Fermentation

Summary

This educational video explores cellular respiration and fermentation, focusing on how cells generate ATP in the absence of oxygen. It explains glycolysis, the first stage of fermentation, and contrasts it with two types of fermentation: lactic acid and alcoholic. The video highlights the role of yeast in alcoholic fermentation and the conversion of glucose to ethanol and carbon dioxide, yielding two ATP per glucose molecule. It also discusses lactic acid fermentation, used by muscle cells during oxygen debt, which also produces two ATP per glucose but is less efficient than cellular respiration. The video concludes by questioning the necessity of the slower, oxygen-dependent cellular respiration, which extracts more energy from glucose, leaving behind only water and carbon dioxide.

Takeaways

• 🔬 Fermentation is an alternative process to cellular respiration, allowing glucose breakdown without oxygen or mitochondria.
• ⚡ Fermentation is a catabolic pathway that generates ATP anaerobically in the cytoplasm, requiring no special organelles.
• 🍞 Yeast undergoes alcoholic fermentation, producing carbon dioxide (which makes bread rise) and ethanol (which is used in alcoholic beverages).
• 💨 Alcoholic fermentation involves two steps: glycolysis and alcohol formation, where glucose is broken down into ethanol and carbon dioxide.
• 🔥 The main purpose of the second stage of fermentation is to regenerate NAD+ for glycolysis, ensuring the process can continue.
• 🚗 Ethanol, the waste product of alcoholic fermentation, still contains a lot of energy, as seen by its use as fuel in race cars.
• 💪 Muscle cells can perform lactic acid fermentation when oxygen is low, producing 2 ATP per glucose molecule, compared to 36 ATP in aerobic respiration.
• 🧪 In lactic acid fermentation, glucose is converted to lactic acid, and like alcoholic fermentation, it regenerates NAD+ for glycolysis.
• ⏱️ Although fermentation is fast and simple, cellular respiration yields far more energy, making it preferable when oxygen is available.
• ❓ The purpose of fermentation is to ensure ATP production when oxygen is unavailable, although it is less efficient compared to aerobic respiration.

Q & A

What is cellular respiration and how does it differ from fermentation?

Cellular respiration is a process where cells use oxygen to convert glucose into ATP. It's a more efficient process that occurs in the presence of oxygen and primarily in mitochondria. Fermentation, on the other hand, is an anaerobic process that occurs without oxygen and in the cytoplasm, producing less ATP but can happen when oxygen is scarce or mitochondria are absent.

What are the two stages of fermentation?

The two stages of fermentation are glycolysis and waste product formation. Glycolysis is the breakdown of glucose into two pyruvate molecules, producing two ATP and two NADH. Waste product formation involves converting pyruvate into either ethanol and carbon dioxide (alcoholic fermentation) or lactate (lactic acid fermentation), and it's crucial for regenerating NAD+ for continued glycolysis.

How many ATP molecules are produced from glycolysis in fermentation?

From glycolysis, two ATP molecules are produced for every glucose molecule that is broken down into two pyruvate molecules.

What is the net profit of ATP in alcoholic fermentation?

The net profit of ATP in alcoholic fermentation is two ATP molecules per glucose molecule, considering the two ATP invested at the beginning of glycolysis are not recovered in the fermentation process.

What is the role of NADH and NAD+ in fermentation?

NADH and NAD+ play a critical role in fermentation as they are part of the redox reactions that allow the process to continue. NAD+ is required for glycolysis, and NADH is produced. The second stage of fermentation regenerates NAD+ from NADH, which is essential for glycolysis to continue.

Why is the second stage of fermentation necessary?

The second stage of fermentation is necessary to regenerate NAD+ from NADH, which is required for the glycolysis process to continue. Without this regeneration, glycolysis would not be sustainable as it relies on NAD+ to convert glucose into pyruvate.

What are the waste products of alcoholic fermentation?

The waste products of alcoholic fermentation are ethanol and carbon dioxide. These are the end products of the conversion of pyruvate into aldehydes and then into ethanol.

How does lactic acid fermentation differ from alcoholic fermentation?

In lactic acid fermentation, pyruvate is converted into lactate (lactic acid) instead of ethanol and carbon dioxide. This type of fermentation does not produce gas, and the net ATP yield is also two ATP per glucose molecule.

Why do muscle cells use lactic acid fermentation during intense exercise?

Muscle cells use lactic acid fermentation during intense exercise when oxygen supply is insufficient to meet the energy demands. This allows them to continue producing ATP, albeit at a lower yield (2 ATP per glucose) compared to aerobic respiration (36 ATP per glucose).

What is the relationship between fermentation and the rise of bread?

The carbon dioxide produced as a waste product during alcoholic fermentation by yeast is what causes bread to rise. The yeast ferments the sugars in the dough, creating carbon dioxide gas which gets trapped, leading to the expansion of the dough.

Why is cellular respiration more efficient than fermentation?

Cellular respiration is more efficient than fermentation because it completely oxidizes glucose in the presence of oxygen, yielding approximately 36 ATP per glucose molecule, compared to the 2 ATP produced by fermentation. Additionally, the byproducts of cellular respiration (water and carbon dioxide) do not contain any leftover energy, unlike ethanol produced in fermentation.

Outlines

00:00

🔬 Cellular Respiration and Fermentation

This paragraph introduces the topic of cellular respiration and fermentation. It explains that cellular respiration involves using glucose and oxygen to produce ATP, but in the absence of oxygen or mitochondria, cells resort to fermentation. Fermentation is a quicker, simpler process that doesn't require oxygen or complex organelles. It breaks down glucose into ATP through glycolysis and waste product formation. The paragraph details the process of glycolysis, which splits glucose into two phosphoglyceraldehyde molecules, converting them to phosphoglycerate, and finally into pyruvate, yielding a net gain of two ATP. It also introduces two types of fermentation: lactic acid fermentation, which produces lactate and two ATP, and alcoholic fermentation, which produces ethanol and carbon dioxide, also yielding two ATP.

05:02

🍺 Alcoholic Fermentation and Lactic Acid Fermentation

This paragraph delves into the specifics of alcoholic fermentation using yeast as an example. It explains how glycolysis is the first step, leading to the production of two pyruvate molecules and two NADH, along with a net gain of two ATP. The second stage involves converting pyruvate into aldehyde, releasing carbon dioxide, and then into ethanol by oxidizing NADH back to NAD+. This stage is crucial for regenerating NAD+, which is necessary for the continuation of glycolysis. The paragraph contrasts fermentation with cellular respiration, highlighting that respiration is more efficient, yielding 18 times more energy. It also discusses lactic acid fermentation, which regenerates NAD+ by converting pyruvate into lactate, again for the purpose of sustaining glycolysis. The paragraph concludes by emphasizing the role of lactic acid fermentation in muscle cells during periods of oxygen debt, allowing them to continue producing ATP when oxygen is scarce.

Keywords

💡Cellular Respiration

Cellular respiration is a process where cells use oxygen to convert glucose into energy in the form of ATP (adenosine triphosphate). In the video, it's mentioned as a process that occurs with the presence of oxygen and is more efficient than fermentation. The script explains that it generates approximately 36 ATP per glucose molecule, contrasting it with fermentation which is less efficient.

💡Anaerobic Environment

An anaerobic environment refers to a condition where there is no oxygen or very low levels of oxygen. The video discusses how cells adapt to such conditions by using fermentation as an alternative energy production method since cellular respiration is not possible without oxygen.

💡Fermentation

Fermentation is an anaerobic process that breaks down glucose into ATP without the need for oxygen. The video explains that fermentation is a simpler and faster alternative to cellular respiration, occurring in the cytoplasm and not requiring organelles like mitochondria. It is highlighted as a process that allows cells to generate ATP in the absence of oxygen.

💡Glycolysis

Glycolysis is the first stage of cellular respiration and fermentation. It involves the breakdown of glucose into two molecules of pyruvate, generating two ATP and two NADH molecules. The video script describes glycolysis as an energy investment step that is common to both cellular respiration and fermentation.

💡Mitochondria

Mitochondria are organelles within cells that are primarily responsible for energy production through cellular respiration. The video mentions that in the absence of mitochondria or oxygen, cells resort to fermentation for energy production.

💡ATP

ATP, or adenosine triphosphate, is the primary energy currency of cells. The video script discusses how both cellular respiration and fermentation aim to produce ATP, with cellular respiration being more efficient at producing it (36 ATP per glucose) compared to fermentation (2 ATP per glucose).

💡Lactic Acid Fermentation

Lactic acid fermentation is a type of fermentation where glucose is broken down into lactic acid, yielding two ATP. The video script contrasts this with alcoholic fermentation, explaining that the choice between these types depends on the cell type and available enzymes.

💡Alcoholic Fermentation

Alcoholic fermentation is another type of fermentation where glucose is converted into ethanol and carbon dioxide, also yielding two ATP. The video uses yeast as an example of an organism that performs alcoholic fermentation, which is relevant in the production of bread and alcoholic beverages.

💡NAD+ and NADH

NAD+ and NADH are important electron carriers in cellular respiration and fermentation. NAD+ is an oxidized form, and NADH is a reduced form. The video script explains that during glycolysis, NAD+ is converted to NADH, and fermentation is necessary to regenerate NAD+ from NADH to continue glycolysis.

💡Pyruvate

Pyruvate is a key molecule resulting from glycolysis. In the video, it's mentioned that after glycolysis, pyruvate can enter different fermentation pathways, such as lactic acid or alcoholic fermentation, depending on the cell's needs and environment.

💡Ethanol

Ethanol is a product of alcoholic fermentation, where it is produced as a waste product along with carbon dioxide. The video script uses ethanol as an example of a high-energy molecule, noting that it is a byproduct that is not further utilized by the cell for energy but can be used as fuel, such as in race cars.

Highlights

Cellular respiration generates ATP by burning glucose in the presence of oxygen.

Fermentation is an anaerobic process that occurs without oxygen and without mitochondria.

Fermentation allows cells to burn glucose for ATP in the absence of oxygen.

Fermentation consists of glycolysis and waste product formation.

Glycolysis splits glucose into two molecules of phosphoglyceraldehyde (2pg).

Glycolysis produces two ATP through substrate level phosphorylation.

At the end of glycolysis, two pyruvate molecules are produced, yielding a net profit of two ATP.

Fermentation comes in different variations, including lactic acid fermentation and alcoholic fermentation.

In alcoholic fermentation, glucose is broken down into ethanol and carbon dioxide, producing two ATP.

Yeast is an organism that performs alcoholic fermentation, which is used in bread rising and alcohol production.

The second stage of fermentation regenerates NAD+ for glycolysis by oxidizing NADH to NAD+.

Cellular respiration is more efficient than fermentation, yielding 18 times more energy from glucose.

Ethanol is a high-energy molecule, but fermentation leaves energy behind due to the lack of complex organelles.

Lactic acid fermentation breaks down glucose into lactic acid, also yielding two ATP.

Muscle cells can perform lactic acid fermentation during oxygen debt to produce ATP.

Muscle cells are facultative anaerobes, preferring cellular respiration when oxygen is available.

The purpose of fermentation is to provide a fast, easy way to get ATP without oxygen and complex organelles.

Aerobic respiration is a slower, more complex process that extracts more energy from molecules.

Transcripts

welcome back to our fourth video in our

three-part series yeah I know doesn't

make much sense to me either

but we've been talking about cellular

respiration where we've been using our

cellular fuel glucose and burning it in

the presence of oxygen to generate ATP

approximately 36 but what happens in an

anaerobic environment when we don't have

oxygen and what would a cell do if it

lacked mitochondria where most of

respiration occurs well the answer is

fermentation fermentation is a simpler

and faster alternative to cellular

respiration it allows us to burn glucose

without oxygen and without complex

organelles like mitochondria

fermentation is a catabolic pathway that

breaks down glucose for ATP it's

anaerobic like we said it occurs in the

cytoplasm requires no special organelles

to set of reactions that occurs in two

stages glycolysis and what we're going

to call for now waste product formation

now we've already spent a lot of time on

God calluses in fact we already looked

at a video and if you want to see that

video the more detailed look at

glycolysis click right over here but for

now I'm just going to run through a

quick version of glycolysis just running

through the steps so in the first step

we split glucose into two pgl

phosphoglyceraldehyde and that costs us

two ATP

in our energy investment step the 2pg al

are converted to be pgl when we reduce

nad plus into NADH the B pgl are then

converted to pga phosphoglycerate and we

produce out the first two of our ATP by

substrate level phosphorylation and in

the final step the pga are converted

into two pyruvate and we make two more

ATP for net profit of two ATP like I

said if you want a more detailed

description of how this occurs go back

to our video that we dental glycolysis

the links over here

now at the end of glycolysis we have two

pyruvate and then those two pyruvate can

enter in what we call fermentation and

fermentation comes a lot of different

variations we can see all these

different end products of the different

types of fermentation but for our

purposes we're going to focus in on two

lactic acid fermentation and alcoholic

fermentation let's compare the two just

by looking at their formulas an

alcoholic form fermentation we break

down glucose into alcohol ethanol we get

to carbon dioxide as a product and we

make a profit of two ATP for every one

glucose and lactic acid fermentation we

take that same glucose and we break it

down to lactate or lactic acid and

produce again two ATP so let's take a

closer look at the details and we'll do

alcoholic fermentation first so we need

an organism that does alcoholic

fermentation how about yeast yeast does

alcohol fermentation in fact it's

because G's produces carbon dioxide that

it makes bread to rise and it's the

ethanol or alcohol that yeast produce as

a waste product that makes alcoholic

beverages alcoholic so let's look at the

metabolic pathway we start with

glycolysis this is step one of all

fermentation reactions and I've

condensed glycolysis here in this

diagram from glucose and I skipped all

the way to the end of pyruvate we see

our two nadh being produced and a net

profit of two ATP I've just skip the

intermediate details in the second stage

of fermentation if it's alcoholic

fermentation the two pyruvates are

converted into two molecules of aldehyde

and in doing so we release to carbon

dioxide then the two aldehydes are

converted into ethanol

by the oxidation of NADH to NAD+ so we

call the second stage alcohol formation

so glycolysis followed by alcohol

formation so let's summarize here we

have the overall formula its anaerobic

we need no oxygen it's in the cytoplasm

we need to know organelles it comes in

two stages glycolysis where we break

down glucose into two pyruvate molecules

producing two NADH and yielding to ATP

and then alcohol formation the two

pyruvate are converted into two

aldehydes while two carbon dioxides are

released then the two aldehydes are

converted into two ethanol by oxidizing

two NADH into two nad plus the two waste

products of this reaction are carbon

dioxide and alcohol which both diffuse

from the cells well this raises an

interesting question why why do stage

two let's look back at the flowchart

here everything that we're going to get

kind of on the positive side from

fermentation we get from glycolysis the

whole point of fermentation was to get

energy out of glucose and we only are

going to earn two ATP and we have those

two ATP by the end of glycolysis and so

we might as well just stop here pyruvate

what's the point of method making two

molecules carbon dioxide and ethanol

which are waste products and not use by

the cell well I'm going to give you a

hint

you see the alcohol formation stage -

this allows us to regenerate NAD+ for

glycolysis

we've been reducing NAD+ during

glycolysis to make nadh after a while we

have a limited supply of NAD+ and so if

we don't oxidize NADH to return the NAD+

back to glycolysis we can't do this part

at the top over and over again let's do

one more interesting thing

let's compare fermentation to cellular

respiration we see that instead of

respiration we use oxygen and our energy

yield is 18 times greater so the

question is where is the rest of the

energy up here how do we get so much

more energy out of glucose here and the

answer is the energy is left behind an

ethanol ethanol is a high-energy

molecule how high energy well you can

run racecars on it

that's pretty high energy without the

complex machinery of an organelle like

mitochondria we're not able to tap into

all the energy that's available in this

glucose and we just leave it behind

ethanol now let's look at lactic acid

fermentation here's the formula glucose

breaks down into lactic acid and we get

a profit of 2 ATP so here we have

glycolysis again in a shortened version

glucose to pyruvate making 2 NADH in a

profit of 2 ATP in lactate formation the

two pyruvate are converted into two

molecules of lactate or lactic acid and

again we should see that the only reason

to have this second reaction is to

regenerate NAD+ for glycolysis the type

of fermentation that a cell employs you

know whether it be alcoholic or lactate

form fermentation lactic acid

fermentation it depends on the type of

cell and the enzymes that has available

but one interesting thing is that muscle

cells have the ability to do lactic acid

fermentation now ideally muscle cells

would do cellular respiration where for

every one glucose molecule you'd get 36

ATP because in lactic acid fermentation

for every one glucose

you only make two ATP so our yield is

much much lower and so when you're

running your cells on lattic acid

fermentation you're going to run out of

energy pretty quick I snapped this whole

photo of myself working out the other

day I don't believe that but muscle

cells are facultative anaerobes that

means when oxygen is available they'll

use it so as much as you can deliver

oxygen to your muscles the more

efficiently you can burn glucose 36 ATP

for every one glucose but in times of

oxygen debt instead of muscle cells

being having no ATP production they can

switch over to lactic acid fermentation

and at least get 2 ATP for every one

glucose rather than zero so to wrap up I

have a couple questions what's the

purpose of fermentation if fermentation

is a fast easy way to get ATP without

oxygen and without requiring complex

organelles then why is there a slower

more complex process involving oxygen I

think we kind of just hinted at that in

aerobic respiration the alternative to

fermentation we break down molecules to

get much more to get more energy out of

them and the leftover products have no

useful energy left in them remember our

byproducts of cellular respiration were

just water and carbon dioxide comparing

that to the fact that racecars can use

alcohols fuel I think we can see a

difference so that does it on our series

on respiration and fermentation review

the videos and send questions if you

have them