaust gas” by Ruben de Rijcke – Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons

Burning gasoline in a car is also combustion.

 Gasoline +  oxygen –>  energy (heat) + carbon dioxide + water

The car’s engine transforms the heat into kinetic energy (motion). If you stand behind a car on a cold day, you can see the water released as steam going into the air.

Let’s see if you can complete the missing parts in the chemical reaction below.

[qwiz qrecord_id=”sciencemusicvideosMeister1961-Combustion, Checking Understanding”]

[h]Checking Understanding: Combustion

[!!!]question 1 [/!!!]

[q labels = “top”]Note: not every term below has to be used to answer this question.

 

_______ + oxygen –>  energy (heat) + ________ + water

[l]energy

[fx] No. Please try again.

[f*] Great!

[l]CO2

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[l]fuel

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[!!!]question 2 [/!!!]

[q labels = “top”]

 FUEL +  _________ –>  energy + carbon dioxide + _______

[l]oxygen

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]water

[fx] No, that’s not correct. Please try again.

[f*] Good!

[/qwiz]

3. In cells, food energy gets transformed into ATP

simple-ATP
Adenosine triphosphate: ATP (simplified structure)

In a car, the engine combusts a fuel like gasoline, transforming the chemical energy in the fuel into heat. Then the heat is transformed into kinetic energy: energy of motion.

In living cells, things are more complex. In animals like us, the fuel comes from food, and to make the energy in food available for cellular work, cells first have to transfer the chemical bond energy in the molecules in the food we eat into the chemical bond energy in one of ATP’s chemical bonds: the bond indicated by “A” below, which holds ATPs third phosphate group to its second phosphate group.

ATP with letters on phosphate bonds

Why? Note that each phosphate group consists of one phosphorus atom surrounded by oxygen atoms. As you can see in the diagram, the oxygen shown on the bottom of each phosphate has a negative charge. Negative charges repel one another. In other words, each of these phosphate groups is simultaneously bonded to the others, but also pushing away.

Almost all of the energy transfer in living things is catalyzed by enzymes (which you can learn more about in my enzyme tutorial and song). A typical enzymatic move in order to get some work done for the cell involves breaking off the last phosphate in ATP, and attaching that phosphate onto another molecule. Breaking the bonds that holds the last phosphate onto ATP requires only a small amount of energy. Attaching the phosphate onto another molecule, however, releases enough energy to make the overall reaction have a negative ?G. And that’s how the work of life takes place. It’s how you move your muscles. It’s how your nerve cells set themselves up to send impulses, which allows you to do the thinking about ATP that you’re doing now.

4. The ATP/ADP cycle is how cells release and store energy

To repeat: when a cell needs to release a bit of energy to get some work done, it will,  through the action of an enzyme, break off the last phosphate in ATP, and place that phosphate onto another molecule. This releases a small amount of energy, and transforms ATP into its counterpart, ADP.

Here’s the structure of ATP and ADP, side by side. ADP stands for Adenosine di-phosphate, and as you can see below, it has two phosphate groups. Note that the last phosphate group in ATP or ADP can be shown either in an ionized (charged form) or an unionized (uncharged form). Below, ATP is shown in its uncharged form (with an -OH group on its last phosphate). ADP is shown in its charged form (note the oxygen with a minus sign). In textbooks and tests you can see either form, so get used to seeing both.

You can think of ADP as a rechargeable battery that has run out of electrical energy. ATP, with its three phosphates, is like a fully charged up battery, ready to power whatever it is that a cell needs to do.

ATP and ADP are linked in a cycle. See if by analyzing what you see below you can figure out the parts.

[qwiz qrecord_id=”sciencemusicvideosMeister1961-ATP-ADP Cycle, Interactive Diagram”]

[h]Interactive Diagram: ATP/ADP Cycle

[q labels = “top”]

 

[l]ADP

[fx] No. Please try again.

[f*] Correct!

[l]ATP

[fx] No. Please try again.

[f*] Excellent!

[l]Energy from food

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]Energy released for work

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]Phosphate group

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[/qwiz]

Cells convert ATP into ADP and phosphate in order to do some work. For example, when you’re kicking a ball, the contraction of your muscles is powered by conversion of trillions of ATPs into ADP and phosphate. And this is made possible by the food you eat, which powers the creation of ADP and P into ATP.

5. Checking Understanding

In the next unit, we’ll start to look at how cells make ATP in more detail. But for now, make sure you’ve got the big picture by taking the quiz below.

[qwiz random = “true” qrecord_id=”sciencemusicvideosMeister1961-Combustion, ATP, ADP (M10)”]

[h]Quiz: Combustion, ATP, ADP

[!!!!!!] question 1 +++++++++[/!!!!!!]
[q topic= “ATP”]When you strike a match, the chemical energy in the match is released in the form of

[c] ADP

[c*] Heat and light

[c] carbon dioxide

[f] No. Striking a match is an example of combustion. ADP is produced when ATP is used by cells. What do you see and feel from a lighted match?
[f] Correct. This is an example of combustion, and the energy is released as heat and light.
[f] No. Carbon dioxide is one of the waste products of a combustion reaction, but it’s not energy – it’s an exhaust product. What do you see and feel from a lighted match?

[!!!!!!] question 2 +++++++++[/!!!!!!]
[q topic= “ATP”]In living things, the chemical energy in food is transformed into

[c*] the chemical energy in ATP

[c] Heat and light

[c] carbon dioxide

[f] Yes. Living things have to transfer the energy in foods (such a glucose) into the energy in ATP.
[f] No. Production of heat and light is what happens when a fuel is burned. But that’s not what happens in living things.
[f] No. Carbon dioxide is one of the waste products of a cellular respiration, which is the process that cells use to get energy from food. But carbon dioxide is a waste product. Look for something that cells can use to power their life processes.

[!!!!!!] question 3 +++++++++[/!!!!!!]
[q topic= “ATP”]In this diagram of ATP, the phosphate groups are shown at

[c] 1

[c] 2

[c*] 3

[f] No. Number 1 is the sugar, ribose. To find the phosphate groups, look for the chemical symbol for phosphorus, ‘P.’
[f] No. Number 2 is the nitrogenous base, adenine. To find the phosphate groups, look for the chemical symbol for phosphorus, ‘P.’
[f] Yes. Number 3 refers to the phosphate groups, which is where ATP stores its energy.

[!!!!!!] question 4 +++++++++[/!!!!!!]
[q topic= “ATP”]In this diagram of ATP, the nitrogenous base adenine is found at

[c] 1

[c*] 2

[c] 3

[f] No. Number 1 is the sugar, ribose. To find the nitrogenous base adenine, look for the nitrogen-containing rings. ‘N’ is the symbol for nitrogen.
[f] Yes! Number 2 is the nitrogenous base, adenine.
[f] No. Number 3 refers to the phosphate groups, which is where ATP stores its energy. To find the nitrogenous base adenine, look for the nitrogen-containing rings. ‘N’ is the symbol for nitrogen.

[!!!!!!] question 5 +++++++++[/!!!!!!]
[q topic= “ATP”]In this diagram of ATP, the sugar ribose is found at

[c*] 1

[c] 2

[c] 3

[f] Yes. Number 1 is the sugar, ribose, which you can identify by its pentagonal shape.
[f] No. Number 2 is the nitrogenous base, adenine. You can identify the sugar ribose by its pentagonal shape.
[f] No. Number 3 refers to the phosphate groups, which is where ATP stores its energy. You can identify the sugar ribose by its pentagonal shape.

[!!!!!!] question 6 +++++++++[/!!!!!!]
[q topic= “ATP”]In this diagram of ATP, the part that contains chemical bonds that are broken down for energy is

[c] 1

[c] 2

[c*] 3

[f] No. Number 1 is the sugar, ribose. In ATP, it’s the last phosphate group that gets broken off the molecule to release energy for cellular work. Which number is pointing to the phosphate groups?
[f] No. Number 2 is the nitrogenous base, adenine. In ATP, it’s the last phosphate group that gets broken off the molecule to release energy for cellular work. Which number is pointing to the phosphate groups?
[f] Yes. Number 3 refers to the phosphate groups, which is where ATP stores its energy. By breaking off the last phosphate group, cells release energy for cellular work.

[!!!!!!] question 7 +++++++++[/!!!!!!]
[q topic= “ATP”]When ATP is converted to ADP and Phosphate, which chemical bond is broken?

[c*] A

[c] B

[c] C

[f] Yes. Breaking the bond at ‘A’ converts ATP to ADP and phosphate, releasing energy for cellular work.
[f] No. To convert ATP to ADP and phosphate, the outermost phosphate group is broken off. Which bond would have to break in order to release the outermost phosphate group?
[f] No. To convert ATP to ADP and phosphate, the outermost phosphate group is broken off. Which bond would have to break in order to release the outermost phosphate group?

[!!!!!!] question 8 +++++++++[/!!!!!!]
[q topic= “ATP”]Which molecule shown below is ADP?

[c] 1

[c*] 2

[f] No. ADP is short for ‘adenosine di-phosphate.’ The ‘di’ stands for two, and refers to the two phosphate groups. Which of these two molecules has TWO phosphate groups?
[f] Yes. Molecule 2 is ADP, which you can identify by its two phosphate groups.

[!!!!!!] question 9 +++++++++[/!!!!!!]
[q topic= “ATP”]Which molecule below has more stored chemical energy?

[c*] 1

[c] 2

[f] Yes. ATP, with its three phosphate groups, has more stored chemical energy than does ADP.
[f] No. In the ATP-ADP system, having three phosphate groups means having more energy than having two. Next time, choose ATP, which has three phosphate groups.

[!!!!!!] question 10 +++++++++[/!!!!!!]
[q topic= “ATP”]When a cell needs to release a small amount of energy, it converts

[c*] ATP to ADP and phosphate

[c] ADP and phosphate to ATP

[f] Yes. Conversion of ATP to ADP and phosphate releases energy for cellular work.
[f] No. Converting ADP and phosphate to ATP is how cells STORE energy. How do cells release energy?

[!!!!!!] question 11 +++++++++[/!!!!!!]
[q topic= “ATP”]When a cell needs to store a small amount of energy, it converts

[c] ATP to ADP and phosphate

[c*] ADP and phosphate to ATP

[f] No. Conversion of ATP to ADP and phosphate releases energy.
[f] Yes. Converting ADP and Phosphate to ATP is how cells store energy.

[!!!!!!] question 12 +++++++++[/!!!!!!]
[q topic= “ATP”]In this diagram of the ATP-ADP cycle, which letter represents energy release?

[c] A
[c*] B

[f] No. Letter A shows ADP and Phosphate being converted into ATP, which is how cells store energy for cellular work.
[f] Yes. Letter B shows conversion of ATP to ADP and phosphate, which is how cells release energy for cellular work.

[!!!!!!] question 13 +++++++++[/!!!!!!]
[q topic= “ATP”]Which of the following best describes the flow of energy in cells performing cellular respiration?

[c] Food to ADP to cell work

[c] food directly to cell work

[c] ATP to food

[c*] food to ATP to cell work

[f] No. ADP isn’t the molecule that’s broken down for cell work. Find a path where ATP precedes cell work.
[f] No. Cells have to convert food energy to ATP before they can perform work. Find a path where ATP precedes cell work.
[f] No. In cellular respiration, food is used to make ATP. Find a path where ATP precedes cell work.
[f] Yes. For cells to have the type of energy they need to perform work, they must first convert the chemical energy in food into the chemical energy in ATP, which they can then use to perform cellular work .

[x]

[restart]
[/qwiz]

Next Moves