Introduction to nucleic acids and nucleotides | High school biology | Khan Academy

Summary

This educational video delves into nucleic acids, highlighting DNA as a critical macromolecule for life. Originating in the cell nucleus, DNA's structure comprises a double helix with millions of nucleotides, each consisting of a phosphate group, a five-carbon sugar, and a nitrogenous base. The sequence of these bases encodes genetic information, with adenine pairing with thymine and guanine with cytosine. The video promises further exploration of DNA's role in heredity and the intriguing hypothesis that life began with self-replicating RNA molecules.

Takeaways

• 🧬 Nucleic acids are considered the most important macromolecules in life, with DNA being the most famous.
• 🔬 The name 'nucleic acid' comes from the molecule's discovery in the nucleus of cells and its acidic properties.
• 🌟 DNA is a macromolecule composed of many millions of atoms, forming the double helix structure seen in the human genome.
• 🧬 DNA's structure consists of a twisted ladder with rungs made of nucleotides, which are the building blocks of nucleic acids.
• 🔍 Each nucleotide is made up of a phosphate group, a five-carbon sugar (ribose in DNA), and a nitrogenous base.
• 🔬 Nitrogenous bases in DNA include adenine, guanine, cytosine, and thymine, which pair up to form the rungs of the DNA ladder.
• 🔄 The sequence of nucleotides encodes the genetic information in DNA, determining the hereditary traits of an organism.
• 🧪 RNA, or ribonucleic acid, is similar to DNA but has a different sugar (ribose instead of deoxyribose) and uses uracil instead of thymine.
• 🌐 The acidic nature of nucleic acids is due to the phosphate groups on the outside of the molecule, making them more reactive.
• 🔮 The significance of nucleic acids extends to theories about the origins of life, with self-replicating RNA molecules being a possible starting point.

Q & A

What is the most important macro molecule in life according to the script?

The most important macro molecule in life, as mentioned in the script, is nucleic acid.

Where does the term 'nucleic acid' originate from?

The term 'nucleic acid' comes from the fact that scientists first observed it in the nucleus of cells, which gives us the 'nucleic' part, and it has acidic properties, hence the 'acid' part.

What is the most famous type of nucleic acid?

The most famous type of nucleic acid is deoxyribonucleic acid, commonly abbreviated as DNA.

What is the role of DNA in living organisms?

DNA stores hereditary information and to a large degree, it is responsible for making an individual who they are.

Why is DNA considered a macro molecule?

DNA is considered a macro molecule because it can be made of many millions of atoms, forming a large, complex structure like the double helix.

What are the building blocks of nucleic acids?

The building blocks of nucleic acids, including DNA, are known as nucleotides.

What are the three components of a nucleotide?

A nucleotide consists of a phosphate group, a five-carbon sugar (ribose in DNA), and a nitrogenous base.

What is the structure of the DNA double helix?

The DNA double helix structure consists of two strands with alternating phosphate and ribose forming the backbone, and nitrogenous bases forming the rungs of the twisted ladder.

How does DNA store information?

DNA stores information through the specific sequence of its nucleotides, where each nitrogenous base pairs with a complementary base (adenine with thymine, and guanine with cytosine).

What is the difference between DNA and RNA nucleotides?

The difference between DNA and RNA nucleotides is that DNA nucleotides have deoxyribose (lacking one oxygen atom) while RNA nucleotides have ribose.

Why is DNA considered to have acidic characteristics?

DNA is considered to have acidic characteristics because the phosphate groups, which are on the outside of the molecule and more reactive, contribute to its overall acidity.

What is the significance of nucleic acids in the origin of life?

Nucleic acids are considered the most fundamental macromolecules to life, with some theories suggesting that the first signs of life were self-replicating RNA molecules.

Outlines

00:00

🧬 Nucleic Acids: The Building Blocks of Life

The script introduces nucleic acids as the most important macromolecules in life, with a focus on DNA. It explains the origin of the term 'nucleic acid', highlighting its discovery in the nucleus of cells and its acidic properties. DNA is described as a molecule that stores hereditary information and is composed of millions of atoms, forming a double helix structure. The script further discusses DNA as a polymer made up of nucleotides, which are the building blocks of nucleic acids. Nucleotides consist of a phosphate group, a five-carbon sugar (deoxyribose in DNA), and a nitrogenous base. The bases adenine, thymine, guanine, and cytosine are mentioned, with adenine pairing with thymine in DNA. The video script promises to delve deeper into DNA and RNA in future videos.

05:00

🔬 DNA's Acidic Nature and Reactivity

This paragraph delves into the acidic nature of DNA, explaining that while the basic nitrogenous bases are on the inside of the DNA molecule, forming the rungs of the ladder, the acidic phosphate groups are on the outside, making them more reactive. The overall molecule exhibits an acidic characteristic due to the external phosphate groups. The script concludes by hinting at future discussions on the significance of nucleic acids, suggesting that early life may have originated from self-replicating RNA molecules that eventually led to cellular structures and genetic machinery.

Keywords

💡Nucleic acid

Nucleic acids are essential macromolecules found in all living cells, responsible for storing and transmitting genetic information. They are so named because they were first found in the nucleus of cells and exhibit acidic properties. DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are the most well-known nucleic acids, with DNA storing hereditary information.

💡DNA

Deoxyribonucleic acid (DNA) is the molecule that holds the genetic blueprint for all living organisms. It is a long polymer made of nucleotides and forms a double helix structure. DNA is crucial because it stores hereditary information, making each organism unique. In the video, DNA is introduced as a macromolecule and one of the most important nucleic acids.

💡RNA

Ribonucleic acid (RNA) is a nucleic acid that plays a key role in coding, decoding, regulation, and expression of genes. While similar to DNA, RNA contains ribose sugar instead of deoxyribose and uses uracil in place of thymine. RNA's function is highlighted as significant in biology, with some theories suggesting it was the first molecule involved in life processes.

💡Macromolecule

A macromolecule is a large molecule made up of smaller subunits, known as monomers, linked together. DNA is classified as a macromolecule because it consists of many millions of atoms. The term is important to understanding how biological structures like DNA and RNA are composed of repeating nucleotide units.

💡Nucleotide

Nucleotides are the building blocks (monomers) of nucleic acids like DNA and RNA. Each nucleotide consists of a phosphate group, a five-carbon sugar (ribose or deoxyribose), and a nitrogenous base. The sequence of nucleotides in DNA encodes genetic information. In the video, nucleotides such as deoxyadenosine monophosphate are shown to illustrate how DNA is structured.

💡Double helix

The double helix is the structure of DNA, in which two long strands of nucleotides are coiled around each other, forming a twisted ladder-like shape. The 'rungs' of the ladder are pairs of nitrogenous bases. This structure is essential for DNA's ability to store genetic information and replicate. The video describes this iconic shape while explaining DNA.

💡Nitrogenous base

Nitrogenous bases are molecules that contain nitrogen and act as the building blocks of nucleotides. In DNA, there are four nitrogenous bases: adenine, thymine, guanine, and cytosine. These bases pair in specific ways (adenine with thymine and guanine with cytosine) to form the 'rungs' of the DNA ladder. Their order encodes the genetic instructions.

💡Phosphate group

The phosphate group is a part of the nucleotide structure and forms the backbone of the DNA or RNA molecule along with the sugar (ribose or deoxyribose). Phosphate groups alternate with sugars to create the structural framework of nucleic acids. The acidic properties of DNA are largely due to these phosphate groups.

💡Deoxyribose

Deoxyribose is the sugar found in DNA, making it distinct from RNA, which contains ribose. Deoxyribose lacks one oxygen atom compared to ribose, which is why DNA is called deoxyribonucleic acid. This difference is crucial to DNA's structure and function, as it impacts the stability of the molecule.

💡Polymer

A polymer is a large molecule made up of repeating units called monomers. DNA and RNA are polymers of nucleotides, with each nucleotide acting as a monomer. This concept is important to understanding how nucleic acids are structured and how they function in living organisms.

Highlights

Nucleic acids are the most important macro molecules in life.

The name 'nucleic acid' originates from its discovery in the nucleus of cells and its acidic properties.

Deoxyribonucleic acid (DNA) is the most famous nucleic acid and stores hereditary information.

DNA is a macro molecule composed of many millions of atoms, forming a double helix structure.

A human chromosome is a very long DNA molecule with approximately a hundred million base pairs.

Nucleic acids, including DNA and RNA, are polymers made up of building blocks called nucleotides.

Nucleotides consist of a phosphate group, a five-carbon sugar, and a nitrogenous base.

The nitrogenous bases in DNA are adenine, guanine, cytosine, and thymine.

Adenine pairs with thymine in DNA, and guanine pairs with cytosine to form the rungs of the DNA ladder.

The order of nucleotides encodes the information within DNA.

DNA is considered an acid due to the presence of reactive phosphate groups on the outside of the molecule.

The basic parts of the molecule, including the nitrogenous bases, are less reactive and form the ladder's rungs.

The structure of DNA with its complementary base pairing is crucial for storing genetic information.

Ribonucleic acid (RNA) is similar to DNA but contains ribose sugar and uracil instead of thymine.

Nucleic acids are fundamental to life, with some theories suggesting that early life forms were self-replicating RNA molecules.

DNA and RNA's roles in the genetic machinery of cells highlight their importance in biology.

Transcripts

- [Narrator] We are now going to talk about

what is perhaps the most important macro molecule in life,

and that is known as nucleic acid.

Now first of all where does that name come from?

Well scientists first observed this in the nucleus

of cells and so that's where you get the nucleic part.

And it has some acidic properties

and so that's where you get the acid part.

And perhaps the most famous of the nucleic acids

is deoxyribonucleic acid or DNA for short.

And we'll go into some depth in this as we go

through our journey in biology,

but you might already know that this is the molecule

that stores our hereditary information.

This DNA, to a large degree, makes you you.

And it's known as a macro molecule,

and we've talked about macro molecules in other videos,

we've talked about carbohydrates,

and we have talked about proteins.

And DNA is a macro molecule

because it can be made of many millions of atoms.

Just to get a sense of it, you can see right over here,

the double helix of DNA, where you have one side

of your helix right over there and then another one

right over here and then you kind of have these rungs

of this twisted ladder.

A DNA molecule, let's say in the human genome,

a chromosome, for example,

is primarily a really long DNA molecule.

And they can have on the order of a hundred million

rungs to this ladder.

Now another thing to appreciate like many other macro

molecules, DNA, or nucleic acids in general,

they are polymers in that they're made up of building block

molecules and those building blocks for nucleic acids

and DNA is the most famous nucleic acid

and RNA, Ribonucleic acid would be a close second.

But the building blocks of them are known as nucleotides.

Nucleotides.

And we see some examples of nucleotides over here.

This is deoxyadenosine monophosphate,

which would be a nucleotide found in DNA.

You can see the various parts of it.

You have a phosphate group right over here.

You have a five carbon sugar, which in this case, is ribose.

And then you have what is known as a nitrogenous base.

And why is it called nitrogenous?

Well all those blue circles represent nitrogen

and we've seen this before, the grays are carbons.

And the reds are oxygens and the whites hydrogens.

And so this part of the molecule

has some basic characteristics.

While this phosphate group at the end this

has some acidic characteristics.

And what happens is they get stacked onto each other

where the ribosephosphates alternate to form

the backbone of this DNA molecule.

You can see it right over here

where you have a phosphate and a ribose

and a phosphate and a ribose.

And then you have the nitrogenous base forming

part of the rung of the ladder.

And the way that DNA stores information is,

every one of these nitrogenous bases right over here

this is adenine, it has a complimentary nitrogenous base

on the other to complete that rung of the ladder.

So adenine matches with thiamine and DNA

and we'll see in future videos in RNA,

it's a nitrogenous base known as urasil,

and guanine matches with cytosine.

Don't worry too much about this now,

we'll go into some depth in this in future videos

when we talk about DNA and how information is stored in it.

But for the sake of this video, just appreciate

that the monomer for a nucleic acid

like DNA is a nucleotide.

So monomer, and to be very clear, this would not be

the only monomer, the analogous nucleotide in RNA,

which stands for ribonucleic acid would be

adenosine monophosphate right over here.

You can see the difference between the two

that we have an oxygen right over here,

and we don't have an oxygen right over here.

That's why this is called deoxy, and that's

why it's deoxyribonucleic acid.

You're missing one of those oxygens

on your five carbon sugar.

But adenine as I mentioned is not the only nitrogenous base.

You could have a nucleotide where the nitrogenous base

is thiamine, and so once again, this looks very similar

but notice what is going on over here.

You could have a nucleotide that looks like this.

Once again, you have your five carbon sugar here,

you have your phosphate group, but the nitrogenous base

here keeps on changing.

And it's the order of these different nucleotides

that actually encodes the information in DNA.

Now one question you might say is, well look,

if I have this part of the molecule that has

basic characteristics, why is it considered an acid?

Well look at how this molecule is structured.

The basic parts form the rungs of this ladder.

So they're not going to be as reactive

because they're really tied, they're closer

to the inside of the molecule while the acidic parts,

the phosphate groups are on the outside.

So they're going to be more reactive.

And so the molecule as a whole is going to have

an acidic characteristic.

I'm going to leave you there.

In future videos we're going to go into

a lot more depth in the importance of nucleic acid,

especially DNA and RNA.

And to just appreciate how amazing these molecules are.

Some folks theorize that the first signs of life

were nothing more than self-replicating RNA molecules

that eventually got enclosed in some type of membrane

structures, which eventually started forming the

genetic machinery of a cell etc, etc, etc.

So this is why these nucleic acids are sometimes

considered the most fundamental macromolecules to life.