In this module we focus primarily on the chemical structures of DNA and RNA and how they can be distinguished from one another. Individual nucleotides condense with one another to form a nucleic acid polymer. Each nucleotide is made up of three components: a nitrogenous base for which there are five different types , a pentose sugar, and a phosphate group.
These are depicted below. The main difference between these two types of nucleic acids is the presence or absence of a hydroxyl group at the C 2 position, also called the 2' position read "two prime" , of the pentose see Figure 1 legend and section on the pentose sugar for more on carbon numbering.
RNA has a hydroxyl functional group at that 2' position of the pentose sugar; the sugar is called ribose, hence the name ribo nucleic acid. By contrast, DNA lacks the hydroxyl group at that position, hence the name, "deoxy" ribo nucleic acid.
DNA has a hydrogen atom at the 2' position. The nitrogenous bases of nucleotides are organic molecules and are so named because they contain carbon and nitrogen. They are bases because they contain an amino group that has the potential of binding an extra hydrogen, and thus acting as a base by decreasing the hydrogen ion concentration in the local environment. Adenine and guanine are classified as purines. The primary distinguishing structural feature of a purine is double carbon-nitrogen ring.
Cytosine, thymine, and uracil are classified as pyrimidines. These are structurally distinguished by a single carbon-nitrogen ring. You will be expected to recognize that each of these ring structures is decorated by functional groups that may be involved in a variety of chemistries and interactions.
Take a moment to review the nitrogenous bases in Figure 1. Identify functional groups as described in class. For each functional group identified, describe what type of chemistry you expect it to be involved in. Try to identify whether the functional group can act as either a hydrogen bond donor, acceptor, or both? The pentose sugar contains five carbon atoms. The two main functional groups that are attached to the sugar are often named in reference to the carbon to whch they are bound.
We will often use the carbon number to refer to functional groups on nucleotides so be very familiar with the structure of the pentose sugar.
The difference between the sugars is the presence of the hydroxyl group on the 2' carbon of the ribose and its absence on the 2' carbon of the deoxyribose.
You can, therefore, determine if you are looking at a DNA or RNA nucleotide by the presence or absence of the hydroxyl group on the 2' carbon atom—you will likely be asked to do so on numerous occasions, including exams. There can be anywhere between one and three phosphate groups bound to the 5' carbon of the sugar. The phosphoanhydride bonds between that link the phosphate groups to each other have specific chemical properties that make them good for various biological functions.
The hydrolysis of the bonds between the phosphate groups is thermodynamically exergonic in biological conditions; nature has evolved numerous mechanisms to couple this negative change in free energy to help drive many reactions in the cell. Figure 2 shows the structure of the nucleotide triphosphate Adenosine Triphosphate, ATP, that we will discuss in greater detail in other chapters.
The term "high-energy bond" is used A LOT in biology. This term is, however, a verbal shortcuts that can cause some confusion. The term refers to the amount of negative free energy associated with the hydrolysis of the bond in question. The water or other equivalent reaction partner is an important contributor to the energy calculus. In ATP, for instance, simply "breaking" a phosphoanhydride bond - say with imaginary molecular tweezers - by pulling off a phosphate would not be energetically favorable.
We must, therefore, be careful not to say that breaking bonds in ATP is energetically favorable or that it "releases energy".
Rather, we should be more specific, noting that they hydrolysis of the bond is energetically favorable. Meet The Author. Ruairi J Mackenzie. Chosen for you. Deoxyribonucleic Acid. Ribonucleic Acid. DNA replicates and stores genetic information. It is a blueprint for all genetic information contained within an organism. RNA converts the genetic information contained within DNA to a format used to build proteins, and then moves it to ribosomal protein factories.
DNA consists of two strands, arranged in a double helix. These strands are made up of subunits called nucleotides. Each nucleotide contains a phosphate, a 5-carbon sugar molecule and a nitrogenous base. RNA sometimes forms a secondary double helix structure, but only intermittently. A chromosome, for example, is a single, long DNA molecule, which would be several centimetres in length when unravelled.
A large RNA molecule might only be a few thousand base pairs long. But see also "The Origin of the Genetic Code" by cdk in the same series. Also there is an excellent 3 videos on abiogenesis, RNA and fatty acid vesicle "protocells" by Jack Szostak on ibiology. Just search for them. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Learn more. Ask Question. Asked 6 years, 11 months ago. Active 5 years, 6 months ago. Viewed 64k times. Improve this question. TanMath TanMath 3, 3 3 gold badges 24 24 silver badges 41 41 bronze badges.
Add a comment. Active Oldest Votes. Ribose and Deoxyribose From the fig above we can see that the principal difference between the two molecules is the presence of OH in ribose 2' tail and absence in deoxyribose.
Answer DNA is such an important molecule so it must be protected from decomposition and further reactions. Improve this answer. Jayachandran Jayachandran 1, 1 1 gold badge 9 9 silver badges 20 20 bronze badges. My intuitive guess would be that active degradation by RNAses would be far more important than the chemical instability by the 2'OH.
It is chemically unstable given the physiological or alkaline environment. Prokaryotic bacteria and Archaea also use DNA, but don't have nuclei. Mitochondria have their own DNA and genome, yet they are organelles inside the majority of Eukaryotic cells.
Red Blood Cells discard their genomes when they terminally differentiate, and those are kind of important to the life of most land animals. RNA forms double strands frequently, and needs to be straightened out when entering the ribosome.
Show 6 more comments. Why RNA for other informational functions? David David Could you mention what the half-life of RNA in water is? Would help to judge how serious the RNA hydrolysis issue is.
The paper quotes half lives for the much greater rate constant at C, in relation to thermophiles. That definitely shows RNA is too easily degraded to be viable as genetic material.
Cian Moriarty Cian Moriarty 1. I am also unclear what you mean by stronger.
0コメント