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Apr 30, 2024 · DNA, organic chemical of complex molecular structure found in all prokaryotic and eukaryotic cells. It codes genetic information for the transmission of inherited traits. The structure of DNA was described in 1953, leading to further understanding of DNA replication and hereditary control of cellular activities.
- The Editors of Encyclopaedia Britannica
- What does DNA do?Deoxyribonucleic acid (DNA) is an organic chemical that contains genetic information and instructions for protein synthesis. It is found in most ce...
- What is DNA made of?DNA is made of nucleotides. A nucleotide has two components: a backbone, made from the sugar deoxyribose and phosphate groups, and nitrogenous base...
- Who discovered the structure of DNA?The discovery of DNA’s double-helix structure is credited to the researchers James Watson and Francis Crick, who, with fellow researcher Maurice Wi...
- Can you edit DNA?Gene editing today is mostly done through a technique called Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR), adopted from a bac...
- What’s the difference between DNA and RNA?DNA is the master blueprint for life and constitutes the genetic material in all free-living organisms. RNA uses DNA to code for the structure of p...
The Structure and Function of DNA. Biologists in the 1940s had difficulty in accepting DNA as the genetic material because of the apparent simplicity of its chemistry. DNA was known to be a long polymer composed of only four types of subunits, which resemble one another chemically. Early in the 1950s, DNA was first examined by x-ray diffraction ...
- Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, Peter Walter
- 2002
- 2002
- Overview
- The molecular structure of DNA
- DNA molecules are polymers
- DNA monomers are called nucleotides
- There are four nucleotide monomers
- The sugar and acid in all four monomers are the same
- The four nucleotide monomers are distinguished by their bases
- Phosphodiester bonds in DNA polymers connect the 5’ carbon of one nucleotide to the 3’ carbon of another nucleotide
- Chromosomes are made of two DNA polymers that stick together via non-covalent hydrogen bonds
- DNA polymers direct the production of other polymers called proteins
DNA is the information molecule. It stores instructions for making other large molecules, called proteins. These instructions are stored inside each of your cells, distributed among 46 long structures called chromosomes. These chromosomes are made up of thousands of shorter segments of DNA, called genes. Each gene stores the directions for making protein fragments, whole proteins, or multiple specific proteins.
DNA is well-suited to perform this biological function because of its molecular structure, and because of the development of a series of high performance enzymes that are fine-tuned to interact with this molecular structure in specific ways. The match between DNA structure and the activities of these enzymes is so effective and well-refined that DNA has become, over evolutionary time, the universal information-storage molecule for all forms of life. Nature has yet to find a better solution than DNA for storing, expressing, and passing along instructions for making proteins.
The molecular structure of DNA
In order to understand the biological function of DNA, you first need to understand its molecular structure. This requires learning the vocabulary for talking about the building blocks of DNA, and how these building blocks are assembled to make DNA molecules.
In order to understand the biological function of DNA, you first need to understand its molecular structure. This requires learning the vocabulary for talking about the building blocks of DNA, and how these building blocks are assembled to make DNA molecules.
Polymers are large molecules that are built up by repeatedly linking together smaller molecules, called monomers. Think of how a freight train is built by linking lots of individual boxcars together, or how this sentence is built by sticking together a specific sequence of individual letters (plus spaces and punctuation). In all three cases, the la...
Just like a sentence “polymer” is composed of letter “monomers,” a DNA polymer is composed of monomers called nucleotides. A molecule of DNA is a bunch of nucleotide monomers, joined one after another into a very long chain.
The English language has a 26 letter alphabet. In contrast, the DNA “alphabet” has only four “letters,” the four nucleotide monomers. They have short and easy to remember names: A, C, T, G. Each nucleotide monomer is built from three simple molecular parts: a sugar, a phosphate group, and a nucleobase. (Don’t confuse this use of “base” with the oth...
All four nucleotides (A, T, G and C) are made by sticking a phosphate group and a nucleobase to a sugar. The sugar in all four nucleotides is called deoxyribose. It’s a cyclical molecule—most of its atoms are arranged in a ring-structure. The ring contains one oxygen and four carbons. A fifth carbon atom is attached to the fourth carbon of the ring. Deoxyribose also contains a hydroxyl group (-OH) attached to the third carbon in the ring.
The phosphate group is a phosphorous atom with four oxygen atoms bonded to it. The phosphorous atom in phosphate has a marked tendency to bond to other oxygen atoms (for instance, the oxygen atom sticking off the deoxyribose sugar of another nucleotide).
Each type of nucleotide has a different nucleobase stuck to its deoxyribose sugar.
•A nucleotide contains adenine
•T nucleotide contains thymine
•G nucleotide contains guanine
•C nucleotide contains cytosine
All four of these nucleobases are relatively complex molecules, with the unifying feature that they all tend to have multiple nitrogen atoms in their structures. For this reason, nucleobases are often also called nitrogenous bases.
The nucleotide monomers in a DNA polymer are connected by strong electromagnetic attractions called phosphodiester bonds. Phosphodiester bonds are part of a larger class of electromagnetic attractions between atoms that chemists refer to as covalent bonds.
In order to keep things organized, biochemists have developed a numbering system for talking about the molecular structure of nucleotides. These numbers are applied to the carbon atoms in the sugar, starting at the carbon immediately to the right of the oxygen in the deoxyribose ring, and continuing in a clockwise fashion: the numbers range from 1’ (“one prime”), identifying the carbon immediately to the right of the oxygen) all the way to 5’ (“five prime”), identifying the carbon that sticks off the fourth and final carbon in the deoxyribose ring.
Chromosomal DNA consists of two DNA polymers that make up a 3-dimensional (3D) structure called a double helix. In a double helix structure, the strands of DNA run antiparallel, meaning the 5’ end of one DNA strand is parallel with the 3’ end of the other DNA strand.
The nucleotides forming each DNA strand are connected by noncovalent bonds, called hydrogen bonds. Considered individually, hydrogen bonds are much weaker than a single covalent bond, such as a phosphodiester bond. But, there are so many of them that the two DNA polymers are very strongly connected to each other.
The hydrogen bonds that join DNA polymers happen between certain hydrogen atoms on one base (called hydrogen bond donors) and certain oxygen or nitrogen atoms on the base across from it (called hydrogen bond acceptors). Adenine (“A”) and Thymine (“T”) each have one donor and one acceptor, whereas Cytosine (“C”) has one donor and two acceptors, and Guanine (“G”) has one acceptor and two donors.
The A nucleotides are always hydrogen bonded to T nucleotides, and C nucleotides are always hydrogen bonded to G nucleotides. This selective binding is called complementary base pairing, and creates consistency in the nucleotide sequences of the two DNA polymers that join together to make a chromosome. This was first observed by Erwin Chargaff, who developed methods for counting nucleotides in DNA samples, and found that the percent of A nucleotides always equaled the percent of T nucleotides, and the percent of G nucleotides always equaled the percent of C nucleotides (within a margin of error). Now, we know that complementary base pairing can be explained by reference to hydrogen bonding between the donors and acceptors on the bases of each nucleotide: A nucleotides and T nucleotides have a match (one donor and one acceptor each), and C nucleotides and G nucleotides have a match (the former has one donor and two acceptors, while the latter has one acceptor and two donors).
A protein is one or more polymers of monomers called amino acids. Proteins are the workhorse molecules in your cells. They act as enzymes, structural support, hormones, and a whole host of other functional molecules. All traits derive from the interactions of proteins with each other and the surrounding environments.
Mar 17, 2022 · The building blocks of DNA are nucleotides, which are made up of three parts: a deoxyribose (5-carbon sugar), a phosphate group, and a nitrogenous base (Figure 9.1.2 ). There are four types of nitrogenous bases in DNA. Adenine (A) and guanine (G) are double-ringed purines, and cytosine (C) and thymine (T) are smaller, single-ringed pyrimidines.
Apr 8, 2019 · By the turn of the twentieth century, molecular biology experienced a number of seminal discoveries that brought about an enhanced understanding of the chemical basis of life and cell division. In 1944, experiments by three scientists, (Avery, McCarty and McLeod) provided strong evidence that nucleic acids, specifically DNA, was probably the ...
The most frequently used nucleases in molecular biology are the restriction endonucleases, which cut DNA at specific sequences. For instance, the EcoRV enzyme shown to the left recognizes the 6-base sequence 5′-GATATC-3′ and makes a cut at the horizontal line.
Oct 9, 2019 · In the early 1950s, the identity of genetic material was still a matter of debate. The discovery of the helical structure of double-stranded DNA settled the matter — and changed biology forever.
