Click this link for a Cellular Respiration Student Learning Guide

1. Introduction

If oxygen is present in a cell where respiration is occurring, then glycolysis is followed by a series of reactions that completely oxidize pyruvate (pyruvic acid) and the molecules it gets broken down into. You can see this in steps “2” and “3” in the diagram below.

06_for-every-glucose-w-etc_for-every-glucose-w-etc

Step 2 is called the Link Reaction, because it links glycolysis (which began the oxidation of glucose) with Step 3, the Krebs cycle (which completes this oxidation). By the end of the Krebs Cycle, the food that diffused into the cell in the form of glucose has been completely oxidized to carbon dioxide, the exhaust gas that we exhale. At the same time, the oxidation of food molecules (such as glucose) has generated the reduced, energy–rich, mobile electron carriers NADH and FADH2, which will, in the last phase of cellular respiration, power the creation of ATP through the reactions of the electron transport chain. And if that weren’t enough, substrate level phosphorylations that occur during glycolysis and the Krebs cycle directly create a small amount of ATP that’s immediately available for cellular work.

2. The Link Reaction

The starting compound in the link reaction is pyruvic acid, or pyruvate, the molecule that comes out of glycolysis.

11_very-simplified-glycolysis

As you can see above, two pyruvates are generated for each molecule of glucose that enters glycolysis. Though glucose was pretty worked over during glycolysis, with enzymes using its chemical bond energy to generate two NADHs and two ATPs, pyruvic acid still has plenty of energy that the cell can harvest. That harvest begins in the link reaction, which can be organized into three steps:

01b_link-reaction-numbered-and-lettered

  1. The link reaction begins with pyruvic acid (shown at letter “A”) diffusing into the mitochondrial matrix through the mitochondrial membrane (“B”). As pyruvate enters, enzymes snip off its carboxyl group (which you can see on the left side of the structural formula of pyruvate: it’s the carbon that’s double bonded to one oxygen, and then attached to a second oxygen that has a negative charge). Snipping off the carboxyl group releases a molecule of carbon dioxide (CO2). That CO2 makes up one third of of the CO2 generated in cellular respiration. Think about that the next time you exhale.
  2. In the second step, enzymes take what’s left of pyruvate and oxidize it. The energetic electrons harvested in this oxidation flow to the mobile electron carrier NAD+, reducing it to NADH.
  3. What were left with is a two carbon molecule that’s called an acetyl group (C2H3O). Enzymes attach this acetyl group to Coenzyme A, which acts as a kind of shuttle, delivering the acetyl group to the Krebs cycle. This combination of an acetyl group and Coenzyme A is called acetyl CoA.

The chemical bonds in the acetyl group are full of potential energy. During the Krebs cycle, those bonds will power the formation of ATP, NADH, and FADH2. We’ll study Krebs below, but first, let’s make sure we understand the link reaction.

[qwiz random = “true” qrecord_id=”sciencemusicvideosMeister1961-Link Reaction Quiz (M10)”]

[h]The Link Reaction

[i]

[q labels = “top”]

 

[l]Acetyl-CoA

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

[f*] Good!

[l]Coenzyme A

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

[f*] Good!

[l]CO2

[fx] No. Please try again.

[f*] Excellent!

[l]NADH

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

[f*] Correct!

[l]NAD+

[fx] No. Please try again.

[f*] Great!

[l]Pyruvate

[fx] No. Please try again.

[f*] Excellent!

[l]cytoplasm

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

[f*] Good!

[l]mitochondrial matrix

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

[f*] Correct!

[!]++++Question 2+++[/!!!]

[q]Which letter or number refers to pyruvic acid?

[textentry single_char=”true”]

[c*] A

[f] Yes, “A” is the pyruvic acid.

[c]*

[f]No. Here’s a hint. Pyruvic acid (or pyruvate) is the three carbon molecule that end glycolysis and begins the link reaction

[!]++++Question 3+++[/!!!]

[q]Which letter or number refers to the mitochondrial membrane?

[textentry single_char=”true”]

[c*] B

[f] Yes, “B” is the mitochondrial membrane.

[c]*

[f]No. What’s the only thing in this diagram that remotely looks like it could be a membrane?

[!]++++Question 4+++[/!!!]

[q]Which letter or number refers to co-Enzyme A?

[textentry single_char=”true”]

[c*] C

[f] Yes, “C” is co-Enzyme A.

[c]*

[f]No. Here’s a hint. Co-enzyme A enters the link reaction and binds with the two carbon molecule that’s left after pyruvate has had a CO2 removed from it and has been oxidized (in steps 1 and 2). What do you see coming into the link reaction to bind with the two carbon molecule that remains?

[!]++++Question 5+++[/!!!]

[q]Which letter or number refers to Acetyl CoA?

[textentry single_char=”true”]

[c*] D

[f] Yes, “D” is Acetyl CoA.

[c]*

[f]No. Here’s a hint. Acetyl CoA is a two carbon molecule, attached to Coenzyme A.

[!]++++Question 6+++[/!!!]

[q]Which letter or number refers to the step where molecules from food are oxidized?

[textentry single_char=”true”]

[c*] 2

[f] Yes, “2” involves an oxidation of molecules derived from food (such as glucose). That oxidation is powering the reduction of NAD+ to NADH.

[c]*

[f]No. Here’s a hint. Oxidations are paired with reductions, and the reduced product of the link reaction is NADH.

[!]++++Question 7+++[/!!!]

[q]Which number refers to the step where Acetyl CoA gets produced?

[textentry single_char=”true”]

[c*] 3

[f] Yes. In step “3,” a two carbon acetyl group is attached to Coenzyme A, resulting in acetyl CoA.

[c]*

[f]No. Here’s a hint. Look for a two carbon acetyl group, attached to CoEnzyme A (look for ~S-CoA). Where is this being formed?

[!]++++Question 8+++[/!!!]

[q]In which step are enzymes snipping a carboxyl group off of pyruvic acid?

[textentry single_char=”true”]

[c*] 1

[f] Yes. In step “1,” enzymes are removing a carboxyl group from pyruvic acid.

[c]*

[f]No. Here’s a hint. When that carboxyl group gets removed, a CO2 gets released. Which step releases a CO2?

[!]++++Question 9+++[/!!!]

[q]In which step is a reduced electron carrier being generated?

[textentry single_char=”true”]

[c*] 2

[f] Yes. In step “2” NADH, a reduced electron carrier, is being generated.

[c]*

[f]No. Here’s a hint. The two electron carriers involved in cellular respiration are NADH and FADH2. Where do you see either of these molecules being generated?

[/qwiz]

3. The Krebs Cycle

08_citric-acid
Citric Acid (citrate)

The Krebs cycle lies at the center of aerobic (oxygen-using) metabolism. The cycle goes by three names.

  • Krebs Cycle: for Hans Krebs (1900 – 1981) the scientist who worked out the cycle in the 1930s.  Krebs won the Nobel prize for this work in 1953.
  • Citric Acid Cycle: for the six carbon compound (Citric Acid, or citrate) that forms at the start of the cycle. If you haven’t already, take a look at the structural formula for citric acid to your left.
  • TCA cycle: TCA is an acronym for tri-carboxylic acid, another name for Citric Acid. Look at the structural formula for Citric Acid find the three carboxyl groups.

02a_krebs-simplifiedTo emphasize the key points about the Krebs Cycle, I’ve created the diagram to your left. Note that it includes only three named compounds (which I’ll say more about below). For all of the other primary substrates for the enzymatic reactions that make up the cycle, I’ve listed only the number of carbons that make up the compound. That’s because that’s more than enough detail for AP Biology.

Here are the key things to know. Refer to the diagram as you read.

  1. Acetyl CoA brings chemical energy into the cycle in the form of a two carbon acetyl group. Those two carbons, with their attached hydrogen atoms, were at one point a part of glucose (or another food molecule).
  2. At the start of the Krebs cycle, enzymes detach the two-carbon acetyl group from Acetyl CoA, and attach it to a four-carbon molecule called oxaloacetate (also known as oxalic acid). This is reaction “1” in the diagram above. The result is the six carbon molecule Citric Acid.
  3. The rest of the cycle involves enzymes that do one or more of the following:
    1. molecular rearrangements that change citric acid or its derivatives into other forms that become the substrates for the next reaction. Reactions “2” and “7” are rearrangements.
    2. removing carboxyl groups, resulting in the release of carbon dioxide. You can see removal of CO2s at “3” and “4.” Note that when this occurs, the molecules in the cycle are losing carbon atoms (and hence, 6-carbon molecules become 5-carbon molecules, and 5-carbon molecules become 4-carbon molecules)
    3. Oxidation-Reduction reactions. The food-derived molecules in the cycle are oxidized. These oxidations power the reduction of the electron carriers NAD+ to NADH and FAD to FADH2. Oxidation-reductions occur in reactions “3,” “4,” “6,” and “8.”
    4. Substrate-level phosphorylations:  At one point in the cycle (reaction “5”), enzymes use the chemical energy that was provided by acetyl-CoA to phosphorylate an ADP, creating an ATP that the cell can immediately use for energy.
      09_gtp-as-an-intermediate-in-phosphorylationNote that in a more complex presentation of the cycle, (a tiny piece of which is shown at left) you’d see that at step 5, a molecule called GTP (a compound closely related in structure and function to ATP) gets created before ATP itself appears. It’s a complication that you don’t need to worry about, but you’ll see in in every textbook, website, and diagram. Just know that Krebs directly creates one ATP for every two carbon acetyl group entering the cycle.

Krebs: Six things to memorize

  1. Energy enters the cycle in the form of a two carbon molecule, brought in by acetyl Co-A.
  2. This two carbon molecule combines with a four-carbon molecule called oxalic acid, generating the six-carbon molecule citric acid.
  3. During the course of the cycle, the cell harvests
    1. One ATP
    2. Three NADHs
    3. One FADH2.
  4. Two CO2 are released as a waste product. This accounts for 2/3 of the CO2 produced during cellular respiration (the other third, you’ll remember, was produced in the link reaction).
  5. For every glucose that enters cellular respiration, the Krebs cycle runs twice (because glucose gets broken down to two pyruvates, which become two Acetyl CoAs.
  6. This is all occurring in the mitochondrial matrix.

Got it? Let’s work with these diagrams and some of the key facts to make sure that they become consolidated in memory.

[qwiz qrecord_id=”sciencemusicvideosMeister1961-Krebs Cycle Quiz 1 (M10)”]

[h]The Krebs Cycle Quiz 1

[i]

[!]++++Question 1+++[/!!!]

[q]For every two carbons that acetyl-CoA brings into the cycle, how many FADH2s will the Krebs cycle produce?

[textentry single_char=”true”]

[c*]1

[f] Yes. For every two carbons that acetyl-CoA brings into the cycle, the Krebs cycle will produce one FADH2

[c]*

[f]No. Study the diagram below, and remember the answer when you see this question again.

[!]++++Question 2+++[/!!!]

[q]For every two carbons that acetyl-CoA brings into the cycle, how many NADHs will the Krebs cycle produce?

[textentry single_char=”true”]

[c*]3

[f] Yes. For every two carbons that acetyl-CoA brings into the cycle, the Krebs cycle will produce three NADHs

[c]*

[f]No. Study the diagram below, and remember the answer when you see this question again.

 

[!]++++Question 3+++[/!!!]

[q]For every two carbons that acetyl-CoA brings into the cycle, how many ATPs will the Krebs cycle produce?

[textentry single_char=”true”]

[c*]1

[f] Yes. For every two carbons that acetyl-CoA brings into the cycle, the Krebs cycle will produce one ATP.

[c]*

[f]No. Study the diagram below, and remember the answer when you see this question again.

[!]++++Question 4+++[/!!!]

[q]When acetyl-CoA brings chemical energy into the TCA cycle, how many carbon atoms are being brought in?

[textentry single_char=”true”]

[c*]2

[f] Yes. Acetyl CoA, as it shuttles material into the TCA cycle, is bringing in 2 carbon atoms.

[c]*

[f]No. Study the diagram below, and remember the answer when you see this question again.

[!]++++Question 5+++[/!!!]

[q]Oxaloacetate (or oxalic acid) is the molecule that accepts the carbons that Acetyl CoA brings into the Krebs cycle. How many carbons are in oxaloacetate?

[textentry single_char=”true”]

[c*]4

[f] Yes. Oxaloacetate is a four carbon molecule. By combining with two carbons from Acetyl CoA, it creates the six carbon compound Citric Acid.

[c]*

[f]No. Study the diagram below, and remember the answer when you see this question again.

[!]++++Question 6+++[/!!!]

[q]Citrate (or citric acid) results from the combination of oxaloacetate and the two carbons brought to the Citric Acid cycle by Acetyl CoA. How many carbons are in citrate (or citric acid)?

[textentry single_char=”true”]

[c*]6

[f] Yes. Citric acid is a 6 carbon molecule, formed as enzymes combine the two carbons from Acetyl CoA with the four carbon oxaloacetate.

[c]*

[f]No. Study the diagram below, and remember the answer when you see this question again.

[!]++++Question 7+++[/!!!]

[q]In reaction 3 in the diagram below, NAD+ is being

[c]oxidized

[c*]reduced

[c]phosphorylated

[f]No. NAD+ is gaining electrons. Gain of electrons is the opposite of oxidation.

[f]Yes! NAD+ is gaining electrons and being reduced to NADH.

[f]No. Phosphorylation happens in the Krebs cycle, but not here in reaction 3. What’s the name for the process when a substance gains electrons (as well as hydrogen)?

[!]++++Question 8+++[/!!!]

[q]Reaction 5 in the diagram below involves a(n)

[c]oxidation

[c]reduction

[c*]phosphorylation

[f]No. Oxidation involves loss of electrons. In the Krebs cycle, molecules from food are oxidized so that the electron carriers NAD+ and FAD can  be reduced to NADH and FADH2

[f]No. Reduction involves gain of electrons (and hydrogen). In the Krebs cycle, there are steps where NAD+ and FAD are reduced to NADH and FADH2 (but that’s not happening here in step 5). What’s it called when ADP and Pi are made into ATP through the action of enzymes?

[f]Yes. The reaction shown at step 5 is a substrate level phosphorylation, converting ADP to ATP.

[!]++++Question 9+++[/!!!]

[q]In reaction 6 in the diagram below, FAD is being

[c]phosphorylated

[c]oxidized

[c*]reduced

[f]No. Substrate level phosphorylation involves enzymes adding phosphate to ADP, creating ATP. Here, in step 6, FAD is gaining electrons (and hydrogens). What’s the name for the gain of electrons?

[f]No. Oxidation is the loss of electrons. Something is being oxidized here, but it’s not FAD, which is experiencing the opposite of oxidation. What’s is called when a substance gains electrons (and hydrogen)?

[f]Yes. In step 6, FAD is gaining electrons (and hydrogens), becoming reduced to FADH2.

[!]++++Question 10+++[/!!!]

[q]In reaction 8, molecules originally from food are being

[c]phosphorylated

[c*]oxidized

[c]reduced

[f]No. Phosphorylation involves adding a phosphate group to a substance. In the Krebs cycle, one phosphorylation occurs when ADP is made into ATP, but that’s not what’s happening here. What has to happen to food so that NAD+ can be reduced to NADH?

[f]Yes. In order for NAD+ to be reduced to NADH, food has to be oxidized (which provides the electrons and hydrogens for NAD+ reduction).

[f]No. In step 8, NAD+ is being reduced to NADH. In order for this reduction to happen, what has to be happening to food (in order to provide the electrons and hydrogens for this reduction).

[!]++++Question 11+++[/!!!]

[q]In the diagram below, which number shows where the Krebs Cycle occurs?

[textentry single_char=”true”]

[c*]5

[f] Yes. The Krebs cycle occurs in the mitochondrial matrix, which is at number 5.

[c]*

[f]No. Here’s a hint. The Krebs cycle occurs within the mitochondrial matrix. What number could that be?

[!]++++Question 12+++[/!!!]

[q]Before the link reaction, you’d find pyruvate in which part of the cell?

[textentry single_char=”true”]

[c*]3

[f] Yes. Pyruvate is made during glycolysis, which occurs in the cytoplasm of the cell, shown at number 3.

[c]*

[f]No. Here’s a hint. Pyruvate is generated during the last phase of glycolysis, which occurs in the cell’s cytoplasm. Which number could be the cytoplasm?

[!]++++Question 13+++[/!!!]

[q]In the diagram below, which numbered step shows the link reaction?

[textentry single_char=”true”]

[c*]2

[f] Yes. The Link Reaction is occurring at step 2, as pyruvate enters the mitochondria, gets converted to Acetyl CoA, releases a CO2 and generates one NADH.

[c]*

[f]No. Here’s a hint. The link reaction links glycolysis and the Krebs cycle. Which step provides a link between those two processes?

[!]++++Question 14+++[/!!!]

[q]In the diagram below, which number would be the Krebs cycle?

[textentry single_char=”true”]

[c*]3

[f] Yes. The Krebs cycle is at number 3.

[c]*

[f]No. Here’s a hint. Which of the processes shown in this diagram could possibly be a cycle?

[!]++++Question 15+++[/!!!]

[q]For each molecule of glucose that enters cellular respiration, which of the processes below generates the most NADH?

[c]glycolysis

[c]link reaction

[c*]Krebs cycle

[c]electron transport chain

[f]No. Glycolysis generates only two NADHs/glucose. Study the diagram below and remember your answer the next time you see this question.

[f]No. The link reaction generates one NADH/pyruvate, and two NADHs/glucose. Study the diagram below and remember your answer the next time you see this question.

[f]Yes. The Krebs cycle generates more NADH/glucose than any other phase of cellular respiration.

[f]No. Electron transport chain doesn’t produce NADH: it consumes it. Study the diagram below and remember your answer the next time you see this question.

[x][restart]

[/qwiz]

4. Interactive Diagram: Products of the Krebs Cycle

The diagram below is a bit more detailed than anything you’ve seen before on this page. But you can figure it out by following these hints:

  1. If a molecule within the cycle is losing a hydrogen, then it’s being oxidized, and it can power the reduction of NAD+ to NADH.
  2. If a molecule loses a carboxyl group, then it’s almost certainly releasing a CO2.
  3. At one point in the cycle, one of the substrates loses two hydrogens. That loss enables the reduction of an FAD to FADH2.
  4. ATP is made from ADP in two steps. First, a related molecule (GTP) is synthesized from its counterpart, GDP. Then GTP powers ATP creation. See if you can figure it out.

DON’T WORRY ABOUT MAKING MISTAKES!

[qwiz qrecord_id=”sciencemusicvideosMeister1961-Products of the Krebs Cycle Interactive Diagram”]

[h]Products of the Krebs Cycle interactive diagram

[q labels = “top”]

 

[l]NAD+ 

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

[f*] Correct!

[l]NADH

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

[f*] Correct!

[l]CO2

[fx] No. Please try again.

[f*] Great!

[l]FADH2 

[fx] No. Please try again.

[f*] Good!

[l]GDP

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

[f*] Correct!

[l]GTP

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

[f*] Correct!

[l]ADP

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

[f*] Great!

[l]ATP

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

[f*] Good!

[l]FAD

[fx] No. Please try again.

[f*] Great!

[/qwiz]

5. Krebs and Link Reaction Fill in the Blanks Quiz

[qwiz qrecord_id=”sciencemusicvideosMeister1961-Krebs and Link Fill-in-the-Blanks (M10)”]

[h]Krebs Cycle and Link Reaction Fill-in-the-Blanks Quiz

[i]

[!!!]Card  1[/!!!!]

[q topic = “krebs cycle”] The Krebs cycle occurs in the _____ of the mitochondria

[hangman]

[c]matrix

[f]Yes! The Krebs cycle occurs in the matrix of the mitochondria

[q topic = “krebs cycle”]The Krebs cycle makes the _____ carriers NADH and FADH2

[hangman]

[c]electron

[f]Yes! The Krebs cycle makes the electron carriers NADH and FADH2

[!!!]Card  4[/!!!!]

[q topic = “krebs cycle”]The Krebs cycle makes the electron carriers _____ and FADH2

[hangman]

[c]NADH

[f]Correct! The Krebs cycle makes the electron carriers NADH and FADH2

[!!!]Card  7[/!!!!]

[q topic = “krebs cycle”]Krebs is also known as the _____ acid cycle

[hangman]

[c]Citric

[f]Perfect! Krebs is also known as the Citric acid cycle

[!!!]Card  10[/!!!!]

[q topic = “krebs cycle”]Each turn of the Krebs cycle produces one ATP, three NADH, and _____ FADH2.

[hangman]

[c]one

[f]Great! Each turn of the Krebs cycle produces one ATP, three NADH, and one FADH2.

[!!!]Card  13[/!!!!]

[q topic = “krebs cycle”]The link reaction converts _____ acid to Acetyl-CoA.  Carbon dioxide is released as a waste product, and one NADH is produced.

[hangman]

[c]pyruvic

[f]Nice! The link reaction converts pyruvic acid to Acetyl-CoA.  Carbon dioxide is released as a waste product, and one NADH is produced.

[!!!]Card  16[/!!!!]

[q topic = “krebs cycle”]The link reaction converts pyruvic acid to Acetyl-CoA.  Carbon dioxide is released as a _____, and one NADH is produced.

[hangman]

[c]waste product

[f]Good job! The link reaction converts pyruvic acid to Acetyl-CoA.  Carbon dioxide is released as a waste product, and one NADH is produced.

[!!!]Card  19[/!!!!]

[q topic = “krebs cycle”]Acetyl-CoA carries _____ carbon atoms into the Krebs cycle

[hangman]

[c]two

[g]Fantastic! Acetyl-CoA carries two carbon atoms into the Krebs cycle

[!!!]Card  22[/!!!!]

[q topic = “krebs cycle”]The chemical energy brought into Krebs by acetyl Co-A was originally energy in ________

[hangman]

[c]food

[f]Awesome! The chemical energy brought into Krebs by acetyl Co-A was originally energy in food.

[!!!]Card  28[/!!!!]

[q topic = “krebs cycle”]At the start of Krebs Acetyl-CoA’s two carbons combine with oxaloacetate, a _____ carbon molecule

[hangman]

[c]four

[f]Yes! At the start of Krebs Acetyl-CoA’s two carbons combine with oxaloacetate, a four carbon molecule.

[!!!]Card  43[/!!!!]

[q topic = “krebs cycle”]During the Krebs cycle, three oxidations power the creation of the electron carrier _______

[hangman]

[c]NADH

[f]Good job! During the Krebs cycle, three oxidations power the creation of the electron carrier NADH.

[!!!]Card 61[/!!!!]

[q topic = “krebs cycle”]The final oxidation reaction in Krebs results in reduction of NAD+, and leaves us with the _____ carbon molecule oxaloacetate.

[hangman]

[c]four

[f]Perfect! The final oxidation reaction in Krebs results in reduction of NAD+, and leaves us with the four carbon molecule oxaloacetate.

[!!!]Card 64[/!!!!]

[q topic = “krebs cycle”]Overall, Krebs produces three NADH, _____ FADH2, and one ATP

[hangman]

[c]one

[f]Great! Overall, Krebs produces three NADH, one FADH2, and one ATP

[!!!]Card  11[/!!!!]

[q topic = “krebs cycle”]The link reaction links _____ to the Krebs Cycle

[hangman]

[c]glycolysis

[f]Correct! The link reaction links glycolysis to the Krebs Cycle

[!!!]Card  17[/!!!!]

[q topic = “krebs cycle”]The link reaction converts pyruvic acid to Acetyl-CoA.  Carbon dioxide is released as a waste product, and one _____ is produced.

[hangman]

[c]NADH

[f]Great! The link reaction converts pyruvic acid to Acetyl-CoA.  Carbon dioxide is released as a waste product, and one NADH is produced.

[!!!]Card  32[/!!!!]

[q topic = “krebs cycle”]Combining Acetyl-CoA with oxaloacetate creates six-carbon _____ acid.

[hangman]

[c]citric

[f]Genius! Combining Acetyl-CoA with oxaloacetate creates six-carbon citric acid.

[!!!]Card 71[/!!!!]

[q topic = “krebs cycle”]During Krebs _____ molecules of carbon dioxide are released as exhaust.

[hangman]

[c]two

[f]Great! During Krebs two molecules of carbon dioxide are released as exhaust.

[x][restart]

[/qwiz]

6. Krebs Cycle Interactive Lyrics

Ok: You’ve watched the video and heard the song. Now read through the lyrics, dragging in words as needed. Why? Research shows that adding this little bit of interactivity will increase your memory of what you read. Give it a try!

[qwiz qrecord_id=”sciencemusicvideosMeister1961-Krebs Interactive Lyrics (M10)”]

[h]Interactive Lyrics: Krebs Cycle

[i]

[q labels = “top”]

In the _______ of the mitochondria of all our cells
Is the cycle of reactions that won Hans Krebs the Nobel Prize
This cycle takes the ______ in food
And makes it into other forms that your cells can use.

Krebs Cycle makes the electron carrier ______
Which later brings _________ to the electron transport chain.
And Krebs makes FADH2 its function is the same,
Krebs also makes some ATP another claim to fame.

[l]electrons

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

[f*] Great!

[l]energy

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

[f*] Great!

[l]matrix

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

[f*] Correct!

[l]NADH

[fx] No. Please try again.

[f*] Great!

[q labels = “top”]

CHORUS

(we’re talking) KREBS!
It’s the ______ Acid Cycle
KREBS!
Tricarboxylic Acid Cycle
Krebs– each cycle makes
_____ ATP, _____ NADH, one FADH2

[l]Citric

[fx] No. Please try again.

[f*] Great!

[l]one

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

[f*] Correct!

[l]three

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

[f*] Excellent!

[q labels = “top”]

Right before the cycle’s a transitional part
Links Krebs to glycolysis, so Krebs can start
Enzymes break a CO2 off a ________
Yields an NADH and ___________

 

Acetyl-CoA carries _________ two
With all the energy that derives from food
It’s a highly ________ molecule with energized electrons
It fuels up the Krebs cycle as it cycles on.

[l]Acetyl-CoA

[fx] No. Please try again.

[f*] Excellent!

[l]carbons

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

[f*] Good!

[l]Pyruvate

[fx] No. Please try again.

[f*] Great!

[l]reduced

[fx] No. Please try again.

[f*] Excellent!

[q labels = “top”]

Now at the start of Krebs this Acetyl-CoA
Has the two carbons it carries in ripped away
Enzymes put these on ____________ with carbons four,
Makes ___________ citric acid who could ask for more?

 

Notice ______ carboxyl groups on that citric acid
It’s why the cycle’s also named for ____________ Acid
Or TCA Cycle, if it’s acronyms that you prefer
Or Krebs in honor of its discoverer!

CHORUS

[l]oxaloacetate

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

[f*] Excellent!

[l]six-carbon

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

[f*] Good!

[l]three

[fx] No. Please try again.

[f*] Excellent!

[l]Tricarboxylic

[fx] No. Please try again.

[f*] Great!

[q labels = “top”]

Enzymes work on Citric Acid and remove a _____
and other enzymes modify and oxidize it too,
The five carbon result is ________________.
Krebs cycle, it’s so great!

 

Every oxidation, can power the reduction,
of NAD plus which gains electron carrying function,
Becoming ________, that energy sensation
Which later on in respiration powers _____ creation

[l]?-Ketoglutarate

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

[f*] Correct!

[l]ATP

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

[f*] Excellent!

[l]CO2

[fx] No. Please try again.

[f*] Correct!

[l]NADH

[fx] No. Please try again.

[f*] Great!

[q labels = “top”]

Another __________ follows, another  CO2 removed
Leaving us with a _____ carbon molecule
Another ______ results from this oxidation
As Krebs does its energy transformations

 

This four carbon molecule (Succinyl CoA),
Still has lots of energy, enzymes can take away
A series of reactions yield one _____
The cell’s main energy currency.

[l]ATP

[fx] No. Please try again.

[f*] Good!

[l]four

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

[f*] Great!

[l]NADH

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

[f*] Correct!

[l]oxidation

[fx] No. Please try again.

[f*] Great!

[q labels = “top”]

Leavin’ just enough energy for enzymes to reduce
An FAD to _______
And one last ______ will also get reduced
As the final ‘lectron carrier NADH gets produced.

 

We’ve harvested what energy came in at Krebs’s start,
Now we have ____________ at this final part
Oxaloacetate is the commencement and finale
Ready to meet _______ CoA, and here at the final tally

[l]acetyl

[fx] No. Please try again.

[f*] Great!

[l]FADH2

[fx] No. Please try again.

[f*] Excellent!

[l]NAD+

[fx] No. Please try again.

[f*] Excellent!

[l]oxaloacetate

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

[f*] Correct!

[q labels = “top”]

BRIDGE

______ goes round and round, such an ancient cycle,
Spinning like the wheels of my bicycle.
Krebs is like the axle of ________ respiration,
I breathe out its CO2 with every exhalation!

 

We’ve walked through the cycle, so now lets review
Input is ___________ with carbons two
The carbons get removed, releasing _____
Exhaling sends this CO2 out of you.

[l]Acetyl-CoA

[fx] No. Please try again.

[f*] Correct!

[l]aerobic

[fx] No. Please try again.

[f*] Great!

[l]CO2

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

[f*] Great!

[l]Krebs

[fx] No. Please try again.

[f*] Good!

[q labels = “top”]

The cycle’s function’s energy transformation
Three ______, one _______ creation
And also synthesis of one _____
Which cells directly utilize for energy

 

For every glucose cells absorb the cycle runs _____ times
As long as cells get fuel, Krebs is running just fine,
It precedes electron transport chain, it follows __________
It’s spinning round and round in the mitochondrial matrix

[l]ATP

[fx] No. Please try again.

[f*] Great!

[l]FADH2

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

[f*] Good!

[l]glycolysis

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

[f*] Great!

[l]NADH

[fx] No. Please try again.

[f*] Excellent!

[l]two

[fx] No. Please try again.

[f*] Correct!

[/qwiz]

Links

    1. The Electron Transport Chain Tutorial (the next tutorial in this series)
    2. Cellular Respiration Tutorials Menu