Hydrolysis | Macromolecules | Biology | Khan Academy

Summary

The video script delves into the process of dehydration synthesis, illustrating how glucose molecules form disaccharides like maltose and longer polysaccharides such as starch, glycogen, and cellulose. It highlights the structure and function of these carbohydrates in nature and within organisms. The script also explains the reverse process, hydrolysis, detailing how these complex carbohydrates are broken down into glucose for energy utilization in biological systems.

Takeaways

• 🧬 Dehydration synthesis is the process where monosaccharides like glucose form bonds to create disaccharides like maltose and polysaccharides.
• 🍚 Starch, found in foods like mashed potatoes, is a polysaccharide composed mainly of glucose chains.
• 🦂 Chitin, a polysaccharide similar to starch, forms the exoskeleton of insects and crustaceans like lobsters.
• 🏃 Glycogen, stored in our muscles, is a polysaccharide that serves as an energy reserve and is made of glucose chains.
• 🌳 Cellulose, a major component of plant cell walls, paper, and wood, is a polysaccharide with glucose chains arranged differently from starch.
• 💭 Cotton is nearly pure cellulose, with about 90 percent of its composition being this polysaccharide.
• 🔬 The structure of cellulose is unique due to the hydrogen bonds formed between oxygen atoms and hydrogen atoms across different glucose chains.
• 🍽 Hydrolysis is the process used to break down polysaccharides into monosaccharides, such as glucose, using water.
• 🚰 The prefix 'hydro' in hydrolysis indicates the involvement of water, while 'lysis' means breaking down.
• 🔄 Hydrolysis is essentially the reverse of dehydration synthesis, involving the breaking of bonds with the help of water molecules.
• 🛠️ The hydrolysis mechanism involves the transfer of hydrogen protons and the formation and breaking of covalent bonds, leading to the release of individual glucose molecules.

Q & A

What is the process of dehydration synthesis in the context of carbohydrates?

Dehydration synthesis is a chemical reaction where two molecules combine to form a larger molecule, with the removal of a water molecule. In the context of carbohydrates, this process allows monosaccharides like glucose to bond together, forming disaccharides or polysaccharides.

What is maltose and how is it formed?

Maltose is a disaccharide formed when two glucose molecules bond together through a dehydration synthesis reaction. It is a simple example of how monosaccharides can combine to form larger carbohydrate structures.

What are polysaccharides and how do they differ from disaccharides?

Polysaccharides are complex carbohydrates consisting of long chains of monosaccharide units, often glucose. They differ from disaccharides, which are only two monosaccharide units linked together, in that polysaccharides can have many more monosaccharide units and can be derived from various sources.

What is the primary component of mashed potatoes and how is it related to glucose?

The primary component of mashed potatoes is starch, which is a polysaccharide made up of long chains of glucose molecules. This shows the prevalence of glucose as a building block in various carbohydrate structures.

What is chitin and how is it similar to starch?

Chitin is a polysaccharide found in the exoskeletons of insects and crustaceans, as well as in the cell walls of fungi. It is similar to starch in that both are composed of chains of glucose or glucose-derived units, but chitin has a different structural arrangement.

What is glycogen and where is it typically stored in the body?

Glycogen is a form of polysaccharide that serves as the primary storage form of glucose in animals, including humans. It is typically stored in the liver and muscles to provide a readily available energy source.

What is cellulose and where can it be commonly found?

Cellulose is a polysaccharide that is a major component of the cell walls of plants. It can be commonly found in paper, wood, and cotton, which is one of the purest forms of cellulose.

What is the structural difference between starch and cellulose?

The structural difference between starch and cellulose lies in the orientation of the glucose molecules in their chains. In starch, the glucose molecules are linked in the same orientation as in the original glucose molecule, while in cellulose, the glucose units are flipped over, creating a different bonding pattern.

What are hydrogen bonds and how do they contribute to the structure of cellulose?

Hydrogen bonds are a type of chemical bond that occurs between a hydrogen atom covalently bonded to an electronegative atom and an electronegative atom in a different molecule. In cellulose, hydrogen bonds form between the oxygen atoms of one glucose strand and the hydrogen atoms of another, contributing to its strong and rigid structure.

What is hydrolysis and how does it relate to breaking down polysaccharides?

Hydrolysis is a chemical process that involves the breaking of a bond in a molecule using water. In the context of polysaccharides, hydrolysis is the process by which these large carbohydrate chains are broken down into their constituent monosaccharide units, such as glucose, through the addition of water.

Can you describe the mechanism of hydrolysis in breaking the bond between glucose molecules in a polysaccharide?

The mechanism of hydrolysis involves a water molecule interacting with the bond between glucose units in a polysaccharide. An oxygen atom in the water molecule can grab a hydrogen proton from a nearby hydronium molecule, forming a covalent bond and becoming positively charged. This allows another water molecule to form a bond with the carbon atom, leading to the breaking of the original bond and the release of individual monosaccharide units.

How is the process of hydrolysis important in biology?

Hydrolysis is crucial in biology as it allows organisms to break down complex carbohydrates like starch, glycogen, and cellulose into simpler monosaccharides, such as glucose. This process is essential for energy production and metabolic processes within cells.

Outlines

00:00

🍚 Formation and Examples of Polysaccharides

This paragraph introduces the concept of polysaccharides, which are long chains of glucose molecules linked together through dehydration synthesis. The video script explains how glucose can form different types of polysaccharides such as maltose, starch, chitin, glycogen, and cellulose. It provides examples of where these polysaccharides can be found, such as in mashed potatoes (starch), insect shells and lobsters (chitin), and in the cell walls of plants (cellulose). The paragraph also touches on the structural differences between starch and cellulose, highlighting the hydrogen bonds that give cellulose its strength. The script sets the stage for the discussion of hydrolysis, the process by which these complex carbohydrates are broken down into simpler glucose molecules for energy.

05:01

💧 Hydrolysis: The Mechanism of Breaking Polysaccharides

The second paragraph delves into the process of hydrolysis, which is the biochemical method used to break down polysaccharides into glucose molecules. It describes the mechanism of hydrolysis as the reverse of dehydration synthesis, where a water molecule is used to break the bond between glucose units in a polysaccharide chain. The script explains the role of the hydronium ion (H3O+) and the water molecule in facilitating the transfer of hydrogen protons, which leads to the cleavage of the glycosidic bond. This process results in the formation of individual glucose molecules, which can then be used by the body for energy. The paragraph also mentions that hydrolysis is not limited to glucose but can also be applied to other disaccharides like sucrose, which can be broken down into glucose and fructose. Hydrolysis is presented as a crucial reaction in biology for the digestion and utilization of carbohydrates.

Keywords

💡Dehydration Synthesis

Dehydration synthesis is a chemical reaction where two molecules combine to form a larger molecule while releasing a molecule of water. In the context of the video, this process is used to explain how glucose molecules can bond together to form disaccharides like maltose and polysaccharides such as starch and cellulose. The video emphasizes this as the foundational process for creating complex carbohydrates from simple sugar units.

💡Disaccharide

A disaccharide is a carbohydrate composed of two monosaccharide units. Maltose, which is formed by the bonding of two glucose molecules, is given as an example in the video. This keyword is crucial for understanding the progression from simple sugars to more complex structures and highlights the role of dehydration synthesis in food and energy storage.

💡Polysaccharides

Polysaccharides are complex carbohydrates made up of long chains of monosaccharide units. The video discusses several types of polysaccharides, including starch, glycogen, and cellulose, which are essential for energy storage in plants and animals, and structural components in plants, respectively. This term is central to the video's exploration of how glucose can be used to form various biologically significant molecules.

💡Starch

Starch is a polysaccharide that serves as the primary form of energy storage in plants. It is composed of long chains of glucose molecules. The video uses mashed potatoes as a relatable example of starch, illustrating how it is a common component of the human diet and a source of energy for the body.

💡Chitin

Chitin is a polysaccharide found in the exoskeletons of insects and crustaceans, providing structural support. The video mentions chitin as an example of how polysaccharides have diverse functions in nature, including forming protective layers in various organisms.

💡Glycogen

Glycogen is a branched polysaccharide of glucose that serves as the primary form of energy storage in animals, including humans. It is stored in the liver and muscles. The video points out that glycogen in muscles is an important energy reserve, demonstrating the role of polysaccharides in energy metabolism.

💡Cellulose

Cellulose is a polysaccharide made up of glucose molecules linked together in a specific way that allows for the formation of strong, fibrous structures. It is a key component of plant cell walls and is also the main constituent of materials like paper and cotton. The video explains that the unique structure of cellulose, with its hydrogen bonding, gives it strength and rigidity.

💡Hydrolysis

Hydrolysis is the chemical process of breaking down a compound by reacting it with water. In the video, hydrolysis is described as the reverse of dehydration synthesis, where water molecules are used to break the bonds in polysaccharides, such as starch, to release glucose. This process is essential for digestion and the absorption of nutrients from carbohydrates.

💡Cotton

Cotton is highlighted in the video as a natural source of cellulose, with cotton fibers being nearly pure cellulose. This keyword serves to connect the abstract concept of cellulose with a tangible, everyday material, helping to illustrate the ubiquity and versatility of polysaccharides in nature.

💡Leaving Group

In the context of the video, a leaving group refers to a molecule or ion that departs from the reaction center during a chemical reaction, such as hydrolysis. The video uses the term to explain how the breaking of bonds in polysaccharides occurs, with the oxygen in the water molecule acting as a leaving group, which is crucial for understanding the mechanism of hydrolysis.

💡Hydrogen Bonds

Hydrogen bonds are a type of intermolecular force that occurs between a hydrogen atom and a more electronegative atom. The video explains that hydrogen bonds between cellulose chains give cellulose its structural integrity. This keyword is important for understanding how the physical properties of polysaccharides, like their strength and flexibility, are influenced by their molecular structure.

Highlights

Dehydration synthesis is a process where glucose molecules can form bonds to create disaccharides like maltose.

Polysaccharides are long chains of glucose molecules, including common substances like starch and glycogen.

Starch, the main component of mashed potatoes, is a polysaccharide made of glucose chains.

Chitin, found in the exoskeletons of insects and crustaceans, is a polysaccharide similar to starch but with a different structure.

Glycogen, stored in muscle tissue, serves as an energy reserve and is structurally similar to glucose chains.

Cellulose, a key component of paper, wood, and plant cell walls, is a glucose-based polysaccharide with a unique arrangement.

Cotton is nearly pure cellulose, highlighting its abundance and importance in various industries.

The difference between starch and cellulose lies in the orientation of glucose molecules and the resulting hydrogen bonds.

Hydrogen bonds between oxygen and hydrogen atoms are crucial for the structure of cellulose.

Hydrolysis is the process of breaking down polysaccharides using water, which is essential for digesting starch.

The prefix 'hydro' in hydrolysis indicates an involvement of water, while 'lysis' means breaking down.

Hydrolysis involves a water molecule breaking the bond between glucose units in a polysaccharide.

The mechanism of hydrolysis is a reversal of dehydration synthesis, utilizing water to break the glycosidic bond.

In hydrolysis, an oxygen atom in the polysaccharide can capture a hydrogen proton from a hydronium molecule.

A good leaving group in hydrolysis can facilitate the breaking of the glycosidic bond.

The hydrolysis process can result in the formation of standalone glucose molecules from a polysaccharide chain.

Hydrolysis is a vital biological reaction for breaking down complex carbohydrates into usable glucose.

The example of sucrose hydrolysis demonstrates the breakdown into glucose and fructose molecules.

Transcripts

- In the video on dehydration synthesis,

we saw how we could start with a glucose molecule,

and through dehydration synthesis

form a bond with another glucose molecule.

And just by doing that, you'd form the disaccharide maltose

if these were both glucose molecules.

But then you could keep going,

and you could form longer chains of glucose molecules.

And to these things, where you would take a monosaccharide,

glucose is the most common example of that,

and you create chains of these,

we call these polysaccharides.

Polysaccharides, this is a polysaccharide.

And there's all sorts of interesting examples

of polysaccharides all around you,

especially polysaccharides of glucose,

or things that are derived from glucose.

This right here this is a bowl of mashed potatoes,

which is mostly starch.

Which is mainly just chains of glucose.

So this right over here, that is starch.

The shell of a lot of insects and things like lobsters,

and the wings of these insects right over here,

that's made of something called chitin.

And chitin is also a polysaccharide.

It's made of chains, a modification of glucose

chains of that, that's chitin right over there.

Very similar to starch, in our muscles we have glycogen,

which is our store of energy in our muscles.

You have cellulose,

which is probably all around you right now.

Cellulose are things like--

Because this is something that's all around you,

and you don't even realize it.

Cellulose, this is what constitutes things

like paper and wood.

It's involved in the cell walls of plants.

This right over here is a picture of cotton,

cotton in its natural form.

And cotton is actually one of the purest forms of cellulose,

it's roughly 90 percent cellulose.

And if you take a zoom in on a cotton fiber,

actually a fiber of cellulose,

you'll see chains of glucose molecules.

So you see this right over here, that is a glucose molecule.

Then you see another glucose molecule.

And this chain has been formed

through dehydration synthesis.

And difference between starch and cellulose,

for the main difference,

in terms of how this bonding has.

With starch, the glucose molecules just keep forming

the way that you saw in the video on dehydration synthesis.

While in cellulose, they get flipped over.

So you can see here, this oxygen is pointing that way,

this oxygen is pointing that way,

that oxygen is pointing that way.

And you could look up more about cellulose.

But it's really interesting, what gives it its structure

are these hydrogen bonds that form

between the partially negative,

the very electronegative oxygens on one strand.

And the partially positive hydrogens on another strand,

and that's actually what give its structure.

So really, really interesting things, these polysaccharides.

The question is,

how do you actually break these things down?

If I were to eat these mashed potatoes,

how do I eventually turn this thing into glucose,

so I could use it for energy?

And the way that happens is through hydrolysis.

And you could break down this word.

The "hydro", if you see hydro, the prefix hydro,

that's a good clue that it has something to do with water.

And then if you see "lysis", if you're lysing something,

this means that you're gonna break it down.

So this is breaking down something using water.

And that's exactly what happens with hydrolysis.

If you have this polysaccharide,

and let's throw a water molecule in there,

this water molecule is going to be able

to break one of these bonds.

So we might end up with something like--

This chain could keep going in both directions,

but we could end up with something that looks like this.

That looks something like that.

So half of this water molecule gets broken up,

essentially to break this bond.

It's the opposite of dehydration synthesis.

So let's see if we can understand,

get an overview of exactly how that happens.

So this right over here, this is maltose right over here.

It's disaccharide, it's just two glucose molecules

attached to each other.

If we kept doing this, if this kept going,

if this guy had bond to another glucose molecule,

and this guy had a bond to another glucose molecule,

then we'd be dealing with starch.

Or we could be dealing with glycogen.

If this was flipped over,

and they kept flipping over and over,

then we could be talking about cellulose.

But let's just thing about how this is the mechanism.

The mechanism by which this bond can actually be broken.

It's really just the reverse of dehydration synthesis.

This is going to just be an overview of it.

This oxygen right over here, it's got two lone pairs.

There's always a chance that if it bumps into something

in just the right way, it could nab a hydrogen proton

that is just sitting out there in the fluid.

We're assuming that this is happening

in an aqueous solution, it's happening in water.

So it can just grab a hydrogen proton

from a passing hydronium molecule.

And so if it does that, it would form a covalent bond,

and have a positive charge.

And now relative to actually both carbons,

but let's focus on this carbon right over here.

This guy would be, what we call in organic chemistry,

a good leaving group.

So these electrons,

the oxygen might want to just take these back,

because it's got a positive charge,

oxygen is really electronegative,

so things just bump in exactly the right way.

If things interact in exactly the right way,

you might have another water molecule.

And this is where that extra water molecule is valuable

in our hydrolysis.

So let's say this is just another water molecule

just passing by in exactly the right way.

This could form a bond with that carbon

right over there.

And just as it forms a bond with that carbon,

the carbon says, "Okay, I'm getting to share

"some other electrons, let me let go of these electrons."

So it lets go of these electrons.

And what do you have left?

Well, we can go over here,

and so now this carbon has, let me color code it,

so this bond that was just forming,

that is this bond right over here.

This oxygen is this oxygen right over there.

It actually has another hydrogen attached to it,

so let me do that.

So right when it makes the bond,

it will have a positive charge.

And then, this bond right over goes back to this oxygen.

This oxygen right over here,

is that oxygen right over there.

Now when it started off, this guy grabbed--

The hydrogen proton that I grabbed, I showed in orange,

that's this one.

That's this one right over here.

Now, this one grabbed a hydrogen proton,

and now this one can actually give back

a hydrogen proton through solution.

If a water molecule passing by could just grab

this hydrogen proton and then become a hydronium molecule.

So it took a hydrogen proton, it's giving it back,

and so what we are left with--

It took up this water molecule right over here

to break the bond.

And so this is a positive charge.

It could be a passing hydronium molecule,

and it'll just hand it off to that.

And there you have it,

we have two standalone glucose molecules right over there.

We have broken the bond.

And these could be parts of chains,

in which case, we've just broken the chain.

Or, if we're just dealing with maltose,

now we've broken it down

into the individual glucose molecules.

And the example here is with glucose,

but it could've been the case with maltose,

and it could've been the case with sucrose

where we break sucrose down using hydrolysis

into a glucose molecule and a fructose molecule.

So it's a very important reaction in biology.