Introduction to amino acids | Macromolecules | Biology | Khan Academy

Summary

This script delves into the fundamental role of DNA in storing genetic information and its replication process. It highlights the crucial transition from DNA to RNA, specifically messenger RNA, through transcription. The focus then shifts to proteins, the workhorses of organisms, constructed from amino acids. The script explains the 20 common amino acids, their structures, and how their side chains (R groups) influence protein shape and function. It also touches on peptide bonds that link amino acids into polypeptides and proteins, and introduces the concept of zwitterions, the neutral state of amino acids at physiological pH.

Takeaways

• 🧬 DNA is crucial for storing genetic information and maintaining the identity of organisms.
• 🔄 DNA has the ability to replicate itself, a process fundamental to the creation of new organisms.
• 📜 The process of creating an organism involves translating DNA information into functional molecules.
• 📝 Transcription is the first step in this process, converting DNA to messenger RNA (mRNA).
• 🌐 mRNA moves to ribosomes where, with the help of transfer RNA (tRNA) and amino acids, it forms proteins.
• 🔗 Proteins are chains of amino acids and perform a variety of functions within an organism.
• 🌟 There are 20 common amino acids that make up the proteins in most biological systems.
• 🔑 Each amino acid has a unique side chain (R group) that influences the protein's shape and function.
• 💧 The side chains can be hydrophilic or hydrophobic, affecting how proteins interact with their environment.
• 🔗 Amino acids link together through peptide bonds to form polypeptide chains, which fold into functional proteins.
• 🌀 The final protein structure is influenced by the properties of its amino acid side chains, including size and polarity.
• 🛡️ At physiological pH, amino acids often exist as zwitterions, with both positive and negative charges balancing to neutrality.

Q & A

What is the primary role of DNA in organisms?

DNA serves as the storage of genetic information, which is essential for maintaining the characteristics that define each organism.

Why is the ability of DNA to replicate itself important?

DNA replication is crucial because it allows for the production of more DNA, ensuring the continuity of genetic information during cell division and reproduction.

What is the process called when DNA information is transcribed into RNA?

The process is called transcription, where DNA is used as a template to create a complementary strand of messenger RNA (mRNA).

What is the role of messenger RNA (mRNA) in protein synthesis?

mRNA carries the genetic code from DNA to the ribosomes, where it serves as a template for the assembly of amino acids into proteins.

What is the function of transfer RNA (tRNA) in the process of protein synthesis?

tRNA is responsible for bringing the correct amino acids to the ribosomes during protein synthesis, matching the amino acids to the codons on the mRNA.

How do proteins contribute to the functioning of an organism?

Proteins perform a wide range of functions within an organism, including acting as enzymes, structural components, signaling molecules, and transporters, among others.

What are the basic units that make up proteins?

The basic units of proteins are amino acids, which are linked together to form polypeptide chains that fold into functional proteins.

How many common amino acids are there in most biological systems?

There are typically 20 common amino acids that are coded for by DNA in most biological systems.

What is the significance of the R group in amino acids?

The R group, or side chain, of an amino acid is significant because it determines the amino acid's chemical properties and influences the shape and function of the resulting protein.

What is the term for the bond that connects two amino acids together?

The bond that connects two amino acids is called a peptide bond, and the resulting chain of amino acids is known as a polypeptide.

What is the term for an amino acid at physiological pH that has both a positive and negative charge but is overall neutral?

An amino acid at physiological pH that exhibits this property is called a zwitterion, reflecting its hybrid charge state.

Outlines

00:00

🧬 DNA to Proteins: The Central Dogma

The paragraph discusses the critical role of DNA in storing genetic information and its ability to replicate. It emphasizes that DNA replication alone isn't sufficient for organism development; the genetic information must be translated into functional molecules. The process starts with transcription, where DNA is transcribed into messenger RNA (mRNA). This mRNA then moves to ribosomes, where transfer RNA (tRNA) brings amino acids to form proteins. Proteins, composed of amino acids, perform the bulk of an organism's functions, such as immune response, enzymatic reactions, signaling, and muscle contraction. The paragraph introduces the concept of amino acids, the building blocks of proteins, and highlights the 20 common amino acids coded by DNA. It describes the general structure of amino acids, featuring an amino group, a carboxyl group, and a variable side chain (R group) that determines the amino acid's properties and the protein's function.

05:01

🌊 Amino Acids and Protein Interactions

This paragraph delves into the interaction of amino acids with their environment, influenced by their side chains. It contrasts the hydrophilic (water-attracting) nature of serine, with its alcohol side chain, to the hydrophobic (water-repelling) nature of valine, with its hydrocarbon side chain. The paragraph explains how these properties affect protein structure, with hydrophilic parts tending to face outwards and hydrophobic parts tending to be internal in an aqueous environment. It also touches on how the size and nature of side chains impact protein folding and packing. The concept of peptide bonds, which link amino acids to form polypeptides and ultimately proteins, is introduced. Lastly, the paragraph discusses the zwitterion form of amino acids at physiological pH, where the carboxyl group is deprotonated and the amino group is protonated, resulting in a neutrally charged molecule with both positive and negative ends.

Keywords

💡DNA

DNA, or deoxyribonucleic acid, is the molecule that stores the genetic information necessary for the growth, development, functioning, and reproduction of all known living organisms. In the video, DNA is highlighted as the fundamental carrier of hereditary information, and its ability to replicate itself is a key aspect of its function, as mentioned in the script.

💡Replication

Replication refers to the process by which a DNA molecule makes an identical copy of itself. This is vital for the continuity of genetic information from one generation to the next. The script emphasizes replication as a neat property of DNA, which is essential for the production of an organism.

💡Organism

An organism is any individual entity that embodies the properties of life. The video discusses how DNA replication alone is insufficient to produce an organism; it must also be used to create the various molecules that perform the organism's functions.

💡Transcription

Transcription is the first step in gene expression, where the information from a strand of DNA is copied into a new molecule of messenger RNA (mRNA). The script describes transcription as the process leading from DNA to RNA, which is a crucial step in the creation of proteins.

💡Messenger RNA (mRNA)

mRNA carries the genetic information from DNA to the ribosomes, the cellular structures where proteins are synthesized. In the video, mRNA is described as the intermediate molecule between DNA and proteins, essential for the translation process.

💡Ribosomes

Ribosomes are the cellular components responsible for protein synthesis. They 'read' the sequence of the mRNA and assemble the corresponding amino acids to form a protein. The script mentions ribosomes as the site where tRNA and amino acids come together to form proteins.

💡Transfer RNA (tRNA)

tRNA is a type of RNA that helps in the translation process by bringing the correct amino acids to the ribosome to be incorporated into the growing protein chain. The video script highlights tRNA's role in conjunction with amino acids in protein synthesis.

💡Amino Acids

Amino acids are the building blocks of proteins, each with a unique side chain that contributes to the protein's structure and function. The script provides examples of amino acids and discusses their importance in determining the properties and functions of proteins.

💡Proteins

Proteins are large molecules composed of one or more chains of amino acids and are essential for the structure, function, and regulation of the body's cells, tissues, and organs. The video emphasizes that proteins perform much of the work within an organism, as they are the molecules that carry out many biological functions.

💡Peptide Bonds

A peptide bond is a chemical bond that links two amino acids together in a protein. The script describes how peptide bonds form between amino acids, such as serine and valine, creating a chain that can become a protein.

💡Zwitterion

A zwitterion is a molecule that has both positive and negative charges but is overall neutral. The script explains that at physiological pH, amino acids often exist as zwitterions, with the carboxyl group deprotonated and the amino group protonated.

Highlights

DNA is essential for storing genetic information and maintaining individual characteristics of organisms.

DNA has the unique ability to replicate itself, a process fundamental to its role in biological systems.

Replication alone is insufficient for creating organisms; the DNA information must be used to produce functional molecules.

The process of DNA to RNA conversion, known as transcription, is the first step in producing an organism.

Messenger RNA (mRNA) plays a crucial role in the transcription process, carrying genetic information for protein synthesis.

Proteins, constructed from amino acids, perform the majority of an organism's functions.

Amino acids are the building blocks of proteins, with 20 common types found in most biological systems.

Each amino acid has a unique side chain (R group) that influences the protein's shape and function.

The side chains' polarity affects how proteins interact with their environment, with hydrophilic and hydrophobic properties.

Protein structures are influenced by the hydrophobic and hydrophilic properties of amino acid side chains.

Amino acids connect through peptide bonds to form polypeptide chains, which can become proteins.

The term 'peptide bond' refers to the linkage between two or more amino acids in a chain.

At physiological pH, amino acids often exist as zwitterions, with both positive and negative charges neutralizing each other.

The zwitterion form of amino acids is significant for understanding their behavior in biological systems.

Electronegativity plays a key role in determining the polarity and interactions of amino acid side chains.

Proteins serve various functions, including immune response, enzymatic activity, and muscle contraction.

The diversity of amino acid side chains allows for a wide range of protein structures and functions.

Understanding the properties of amino acids is fundamental to grasping protein synthesis and function.

Transcripts

- DNA gets a lot of attention as the store

of our genetic information, and it deserves that.

If we didn't have DNA, there would be no way

of keeping the information that makes us us,

and other organisms what those organisms are.

And DNA has some neat properties, it can replicate itself,

and we go into a lot of depth on that in other videos.

So DNA producing more DNA, we call that,

we call that replication, but just being able

to replicate yourself on its own isn't enough

to actually produce an organism.

And to produce an organism, you somehow have to

take that information in the DNA, and then

produce things like a structural molecules,

enzymes, transport molecules, signaling molecules,

that actually do the work of the organism.

And that process, the first step, and this is all a review

that we've seen in other videos.

The first step is to go from DNA to RNA,

and in particular, messenger RNA.

"Messenger RNA," and this process right over here,

this is called transcription.

"Transcription," we go into a lot of detail

on this in other videos.

And then you wanna go from that messenger RNA,

it goes to the ribosomes and then tRNA goes and grabs

amino acids, and they form actual proteins.

So you go from messenger RNA, and then in conjunction,

so this is all, this is in conjunction with tRNA

and amino acids, so let me say "+tRNA," and "amino acids."

And I'll write "amino acids" in, I'll write it in a brighter

color, since that's going to be the focus of this video.

So tRNA and amino acids, you're able to construct proteins.

You are able to construct proteins,

which are made up of chains of amino acids,

and it's the proteins that do

a lot of the work of the organism.

Proteins, which are nothing but chains of amino acids,

or they're made up of, sometimes

multiple chains of amino acids.

So you can image, I'm just going to, that's an amino acid.

That's another amino acid.

This is an amino acid.

This is an amino acid, you could keep going.

So these chains of amino acids, based on

how these different, based on the properties

of these different amino acids,

and how the protein takes shape and how

it might interact with its surrounding,

these proteins can serve all sorts of different functions.

Anything from part of your immune system,

antibodies, they can serve as enzymes,

they can serve as signaling hormones, like insulin.

They're involved in muscle contraction.

Actin and myosin, we actually have

a fascinating video on that.

Transport of oxygen.

Hemoglobin.

So proteins, the way at least my brain of it,

is they do a lot of the work.

DNA says, well, what contains the information,

but a lot of the work of organism is actually done,

is actually done by the proteins.

And as I just said, the building blocks

of the proteins are the amino acids.

So let's focus on that a little bit.

So up here are some examples of amino acids.

And there are 20 common amino acids,

there are a few more depending on what organism you look at,

and theoretically there could be many more.

But in most biological systems,

there are 20 common amino acids that the DNA is coding for,

and these are two of them.

So let's just first look at what is common.

So, we see that both these, and actually all three of this,

this is just a general form, you have an amino group.

You have an amino group, and this where,

this is why we call it an "amino," an amino acid.

So you have an amino group.

Amino group right over here.

Now you might say, "well, it's called an amino acid,"

"so where is the acid?"

And that comes from this carboxyl group right over here.

So that's why we call it an acid.

This carboxyl group is acidic.

It likes to donate this proton.

And then in between, we have a carbon,

and we call that the alpha carbon.

We call that the alpha carbon.

Alpha carbon, and that alpha carbon is bonded,

it has a covalent bond to the amino group,

covalent bond to the carboxyl group,

and a covalent bond to a hydrogen.

Now, from there, that's where you get the variation

in the different amino acids, and actually,

there's even some exceptions for how the nitrogen is,

but for the most part, the variation between

the amino acids is what this fourth covalent bond

from the alpha carbon does.

So you see in serine, you have this,

what you could call it an alcohol.

You could have an alcohol side chain.

In valine right over here, you have a

fairly pure hydrocarbon, hydrocarbon side chain.

And so in general, we refer to these side chains

as an R group, and it's these R groups

that play a big role in defining the shape of the proteins,

and how they interact with their environment

and the types of things they can do.

And you can even see, just from these examples

how these different sides chains might behave differently.

This one has an alcohol side chain,

and we know that oxygen is electronegative,

it likes to hog electrons, it's amazing how much

of chemistry or even biology you can deduce

from just pure electronegativity.

So, oxygen likes to hog electrons, so you're gonna have

a partially-negative charge there.

Hydrogen has a low electronegativity relative to oxygen,

so it's gonna have its electrons hogged,

so you're gonna have a partially positive charge,

just like that, and so this has a polarity to it,

and so it's going to be hydrophilic, it's going to,

at least this part of the molecule is going to

be able to be attracted and interact with water.

And that's in comparison to what we have over here,

this hydrocarbon side chain, this has no polarity over here,

so this is going to be hydrophobic.

So this is going to be hydrophobic.

And so when we start talking about the structures

of proteins, and how the structures of proteins

are influenced by its side chains,

you could image that parts of proteins that have

hydrophobic side chains, those are gonna

wanna get onto the inside of the proteins

if we're in an aqueous solution,

while the ones that are more hydrophilic

will wanna go onto the outside,

and you might have some side chains

that are all big and bulky, and so they might

make it hard to tightly pack, and then you might have

other side chains that are nice and small

that make it very easy to pack, so these things

really do help define the shape,

and we're gonna talk about that a lot more

when we talk about the structure.

But how do these things actually connect?

And we're gonna go into much more detail

in another video, but if you have...

If you have serine right over here, and then you have

valine right over here, they connect through

what we call peptide bonds, and a peptide

is the term for two or more amino acids connected together,

so this would be a dipeptide, and the bond

isn't this big, I just, actually let me just,

let me draw it a little bit smaller.

So...

That's serine.

This is valine.

They can form a peptide bond, and this would be the smallest

peptide, this would be a dipeptide right over here.

"Peptide," "peptide bond," or sometimes

called a peptide linkage.

And as this chain forms, that polypeptide,

as you add more and more things to it,

as you add more and more amino acids,

this is going to be, this can be a protein

or can be part of a protein that does all of these things.

Now one last thing I wanna talk about,

this is the way, the way these amino acids have been drawn

is a way you'll often see them in a textbook,

but at physiological pH's, the pH's inside of your body,

which is in that, you know, that low sevens range,

so it's a pH of roughly 7.2 to 7.4.

What you have is this, the carboxyl group right over here,

is likely to be deprotonated, it's likely

to have given away its hydrogen,

you're gonna find that more likely than when you have...

It's gonna be higher concentrations having been

deprotonated than being protonated.

So, at physiological conditions, it's more likely

that this oxygen has taken both of those electrons,

and now has a negative charge,

so it's given, it's just given away the hydrogen proton

but took that hydrogen's electron.

So it might be like this, and then the amino group,

the amino group at physiological pH's,

it's likely to actually grab a proton.

So nitrogen has an extra loan pair,

so it might use that loan pair to grab a proton,

in fact it's physiological pH's,

you'll find a higher concentration of it having

grabbed a proton than not grabbing a proton.

So, the nitrogen will have grabbed a proton,

use its loan pairs to grab a proton,

and so it is going to have...

So it is going to have a...

It is going to have a positive charge.

And so sometimes you will see amino acids

described this way, and this is actually more accurate

for what you're likely to find at physiological conditions,

and these molecules have an interesting name,

a molecule that is neutral even though

parts of it have charge, like this,

this is called a zwitterion.

That's a fun, fun word.

Zwitterion.

And "zwitter" in German means "hybrid,"

and "ion" obviously means that it's going to have charge,

and so this has hybrid charge,

even though it has charges at these ends,

the charges net out to be neutral.