12-5 Glycolysis (Cambridge AS A Level Biology, 9700)

Summary

This script delves into the intricacies of aerobic respiration, focusing on the process of glycolysis. It explains how glucose, a stable energy molecule, is made reactive through phosphorylation using ATP, transforming into fructose 1,6-bisphosphate. This molecule then splits into triose phosphates, undergoing substrate-linked reactions and oxidation, ultimately yielding two ATP, two NADH, and pyruvate molecules. The explanation simplifies complex biochemical steps, highlighting the net gain in energy and the preparation for further stages of cellular respiration.

Takeaways

• 🧬 Aerobic respiration is the breakdown of organic molecules, such as glucose (C6H12O6), in the presence of oxygen, resulting in the production of carbon dioxide, water, and ATP.
• 🔍 Aerobic respiration is divided into four stages: glycolysis, link reaction, citric acid cycle (also known as Krebs cycle or TCA cycle), and oxidative phosphorylation along with chemiosmosis.
• 📍 Glycolysis occurs in the cytoplasm, the link reaction and citric acid cycle take place in the mitochondrial matrix, while oxidative phosphorylation and chemiosmosis happen in the inner mitochondrial membrane.
• 🍬 Glycolysis is the initial step of aerobic respiration, involving the breakdown of a glucose molecule into two molecules of pyruvate.
• ⚡ To initiate glycolysis, glucose is phosphorylated using two ATP molecules, making it more reactive and transforming it into fructose 1,6-bisphosphate.
• 🔄 The process of isomerization converts glucose into fructose 1,6-bisphosphate without the need for the student to memorize the intermediate steps.
• 💥 Fructose 1,6-bisphosphate is then split into two three-carbon sugars, or triose phosphates, during glycolysis.
• 🔋 Glycolysis results in a net gain of two ATP molecules after the initial investment of two ATP, as four ATP are produced during the substrate-linked reaction.
• 🌀 Oxidation, or dehydrogenation, occurs during glycolysis, where hydrogen atoms are released and carried by NAD+ to become reduced NADH.
• 🔑 The end products of glycolysis are two molecules of pyruvate, two NADH molecules, and a net gain of two ATP molecules.
• 🚫 It's important to note that students should not abbreviate 'substrate-linked reaction' as 'SLR' in exams but should write out the full name.

Q & A

What is aerobic respiration?

Aerobic respiration is the process of breaking down organic molecules, such as glucose (C6H12O6), in the presence of oxygen to produce carbon dioxide, water, and ATP (energy).

How many stages are there in aerobic respiration?

Aerobic respiration is divided into four main stages: glycolysis, link reaction, citric acid cycle (also known as Krebs cycle or TCA cycle), and oxidative phosphorylation along with chemiosmosis.

Where does glycolysis occur within a cell?

Glycolysis takes place in the cytoplasm of the cell.

What is the purpose of adding a phosphate group to glucose during glycolysis?

Adding a phosphate group to glucose makes it more reactive and less stable, facilitating its breakdown in the glycolysis process.

What molecule is formed after glucose is phosphorylated and undergoes isomerization?

After glucose is phosphorylated and undergoes isomerization, it becomes fructose 1,6-bisphosphate.

What happens to fructose 1,6-bisphosphate during glycolysis?

Fructose 1,6-bisphosphate breaks down into two molecules of glyceraldehyde 3-phosphate (triose phosphates).

What is the net gain of ATP molecules from glycolysis?

The net gain of ATP molecules from glycolysis is two, as two ATP are used at the beginning and four ATP are produced at the end.

What is the role of NAD in glycolysis?

NAD acts as a hydrogen carrier in glycolysis, accepting hydrogen atoms released during the oxidation of triose phosphates and becoming reduced to NADH.

What is the end product of glucose after glycolysis?

The end product of glucose after glycolysis is two molecules of pyruvate.

What are the four steps of glycolysis?

The four steps of glycolysis are phosphorylation using two ATP molecules, lysis to break it down into triose phosphates, substrate-linked reaction (SLR), and oxidation or dehydrogenation.

Why is glucose considered an energy storage molecule?

Glucose is considered an energy storage molecule because it is quite stable and not easily broken down, making it a good candidate for storing energy in a form that can be later released during cellular respiration.

Outlines

00:00

🌀 Aerobic Respiration and Glycolysis

This paragraph introduces the concept of aerobic respiration, which is the breakdown of organic molecules like glucose in the presence of oxygen, resulting in carbon dioxide, water, and ATP. It emphasizes the complexity of this process at the A-level compared to O-level, and outlines the four main stages of aerobic respiration: glycolysis, link reaction, citric acid cycle (also known as Krebs cycle), and oxidative phosphorylation along with chemiosmosis. The paragraph also explains where each of these processes occurs within the cell, highlighting that glycolysis takes place in the cytoplasm, while the other stages occur in the mitochondria. The focus then shifts to glycolysis, the first step of cellular respiration, which is the breakdown of glucose molecules in the cytoplasm. The paragraph describes the process of making glucose more reactive by phosphorylation using ATP, leading to the formation of fructose 1,6-bisphosphate, and then its breakdown into two molecules of triose phosphate, which is a precursor for further reactions in cellular respiration.

05:03

🔄 Glycolysis Process and Energy Dynamics

This paragraph delves deeper into the glycolysis process, detailing the transformation of glucose into fructose 1,6-bisphosphate through isomerization and its subsequent breakdown into two triose phosphate molecules. It explains the net gain of two ATP molecules from the initial investment of two ATPs at the start of glycolysis, thus making it an energetically favorable process. The paragraph also covers the substrate-linked reaction and oxidation steps, where triose phosphates release energy and hydrogen atoms, respectively. The hydrogen atoms are transported to the inner mitochondrial membrane by NAD+, which acts as a hydrogen carrier and becomes reduced NADH in the process. The final products of glycolysis are two pyruvate molecules and two NADH molecules, with pyruvate being a three-carbon compound resulting from the breakdown of glucose. The summary underscores the key steps of glycolysis: phosphorylation, breakdown into triose phosphates, substrate-linked reaction, and oxidation, culminating in the production of ATP and NADH.

10:03

🛢 Energy and Hydrogen Transfer in Glycolysis

The final paragraph wraps up the discussion on glycolysis by summarizing the energy and hydrogen transfer that occurs during the process. It reiterates the conversion of glucose into pyruvate, the release of energy to produce ATP, and the release of hydrogen to form reduced NAD. This paragraph succinctly captures the essence of glycolysis, highlighting the preparation of glucose for further metabolic reactions and the initial steps that set the stage for the generation of ATP and NADH, which are crucial for the subsequent stages of cellular respiration.

Keywords

💡Respiration

Respiration is a biological process where cells convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products. In the context of the video, it specifically refers to aerobic respiration, which involves the breakdown of glucose in the presence of oxygen. The script discusses the stages of respiration, emphasizing its importance in cellular energy production.

💡Aerobic Respiration

Aerobic respiration is the process by which organic molecules, such as glucose, are broken down in the presence of oxygen to produce ATP, carbon dioxide, and water. The video script delves into the specifics of aerobic respiration, highlighting its role in cellular metabolism and the production of energy.

💡Glucose

Glucose, with the chemical formula C6H12O6, is a simple sugar and a primary source of energy for cellular respiration. The video script explains that glucose is broken down through a series of processes in aerobic respiration, starting with glycolysis, to ultimately produce ATP.

💡Glycolysis

Glycolysis is the first stage of cellular respiration, where one molecule of glucose is broken down into two molecules of pyruvate, generating a small amount of ATP and NADH. The script describes glycolysis as taking place in the cytoplasm and being crucial for initiating the process of energy extraction from glucose.

💡Cytoplasm

The cytoplasm is the gel-like substance within a cell, outside the nucleus, and contains many of the cell's organelles. In the script, it is mentioned as the location where glycolysis occurs, emphasizing the compartmentalization of cellular processes.

💡Mitochondria

Mitochondria are organelles found in the cytoplasm of eukaryotic cells, known as the 'powerhouses' of the cell because they generate most of the cell's supply of ATP. The script mentions that after glycolysis, the subsequent stages of aerobic respiration occur within the mitochondria.

💡ATP (Adenosine Triphosphate)

ATP is the primary energy currency of the cell, used to power various cellular processes. The video script discusses how ATP is both consumed and produced during glycolysis, highlighting its role in energy transfer within the cell.

💡Phosphorylation

Phosphorylation is the process of adding a phosphate group to a molecule, which can increase its reactivity. In the context of the script, glucose is phosphorylated to make it more reactive, facilitating its breakdown in glycolysis.

💡Fructose 1,6-bisphosphate

Fructose 1,6-bisphosphate is an intermediate in glycolysis, formed when glucose is phosphorylated. The script describes how this molecule is created during the process of making glucose more reactive, leading to its subsequent breakdown.

💡Triose Phosphate

Triose phosphate is a three-carbon sugar phosphate that is produced during glycolysis when fructose 1,6-bisphosphate is split. The script explains that these molecules are key in the continuation of glycolysis and the production of ATP.

💡NAD (Nicotinamide Adenine Dinucleotide)

NAD is a coenzyme that plays a critical role in redox reactions, acting as an electron carrier. In the script, NAD is described as accepting hydrogen atoms during the oxidation step of glycolysis, becoming reduced NADH, which is then used in later stages of aerobic respiration.

Highlights

Aerobic respiration is the breakdown of organic molecules in the presence of oxygen, such as glucose.

Aerobic respiration is divided into four stages: glycolysis, link reaction, citric acid cycle, and oxidative phosphorylation with chemiosmosis.

Glycolysis occurs in the cytoplasm, while the link reaction and citric acid cycle occur in the mitochondrial matrix.

Oxidative phosphorylation and chemiosmosis take place in the inner mitochondrial membrane.

Glycolysis is the initial step of aerobic respiration, breaking down glucose molecules.

Glucose is energy-stable and not easily broken down, requiring activation through phosphorylation.

Phosphorylation of glucose is achieved by transferring phosphate groups from ATP, resulting in ADP.

The process of isomerization converts glucose into fructose 1,6-bisphosphate.

Fructose 1,6-bisphosphate breaks down into two molecules of triose phosphate.

Triose phosphates undergo substrate-linked reactions, releasing energy to produce ATP.

Oxidation or dehydrogenation occurs during glycolysis, where hydrogen atoms are released and carried by NAD+.

The end product of glycolysis is two molecules of pyruvate, each with three carbons.

Glycolysis results in a net gain of two ATP molecules after the initial investment of two ATP.

The importance of understanding the location of each process within the cell for a comprehensive grasp of aerobic respiration.

The necessity of glucose phosphorylation to increase its reactivity for the glycolysis process.

The role of NAD+ as a hydrogen carrier in the glycolysis process.

The summary of glycolysis steps: phosphorylation, breakdown into triose phosphates, substrate-linked reaction, and oxidation.

Transcripts

so now that we have sort of talked about

the overall steps in respiration we have

to go into the specifics and you cannot

talk about respiration without talking

about aerobic respiration now if you

have done o levels uh you will know that

aerobic respiration is the breakdown of

organic molecules in the presence of

oxygen okay uh for example glucose which

is C6 h126 will be broken down with the

assistance of six molecules of oxygen

where it forms six molecules of carbon

dioxide six molecules of water and ATP

uh that was what you just had to know

for o levels but in a levels however

it's going to become painful you have

been

warned so aerobic respiration is divided

into four big stages glycolysis link

reaction crap cycle and also oxidative

phosphorilation and chemiosmosis uh

oxidative phosphorilation and chem

osmosis are put together they are well

technically they are two separate

processes but we just lump it in as one

now it is very important as a student to

know where these processes happen inside

the cell glycolysis happens in the

cytoplasm link reaction and crap cycle

happen in The Matrix of the mitochondria

and oxidative phosphorilation together

with chem osmosis happen in the inner

mitochondrial membrane or the chrisy you

can refer to them as both that's fine so

without wasting any time we have to look

at the first step to start the ball

rolling and that step is known as

glycolysis so what exactly is glycolysis

all about glyco basically means sugar

related lysis in this case means

breakdown so it's the breakdown of sugar

molecule ules and it happens in the

cytoplasm that is the first important

thing that you have to know about

glycolysis we started off with glucose

molecules right okay but I know glucose

is a ring structure but to make life

easier for us I'm not going to represent

glucose as a ring structure I'm going to

represent them as a linear structure

instead so as you can see the six balls

over here the six dots uh those six

balls represent carbon six C6

h126 so it's the same glucose in its

ring structure but I'm just drawing it

as a linear form because it's easier to

do so trust me on this okay

so before glycolysis begins you know we

have a bit of problem because you want

to break down the glucose molecules

obviously that's what respiration is all

about but the problem here is glucose is

quite energy stable uh energy stable

meaning to say it is just not easily

broken down so you're like God damn it I

want to break something down but you

know uh it's not easy to break down the

glucose molecule that is why glucose is

referred to as an energy uh storage

molecule right it is different from ATP

because ATP can easily be hydrolized but

glucose isn't so the solution is you got

to make glucose more reactive or

unstable so

how do you make it unstable so some of

my students will say well you can

increase the temperature but remember

these this is in your cell you cannot

just increase the temperature of your

cells easily because your enzymes can

denature so we need to have a different

solution to that and the solution is to

phosphorate the glucose molecule sounds

very fancy but what exactly does

phosphorate the glucose mean phosphorate

the glucose just means adding phosphat

so then comes the question where does

the phosphate come from the phosphate

comes from at TP remember I told you

before that ATP is an immediate source

of energy so if you want glucose to have

more energy it can receive energy from

ATP that's one function of ATP too so

each ATP molecule will provide one

phosphate group or the pi

and to the to the glucose molecule what

exactly happens is look at the ATP the

phosphate has gone to the glucose

molecule attached to either sides as you

can see over there okay and what happens

to the ATP molecule the ATP is now

called a DP adenosin D phosphate so to

simplify this you just have to say that

the glucose molecule is first

phosphorilated using two ATP molecules

which will become 2 ADP and that glucose

molecule now has two phosphates attached

to either sides okay and from stable it

becomes unstable okay or more

reactive this is good it becomes more

reactive and you have to know the name

of that molecule the name of that

molecule is known as fructose

bisphosphate or fructose 16 bis

phosphate why is it called fructose 16

bis phosphate is because the phosphate

is attached to carbon number one and

carbon number six now as a student you

might go how the hell did the glucose

actually become fructose uh that is

through a process known as isomerization

by the way uh in reality between between

the steps of glucose to fructose 16 bis

phosphate there are actually three to

four steps you don't have to know that

extra three to four steps by the way in

glycolysis um but um the glucose

structure changes slightly and becomes

fructose 16 bis phosphate you have to

know that it becomes fructose 16 bis

phosphate by the way God it's a mouthful

to mention uh the name of this

molecule once it becomes fructose 6 bis

phosphate this is good because it's more

reactive so it's easier for the next

reaction to happen so based on my

diagram here tell me what happens to the

fructose 16 bis

phosphate as you can see it breaks down

right in the middle and it forms two

molecules of trios phosphate what are

trios phosphates triose is just a sugar

with three carbons chapter 2 biological

molecules and why is it called trios

phosphate because each of the sugar has

a phosphate added to it so the fructose

has been broken down in the middle and

that is the lysis and of course what

needs to happen is um

the trios phosphate will undergo the

next stage which is known as substrate

linked reaction where it releases a

little bit of energy and that energy is

used to make four ATP molecules so you

see at the beginning of glycolysis you

had to spend 2 ATP but towards the end

of glycolysis you get four ATP molecules

so it's a net gain of two ATP molecules

which is a good thing okay over here and

of course what actually happens is uh

the molecule also under goes oxidation

oxidation in this case means

dehydrogenation what is dehydrogenation

it releases the hydrogen atoms and in

the previous video I told you that the

hydrogen atom doesn't know where to go

it needs to go into the inner

mitochondrial membrane uh so to

transport it to the inner mitochondrial

membrane we enlist the help of Neds

nicotinamide adinin dinucleotide you

don't have to memorize the long name I'm

just showing off a little bit you know

whatever the NAD acts as the hydrogen

carrier uh what does it mean by it acts

as the hydrogen carrier it accepts the

hydrogen and when it accepts the

hydrogen it becomes reduced NAD the

reason why it becomes reduced NAD is

because the NAD has received the

hydrogen so the trios phosphates undergo

oxidation but the

NAD under goes reduction and the final

molecule that is formed in glycolysis is

the two pyate molecules so so

essentially glycolysis is made up of the

four steps the four steps are as follows

phosphorilation using two ATP

molecules Lis to break it down into

trios phosphates substrate linked

reaction SLR you cannot write SLR in the

exam you have to write out the full name

and of course oxidation or

dehydrogenation so these are the four

steps of glycolysis in a

nutshell so in summary for glycolysis

what you have to know

is that uh the glucose molecule again

just writing it back again the glucose

molecule is phosphorilated using 2 ATP

why you must know the reason why because

glucose is too stable so we phosphorate

it by spending to ATP to make it more

reactive it becomes fructose 16 bis

phosphate which will break down into

trios phosphates the trios phosphates

will then undergo substrate link

reaction and also oxidation to produce

four ATP molecules and two reduced n and

the end product of the glucose when it's

broken down is two pyate molecules and

each of the pyate are just three carbon

so in a nutshell what have you done to

the glucose molecule you have broken it

down into half to become pyro you've

released out some of the energy to get

ATP and you've also released out some of

its hydrogen to get the reduced NAD so

that is what pyrovate uh that is what

glycolysis is all

about