Each consists of three smaller molecules a sugar a phosphate group and a nitrogen base

Animal Genetics

DNA - primary structure

A series of experiments proved that the genetic material consists of one of two types of nucleic acids: DNA or RNA. Of the two, DNA is the genetic material of all living organisms and of some viruses, and RNA is the genetic material of the remaining viruses.

DNA and RNA are polymers - large molecules that consist of many similar smaller molecules, called monomers, linked together. The monomers that make up DNA and RNA are called nucleotides. Each nucleotide consists of three distinct parts: a pentose (five-carbon) sugar, a nitrogenous (nitrogen-containing) base, and a phosphate group.

The pentose sugar in DNA is deoxyribose, and the sugar in RNA is ribose. The two sugars differ by the chemical groups attached to the 2' carbon: a hydrogen atom (H) in deoxyribose and a hydroxyl group (OH) in ribose. In DNA and RNA, bases are always attached to the 1' carbon of the pentose sugar by a covalent bond.

The combination of a sugar and a base is called a nucleoside.

Addition of a phosphate group to a nucleoside yields a nucleoside phosphate, also called a nucleotide. The phosphate group (PO42-) is attached to the 5' carbon of the sugar in both DNA and RNA.

Nomenclature

A segment of a polynucleotide chain, in this case a single strand of DNA. The deoxyribose sugars are linked by phosphodiester bonds between the 3' carbon
of one sugar and the 5' carbon of the next sugar. The phosphodiester bonds are relatively strong, so the repeated sugar-phosphate-sugar-phosphate backbone of DNA and RNA is a stable structure.

DNA and RNA occur in nature as macromolecules composed of smaller building blocks called nucleotides. Each nucleotide consists of a 5-carbon sugar (deoxyribose in DNA, ribose in RNA)" to which is attached a phosphate group and one of four nitrogenous bases: adenine, guanine, cytosine, and thymine (in DNA) or adenine, guanine, cytosine, and uracil (in RNA).

DNA - secondary structure

In 1953, James D. Watson and Francis H. C. Crick published a very important paper in which they proposed a model for the physical and chemical structure of the DNA molecule. The model they devised, which fit all the known data on the composition of the DNA molecule, is the double helix model for DNA.

Four different bases are present in DNA: adenine A, thymine T, cytosine C and guanine G. The base guanine only bonds to cytosine, and adenine only bonds to thymine.

DNA molecule consists of two strands that wrap around each other to resemble a twisted ladder whose sides, made of sugar and phosphate molecules are connected by rungs of nitrogen containing chemicals called bases. Each strand is a linear arrangement of repeating similar units called nucleotides, which are each composed of one sugar, one phosphate, and a nitrogenous base.

Watson and Crick's double-helical model of DNA

• The DNA molecule consists of two polynucleotide chains wound around each other in a right-handed double helix; that is, viewed on end (from either end), the two strands wind around each other in a clockwise (right-handed) fashion.
• The two chains are antiparallel (show opposite polarity); that is, the two strands are oriented in opposite directions, with o ne strand oriented in the 51 - to-3 1 way and the other strand oriented 3´ to 5´. More simply if the 5´ end is the "head" of the chain and the 3´ end is the "tail," antiparallel means that the head of one chain is against the tail of the other chain and vice versa.
• The sugar-phosphate backbones are on the outsides of the double helix, with the bases oriented toward the central axis.
• The bases in each of the two polynucleotide chains are bonded together by hydrogen bonds, which are relatively weak chemical bonds. The specific pairings
• observed are A bonded with T (two hydrogen bonds) and G bonded with C (three hydrogen bonds). The A-T and G-C base pairs are the only ones that can fit the physical dimensions of the helical model, and their arrangement is in accord with Chargaff's rules. The specific A-T and G-C pairs are called complementary base pairs, so the nucleotide sequence in one strand dictates the nucleotide sequence of the other.
• The base pairs are 0.34 nm apart in the DNA helix. A complete (360°) turn of the helix takes 3.4 nm; therefore, there are 10 base pairs per turn. The external diameter of the helix is 2 nm.
• Because of the way the bases bond with each other, the two sugar-phosphate backbones of the double helix are not equally spaced from one another along the helical axis. This unequal spacing results in grooves of unequal size between the backbones; one groove is called the major (wider) groove, the other the minor (narrower) groove.

RNA Structure

RNA has a structure similar to that of DNA. The RNA molecule is a polymer of RNA nucleotides (ribonucleotides) in which the sugar is ribose. Three of the four bases in RNA are the same as those in DNA: A, G, and C. The distinctive base in RNA is uracil, and that in DNA is thymine (T).

In the cell, the various functional forms of RNA - messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA), and small nuclear RNA (snRNA) - are
single-stranded molecules.

Anatomy and function of genes

Historical overview of gene definition:

Definition 1860s–1900s: Gene as a discrete unit of heredity (the word gene was first used by Wilhelm Johannsen in 1909, based on the concept developed
by Gregor Mendel in 1866).

Definition 1910s: Gene as a distinct locus (gene was an abstract entity whose existence was reflected in the way phenotypes were transmitted between generations).

Definition 1940s: Gene as a blueprint for a protein (“one gene, one enzyme” view, which later became “one gene, one polypeptide” - the gene is being implicitly considered as the information behind the individual molecules in a biochemical pathway).

Definition 1950s: Gene as a physical molecule (gene’s product is a diffusible substance underlies the complementation test that was used to define genes in the early years of bacteriology. A practical view of the gene was that of the cistron, a region of DNA defined by mutations that in trans could not genetically complement each other).

Definition 1960s: Gene as transcribed code (gene is a code residing on nucleic acid that gives rise to a functional product - protein, RNA).

Definition 1970s–1980s: Gene as open reading frame (ORF) sequence pattern (concept of the “nominal gene,” which is defined by its predicted sequence; the gene effectively became identified as an annotated ORF in the genome).

Definition 1990s–2000s: Annotated genomic entity, enumerated in the databanks (the Sequence Ontology Consortium reportedly called the gene a “locatable region of genomic sequence, corresponding to a unit of inheritance, which is associated with regulatory regions, transcribed regions and/or other functional sequence regions”).

A current computational metaphor: Genes as “subroutines” in the genomic operating system (one metaphor that is increasingly popular for describing genes is to think of them in terms of subroutines in a huge operating system (OS). That is, insofar as the nucleotides of the genome are put together into a code that is executed through the process of transcription and translation, the genome can be thought of as an operating system for a living being. Genes are then individual subroutines in this overall system that are repetitively called in the process of transcription.)

A gene is the basic unit of heredity in a living organism. All living things depend on genes. Genes hold the information to build and maintain their cells and pass genetic traits to offspring. In general terms, a gene is a segment of nucleic acid that, taken as a whole, specifies a trait. The colloquial usage of the term gene often refers to the scientific concept of an allele.

In cells, a gene is a portion of DNA that contains both "coding" sequences that determine what the gene does, and "non-coding" sequences that determine when the gene is active (expressed). When a gene is active, the coding and non-coding sequences are copied in a process called transcription, producing an RNA copy of the gene's information. This piece of RNA can then direct the synthesis of proteins via the genetic code. In other cases, the RNA is used directly, for example as part of the ribosome. The molecules resulting from gene expression, whether RNA or protein, are known as gene products, and are responsible for the development and functioning of all living things.

A gene is a locatable region of genomic sequence, corresponding to a unit of inheritance, and is associated with regulatory regions, transcribed regions and/or other functional sequence regions. The physical development and phenotype of organisms can be thought of as a product of genes interacting with each other and with the environment.

Functional structure of a gene

All genes have regulatory regions in addition to regions that explicitly code for a protein or RNA product. A regulatory region shared by almost all genes is known as the promoter, which provides a position that is recognized by the transcription machinery when a gene is about to be transcribed and expressed. A gene can have more than one promoter, resulting in RNAs that differ in how far they extend in the 5' end. Other possible regulatory regions include enhancers, which can compensate for a weak promoter. Most regulatory regions are "upstream" - that is, before or toward the 5' end of the transcription initiation site. Eukaryotic promoter regions are much more complex and difficult to identify than prokaryotic promoters.

Many prokaryotic genes are organized into operons, or groups of genes whose products have related functions and which are transcribed as a unit. By contrast, eukaryotic genes are transcribed only one at a time, but may include long stretches of DNA called introns which are transcribed but never translated into protein (they are spliced out before translation).

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What consists of three smaller molecules a sugar a phosphate group and a nitrogen base?

What consist of three smaller molecules?

Which molecule has sugar nitrogenous base and phosphate group?

What are the three smaller molecules that make up nucleotides?