All viruses contain nucleic acid, either DNA or RNA but not both , and a protein coat, which encases the nucleic acid. Some viruses are also enclosed by an envelope of fat and protein molecules. In its infective form, outside the cell, a virus particle is called a virion. Each virion contains at least one unique protein synthesized by specific genes in its nucleic acid. Viroids meaning "viruslike" are disease-causing organisms that contain only nucleic acid and have no structural proteins.
Other viruslike particles called prions are composed primarily of a protein tightly integrated with a small nucleic acid molecule. Viruses are generally classified by the organisms they infect, animals, plants, or bacteria. Since viruses cannot penetrate plant cell walls, virtually all plant viruses are transmitted by insects or other organisms that feed on plants.
Certain bacterial viruses, such as the T4 bacteriophage, have evolved an elaborate process of infection. The virus has a "tail" which it attaches to the bacterium surface by means of proteinaceous "pins. Viruses are further classified into families and genera based on three structural considerations: 1 the type and size of their nucleic acid, 2 the size and shape of the capsid, and 3 whether they have a lipid envelope surrounding the nucleocapsid the capsid enclosed nucleic acid.
There are predominantly two kinds of shapes found amongst viruses: rods, or filaments, and spheres. The rod shape is due to the linear array of the nucleic acid and the protein subunits making up the capsid. The sphere shape is actually a sided polygon icosahedron. The nature of viruses wasn't understood until the twentieth century, but their effects had been observed for centuries. British physician Edward Jenner even discovered the principle of inoculation in the late eighteenth century, after he observed that people who contracted the mild cowpox disease were generally immune to the deadlier smallpox disease.
By the late nineteenth century, scientists knew that some agent was causing a disease of tobacco plants, but would not grow on an artificial medium like bacteria and was too small to be seen through a light microscope. Advances in live cell culture and microscopy in the twentieth century eventually allowed scientists to identify viruses.
Advances in genetics dramatically improved the identification process. Capsid - The capsid is the protein shell that encloses the nucleic acid; with its enclosed nucleic acid, it is called the nucleocapsid. This shell is composed of protein organized in subunits known as capsomers. They are closely associated with the nucleic acid and reflect its configuration, either a rod-shaped helix or a polygon-shaped sphere.
The capsid has three functions: 1 it protects the nucleic acid from digestion by enzymes, 2 contains special sites on its surface that allow the virion to attach to a host cell, and 3 provides proteins that enable the virion to penetrate the host cell membrane and, in some cases, to inject the infectious nucleic acid into the cell's cytoplasm.
Under the right conditions, viral RNA in a liquid suspension of protein molecules will self-assemble a capsid to become a functional and infectious virus. Envelope - Many types of virus have a glycoprotein envelope surrounding the nucleocapsid. In a typical year, CDC performs whole genome sequencing on about 7, influenza viruses from original clinical samples collected through virologic surveillance. Comparing the nucleotides in one gene of a virus with that of a different virus can reveal variations between the two viruses.
Some of these properties include the ability to evade human immunity, spread between people, and susceptibility to antiviral drugs.
The changes to the proteins can come in the form of amino acid substitutions, insertions, or deletions. Full Sized Infographic and Text Version. Genome sequencing reveals the sequence of the nucleotides in a gene, like alphabet letters in words. Comparing the composition of nucleotides in one virus gene with the order of nucleotides in a different virus gene can reveal variations between the two viruses. Proteins are made of sequences of amino acids. The substitution of one amino acid for another can affect properties of a virus, such as how well a virus transmits between people, and how susceptible the virus is to antiviral drugs or current vaccines.
CDC and other public health laboratories around the world have been sequencing the gene segments of influenza viruses since the s. The sequences deposited into these databases allow CDC and other researchers to compare the genes of currently circulating influenza viruses with the genes of older influenza viruses and those used in vaccines.
This process of comparing genetic sequences is called genetic characterization. CDC uses genetic characterization for several reasons:. Each sequence from a specific influenza virus has its own branch on the tree. Viruses are grouped by comparing changes in nucleotides within the gene. Viruses which share a common ancestor can also be described as belonging to the same clade. The degree of genetic difference number of nucleotide differences between viruses is represented by the length of the horizontal lines branches in the phylogenetic tree.
The further apart viruses are on the horizontal axis of a phylogenetic tree, the more genetically different the viruses are to one another. In other words, we apply any technique at our disposal to solve particular problems of interest. In general, we work on three areas at the interface of organic chemistry and nanotechnology. The first is interactions between light and self-assembled nanostructured matter.
We look at how self-assembly can drive emergent optoelectronic properties. We follow designs common in nature to reproduce natural emergent phenomena for applications like solar energy harvesting. Andrew Levine is a PhD student in Braunschweig's group.
Before beginning his PhD, he taught high school chemistry for five years. He became interested in solar energy through his mother, who worked in the industry. Andrew Levine , a fourth-year chemistry PhD student in my group, has been synthesizing supramolecular assemblies driven mostly by hydrogen bonding interactions to direct specific packing arrangements of organic semiconductor molecules.
The properties of organic semiconductors are easily tunable by substituting different functional groups in the molecules. And organic semiconductors do not require high-energy processes to crystallize like silicon, the material conventionally used to make solar cells. Every animal produces at least five different mucuses. Mucus is a material whose properties arise from organization at the molecular, nanometer, and millimeter length scales. Subtle differences in the structure of proteins that make up a mucus can render one mucus an adhesive, another a lubricant, and another a semipermeable barrier.
For example, pygmy hippos live most of their lives in water. If we can understand how nature does it, then we can introduce principles from nature to design synthetic materials with similar properties. Another focus of my group is making combinatorial biomolecular arrays by developing new printing tools. In this project, we build new instruments that can perform iterative chemical reactions on surfaces, where the feature diameters are in the nanoscale regime. The resulting arrays can be used for applications ranging from assessing single-cell genomics to driving stem cell differentiation.
A final project involves the development of small molecules that selectively bind the carbohydrates found on the surfaces of cells and viruses. Then, I completely switched fields from chemistry to instrumentation development for a postdoc at Northwestern. I started my first faculty appointment at NYU in Two years later, I joined the faculty at UMiami. Having this mix of organic chemistry, surface science, and instrumentation development experience has been invaluable.
It made me less fearful about taking on problems in different fields, and I still rely a lot on these three areas for my research. Beyond my expertise, our group of organic chemists, engineers, and biochemists brings together a unique skillset.
My group started working on antivirals several years ago. In response to the Zika outbreak of —, we reported molecules that were active against the virus.
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