1. Glycolysis: A Musical Introduction

I’ve written a song about glycolysis that covers just about everything an AP Biology student needs to know.

2.Eight things to know about glycolysis

Now that you’ve watched the video, take the quiz below.

[qwiz]

[h]Eight things to know about glycolysis

[i]

[q labels = “top”]

1. Glycolysis is the _______ stage of cellular respiration.

2. It occurs in the cell’s _____________.

3. Glucose, a molecule with _____ carbons, is the starting compound.

4. Glycolysis means “__________ sugar.” During glycolysis, glucose gets split apart into two ______-carbon molecules.

5. The process involves _______ reactions that power the reduction of the mobile _________ carrier ______ into ______.

6. The chemical energy in glucose is also used to power two
_____________ -level phosphorylations, resulting in the production of two molecules of  _________.

7. The net yield is production of _____ molecules of ATP, and two molecules of _________.

8. In addition to ATP and NADH, the final product of glycolysis is two molecules of _________ acid, also known as _________. This molecule contains ________ carbon atoms,
and still has plenty of potential ____________ energy to power the next stages of cellular respiration.

[l]ATP

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

[f*] Great!

[l]chemical

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

[f*] Excellent!

[l]cytoplasm

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

[f*] Great!

[l]electron

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

[f*] Good!

[l]first

[fx] No. Please try again.

[f*] Correct!

[l]NAD+

[fx] No. Please try again.

[f*] Excellent!

[l]NADH

[fx] No. Please try again.

[f*] Correct!

[l]pyruvate

[fx] No. Please try again.

[f*] Correct!

[l]pyruvic

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

[f*] Great!

[l]redox

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

[f*] Correct!

[l]six

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

[f*] Good!

[l]splitting

[fx] No. Please try again.

[f*] Good!

[l]substrate

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

[f*] Excellent!

[l]three

[fx] No. Please try again.

[f*] Good!

[l]two

[fx] No. Please try again.

[f*] Great!

 

[q]Glycolysis is the first stage of cellular [hangman]. It occurs in the cell’s [hangman]

[c]cmVzcGlyYXRpb24=[Qq]

[c]Y3l0b3BsYXNt[Qq]

[q]The net yield of glycolysis is two molecules of [hangman], which is a molecule that can immediately be used for cellular work. The other product is the electron carrier [hangman]

[c]QVRQ[Qq]

[c]TkFESA==[Qq]

[q]Glycolysis means [hangman] sugar.

[c]c3BsaXR0aW5n[Qq]

[/qwiz]

3. Glycolysis: A bit more detail

Let’s walk through the process in a bit more detail. In the diagram below, every arrow represents a chemical reaction catalyzed by a specific enzyme.  Note that what’s below (however complex it might look) is still highly simplified.

04_glycolysis-partially-numbered

The reactions of glycolysis can be organized into three phases.

3a. Phase 1 is the investment phase.

05a_glycolysis-investment-clarified
Glucose (“A”) enters glycolysis. Enzymes (indicated by arrows) phosphorylate glucose (giving it a phosphate) by removing a phosphate group from ATP (shown above “B”), which becomes ADP. The new compound at “C” is called glucose-6-phosphate: a glucose with a phosphate attached to its sixth carbon. In later reactions (shown at “D”), enzymes rearrange glucose-6-phosphate to fructose, and add another phosphate group, creating fructose-1-6-diphosphate (“E”). This costs the cell a second ATP (shown becoming ADP above “D”). This investment sets the stage for the next two phases.

3b. Phase Two is Cleavage

06_glycolysis-cleavageFructose-1-6-diphosphate (“E”) is the substrate for enzymes which, in the next phase, break this six-carbon molecule into two three-carbon molecules. A bit of enzymatic interconversion (not shown) leaves us with two molecules of glyceraldehyde-3-phosphate, or G3P, shown at “F.”

3c. Phase Three is Energy Harvest

07_glycolysis-harvestDuring this third and last phase of glycolysis, enzymes harvest energy from G3P (“F”), the three-carbon molecule which resulted from splitting fructose-1-6-diphosphate during the cleavage phase. At “G” enzymes oxidize G3P, and transfer electrons and hydrogen atoms to NAD+, which reduces NAD+ to NADH. NADH, you’ll remember, is a mobile electron carrier. Later in glycolysis, it will carry electrons over to the electron transport chain, which is where most of the ATP in cellular respiration is created. Other enzymes will continue to rearrange G3P in ways that enable this molecule (and the molecules it gets made into) to power two substrate-level phosphorylations, creating ATP from ADP.

At the end of this harvest, we’re left with a three-carbon compound called pyruvic acid, or pyruvate (shown at “I”). Despite all of the oxidations and rearrangements that have occurred along the way, pyruvic acid still has lots of potential chemical energy, which will be harvested in later phases of cellular respiration.

4. Glycolysis: Checking Understanding

[qwiz random=”true”]

[h]Glycolysis: Checking Understanding

[i]

[q]Which letter or number indicates the “investment” phase?

[textentry single_char=”true”]

[c]ID E=[Qq]

[f]IFllcywg4oCcMeKAnSBpcyB0aGUgaW52ZXN0bWVudCBwaGFzZS4=[Qq]

[c]Kg==[Qq]

[f]Tm8uIEhlcmUmIzgyMTc7cyBhIGhpbnQuwqBUaGUgaW52ZXN0bWVudCBwaGFzZSBpcyB3aGVuIGVuZXJneSBpcyB1c2VkIGJ5IHRoZSBjZWxsLiBBIHR5cGljYWwgd2F5IHRoaW5nIHRoYXQgaGFwcGVucyB3aGVuIGNlbGxzIHVzZSBlbmVyZ3kgaXMgdGhhdCBBVFAgZ2V0cyBjb252ZXJ0ZWQgdG8gQURQLiBXaGVyZSBkbyB5b3Ugc2VlIHRoaXMgaGFwcGVuaW5nPw==

Cg==

[Qq]

[q]Which letter or number indicates the “cleavage” phase?

[textentry single_char=”true”]

[c]wq Ay[Qq]

[f]IFllcywg4oCcMuKAnSBpcyB0aGUgY2xlYXZhZ2XCoHBoYXNlLg==[Qq]

[c]Kg==[Qq]

[f]Tm8uIEhlcmUmIzgyMTc7cyBhIGhpbnQuIFRoZSBjbGVhdmFnZSBwaGFzZSBpcyB3aGVuIG9uZSBvZiB0aGUgZ2x1Y29zZS1kZXJpdmVkIGNvbXBvdW5kcyBnZXRzIHNwbGl0IGFwYXJ0LiBXaGVyZSBkbyB5b3Ugc2VlIGEgc2l4LWNhcmJvbiBtb2xlY3VsZSBnZXQgc3BsaXQgYXBhcnQgaW50byB0d28sIDMtY2FyYm9uIG1vbGVjdWxlcz8=

Cg==

[Qq]

[q]Which letter or number indicates the “harvest” phase?

[textentry single_char=”true”]

[c]wq Az[Qq]

[f]IFllcywg4oCcM+KAnSBpcyB0aGUgaGFydmVzdMKgcGhhc2Uu[Qq]

[c]Kg==[Qq]

[f]Tm8uIEhlcmUmIzgyMTc7cyBhIGhpbnQuwqBUaGUgaGFydmVzdMKgcGhhc2UgaXMgd2hlbiBlbmVyZ3kgaXPCoGFjcXVpcmVkIGJ5IHRoZSBjZWxsLiBMb29rIGZvciB3aGVyZSBBVFAgb3IgTkFESCBpcyBiZWluZyBmb3JtZWQsIGFuZCB0aGF0JiM4MjE3O3MgdGhlIGhhcnZlc3QgcGhhc2Uu

Cg==

[Qq]

[q]Which letter indicates the step where glucose is first phosphorylated?

[textentry single_char=”true”]

[c]wq BC[Qq]

[f]IFllcywg4oCcQuKAnSBpcyB3aGVyZSBnbHVjb3NlIGlzIHBob3NwaG9yeWxhdGVkLCBiZWNvbWluZyBnbHVjb3NlLTYtcGhvc3BoYXRlLg==[Qq]

[c]Kg==[Qq]

[f]Tm8uIEhlcmUmIzgyMTc7cyBhIGhpbnQuIEZpbmQgYSBzdGVwIHdoZXJlIGdsdWNvc2UgaXMgZ2FpbmluZyBhIHBob3NwaGF0ZSwgYW5kIEFUUCBpcyBsb3NpbmcgYSBwaG9zcGhhdGUu

Cg==

[Qq]

[q]Which letter indicates the step where glucose-6-phosphate is rearranged and phosphorylated, becoming fructose-1-6-bisphosphate?

[textentry single_char=”true”]

[c]wq BE[Qq]

[f]IFllcywg4oCcROKAnSBpcyB3aGVyZSBnbHVjb3NlLTYtcGhvc3BoYXRlIGlzIHJlYXJyYW5nZWQgYW5kIHBob3NwaG9yeWxhdGVkLCBiZWNvbWluZyBmcnVjdG9zZS0xLTYtYmlzcGhvc3BoYXRlLg==[Qq]

[c]Kg==[Qq]

[f]Tm8uIEhlcmUmIzgyMTc7cyBhIGhpbnQuIEZpbmQgYSBzdGVwIHdoZXJlIGEgc2l4LWNhcmJvbiBtb2xlY3VsZSB3aXRoIG9uZSBwaG9zcGhhdGUgaXMgcmVhcnJhbmdlZCBhbmQgYmVjb21lcyBhIHNpeC1jYXJib24gbW9sZWN1bGUgd2l0aCB0d28gcGhvc3BoYXRlcy4=

Cg==

[Qq]

[q]Which letter indicates glucose-6-phosphate?

[textentry single_char=”true”]

[c]wq BD[Qq]

[f]IFllcywg4oCcQ+KAnSBpbmRpY2F0ZXMgZ2x1Y29zZS02LXBob3NwaGF0ZS4=[Qq]

[c]Kg==[Qq]

[f]Tm8uIEhlcmUmIzgyMTc7cyBhIGhpbnQuIEZpbmQgYSBzaXgtY2FyYm9uIG1vbGVjdWxlIHdpdGggb25lIHBob3NwaGF0ZSBhdHRhY2hlZC4=

Cg==

[Qq]

[q]Which letter indicates fructose-1-6-bisphosphate?

[textentry single_char=”true”]

[c]wq BF[Qq]

[f]IFllcywg4oCcReKAnSBpbmRpY2F0ZXMgZnJ1Y3Rvc2UtMS02LWJpc3Bob3NwaGF0ZS4=[Qq]

[c]Kg==[Qq]

[f]Tm8uIFRoaW5rIGFib3V0IHRoZSBuYW1lIG9mIHRoZSBjb21wb3VuZCBmcnVjdG9zZS0xLTYtYmlzcGhvc3BoYXRlLiBCaXNwaG9zcGhhdGUgbWVhbnMgdHdvIHBob3NwaGF0ZXMsIHNvIGxvb2sgZm9yIGEgc2l4LWNhcmJvbiBjb21wb3VuZCB3aXRoIHR3byBwaG9zcGhhdGVzIGF0dGFjaGVkLg==

Cg==

[Qq]

[q]Which letter indicates glyceraldehyde-3-phosphate (G3P)?

[textentry single_char=”true”]

[c]wq BG[Qq]

[f]IFllcywg4oCcRuKAnSBpcyBnbHljZXJhbGRlaHlkZS0zLXBob3NwaGF0ZS4=[Qq]

[c]Kg==[Qq]

[f]Tm8uIEhlcmUmIzgyMTc7cyBhIGhpbnQuIEZpbmQgYSB0aHJlZS1jYXJib24gbW9sZWN1bGUgd2l0aCBhIHNpbmdsZSBwaG9zcGhhdGUgZ3JvdXAgYXR0YWNoZWQu

Cg==

[Qq]

[q]Which letter indicates a step where G3P is oxidized?

[textentry single_char=”true”]

[c]wq BH[Qq]

[f]IFllcywg4oCcR+KAnSBpcyBzaG93aW5nIHRoZSBveGlkYXRpb24gb2YgZ2x5Y2VyYWxkZWh5ZGUtMy1waG9zcGhhdGUsIHdpdGggdGhlIHNpbXVsdGFuZW91cyByZWR1Y3Rpb24gb2YgTkFEKw==IHRvIE5BREgu[Qq]

[c]Kg==[Qq]

[f]Tm8uIEhlcmUmIzgyMTc7cyBhIGhpbnQuIEZvciBOQUQ=Kw==IHRvIGJlIHJlZHVjZWQgdG8gTkFESCwgYW5vdGhlciBtb2xlY3VsZSAob3JpZ2luYWxseSBmcm9tIGZvb2QpIGlzIGdvaW5nIHRvIGhhdmUgdG8gYmUgb3hpZGl6ZWQu

Cg==

[Qq]

[q]Which letter indicates substrate-level phosphorylation?

[textentry single_char=”true”]

[c]wq BI[Qq]

[f]IFllcywg4oCcSOKAnSBpcyBzaG93aW5nIHRoZSBjcmVhdGlvbiBvZiBBVFAgZnJvbSBBRFAuIElmIHRoYXQgcmVhY3Rpb24gaXMgY2F0YWx5emVkIGJ5IGFuIGVuenltZSwgdGhlbiBpdCYjODIxNztzIHN1YnN0cmF0ZS1sZXZlbCBwaG9zcGhvcnlsYXRpb24u[Qq]

[c]Kg==[Qq]

[f]Tm8uIEhlcmUmIzgyMTc7cyBhIGhpbnQuIFN1YnN0cmF0ZSBsZXZlbCBwaG9zcGhvcnlsYXRpb24gaXMgd2hlcmUgQVRQIGlzIGNyZWF0ZWQgdGhyb3VnaCB0aGUgYWN0aW9uIG9mIGVuenltZXMuIFdoZXJlIGRvIHlvdSBzZWUgQVRQIGNyZWF0aW9uPw==

Cg==

[Qq]

[q]Which letter indicates pyruvic acid (or pyruvate)?

[textentry single_char=”true”]

[c]wq BJ[Qq]

[f]IFllcywg4oCcSeKAnSBpcyBzaG93aW5nIHB5cnV2aWMgYWNpZCBvciBweXJ1dmF0ZS4=[Qq]

[c]Kg==[Qq]

[f]Tm8uIEhlcmUmIzgyMTc7cyBhIGhpbnQuIFB5cnV2YXRlLCBvciBweXJ1dmljIGFjaWQsIGlzIHRoZSB0aHJlZS1jYXJib24gbW9sZWN1bGUgdGhhdCYjODIxNztzIGxlZnQgYWZ0ZXIgdGhlIGNsZWF2YWdlLCBveGlkYXRpb24sIGFuZCBzdWJzdHJhdGUtbGV2ZWwgcGhvc3Bob3J5bGF0aW9ucyB0aGF0IG9jY3VyIGR1cmluZyBnbHljb2x5c2lzLg==

Cg==

[Qq]

[q]Which number indicates where in the cell glycolysis occurs?

[textentry single_char=”true”]

[c]wq Az[Qq]

[f]IFllcywg4oCcM+KAnSBpcyBzaG93aW5nwqB0aGUgY3l0b3BsYXNtLCB3aGljaCBpcyB3aGVyZSBnbHljb2x5c2lzIG9jY3Vycy4=[Qq]

[c]Kg==[Qq]

[f]Tm8uIEhlcmUmIzgyMTc7cyBhIGhpbnQuwqBHbHljb2x5c2lzIGlzIHRoZSBvbmUgcGhhc2Ugb2YgY2VsbHVsYXIgcmVzcGlyYXRpb24gdGhhdCBvY2N1cnMgb3V0c2lkZSBvZiB0aGUgbWl0b2Nob25kcmlhLg==

Cg==

[Qq]

[q]Which number indicates where in cellular respiration glycolysis occurs?

[textentry single_char=”true”]

[c]wq Ax[Qq]

[f]IFllcywg4oCcMeKAnSBpcyBzaG93aW5nIGdseWNvbHlzaXMu[Qq]

[c]Kg==[Qq]

[f]Tm8uIEhlcmUmIzgyMTc7cyBhIGhpbnQuwqBHbHljb2x5c2lzIGlzIHRoZcKgZmlyc3QgcGhhc2Ugb2YgY2VsbHVsYXIgcmVzcGlyYXRpb24u

Cg==

[Qq]

[q]Which of the following is NOT needed for glycolysis to occur.

[c]Z2x1Y29zZQ==[Qq]

[c]TkFEKw==[Qq]

[c]QVRQ[Qq]

[c]b3h5 Z2Vu[Qq]

[f]Tm8uIEdsdWNvc2UgaXMgdGhlIHN0YXJ0aW5nIHJlYWN0YW50IGZvciBnbHljb2x5c2lzLg==[Qq]

[f]Tm8uwqBXaXRob3V0IE5BRA==Kw==LCB0aGUgY2VsbCBjYW4mIzgyMTc7dCBveGlkaXplIGdsdWNvc2UgKGJlY2F1c2UgeW91IGNhbiYjODIxNzt0IG94aWRpemUgc29tZXRoaW5nIHdpdGhvdXQgcmVkdWNpbmcgc29tZXRoaW5nIGVsc2Uu[Qq]

[f]Tm8uIFRoZSBjZWxsIG5lZWRzIEFUUCB0byBkbyB0aGUgaW5pdGlhbCBwaG9zcGhvcnlsYXRpb25zIHRoYXQgYXJlIHBhcnQgb2YgdGhlICYjODIyMDtpbnZlc3RtZW50IHBoYXNlLiYjODIyMTs=[Qq]

[f]Q29ycmVjdCEgR2x5Y29seXNpcyBjYW4gb2NjdXIgd2l0aG91dCBveHlnZW4u[Qq]

[x][restart]

[/qwiz]

5. The Gross and Net Yield of Glycolysis

If you owned a movie theater, your gross profit would be the total amount of money that came into your theater: all the money you made by selling tickets, popcorn, drinks, candy, etc. That of course is not the money that you get to take home at the end of the week. That’s because you have expenses: salaries, movie rental costs, the food you buy, etc. What you get to take home is your net profit: gross profit – expenses.

04_glycolysis-partially-numbered

You can think of glycolysis in the same way. The gross yield is all of the useable energy that comes out of the process. To calculate this, you just count all of the ATP (which is immediately available for cellular work) and the NADH (which can be used to power the electron transport chain). Looking at the harvest phase of glycolysis, you can see that your gross yield is

  • 4 ATP, and
  • 2 NADH

If you look at phase 1, the investment phase, you can see that the cell has to expend two ATPs to prepare for phases 2 and 3 (cleavage and harvest). So the net yield is calculated as follows.

Gross v. Net Yield of Glycolysis
Gross Yield minus expenses equals net yield
4 ATP,

2 NADH

2 ATP 2 ATP,

2NADH

6. What happens after glycolysis

Glycolysis is the first stage in cellular respiration. As an oxygen-independent metabolic pathway, it’s also possibly one of the most ancient metabolic pathways and could have arisen early in the history of life, before free oxygen accumulated in the seas.

Within the cells of modern-day organisms that carry out glycolysis, what happens after glycolysis depends mostly on the presence or absence of oxygen. You can trace two possibilities in the diagram below.

10_aerobic-v-anaerobic-respiration

  1. Aerobic pathway: If oxygen is present, then aerobic respiration follows. Aerobic means “with oxygen.” Pyruvate will enter the cell’s mitochondria, where it will be totally oxidized in the Link Reaction and the Krebs cycle. This oxidation will power the reduction of the electron carriers NAD+ and FAD, which, as NADH and FADH2, will carry electrons to the electron transport chain, where they’ll power oxidative phosphorylation, creating lots of ATP for the cell.
  2. Anaerobic pathway: If oxygen is absent, then anaerobic respiration follows. Anaerobic respiration means “without oxygen.” Rather than being oxidized, pyruvate will be fermented. Fermentation doesn’t create additional energy for the cell, but it does regenerate NAD+, making it possible for the cell to continue carrying out glycolysis, which creates a small amount of ATP. Important food-related fermentations occur in yeast, which is used to produce the alcohol in beer or wine, or the bubbles of CO2 that occur when bread rises. Yogurt is another fermented product. Animals can also ferment pyruvic acid as part of anaerobic respiration, which occurs when our muscle cells become low in oxygen.

We’ll return to fermentation (and study it in more depth) at the end of this series on cellular respiration.

7. Glycolysis Fill-in-the-Blanks Quiz

[qwiz]

[h]Glycolysis Fill-in-the-Blanks Quiz

[i]

[q][hangman] is the process that takes glucose and breaks it down in order to create NADH and ATP. It’s a series of reactions controlled by [hangman].

[c]R2x5Y29seXNpcw==[Qq]

[c]ZW56eW1lcw==[Qq]

[q]Glycolysis takes glucose and breaks it down to create NADH and [hangman].

[c]QVRQ[Qq]

[q]Glycolysis is an [hangman] metabolic pathway, meaning that it does not require oxygen.

[c]YW5hZXJvYmlj[Qq]

[q]The three phases of glycolysis are investment, [hangman], and energy harvest.

[c]Y2xlYXZhZ2U=[Qq]

[q]During the [hangman] phase of glycolysis, activation energy is supplied in the form of two phosphate groups supplied by two ATPs.

[c]aW52ZXN0bWVudA==[Qq]

[q]During the cleavage phase of glycolysis, a [hangman] carbon sugar is split into two.

[c]c2l4[Qq]

[q]During the investment phase of glycolysis, enzymes put two ATPs onto glucose, rearranging it into [hangman] 1- 6 bisphosphate

[c]ZnJ1Y3Rvc2U=[Qq]

[q]During the cleavage phase of glycolysis, [hangman] 1- 6 bisphosphate is split into two three-carbon molecules.

[c]RnJ1Y3Rvc2U=[Qq]

[q]The main product of cleavage is [hangman]-3-phosphate, also known as G3P

[c]Z2x5Y2VyYWxkZWh5aGRl[Qq]

[q]Cleavage results in the formation of [hangman] molecules of G3P.

[c]dHdv[Qq]

[q]During the harvest phase, each [hangman] provides the energy to power the creation of one NADH and 2 ATPs

[c]RzNQ[Qq]

[q]The [hangman] energy yield per molecule of glucose in glycolysis is two NADH and four ATPs. However, the [hangman] energy yield per molecule of glucose in glycolysis is two NADH and two ATPs

[c]Z3Jvc3M=[Qq]

[c]bmV0[Qq]

[q]By the end of glycolysis, glucose has been broken down into two molecules of [hangman] acid.

[c]cHlydXZpYw==[Qq]

[q]The [hangman] pathway that follows glycolysis is also known as fermentation. But if pyruvate is broken down [hangman], then it will proceed into the Krebs cycle and be completely oxidized.

[c]YW5hZXJvYmlj[Qq]

[c]YWVyb2JpY2FsbHk=[Qq]

[q]Glycolysis starts with the investment of two [hangman] to the glucose that starts the reaction.

[c]QVRQcw==[Qq]

[q]The main product of cleavage is glyceraldehyde-3-[hangman], also known as [hangman].

[c]cGhvc3BoYXRl[Qq]

[c]RzNQ[Qq]

[x]

[restart]

[/qwiz]

7. Glycolysis Karaoke

Now for the ultimate challenge. See if you can sing your way through this video.

 

What’s next?