Name: 什麼是DNA結構？ 如何用3D筆製作雙螺旋｜生物｜生物化學 (What is DNA Structure? How to Make a Double Helix with a 3D Pen | Biology | Biochemistry)
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This is the molecule we use to store our genetic information.

DNA contains the instructions needed for an organism to develop, survive and reproduce.

If you want to understand how DNA works, the first step is to learn about its structure.

The structure of a molecule determines its function, so making sense of the structure

is essential for you to understand HOW DNA can do its job.

In April of 1953, James Watson and Francis Crick changed the world of biology forever

with a landmark paper published in the journal Nature.

They reported they had determined the structure of DNA was an antiparallel double-helix.

Instead, they built models out of tin and wire that matched measurements derived from

other scientists, including biochemical data from Erwin Chargaff, and X-Ray diffraction

data obtained by Maurice Wilkins, Rosalind Franklin and Raymond Gosling, under the direction

You may have tried making your own DNA molecule using a chemistry molecular modeling kit.

Today we’re building models of DNA using a 3D printing pen.

MorphPen was kind enough to send a 3D printing pen to Socratica for us to test out, so of

You can make whatever you want with YOUR 3D pen.

Single-stranded DNA is a polymer of nucleotides, made up of repeating units of sugar, phosphate,

In double-stranded DNA, two polynucleotides are attached at their complementary bases,

zipping the two strands together with hydrogen bonds.

Keep in mind, most DNA molecules are very, VERY long - thousands or even millions of

We’re going to just make a very short stretch of double-stranded DNA as an illustration.

The sides of the ladder are made of sugars and phosphate groups.

Let’s first make a backbone, using our 3D pen.

We’re actually going to need two of these, one for each side of the ladder.

Now, let’s look at the rungs of the ladder, which is really the business end of DNA.

These “rungs” of the DNA ladder are made of 4 different kinds of nitrogenous bases:

The order of these bases is how information is stored in DNA.

Think of it like the order of letters in a word, and the order of words in a sentence.

These are known as Chargaff’s Rules, in honour of Erwin Chargaff who determined this

Notice that there are 3 hydrogen bonds holding G and C together, while there are 2 hydrogen

Let’s take a closer look at these components.

The 5 carbon sugar in DNA is deoxyribose.

Deoxy, meaning it’s missing an oxygen compared to regular ribose.

This is where it attaches to deoxyribose.

Think of them like little acidic flags hanging off the structure.

This is what gives DNA its acidic nature when in solution in water.

They are called that because they are literally basic, as opposed to acidic, and they all

Two of them, Adenine and Guanine look like this, with two fused rings.

The other two, Cytosine and Thymine, look like this, with only one ring.

Since Adenine always pairs with Thymine, and Guanine always pairs with Cytosine, you can

also say that a purine always pairs with a pyrimidine.

One unit, or monomer of the DNA polymer is called a nucleotide.

This is one sugar, one phosphate, and one nitrogenous base.

In the case of DNA, they are also called “deoxyribonucleotides,” as opposed to in RNA where they are called

“ribonucleotides,” because they contain ribose instead of deoxyribose.

Nucleotides are joined together by covalent bonds.

The phosphate group of one nucleotide is linked to the hydroxyl group on the sugar of the

These are known as phosphodiester linkages.

Biochemists have a particular way of labeling the atoms in DNA, so they know what part of

This is an important shorthand, so you can just say something is happening at C5, for

example, rather than having to point it out on a diagram.

They start with labeling the skeleton - the atoms in the ring area - of the nitrogenous

You can see here, these atoms labeled 1-6, or over here, labeled 1-9.

Then, to label the skeleton of the sugar, they don’t want to use the same numbers

that they used for the base, because that would be confusing, so they label them

The 5’ Carbon is this one that sticks up from the ring.

This is where the notation 5’ to 3’ comes from.

You may have heard that phrase “DNA runs in the 5’ to 3’ direction.”

That’s talking about one of the two strands.

You can see the sides of the ladder run in opposite directions - remember, it’s an

On one end of a DNA strand, there’s a Phosphate group attached to the 5’ carbon, and the

other end of that strand has an -OH group on the 3’ carbon.

We say this side runs in the 5’ to 3’ direction, because of the labeling of the

The other side of the ladder runs in the 3’ to 5’ direction.

This is going to be important to remember later when we study how information is stored

One side is the coding strand, or sense strand, the 5’ to 3’ side.

The other side is called the anticoding strand, or antisense strand.

Because of complementary pairing, if we know the sequence of one strand, we know the sequence

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什麼是DNA結構？如何用3D筆製作雙螺旋｜生物｜生物化學 (What is DNA Structure? How to Make a Double Helix with a 3D Pen | Biology | Biochemistry)

determine

structure

sense

molecule

什麼是DNA結構？ 如何用3D筆製作雙螺旋｜生物｜生物化學 (What is DNA Structure? How to Make a Double Helix with a 3D Pen | Biology | Biochemistry)

determine

structure

sense

molecule

什麼是DNA結構？如何用3D筆製作雙螺旋｜生物｜生物化學 (What is DNA Structure? How to Make a Double Helix with a 3D Pen | Biology | Biochemistry)