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Satellite DNA
Satellite DNA consists of very large arrays of tandem repeat, tandemly repeating, non-coding DNA. Satellite DNA is the main component of functional centromeres, and form the main structural constituent of heterochromatin. The name "satellite DNA" refers to the phenomenon that repetitions of a short DNA sequence tend to produce a different frequency of the bases adenine, cytosine, guanine, and thymine, and thus have a different density from bulk DNA such that they form a second or "satellite" band(s) when genomic DNA is separated along a cesium chloride density gradient using buoyant density centrifugation#DNA separation, buoyant density centrifugation. Sequences with a greater ratio of A+T display a lower density while those with a greater ratio of G+C display a higher density than the bulk of genomic DNA. Some repetitive sequences are ~50% G+C/A+T and thus have buoyant densities the same as bulk genomic DNA. These satellites are called "cryptic" satellites because they form a band ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tandem Repeat
In genetics, tandem repeats occur in DNA when a pattern of one or more nucleotides is repeated and the repetitions are directly adjacent to each other, e.g. ATTCG ATTCG ATTCG, in which the sequence ATTCG is repeated three times. Several protein domains also form tandem repeats within their amino acid primary structure, such as armadillo repeats. However, in proteins, perfect tandem repeats are rare in naturally proteins, but they have been added to designed proteins. Tandem repeats constitute about 8% of the human genome. They are implicated in more than 50 lethal human diseases, including amyotrophic lateral sclerosis, Huntington's disease, and several cancers. Terminology All tandem repeat arrays are classifiable as satellite DNA, a name originating from the fact that tandem DNA repeats, by nature of repeating the same nucleotide sequences repeatedly, have a unique ratio of the two possible nucleotide base pair combinations, conferring them a specific mass density that a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromosome 21
Chromosome 21 is one of the 23 pairs of chromosomes in humans. Chromosome 21 is both the smallest human autosome and chromosome, with 46.7 million base pairs (the building material of DNA) representing about 1.5 percent of the total DNA in cells. Most people have two copies of chromosome 21, while those with three copies of chromosome 21 (trisomy 21) have Down syndrome. Researchers working on the Human Genome Project announced in May 2000 that they had determined the sequence of base pairs that make up this chromosome. Chromosome 21 was the second human chromosome to be fully sequenced, after chromosome 22. Genes Number of genes The following are some of the gene count estimates of human chromosome 21. Because researchers use different approaches to genome annotation, their predictions of the number of genes on each chromosome varies (for technical details, see gene prediction). Among various projects, the collaborative consensus coding sequence project ( CCDS) takes an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inverted Repeat
An inverted repeat (or IR) is a single stranded sequence of nucleotides followed downstream by its complementarity (molecular biology), reverse complement. The intervening sequence of nucleotides between the initial sequence and the reverse complement can be any length including zero. For example, is an inverted repeat sequence. When the intervening length is zero, the composite sequence is a palindromic sequence. Both inverted repeats and direct repeats constitute types of Nucleic acid sequence, nucleotide sequences that occur repetitively. These repeated sequence (DNA), repeated DNA sequences often range from a pair of nucleotides to a whole gene, while the proximity of the repeat sequences varies between widely dispersed and simple tandemly arrayed genes, tandem arrays. The short tandem repeat sequences may exist as just a few copies in a small region to thousands of copies dispersed all over the genome of most eukaryotes. Repeat sequences with about 10–100 base pairs are kn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pagurus Pollicaris
''Pagurus pollicaris'' is a hermit crab commonly found along the Atlantic coast of North America from New Brunswick to the Gulf of Mexico. It is known by a number of common names, including gray hermit crab, flat-clawed hermit crab, flatclaw hermit crab, shield hermit crab, thumb-clawed hermit crab, broad-clawed hermit crab, and warty hermit crab. ''P. pollicaris'' inhabits the shells of shark eye snails and whelks. It grows to a length of and a width of . The shell is often shared by the commensal zebra flatworm (''Stylochus ellipticus''). The diet of the flat-clawed hermit crab comprises organic matter, algae, and sometimes other hermit crabs. Fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ... are the most important predators of this species. References {{Taxonbar, fr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Palindromic Sequence
A palindromic sequence is a nucleic acid sequence in a double-stranded DNA or RNA molecule whereby reading in a certain direction (e.g. 5' to 3') on one strand is identical to the sequence in the same direction (e.g. 5' to 3') on the complementary strand. This definition of palindrome thus depends on complementary strands being palindromic of each other. The meaning of palindrome in the context of genetics is slightly different from the definition used for words and sentences. Since a double helix is formed by two paired antiparallel strands of nucleotides that run in opposite directions, and the nucleotides always pair in the same way (adenine (A) with thymine (T) in DNA or uracil (U) in RNA; cytosine (C) with guanine (G)), a (single-stranded) nucleotide sequence is said to be a palindrome if it is equal to its reverse complement. For example, the DNA sequence ACCTAGGT is palindromic with its nucleotide-by-nucleotide complement TGGATCCA because reversing the order of the n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Subcloning
In molecular biology, subcloning is a technique used to move a particular DNA sequence from a ''parent vector'' to a ''destination vector''. Subcloning is not to be confused with molecular cloning, a related technique. Procedure Restriction enzymes are used to excise the gene of interest (the ''insert'') from the parent. The insert is purified in order to isolate it from other DNA molecules. A common purification method is gel isolation. The number of copies of the gene is then amplified using polymerase chain reaction (PCR). Simultaneously, the same restriction enzymes are used to digest (cut) the destination. The idea behind using the same restriction enzymes is to create complementary sticky ends, which will facilitate ligation later on. A phosphatase, commonly calf-intestinal alkaline phosphatase (CIAP), is also added to prevent self-ligation of the destination vector. The digested destination vector is isolated/purified. The insert and the destination vector ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DNA Supercoil
DNA supercoiling refers to the amount of twist in a particular DNA strand, which determines the amount of strain on it. A given strand may be "positively supercoiled" or "negatively supercoiled" (more or less tightly wound). The amount of a strand's supercoiling affects a number of biological processes, such as compacting DNA and regulating access to the genetic code (which strongly affects DNA metabolism and possibly gene expression). Certain enzymes, such as topoisomerases, change the amount of DNA supercoiling to facilitate functions such as DNA replication and transcription. The amount of supercoiling in a given strand is described by a mathematical formula that compares it to a reference state known as "relaxed B-form" DNA. Overview In a "relaxed" double-helical segment of B-DNA, the two strands twist around the helical axis once every 10.4–10.5 base pairs of sequence. Adding or subtracting twists, as some enzymes do, imposes strain. If a DNA segment under twist s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stem-loop
Stem-loops are nucleic acid Biomolecular structure, secondary structural elements which form via intramolecular base pairing in single-stranded DNA or RNA. They are also referred to as hairpins or hairpin loops. A stem-loop occurs when two regions of the same nucleic acid strand, usually Complementarity (molecular biology), complementary in nucleotide sequence, base-pair to form a double helix that ends in a loop of unpaired nucleotides. Stem-loops are most commonly found in RNA, and are a key building block of many RNA biomolecular structure#Secondary structure, secondary structures. Stem-loops can direct RNA folding, protect structural stability for messenger RNA (mRNA), provide recognition sites for RNA-binding protein, RNA binding proteins, and serve as a Substrate (chemistry), substrate for Enzyme catalysis, enzymatic reactions. Formation and stability The formation of a stem-loop is dependent on the stability of the helix and loop regions. The first prerequisite is the p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Z-DNA
Z-DNA is one of the many possible double helical structures of DNA. It is a left-handed double helical structure in which the helix winds to the left in a zigzag pattern, instead of to the right, like the more common B-DNA form. Z-DNA is thought to be one of three biologically active double-helical structures along with A-DNA and B-DNA. History Left-handed DNA was first proposed by Robert Wells and colleagues, as the structure of a repeating polymer of inosine–cytosine. They observed a "reverse" circular dichroism spectrum for such DNAs, and interpreted this incorrectly to mean that the strands wrapped around one another in a left-handed fashion. The relationship between Z-DNA and the more familiar B-DNA was indicated by the work of Pohl and Jovin, who showed that the ultraviolet circular dichroism of poly(dG-dC) was nearly inverted in 4 M sodium chloride solution and that the structure of poly d(I–C)·poly d(I–C) was in fact a right-handed D-DNA conformation. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Triple-stranded DNA
Triple-stranded DNA (also known as H-DNA or Triplex-DNA) is a DNA structure in which three oligonucleotides wind around each other and form a triple helix. In triple-stranded DNA, the third strand binds to a Nucleic acid double helix#Helix geometries, B-form DNA (via Base pair, Watson–Crick base-pairing) double helix by forming Hoogsteen base pairs or reversed Hoogsteen hydrogen bonds. Structure Examples of triple-stranded DNA from natural sources with the necessary combination of base composition and structural elements have been described, for example in Satellite DNA. Hoogsteen base pairing A thymine (T) nucleobase can bind to a Base pair, Watson–Crick base-pairing of T-A by forming a Hoogsteen base pair, Hoogsteen hydrogen bond. The thymine hydrogen bonds with the adenosine (A) of the original double-stranded DNA to create a T-A*T base-triplet. Intermolecular and intramolecular interactions There are two classes of triplex DNA: intermolecular and intramolecula ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gecarcinus Lateralis
''Gecarcinus lateralis'', also known by the common names blackback land crab, Bermuda land crab, red land crab (leading to easy confusion with ''Gecarcoidea natalis'') and moon crab (leading to easy confusion with '' G. quadratus'' and '' Cardisoma spp.''), is a colourful crab from the family Gecarcinidae. Distribution This species is found along the Atlantic coast from South Padre Island, Texas south to Macuto, Venezuela. It also inhabits the Florida Keys and the islands of the Caribbean. Relatives The taxonomy in relations to the Pacific '' Gecarcinus quadratus'' is disputed, with many considering it and ''G. lateralis'' to be conspecific. Another closely related species, ''Gecarcinus ruricola'', occurs together with ''G. lateralis'' in the tropical western Atlantic, but its carapace is typically almost entirely blackish, dark maroon, purplish or yellowish. Description As suggested by the name blackback land crab, it has a large blackish spot, which, although the exact shape ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DNA Profiling
DNA profiling (also called DNA fingerprinting and genetic fingerprinting) is the process of determining an individual's deoxyribonucleic acid (DNA) characteristics. DNA analysis intended to identify a species, rather than an individual, is called DNA barcoding. DNA profiling is a forensic technique in criminal investigations, comparing criminal suspects' profiles to DNA evidence so as to assess the likelihood of their involvement in the crime. It is also used in paternity testing, to establish immigration eligibility, and in genealogical and medical research. DNA profiling has also been used in the study of animal and plant populations in the fields of zoology, botany, and agriculture. Background Starting in the mid 1970s, scientific advances allowed the use of DNA as a material for the identification of an individual. The first patent covering the direct use of DNA variation for forensicsUS5593832A was filed by Jeffrey Glassberg in 1983, based upon work he had done while ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
