Together, transcription and translation are known as gene expression. During the process of transcription, the information stored in a gene's DNA is passed to a similar molecule called RNA ribonucleic acid in the cell nucleus. Both RNA and DNA are made up of a chain of building blocks called nucleotides, but they have slightly different chemical properties.
Translation, the second step in getting from a gene to a protein, takes place in the cytoplasm. Each sequence of three nucleotides, called a codon, usually codes for one particular amino acid. Amino acids are the building blocks of proteins. Through the processes of transcription and translation, information from genes is used to make proteins.
Other chapters in Help Me Understand Genetics. This remarkable molecule also carries the genetic instructions for many viruses, and it may have helped life get its start. Together, RNA, short for ribonucleic acid, and DNA , short for deoxyribonucleic acid, make up the nucleic acids, one of the three or four classes of major "macromolecules" considered crucial for life.
The others are proteins and lipids. Many scientists also place carbohydrates in this group. Macromolecules are very large molecules, often consisting of repeating subunits.
The two nucleic acids team up to create proteins. The process of creating proteins using the genetic information in nucleic acids is so important to life that biologists call it "the central dogma" of molecular biology. The dogma, which describes the flow of genetic information in an organism, according to Oregon State University , says that DNA's information gets written out, or "transcribed," as RNA information, and RNA's information gets written out, or "translated," into protein.
The nucleotides are organized in specific sequences, which can be read like letters in a word. Each nucleotide has three major parts: a sugar molecule, a phosphate group and a cyclic compound called a nucleobase, or base. Sugars from different nucleotide units hook up via phosphate bridges to create the repeating polymer of an RNA or DNA molecule — like a necklace made of sugar beads linked together by phosphate strings.
The nucleobases attached to the sugars constitute the sequence information needed to build proteins, as described by the National Human Genome Research Institute. The four bases make up the molecules' alphabets, and as such, are denoted as letters: A for adenine, G for guanine and so forth.
Related: How to speak genetics: A glossary. This works because the bases on one RNA or DNA string can stick to bases on another string, but only in a very specific way. Ribosomes "read" mRNA sequences to determine the order in which protein subunits amino acids should join a growing protein molecule.
Scientists consider RNA's central dogma activities central to the molecule's definition. DNA is a relatively stable molecule that is tightly controlled by the host cell. It plays diverse, reactive functions in cells. When most genes are expressed, they are translated into messenger RNA mRNA molecules, which are then transcribed into proteins. Although RNA is critical to cell function, it is a reactive molecule and does not provide a reliable memory system for inheritance in organisms.
In contrast, the structure of DNA molecules makes them much less reactive, and they can be packaged into nested spirals that protect them from damage. Thus, DNA is a more reliable memory system for inheritance. It is used by all organisms except some viruses — if they are organisms to encode critical cell functions. Most of the DNA in cells is packaged into chromosomes that are copied when cells reproduce.
The entire genetic content of a cell is known as its genome. Nucleic acids are made up of nucleotides composed of a nitrogenous base, a pentose sugar, and a phosphate group. The nitrogenous bases have 5 different structures and are the letters that compose the codes in DNA and RNA molecules. DNA and RNA molecules consist of chains of nitrogenous bases bound together by their attached phosphate groups.
Figure Nucleotides: A nucleotide is made up of three components: a nitrogenous base, a pentose sugar, and one or more phosphate groups. Bases can be divided into two categories: purines and pyrimidines. Purines have a double ring structure, and pyrimidines have a single ring. Variations in the structures of these molecules affect their function, differentiating DNA from RNA and the reactivity of the molecules. In DNA, two strands of nucleotides are paired together by hydrogen bonds between their bases in a very systematic way.
A can bond with T, and G can bond with C when the two strands are oriented in opposite directions. The two strands only pair if their sequences of bases are complementary. When each base is matched to its complement on the other strand, the two strands spiral around each other, creating a very stable and famous double-helical structure. Note that the yellow phosphate groups point upward on the right side and downward on the left side.
The grooves are due to asymmetry in the spiral.
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