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Twist ye, twine ye! even so Mingle shades of joy and woe, Hope and fear, and peace and strife, In the thread of human life. All molecules in a living organism serve a purpose, and we cannot say that a particular type is more important than any other. Nevertheless, it would be difficult to identify substances that play more varied and central roles than do the biopolymers. They contribute to the mechanical structure, and in the animal kingdom they provide the means of motion. They facilitate transport of smaller chemical units and mediate the chemical interaction between molecules, the biopolymers that serve this catalytic function being the proteins known as enzymes. There are biopolymers that form the immunological system and others that are involved in the mechanism of tissue differentiation. With so many functions to be fulfilled, we should expect to find many different types of these ubiquitous molecules, and this is certainly the case. It is believed, for example, that there are several hundred distinct enzymes within each cell of a higher organism such as a mammal. Even the task of perpetuating and translating the genetic message is entrusted to biopolymers. The body of a typical mammal is mostly water – about 65% by weight in fact – but of the solid components no group is better represented than the proteins; they make up about 15% of the total weight. [ABSTRACT FROM AUTHOR]

The sequence design is a crucial problem in DNA based computation. We present results about tests carried on sets of DNA strands proposed in DNA computing papers since 1994. Our goal is to direct attention on the necessity of a middle-process between logical designing of input and practical computation in laboratory. The analysis shows that many input sets should not be used for a real DNA computation because they lead to a high probability of incurring in biological faults which result to be very unsafe for a reliable computation. [ABSTRACT FROM AUTHOR]

A definition of the term "Lymphocyte Proliferation" is presented. It refers to the process whereby lymphocytes begin to synthesize DNA after cross-linking of their antigen receptor either following recognition of antigen or stimulation by a polyclonal activator.

Take a large onion and chop finely. Place the pieces in a mediumsized casserole dish. Now mix ten tablespoons of washing-up liquid with a tablespoon of salt, and make up to two pints with water. Add about a quarter of this mixture to the onion and cook in a bain-marie in a very cool oven for five minutes, stirring frequently, and liquidise at high speed for just five seconds. Now strain the mixture and add a few drops of fresh pineapple juice to the strained liquid, mixing well. Pour into a long chilled glass and finish off by dribbling ice-cold alcohol (vodka will do) down the side so that it floats on top of the mixture. Wait a few minutes and watch cloudiness form where the two layers meet. Now lower a swizzle stick into the cocktail and carefully hook up the cloudy material. It should collapse into a web of fibres that you can pull out of the glass. This is DNA (short for deoxyribonucleic acid). DNA is the stuff that genes are made of. Genes carry biological information, which is translated into the characteristics of living things and is passed on down the generations. So genes determine the colour of a butterfly's wings, the scent of a rose, and the sex of a baby. DNA is just a chemical – not a more complex entity like a chromosome or a cell – and it is only in a biological context that it acquires its status as the molecular signature of an organism. [ABSTRACT FROM AUTHOR]

Many types of cancer and genetic diseases are characterized by chromosomal aberrations. Conventional cytogenetics, the analysis of banded metaphase chromosomes, can be very time consuming and, in many cases, marker chromosomes cannot be identified by their banding pattern alone. For some years there has been interest in a more rapid and objective method of analyzing chromosomes. Flow cytometry offers an alternative machine-based approach in which a suspension of metaphase chromosomes is prepared, stained with one or two DNA-binding fluorochromes, and passed through a flow cytometer. The first human flow karyotypes were demonstrated in the mid-1970s using chromosomes isolated from fibroblast cells (1,2). High resolution flow karyotypes were subsequently obtained from PHA-stimulated peripheral blood lymphocytes (3) and lymphoblastoid cell lines (4). In practice, chromosomes can be prepared from almost any culture of growing cells. In the case of the single-laser system in which one nonbase-specific dye, such as ethidium bromide, is used, the intensity of fluorescence from each chromosome is proportional to its DNA content. The signal intensity from each chromosome is measured and recorded as it passes through the focused laser beam. Accumulating data from 10,000-50,000 chromosomes and presenting it as a histogram of fluorescence intensity against frequency produces a distinctive species specific pattern of peaks. Such a histogram is known as a univariate flow karyotype. Not all human chromosomes appear as separate peaks. [ABSTRACT FROM AUTHOR]

Flow cytometric DNA content analysis of human neoplasia provides quantitative information on DNA ploidy, clonal DNA heterogeneity, and proliferative activity. These submicroscopic features are important for the biological and clinical evaluation of tumors as demonstrated in clinical studies of a wide spectrum of human lymphoreticular and solid malignancies (1-24). Although valuable, such information should not be used in isolation from other conventional diagnostic and biological parameters in the risk assessment of cancer patients. [ABSTRACT FROM AUTHOR]

Conventional cDNA library construction often requires a minimum available amount of material (typically 1 or 2 µg of polyA+ RNA). For complex organs, such as brain, or certain species, such as humans, as well as subsets of cell types, this condition is often difficult to fulfill. Amplification by PCR can be used to circumvent this limitation because it is a powerful method to obtain working quantities of low-abundance DNAs. To effectively apply this method, known sequences need to be attached to the ends of the single-stranded cDNA (ss-cDNA). One at the 5′ end of the ss-cDNA is added during the priming of the synthesis, the other, at the 3′ end, is covalently attached by ligation using the SLIC strategy as described elsewhere (Chapter 27). With known DNA sequences attached to both ends of the synthetized cDNA, minute quantities can be amplified with sequence-specific primers to provide sufficient material to successfully generate and screen cDNA libraries. The overall scheme is illustrated in Fig 1. [ABSTRACT FROM AUTHOR]

Rapid amplification of cDNA ends (RACE) allows the amplification of either the 5′ or 3′ end of a specific cDNA starting from a mRNA population (5′-RACE and 3′-RACE respectively: refs. 1,2). The method allows the amplification of regions with unknown sequence and only requires the knowledge of a single short sequence within the mRNA of interest. The method is often used for cloning the remainder of a cDNA using a sequence from an incomplete cDNA. Incomplete cDNAs are frequently obtained by, for instance, the screening of a library or from PCR using degenerate primers. [ABSTRACT FROM AUTHOR]

A definition of the term "genomic DNA" is presented. It refers to a molecular analysis that uses the total set of genes carried by an individual or cell.

The article presents an encyclopedia entry for DNA fingerprinting. It is a technique for identifying specific organisms based upon the uniqueness of an individuals DNA pattern.

The article presents an encyclopedia entry for deoxyribonucleic acid (DNA). It is an informational biomolecule that is found in the nucleus of a cell. DNA is consists of deoxyribose units joined in the 3' and 5' positions through a phosphodiester linkage. It also has a purine or pyrimidine base attached to the 1' position.

A definition of 5' is presented. It refers to the direction of the DNA strands which can be described as double stranded with the top strand in the orientation of 5' to 3'. The bottom strand is considered complimentary to the top strand and is in reverse orientation of 3' to 5'.

A definition of 3' is presented. It refers to the direction of the DNA strands which can be described as double stranded with the top strand in the orientation of 5' to 3'. The bottom strand is considered complimentary to the top strand and is in reverse orientation of 3' to 5'.

An encyclopedia entry for preintegration complex is presented. It is described as a complex retroviral DNA and proteins that translocates from the cytosol into the nucleus prior to integration.

A definition of the term "homologous recombination" is presented. Homologous recombination is a form of genetic alteration that occurs when DNA duplexes align at regions of sequence similarity and new DNA molecules are formed by the breakage and joining of homologous segments.

A definition of the term "helix-loop-helix motif" is presented. It refers to a DNA-binding motif, related to the leucine-zipper. A helix-loop-helix motif consists of a short α helix, connected by a loop to a second, longer α helix. The loop is flexible and allows one helix to fold back and pack against the other.

A definition of the term "DNA response elements" is presented. These response elements are generally found a short distance upstream of promoters in selected genes. The response elements often consist of small sequence repeats separated by a variable number of DNA base pairs.

A definition of the term "DNA methylation" is presented. It is a means by which cells regulate gene expression. In higher eukaryotes, most of the chromosomal DNA carries 5-methyl-cytidine residues located in CpG sequence motifs. There is a close association between transcriptional inactivation and methylation.

A definition of the term "DNA fragmentation" is presented. It occurs in two stages. In the first stage, endonucleolytic activity cleaves the DNA into high molecular weight fragments leading to the morphological picture of chromatin condensation characteristic of apoptosis. Meanwhile, the second stage involves a calcium-magnesium endonuclease.

A definition of the term "conjugative transposon" is presented. It refers to self-transmissible large DNA elements located in the donor chromosome. There will be a formation of a circular intermediate formed that is unable to replicate autonomously after excision. The transposon integrates into the recipient's chromosome after generating a doublestranded circle.

A definition of the term "satellite DNA" is presented. Satellite DNA consists of many tandem repeats of a short basic repeating unit.

An encyclopedia entry for repetitive DNA is presented. It characterizes the behavior of repetitive DNA in a reassociation reaction as though many sequences are present in a component. This allows any pair of complementary sequences to reassociate.

A definition of the term "8-oxoguanine" is presented. It refers to one of many products of the oxidation of DNA and occurs when 8-oxodeoxyguanosine is combined with deoxyribose. It is different from guanine by replacement of a hydrogen atom with a hydroxyl group.

A definition of the term "mutagenic" is presented. The term means causing a heritable change in DNA, the genetic material.

The article presents an encyclopedia entry on the definition of the term "G-quadruplex DNA." The term refers to a guanine-rich, square-planar deoxyribonucleic acid (DNA) structure held together by Hoogsteen base pairing.

A definition of the term "annealing" is presented, which refers to the pairing of complementary single strands of DNA to form a double helix.