Deoxyribo nucleic acid or DNA is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms (with the exception of RNA viruses). The main role of DNA molecules is the long-term storage of information. DNA is often compared to a set of blueprints, like a recipe or a code, since it contains the instructions needed to construct other components of cells, such as proteins and RNA molecules. The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information. Along with RNA and proteins, DNA is one of the three major macromolecules that are essential for all known forms of life.

DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds. These two strands run in opposite directions to each other and are therefore anti-parallel. Attached to each sugar is one of four types of molecules called nucleobases (informally, bases). It is the sequence of these four nucleobases along the backbone that encodes information. This information is read using the genetic code, which specifies the sequence of the amino acids within proteins. The code is read by copying stretches of DNA into the related nucleic acid RNA, in a process called transcription.

Within cells, DNA is organized into long structures called chromosomes. These chromosomes are duplicated before cells divide, in a process called DNA replication. Eukaryotic organisms (animals, plants, fungi, and protists) store most of their DNA inside the cell nucleus and some of their DNA in organelles, such as mitochondria or chloroplasts. In contrast, prokaryotes (bacteria and archaea) store their DNA only in the cytoplasm. Within the chromosomes, chromatin proteins such as histones compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed.

What is Mutation

Mutations are changes in a genomic sequence : The DNA sequence of a cell's genome or the DNA or RNA sequence of a virus.

Mutations are caused by radiation, viruses, transposons and mutagenic chemicals, as well as errors that occur during meiosis or DNA replication. They can also be induced by the organism itself, by cellular processes such as hyper mutation.

Mutation can result in several different types of change in sequences (DNA) these can either have no effect, alter the product of a gene, or prevent the gene from functioning properly or completely. Studies in the fly Drosophila melanogaster suggest that if a mutation changes a protein produced by a gene, this will probably be harmful, with about 70 percent of these mutations having damaging effects, and the remainder being either neutral or weakly..

Viruses that use RNA as their genetic material have rapid mutation rates, which can be an advantage since these viruses will evolve constantly and rapidly, and thus evade the defensive responses of e.g. the human immune system.
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A carcinoma is any malignant cancer that arises from epithelial cells. Carcinomas invade surrounding tissues and organs and may metastasize, or spread, to lymph nodes and other sites.

”Carcinoma in situ” (CIS) is a pre-malignant condition, in which some cytological signs of malignancy are present, but there is no histological evidence of invasion through the epithelial basement membrane.

Carcinoma, like all neoplasia, is classified by its histopathological appearance. Adenocarcinoma and squamous cell carcinoma, two common descriptive terms for tumors, reflect the fact that these cells may have glandular or squamous cell appearances respectively. Severely anaplastic tumors might be so undifferentiated that they do not have a distinct histological appearance (undifferentiated carcinoma).

Sometimes a tumor is referred to by the presumptive organ of the primary (eg carcinoma of the prostate) or the putative cell of origin (hepatocellular carcinoma, renal cell carcinoma).

Metastatic carcinoma can be diagnosed through biopsy, including fine-needle aspiration, core biopsy, or subtotal removal of single node.
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