KREBS CYCLE | Cellular Respiration

Summary

This biology lesson delves into the intricacies of cellular respiration, focusing on the Krebs cycle. After glycolysis, pyruvic acids are converted into acetyl coenzyme A, which enters the mitochondria for the Krebs cycle. The cycle harvests hydrogens from the acetyl compound, forming CO2 and NADH. NADH then carries these hydrogens to the final stage, oxidative phosphorylation, where they're used to produce a significant amount of ATP. The video also explains key terms like decarboxylation, dehydrogenation, and the role of NAD/NADH, setting the stage for the next lesson on oxidative phosphorylation.

Takeaways

• 📚 The lesson is about cellular respiration, specifically focusing on the Krebs cycle, which follows glycolysis.
• 🔗 It's recommended to watch the glycolysis video before this one for a better understanding of the Krebs cycle.
• 🚫 Glycolysis occurs in the absence of oxygen and results in the production of two pyruvic acids.
• 🌀 The Krebs cycle's purpose is to harvest hydrogen molecules from the compound produced at the end of glycolysis.
• 🔄 In the presence of oxygen, pyruvic acid is converted into acetyl, a two-carbon molecule, with the help of coenzyme A.
• 🔄 Acetyl coenzyme A enters the mitochondria, where the Krebs cycle takes place, facilitated by coenzyme A as a transport mechanism.
• 🌿 The Krebs cycle involves the breakdown of a six-carbon compound, losing carbons to form CO2 and harvesting hydrogens.
• 💨 The hydrogens harvested are unstable and are carried by NAD to form NADH, which is crucial for the next stage of cellular respiration.
• 🔋 The final stage of cellular respiration, oxidative phosphorylation, uses the harvested hydrogens to form ATP.
• 🔑 Key terms introduced include decarboxylation (removing a carbon with oxygen to form CO2) and dehydrogenation (removing hydrogens).
• 🔑 NAD is a hydrogen carrier that forms NADH, which is essential for the oxidative phosphorylation phase of cellular respiration.

Q & A

What is the main focus of the video script?

The main focus of the video script is to explain the Krebs cycle, a part of cellular respiration, which follows glycolysis and precedes oxidative phosphorylation.

What is glycolysis and what is its role in cellular respiration?

Glycolysis is the first stage of cellular respiration where a glucose molecule is broken down to access the hydrogen atoms attached to it, which are used to produce ATP for energy.

What happens to the pyruvic acids produced at the end of glycolysis in the absence of oxygen?

In the absence of oxygen, the pyruvic acids produced at the end of glycolysis do not proceed to the Krebs cycle but are instead fermented.

What is the role of coenzyme A in the Krebs cycle?

Coenzyme A acts as a transport mechanism that picks up acetyl groups and delivers them to the Krebs cycle, speeding up the reaction and facilitating the process.

How does the Krebs cycle harvest hydrogen molecules?

The Krebs cycle harvests hydrogen molecules by breaking down the acetyl-CoA and other compounds, detaching hydrogen atoms that are then transferred to NAD+ to form NADH.

What is the final stage of cellular respiration after the Krebs cycle?

The final stage of cellular respiration after the Krebs cycle is oxidative phosphorylation, where the harvested hydrogens are used to form ATP.

What is the purpose of the hydrogen carrier NAD+ in the Krebs cycle?

NAD+ serves as a hydrogen carrier in the Krebs cycle, picking up hydrogen atoms and forming NADH, which then transports the hydrogen to the oxidative phosphorylation stage.

What happens to the carbon atoms during the Krebs cycle?

During the Krebs cycle, the carbon atoms from the original acetyl-CoA are eventually removed, forming carbon dioxide, which is released as a waste product.

Why is oxygen necessary for the Krebs cycle to occur?

Oxygen is necessary for the Krebs cycle because it is required for the final stages of the cycle, where hydrogen atoms combine with oxygen to form water, and the cycle regenerates its starting compounds.

What is the significance of the term 'dehydrogenase' in the context of the Krebs cycle?

The term 'dehydrogenase' refers to the process of removing hydrogen atoms from the compounds in the Krebs cycle, which is essential for harvesting the hydrogens for ATP production.

How many ATP molecules are formed as a result of the Krebs cycle and oxidative phosphorylation combined?

The Krebs cycle itself does not directly produce ATP, but it sets up the conditions for the production of approximately 32 ATP molecules during oxidative phosphorylation.

Outlines

00:00

🔬 Introduction to Cellular Respiration and the Krebs Cycle

This paragraph introduces the topic of cellular respiration, specifically focusing on the Krebs cycle. The speaker welcomes viewers to the biology class and suggests watching the glycolysis video for context. Glycolysis is described as the process of extracting energy from glucose molecules in the absence of oxygen. The Krebs cycle is introduced as the next stage, aiming to harvest hydrogen molecules for energy production. The speaker emphasizes the importance of understanding glycolysis before proceeding to the Krebs cycle and explains the transition from pyruvic acids to acetyl coenzyme A, facilitated by coenzyme A, which acts as a transport mechanism for the acetyl group into the mitochondria.

05:01

🌱 Detailed Explanation of the Krebs Cycle Process

The second paragraph delves deeper into the Krebs cycle, explaining the chemical transformations that occur within the mitochondria. The speaker describes the breakdown of the six-carbon compound, which results in the loss of carbon dioxide and hydrogen atoms. The process of decarboxylation, where carbon dioxide is released, and dehydrogenation, where hydrogens are harvested, are highlighted. The role of NAD as a hydrogen carrier, forming NADH, is introduced, which will later deliver the hydrogen to the oxidative phosphorylation phase for ATP production. The speaker also provides a terminology recap, defining key terms such as decarboxylation, dehydrogenation, and the role of coenzyme A in the Krebs cycle.

10:01

🔚 Concluding the Krebs Cycle and Introducing Oxidative Phosphorylation

In the final paragraph, the speaker wraps up the discussion on the Krebs cycle and teases the next topic, oxidative phosphorylation. The focus is on the importance of the harvested hydrogens and their delivery to the final phase of cellular respiration via NADH. The speaker reiterates the significance of the Krebs cycle in energy production and sets the stage for the next video, which will cover oxidative phosphorylation in detail. The paragraph concludes with an invitation for viewers to engage with the content by liking, subscribing, and commenting on the video.

Keywords

💡Cellular Respiration

Cellular respiration is the process by which cells convert nutrients into energy in the form of ATP (adenosine triphosphate). In the context of the video, it is the overarching theme, explaining how cells, particularly through the Krebs cycle, break down glucose to release energy. The script mentions cellular respiration as the process that includes glycolysis, the Krebs cycle, and oxidative phosphorylation.

💡Krebs Cycle

The Krebs cycle, also known as the citric acid cycle or TCA cycle, is a series of chemical reactions that occur in the mitochondria of cells. Its primary function is to extract energy from acetyl-CoA, which is derived from carbohydrates, fats, and proteins, and convert it into ATP. The video focuses on this cycle as the step following glycolysis in cellular respiration.

💡Glycolysis

Glycolysis is the first step in cellular respiration, where one molecule of glucose is broken down into two molecules of pyruvate, releasing a small amount of energy in the form of ATP and NADH. The script refers to glycolysis as the precursor to the Krebs cycle, where glucose is initially processed.

💡Acetyl-CoA

Acetyl-CoA is a central molecule in metabolism, formed from pyruvate during glycolysis when oxygen is present. It is the entry point of carbon from carbohydrates, fats, and proteins into the Krebs cycle. The script explains that acetyl-CoA is the substance that begins the Krebs cycle after glycolysis.

💡Coenzyme A

Coenzyme A is a cofactor that plays a crucial role in several biochemical reactions, including the Krebs cycle. It transports acetyl groups into the mitochondria, where they are converted into acetyl-CoA. The video script uses the analogy of a 'wheelbarrow' to describe its function in transporting acetyl groups.

💡Mitochondria

Mitochondria are organelles found in eukaryotic cells, known as the 'powerhouses' of the cell because they generate most of the cell's supply of ATP, used as a source of chemical energy. The script mentions that the Krebs cycle takes place within the mitochondria after glycolysis in the cytosol.

💡Oxidative Phosphorylation

Oxidative phosphorylation is the last stage of cellular respiration, occurring in the inner mitochondrial membrane, where the majority of ATP is produced. The script positions it as the final step where harvested hydrogens are used to form ATP, following the Krebs cycle.

💡Hydrogen Carrier

In the context of the Krebs cycle, a hydrogen carrier refers to molecules like NAD+ (nicotinamide adenine dinucleotide) that pick up hydrogen atoms released during the cycle. These carriers are essential for transferring electrons to the electron transport chain in oxidative phosphorylation. The script introduces NAD+ as a crucial component in the harvesting of hydrogens.

💡NAD+ and NADH

NAD+ is an oxidized form of a coenzyme that accepts electrons and hydrogen atoms, becoming reduced to NADH. In the Krebs cycle, NAD+ picks up hydrogen to form NADH, which is later used in oxidative phosphorylation to generate ATP. The script explains the role of NAD+ as a hydrogen carrier that forms NADH during the cycle.

💡Decarboxylation

Decarboxylation is a biochemical process where a carboxylic acid loses a carbon dioxide molecule. In the Krebs cycle, this process occurs when a carbon is removed from the cycle's intermediate compounds, forming CO2, which is then exhaled. The script uses the term to describe the release of carbon dioxide during the breakdown of compounds in the cycle.

💡Dehydrogenation

Dehydrogenation is the process of removing hydrogen from a molecule, typically involving the transfer of hydrogen atoms to a hydrogen acceptor. In the script, dehydrogenation refers to the step in the Krebs cycle where hydrogens are harvested from the cycle's compounds, preparing them for use in oxidative phosphorylation.

Highlights

Introduction to cellular respiration and the Krebs cycle in a biology class.

The importance of watching the glycolysis video before the Krebs cycle video for a better understanding.

Glycolysis as the initial process to access the energy from glucose molecules.

Transition from glycolysis to the Krebs cycle for further energy extraction.

The Krebs cycle's role in harvesting hydrogen molecules for energy.

The final stage of cellular respiration, oxidative phosphorylation, where ATP is formed using harvested hydrogens.

The conversion of pyruvic acids into acetyl in the presence of oxygen for the Krebs cycle.

Coenzyme A's function as a transport mechanism to speed up the Krebs cycle reaction.

The breakdown of the six-carbon compound in the Krebs cycle to release carbon dioxide and hydrogen atoms.

The repetitive process of the Krebs cycle to continuously harvest hydrogens.

The role of NAD as a hydrogen carrier in the Krebs cycle.

The formation of NADH, which transports hydrogens to oxidative phosphorylation.

The potential for hydrogen to cause unwanted chemical reactions if not properly managed.

The significance of the Krebs cycle in producing a large amount of ATP during oxidative phosphorylation.

Terminology explanation: decarboxylation and dehydrogenation in the Krebs cycle.

The role of oxygen in the Krebs cycle and its classification as an aerobic reaction.

The upcoming focus on oxidative phosphorylation in the next video of the cellular respiration series.

Invitation for feedback and suggestions for future video topics.

Transcripts

hi everybody and welcome back to miss

angler's biology class in today's lesson

we are going to be looking at cellular

respiration specifically the krebs cycle

if you're new here don't forget to leave

a like and subscribe and turn your

notifications on because i will be

posting a new video every thursday every

week

now let's get into it

if you haven't already watched the

glycolysis video that precedes this make

sure to go click on that video now and

watch that before you start watching the

krebs cycle video

right let's pick up where we left off

from our previous video at the end of

glycolysis so to refresh your memory

glycolysis is the process where we are

taking a glucose molecule and we are

trying to access all the hydrogens that

are attached to that glucose molecule

the hydrogens are going to provide us

with the energy that we need in order to

make atp

so from glycolysis we go into the next

cycle which is referred to as the krebs

cycle now the krebs cycle's purpose is

to harvest these hydrogen molecules that

we've been looking for

and the way we do that is we essentially

take our compound that we make at the

end of glycolysis and we slowly but

surely pull off and break off the

hydrogens

and we harvest them it's almost like we

collect them in a little basket once

we've collected all those hydrogens we

are going to move into the final stage

of cellular respiration which is

oxidative phosphorylation

and that is where we're going to use our

hydrogens that we have harvested and

we're going to form atp using the energy

that the hydrogen is providing now it's

at this point that if you are not so

sure what's going on it's important to

go back and look at the glycolysis video

before this

so picking up where we left off at the

end of glycolysis you have two pyruvic

acids now that is because there's no

oxygen present but if there is oxygen

present then we need to take those

pyruvic acids and we turn them into

something called acetyl now acetyl has

two carbon molecules as we can see here

the acetyl is represented by the two

pink round ball structures now acetyl

needs to have a little bit of help it

needs to speed up the reactions and so

who comes and helps coenzyme a which in

this picture is represented by the blue

rectangle

so now we have a substance called acetyl

coenzyme a

and now this is where the krebs cycle

begins so we have collected think of a

coenzyme a is like a wheelbarrow we've

collected our acetyl and now we're going

to move it and deliver it to the krebs

cycle so we can't begin

now two things happen here at the

beginning of the krebs cycle as acetyl

coenzyme a enters into the mitochondria

remember

glycolysis takes place in the cytosol

that's the cytoplasm that sits around

the mitochondria now we're moving into

the mitochondria two things happen the

first thing that happens is our acetyl

breaks off and we're now left with a two

carbon structure which is represented

here

now the coenzyme that delivered it it is

going to drop it off and it's going to

leave

and it's going to go back to another

glycolysis reaction

and it is going to pick up another

acetyl drop it off and start the whole

process again so think of coenzyme a as

a transport mechanism to make it go

faster and to speed up this reaction

otherwise it would take forever for the

acetyl to move from the cytosol into the

mitochondria itself

now we're left with the two carbon

compound and just like i've mentioned

before this is sort of like a magic

baking show um products appear out of

nowhere and in this simplistic form of

the krebs cycle i'm not going to explain

necessarily in detail where all of these

products come from because we don't need

to know that at this level all we need

to know is how certain compounds attach

and break down so what i mean by that is

this two carbon compound is joined by a

full

carbon compound and what happens is they

attach to one another

and they then form a six

carbon compound

now this six carbon compound is where

the magic is going to start taking place

we are now going to start breaking down

this six carbon compound each one of

those circles represents a carbon uh it

is not glucose it's important for me to

point that out even though it has the

same carbon number and what we're going

to do now is we finally got a molecule

that we can harvest hydrogens because

remember that's the point of the krebs

cycle we want all the little hydrogens

that are attached to each one of those

ball structures remember we can't see

them in the diagrams that i'm using now

so what happens is this

our six carbon compound is going to

break down

and when it breaks down it's going to

lose a few things along the way

the first thing it is going to lose is

it's going to lose a carbon

and the carbon that breaks off is going

to form carbon dioxide and that's what

we will breathe out

the other thing that it loses and that

breaks off which is really important

hence the harvesting the hydrogen aspect

is going to be our hydrogen atoms so a

hydrogen breaks off

and that then leaves us with a five

carbon compound we've lost one of the

carbons to carbon dioxide now this

process is going to repeat itself one

more time so our five carbon compound

is going to lose a carbon it's going to

basically break off and it's going to

join with an oxygen hence why oxygen

needs to be present in this process and

we end up with co2 and we breathe that

out

we also end up having a hydrogen break

off

and that hydrogen we're going to speak

about what happens to it now soon is

what we want we want to harvest it and

we're finally left with a four carbon

compound once again

and as i mentioned to you earlier that

is where the four carbon came from that

we use in the beginning and so if we arc

it over to the beginning of the cycle we

can see where the four carbon joins the

two and starts the whole process all

over again

but now here's the important part what

is happening to these hydrogens here

that we have harvested because if you

know anything about hydrogen you will

know that hydrogen does not like to be

on its own it often when it's on its own

wants to join with other compounds other

atoms it can cause chemical reactions

and left alone it may cause a reaction

that we don't want and so i need to

introduce you to a very important

carrier mechanism which is our hydrogen

carrier it goes by the name of nad

and nad refers to a carrier that's going

to pick up a hydrogen and it's going to

form a substance called

nadh

now nadh

is actually a little bit similar to

coenzyme a it's going to pick up a

substance in this case hydrogen and it's

going to move it to the final cycle

which is the oxidative phosphorylation

and so what we've done here is we've

taken our acetyl we've broken it down

we've harvested the hydrogens remember

that's the point of the krobe cycle we

want to harvest hydrogens we've attached

our hydrogens to a little buddy nad and

nad is going to look after our hydrogen

make sure hydrogen doesn't do anything

that we don't want it to and it's going

to finally deliver it to the very last

step oxidative phosphorylation and that

the final step is where we're going to

take that hydrogen and we're going to

form

32

atp molecules because at this point we

haven't made very much atp at all the

last phase is the most important phase

when making any energy or should i say

transforming any energy

now just to also point out some

important terminology that may come up

in your textbook and in your notes and i

want to unpack it very quickly in this

diagram is the process whereby the

hydrogens and the carbon dioxides break

off and they actually have names and so

let's look at first of all what do we

call it when these carbon molecules

break off

and essentially it's given its name

based off of what's happening and we

call it

decarboxylase

it means that the carbon has been

removed along with an oxygen hence the

name

decarboxylased and we end up having a

co2 molecule being released

the process where the hydrogens are

broken off is referred to as

dehydrogenase

which it has the word hydrogen in it is

basically when we are removing hydrogens

remember we're harvesting the hydrogens

as always i like to finish off our

lessons with a terminology recap so we

spoke about the end of glycolysis

producing a pyruvic acid and only if

there is oxygen present will the pyruvic

acid go into the sort of in-between

stage and where it formulates a

substance called acetyl now acetyl can't

move around on its own and so along

comes code enzyme a coenzyme a picks up

acetyl and it becomes acetyl coenzyme a

i know very long name but essentially

the coenzyme is speeding up the reaction

and delivering the acetyl where is it

delivering it to the mitochondria

remember glycolysis takes place in the

cytosol we now want to go into the

mitochondria itself now once we're in

the mitochondria we are going to need

oxygen to perform the krebs cycle so we

call this an aerobic reaction

now the next uh two terminology i

mentioned to you was about when we broke

off our hydrogens and our carbons and

remember that's the whole point of this

process to harvest the hydrogens so when

the hydrogens break off of our

four and six carbon compound if you

remember through the krebs cycle we lost

the carbon each time um we call that uh

dehydrogenased

for losing the hydrogen and

decarboxylased

for using the carbon dioxide hence

carbon and oxy carbon dioxide so those

are the terms we use for when a hydrogen

is pulled off and when a carbon dioxide

molecule is pulled off or co2

last but not least we spoke about nad

forming nadh nad is a hydrogen carrier

because hydrogen is a very mischievous

atom it will go and it will interact

with other atoms other compounds and

sometimes it ruins the chemical reaction

that you're trying to perform and so

that's what nad is used for it picks up

the hydrogen it looks after it and it's

going to deliver it into the final phase

which is oxidative phosphorylation

and that brings us to the end of the

krebs cycle the next video is going to

focus on oxidative phosphorylation it's

going to be the final part of our

cellular respiration series as always if

you like this video don't forget to give

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and leave any comments of any videos you

would like to see me do in the future

i'll see you all again soon bye