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The Structure of DNA


The Structure of DNA

An exploration of the structure of deoxyribonucleic acid, or DNA. If you want to learn more, join our free MITx #700x Introduction to Biology course ( Try #705x Biochemistry starting Sept. 22, 2020 ( Our advanced #728x Molecular Biology course restarts October 6, 2020 ( Learn more about our work:
This video was created for MITx 7.28.1x Molecular Biology: DNA Replication & Repair, offered on edX.
Created by Betsy Skrip ( and Sera Thornton ( with special thanks to Mary Ellen Wiltrout, Stephen Bell, Ceri Riley, and Julian Samal.
(c) 2015 Massachusetts Institute of Technology. All rights reserved.

DNA Structure and Replication: Crash Course Biology #10

Hank introduces us to that wondrous molecule deoxyribonucleic acid - also known as DNA - and explains how it replicates itself in our cells.

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1:41 link to Biological Molecules

Table of Contents:
1) Nucleic Acids 1:30
2) DNA
-A) Polymers 1:53
-B) Three Ingredients 2:12
-C) Base Pairs 3:45
-D) Base Sequences 4:13
3) Pop Quiz 5:07
4) RNA 5:36
-A) Three Differences from DNA 5:43
5) Biolography 6:16
6) Replication 8:49
-A) Helicase and Unzipping 9:22
-B) Leading Strand 9:38
-C) DNA Polymerase 10:08
-D) RNA Primase 10:24
-E) Lagging Strand 10:46
-F) Okazaki Fragments 11:07
-F) DNA Ligase 11:47

DNA, deoxyribonucleic acid, chromosome, nucleic acid, ribonucleic acid, RNA, polymer, nucleotide, double helix, nucleotide base, base pair, base sequence, friedrich miescher, rosalind franklin, replication, helicase, leading strand, lagging strand, rna primase, dna polymerase, okazaki fragment Support CrashCourse on Patreon:

DNA- Structure and function of Deoxyribonucleic Acid (DNA)

DNA- Structure and function of Deoxyribonucleic Acid (DNA)


DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).

The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.

DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.

An important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell.


Genetics - Structure of the Double Helix - Lesson 14 | Don't Memorise

The double helical structure of DNA is not as simple as it seems. The molecule has a complex structure. The backbone and the core has molecules arranged in a fixed pattern and at definite positions. Want to know the detailed structure of this molecule? Watch this video to know more!

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In this video, we will learn:
0:00 Introduction
00:33 Rosalind Franklin - the structure of DNA
01:30 Francis Crick and James Watson - the structure of DNA
02:13 Components of DNA
04:17 The dimensions of DNA
06:32 Histone proteins

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Structure Of Nucleic Acids - Structure Of DNA - Structure Of RNA - DNA Structure And RNA Structure

In this video we cover the structure of nucleic acids, DNA and RNA. We discuss the components of each, and the differences between the two.

Transcript with notes.

There are 2 main types of nucleic acids, DNA or deoxyribonucleic acids and RNA or ribonucleic acids. Nucleic acids are large molecules made up of smaller molecules called nucleotides. DNA contains deoxynucleotides and RNA contains ribonucleotides. The nucleotides in these molecules are linked together through covalent bonds or bonds where electrons are shared between atoms.

Let’s start by looking at DNA. The nucleotides that make up DNA have 3 parts, a phosphate group, a nitrogenous base, and a deoxyribose sugar, or 5 carbon sugar. The phosphate group consists of a phosphate bonded to 4 oxygen atoms, with one of the oxygen’s bonded to the number 5 carbon of the deoxyribose sugar. An important note here, the number 2 carbon of the deoxyribose’s sugar is bonded to a hydrogen atom. Carbon atom number one of the deoxyribose sugar is bonded to the nitrogenous base.

There are 4 types of nitrogenous bases that can be found in DNA, adenine, shown bonded here, guanine shown here, cytosine shown here, and thymine shown here. As you can see, adenine and guanine have double ring structures, and cytosine and thymine have sing ring structures. Adenine and guanine are called purine bases and cytosine and thymine are called pyrimidine bases.

DNA is a double stranded nucleic acid and its molecules take on a helical formation. Each helical chain has its phosphate-sugar group toward the outside, and the nitrogenous bases facing inwards towards the nitrogenous bases of the other chain. Each of the bases on one chain is joined to the base in the other chain through either 2 or 3 hydrogen bonds.

Thymine and adenine are joined by 2 hydrogen bonds and cytosine and guanine are joined by 3 hydrogen bonds. Thymine and adenine are always a base pair, and cytosine and guanine are always a base pair. It is estimated that a DNA molecule contains more than 100 million of these base pairings, and in one individuals body, the sequence of these base pairings is the same in every DNA molecule. So this sequence of base pairing is unique to that individual.

DNA is often called the information molecule because it contains the master code needed to make various RNA molecules and protein molecules in the body.

Now for RNA. The nucleotides that make up RNA are very similar to those that make up DNA. RNA nucleotides have a phosphate group with the same structure as in DNA. They have a 5 carbon sugar, but the number 2 carbon is bonded to a hydroxyl OH group instead of a lone hydrogen atom, and this sugar is called ribose.

It also consists of 3 of the same nitrogenous bases as DNA, cytosine, adenine, and guanine. But it does not contain thymine, instead it contains uracil, which is also a single ring structure like thymine, making it a pyrimidine base.

Most RNA molecules are single stranded nucleic acids and many times they form a folded compacted structure with some hydrogen bonding taking place within base pairs of the molecule. These pairings are the same as in DNA, cytosine and guanine are a base pair, and uracil takes the place of thymine and pairs with adenine.

RNA is important in the process of forming different proteins in the body, of which we will cover in depth in a later video.

DNA Structure

Describes DNA - structure
Ref: John Dearnaley USQ


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Nucleic acids - DNA and RNA structure

Nucleic acids DNA and RNA structure


Nucleic acids are biopolymers, or small biomolecules, essential to all known forms of life. They are composed of monomers, which are nucleotides made of three components: a 5-carbon sugar, a phosphate group and a nitrogenous base. If the sugar is a simple ribose, the polymer is RNA (ribonucleic acid); if the sugar is derived from ribose as deoxyribose, the polymer is DNA (deoxyribonucleic acid).

Nucleic acids are the most important of all biomolecules. They are found in abundance in all living things, where they function to create and encode and then store information in the nucleus of every living cell of every life-form organism on Earth. In turn, they function to transmit and express that information inside and outside the cell nucleus—to the interior operations of the cell and ultimately to the next generation of each living organism. The encoded information is contained and conveyed via the nucleic acid sequence, which provides the 'ladder-step' ordering of nucleotides within the molecules of RNA and DNA.

Strings of nucleotides are bonded to form helical backbones—typically, one for RNA, two for DNA—and assembled into chains of base-pairs selected from the five primary, or canonical, nucleobases, which are: adenine, cytosine, guanine, thymine, and uracil; note, thymine occurs only in DNA and uracil only in RNA. Using amino acids and the process known as protein synthesis,[3] the specific sequencing in DNA of these nucleobase-pairs enables storing and transmitting coded instructions as genes. In RNA, base-pair sequencing provides for manufacturing new proteins that determine the frames and parts and most chemical processes of all life forms.

One DNA or RNA molecule differs from another primarily in the sequence of nucleotides. Nucleotide sequences are of great importance in biology since they carry the ultimate instructions that encode all biological molecules, molecular assemblies, subcellular and cellular structures, organs, and organisms, and directly enable cognition, memory, and behavior (See: Genetics). Enormous efforts have gone into the development of experimental methods to determine the nucleotide sequence of biological DNA and RNA molecules,[26][27] and today hundreds of millions of nucleotides are sequenced daily at genome centers and smaller laboratories worldwide

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Nucleic Acids - RNA and DNA Structure - Biochemistry

This Biochemistry video tutorial provides a basic introduction into nucleic acids such as DNA and RNA. DNA stands for deoxyribonucleic acid and RNA stands for ribonucleic acid. Nucleic acids are composed of nucleotides which are made up of a phosphate group, a pentose sugar, and a nitrogenous base.

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Here is a list of topics
1. Intro to Nucleic Acids
2. DNA and RNA
3. DNA Structure - Double Stranded Alpha Helix
4. RNA Structure - Single Stranded Nucleic Acid
5. Basic Parts of a Nucleotide
6. Nitrogenous Bases - Adenine, Guanine, Thymine, Cytosine & Uracil
7. Purine and Pyrimidine Rings
8. Nomenclature of Nucleosides and Nucleotides
9. AMP, ADP, & ATP
10. Basic DNA Structure
11. DNA Strands Held By Hydrogen Bonds
12. The Sugar Phosphate Backbone Structure of DNA
13. How To Write The Sequence of the Complementary Strand of DNA

DNA Structure

Learn about the structure of DNA and how to recognize all the parts in this video!

(OLD VIDEO) DNA Structure and Function

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DNA stands for deoxyribonucleic acid. It is a type of nucleic acid, one of four major types of macromolecules which are essential for life, along with proteins, lipids, and polysaccharides. DNA is a double helix, made up of two single DNA strands. Each DNA strand is in turn composed of many monomers called nucleotides – specifically deoxyribonucleotides. As a result, each strand is a polynucleotide.
A nucleotide has three components: a nitrogenous base, a phosphate group, and a 5-carbon sugar, which for DNA nucleotides is deoxyribose.
The sugar and phosphate groups alternate to form DNA’s “backbone”. The phosphates act like connectors between the sugars by forming phosphodiester bonds between the 3rd C of one sugar ring and the 5th C of the next sugar ring. These special Cs are termed the 3’ and 5’ Cs. As a result, there is a directionality to this backbone. Each strand has a 5’ end with a terminal phosphate group, and a 3’ end with a terminal hydroxyl group.
There are four nitrogenous bases: adenine (A), guanine (G), thymine (T), and cytosine (C). Each of these attaches to deoxyribose via a glycosidic bond. The sequence of these four bases is the means by which DNA encodes genetic information, which can then be used to carry out all the cell’s functions. The central dogma of biology describes how this genetic information is accessed and used by the cell: DNA is transcribed into RNA, which is then translated into proteins.
The four nitrogenous bases can be divided into two groups – cytosine and thymine are pyrimidines, while adenine and guanine are purines. You can use this mnemonic to remember that: Climbing the pyramid, George avoided two pursuers.
The two single strands of DNA composing the DNA double helix are held together via hydrogen bonds, and they run antiparallel; that is, in opposite directions. One strand is 3’-5’, while the other is 5’-3’. Each nitrogenous base on one strand binds to its complementary base pair on the other strand. Purines hydrogen bond to pyrimidines. Specifically, adenine binds only to thymine via two hydrogen bonds, and cytosine binds only to guanine via 3 hydrogen bonds.
Due to this complementary binding, each of the two DNA strands contains the exact SAME information. When the two strands are separated during DNA replication, each of them acts as a template which contains all the information needed for recreating the other. The two DNA strands can be separated, or “melted” in several ways – through mechanical force by enzymes, through high temperatures, or through extreme pH levels.
Going back to the central dogma of biology – DNA gets transcribed into RNA, which then gets translated into protein. However, not all sequences of DNA are actually meant to be transcribed into useful RNA sequences. Those sequences of DNA which are actually meant act as a template for transcription of RNA which then gets translated into functional proteins are called noncoding, or “antisense” sequences. The DNA which is complementary to an antisense sequence is termed a coding, or sense sequence.
Note that transcribed RNA is complementary to the noncoding sequence, and so it exactly matches the coding sequence. Note that both strands of DNA can have sense and antisense sequences. Furthermore, sense and antisense sequences can overlap; for example, there can be overlapping genes, where one protein is encoded on one strand and another is encoded on the opposite strand by the sequence read in the opposite direction.
Since transcription can only proceed in the 3’-5’ direction along the template DNA strand, the RNA being synthesized is always 5’-3’. Thus, a sense sequence - for example, CAAT - will never be transcribed, although if the reverse sequence TAAC is an antisense sequence, it can be transcribed.
The twisting of the double helix creates more interesting features in DNA. The grooves are not equally spaced. One of these grooves is called the major groove, while the other is called the minor groove.
In its relaxed state, each DNA strand makes one loop around the axis of the double helix once every 10.4 base pairs. If the DNA is being twisted tighter in the same direction, this is called “positive supercoiling”, while being twisted in the other direction is called negative supercoiling.
DNA is found in the nucleus in eukaryotes, and in the nucleoid in prokaryotes. In both eukaryotes and prokaryotes, the DNA is packaged into chromosomes, which are a combination of DNA and proteins. Chromosomes make the DNA more condensed and organized, and allow the cell to have controlled access to specific portions of DNA. Eukaryotes have linear chromosomes, while prokaryotes have circular ones. The genome is the complete set of chromosomes in a cell.
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Molecular structure of DNA | Macromolecules | Biology | Khan Academy

Molecular structure of DNA. Nucleotide. Nitrogenous base, phosphate.

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GCSE Biology - What is DNA? (Structure and Function of DNA) #79

This video covers:
- The structure of DNA
- What nucleotides are
- Complementary base pairing
- How genes code for proteins
- The functions of proteins

Exam board specific info: (probably useful for everyone though)
AQA - Separate/triple science only
IGCSE Edexcel - Separate/triple science and higher tier only
Edexcel - Everything is relevant to your course!
OCR 21st Century - Separate/triple science and higher tier only
OCR Gateway - Separate/triple science only

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Structure of DNA: The DNA molecule is a polymer consisting of several thousand pairs of nucleotide monomers.Each nucleotide consists of three components. They are
1. Pentose sugar deoxyribose
2. Phosphate group
3. Nitrogenous base
Nucleoside = deoxyribose + nitrogenous base
Nucleotide = deoxyribose + nitrogenous base + phosphate
Pentose sugar:deoxyribose sugar is a pentose sugar with five carbon atoms.
Phosphate: the phosphate is attached to the adjacent pentose sugar alternately at their 5th and 3rd carbon atoms by phospho -- diester bonds. The phosphate and pentose sugar constitute the back bone of nucleic acids.
Nitrogen bases: there are two types of nitrogen bases
1.Purines adenine and guanine and
2.Pyramidines cytosine and thymine
Nitrogenous base is linked to the pentose sugar through N- glycosidic linkage to form a nucleoside. When a phosphate is linked to 51 OH of a nucleoside through phosphoester linkage a corresponding nucleotide is formed. Two nucleotides are linked through 31 -- 51 phosphodiester linkage to form dinucleotide. More nucleotides are joined to form a polynucleotide chain. A polymer has at one end a free phosphate moiety at 51 end of ribose sugar, at the other end the ribose sugar has 31 OH group. The back bone in a polynucleotide chain formed due to sugar and phosphates. The nitrogenous bases linked to sugar moiety form the back bone.

Structure of DNA - Molecular Basis of Inheritance | Class 12 Biology

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Class: 12th
Subject: Biology
Chapter: Molecular Basis of Inheritance
Topic Name: Structure of DNA (6.4)

Points covered in this video:-
-What is the Structure of DNA?

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The Discovery of the Structure of DNA

This is our second video in the series Amazing Moments in Science: The Discovery of the Structure of DNA.

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A video by Scienseed for Ventana al conocimiento

DNA Structure | A-level Biology | OCR, AQA, Edexcel

DNA Structure in a Snap! Unlock the full A-level Biology course at created by Adam Tildesley, Biology expert at SnapRevise and graduate of Cambridge University.

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The key points covered of this video include:

1. The DNA Double Helix
2. Complementary Base Pairing
3. Antiparallel Strands

The DNA Double Helix

The structure of DNA was first discovered by the scientists, Watson and Crick. However, their discovery was based on pioneering research by Rosalind Franklin. Watson and Crick worked out that DNA was composed of two very long polynucleotide chains twisted into a double helix. The sides of the DNA double helix are made from pentose sugar and phosphate groups forming a sugar-phosphate backbone. The two strands of DNA are held together by hydrogen bonds between the bases forming the rungs of the DNA double helix. The double helix of DNA is also antiparallel - the strands of DNA run in opposite directions to each other.

Complementary Base Pairing

In DNA, the two polynucleotide strands are held together by hydrogen bonds between two bases. The base pairing in DNA is very specific: The correct bases pair up due to: The number of hydrogen bonds each pair of bases can form, The size of the bases - a larger purine must always pair with a smaller pyrimidine. Because the structure and bonding of the bases makes the pairing specific, we say the bases are complementary to each other. Due to base pairing, there will always be the same percentage of complementary bases in a DNA molecule. This is known as Chargaff's Rule after the scientist who discovered it.

Antiparallel Strands

The two polynucleotide strands in DNA run in opposite directions to each other - they are antiparallel. One of the strands runs 5' to 3' while the other strand runs 3' to 5'. The directions are named according to the position number of the carbon atoms in the pentose sugar of each nucleotide. In a mononucleotide, carbon five is bonded to the phosphate group and carbon three has a hydroxyl group. However, in a polynucleotide, carbon three is instead bonded to the phosphate group of the next nucleotide, creating a 5' to 3' strand. In DNA, the strands run in opposite directions, creating one 5' to 3' strand and one 3' to 5' strand.


DNA is composed of two polynucleotide chains twisted into a double helix
DNA has a sugar-phosphate backbone and bases joined together by hydrogen bonds
Adenine pairs with thymine by two hydrogen bonds and guanine pairs with cytosine by three hydrogen bonds
The two DNA strands are antiparallel, with one running 5' to 3' and the other running 3' to 5'

GCSE Science Revision Biology DNA Structure (Triple)

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In this video, we look in more detail at the structure of DNA. We look at what is meant by nucleotides and how the two DNA strands are complementary.

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DNA structure By Forluvoft - File:DNA simple2.svg, Public Domain,

Deliberate Thought by Kevin MacLeod is licensed under a Creative Commons Attribution licence (

DNA Structure

What is the DNA molecule made of?
Learn about the structure of DNA
( Deoxyribonucleic acid )
DNA is a very large molecule made of nucleotides.
Each nucleotide is made of a phosphate, a sugar and a nitrogen base.
The four bases are thymine, adenine, cytosine, and guanine.
Together they form a double helix.
For more Life Science videos and summaries see,

What is DNA?

Paul Andersen describes the molecular structure of DNA. He describes the major parts of a nucleotide and explains how they are assembled into a nucleic acid. The nitrogenous base, deoxyribose sugar and phosphate group make up a single nucleotide. The 5' and 3' end of DNA is described. The importance of hydrogen bonds in the 3-dimensional shape is also included.

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Title: I4dsong_loop_main.wav
Artist: CosmicD
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