Higher order chromatin organization

The winding of DNA into nucleosomes represents only the first level of structural organization. When nuclei are lysed in a low salt solution, the characteristic beads on a string structure, termed the 10 nm fiber, represents a packaging ratio of five and lacks histone HI. At a higher salt concentration, chromatin adopts a more compact structure which requires histone HI. This is probably a coiled fiber of 25-45 nm in diameter it is termed the 30 nm fiber), although alternative...

Chromosome Structure and Function

Fundamental concepts and definitions A chromosome is a discrete DN A molecule which carries essential genetic information, together with any associated proteins which define its structure. The scope of the term can include the bacterial nucleoid, organelle genomes and virus genomes, as well as eukaryotic nuclear chromosomes, but only the last is considered in this chapter * The original suggestion that genes were carried on chromosomes was based on the parallel behavior of chromosomes and...

Yem Transcription

Induce dorsal mesoderm, which has organizer activity, whilst the ventral vegetal cells induce ventral mesoderm. The organizer is so called because it initiates gastrulation and specifies the anteroposterior axis of the embryo, and can do so when transferred to an ectopic site. The organizer also has a number of further specialized properties. Firstly, It can differentiate into dorsal mesoderm structures (notochord, somites, head mesenchyme) secondly, prior to gastrulation, it can signal the...

Cl Wwmjji I fr

Of the product and, in many cases, its subcellular localization and likely partners for interaction are known, but a precise function has yet to be determined. The tral locus encodes two products Tral and Tral* (formerly TraZ) by nested translation. The function of Tral* is unknown. tra V, traC, traW, trail, trbC, traF, traH, traG The tra region of the F plesmid, comprising from 5'-i3') oriT, traM, traJ and the fra operon. The tra operon is continuous there is no physical break between trbB and...

The Genetic Code

Fundamental concepts and definitions Genetic information is the sequence of bases in DNA. Information may also be carried in the physical structure of the chromosome, which may be indirectly specified by the base sequence this is termed epigenetic information (see Chromatin, DNA Methylation and Epigenetic Regulation, Nucleic Acid Structure). Genetic information that is expressed as a polypeptide sequence must be translated from the four-letter language of nucleotides into the 21-letter language...

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A 0 C D ib J a v b l J ( a v b l J ( Figure 4,2 The effects of crossing over in inversion heterozygotes. An inversion reverses the orientation of loci C, D and E on one chromosome and an inversion loop forms at meiosis. In a pericentric inversion (left), the centromere lies within the inversion and crossing over generates unbalanced products containing deletions or duplications. In a paracentric inversion (right), the centromere lies outside the inversion and crossing over within the loop...

The Polymerase Chain Reaction PCR

Fundamental concepts and definitions The polymerase chain reaction (PCR) is a technique for amplifying DNA sequences in vitro, i.e. the DNA is not replicated in a cell, as is the case in molecular cloning (q.v.), but using purified enzymes. M The basic PCR uses pairs of oligonucleotide primers designed to flank the target for amplification. The primers anneal to opposite DNA strands and face inwards, so that DNA synthesis proceeds across the central region. The reaction involves three stages...

Info

Complexity is given as percent unique sequence DMA, The number of genes is taken from genome sequencing projects where appropriate, but where a complete genome sequence is unavailable, it is estimated by extrapolation from existing sequence data. content) as the G C rich genome helps maintain DNA in a duplex at high temperatures. The GC contents of various organisms are shown in Table 12.1. The base ratio and GC content are averages across the entire genome. However, the base composition varies...

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DNA replication RNA replication Prions The multiple levels of gene expression. A level of gene expression (Table 9.2) can be thought of as a discrete stage in the pathway of information transfer from gene to product where regulation is possible. Transcription is usually regarded as the initial stage of gene expression and is the predominant level for gene regulation, but before transcription is possible, the gene must be made accessible in a form suitable for transcription. This preparatory...

Oncogenes and Cancer

Fundamental concepts and definitions Cancer is a disease of multicellular organisms whose basis is abnormal, unregulated cell proliferation, often accompanied by abnormal differentiation (neoplasia). Cancers are generally caused by the accumulation of mutations (see below) they are common in higher vertebrates, but many other organisms do not manifest cancer because they do not live long enough. Cancer is well studied in animals, but tumors also occur in plants (q.v. crozun gall disease). When...

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F undergoes imprecise excision F' plasmid F sexduction F mobilises entire donor chromosome Recipient remains F* because ira genes rarely transferred F undergoes imprecise excision F' plasmid F sexduction F mobilises entire donor chromosome Recipient remains F* because ira genes rarely transferred F' sexduciion F mobilises small excised region of donor chromosome Recipient becomes F* because genes usualy transferred Figure 10.2 Sexduction the transfer of chromosomal DNA during conjugation. The F...

The bacterial cell cycle

DNA replication and growth coordination. The Helmstetter-Cooper model (or I + C + D model) divides the bacterial chromosome cycle into three phases, the interval phase, the chromosome replication phase and the division phase, represented by the letters I, C and D, respectively. DNA replication occurs during the C phase its duration is fixed (about 40 min in E. colt), reflecting the time taken to replicate the whole chromosome (see Replication). The D phase begins when replication is complete,...

The Gene

Fundamental concepts and definitions h A gene is a physical and functional unit of genetic information with the potential to be expressed, i.e. to be used as a template to generate one or more gene products of RN A or protein. The genome (q.v.) is the total genetic information in the cell, and that information is stored as the nucleotide sequence. While all genetic information can be stored and transmitted from generation to generation as part of a chromosome, only the genes are expressed....

C

The point at which half the DNA has reassociated (to.s) is chosen as a reference. At this point, C Co 0.5, and by rearranging Equation 12.2, it can be shown that Cofo.s Vk. Cgfo s is described as the Cot value, and is proportional to genome complexity. This is because as complexity increases, the relative concentration of any individual sequence decreases and takes longer to find a complemen tary strand. The reassociation reaction thus takes longer to reach the half-way point. Cot curves. Data...

Plastidone Ct

Biogenesis is controlled mainly by the nuclear genome, so mitochondria are constructed even in the absence of their entire genome Similar classes are seen in chloroplast mutants and animal mitochondrial mutants, reflecting two common themes (1) dual control of organelle function by the organelle and nuclear genomes, and (2) the ability of mutant organelles to dominate wild-type organelles in the same cell. Table 19.2 Some terms used to describe the behavior of organelle genomes Cytotype A...

Contents

Biological Heredity and Variation 1 2. The Cell Cycle 21 The bacterial eel cycle 21 The eukaryotic cell cycle 23 The molecular basis of cell cycle regulation 26 Progress through the cell cycle 28 Special cell cycle systems in animals 33 Higher order chromatin organization 38 Chromatin and chromosome function 39 Molecular structure of the bacterial nucleoid 42 Numerical chromosome mutations 45 Structural chromosome mutations 49 5. Chromosome Structure and Function 57 Normal chromosomes gross...

Gene Transfer in Bacteria

Fundamental concepts and definitions Gene transfer describes the introduction of genetic information into a cell from an exogenous source (ultimately, another cell). This process occurs naturally in both bacteria and eukaryotes, and may be termed horizontal or lateral genetic transmission to distinguish it from the transmission of genetic information from parent to offspring, which is vertical genetic transmission. Intraspecific gene transfer facilitates genetic mixing in asexual species and...

Vfu

Figure 14.2 Nucleotide excision repair in E. coli. UvrA loads UvrB onto damaged DNA and then dissociates there is hydrolysis of ATP during this process. UvrC then binds to the complex and nicks are introduced 5' and 3' to the lesion (arrows), UvrD helicase then removes the oligonucleotide fragment and UvrC, leaving UvrB bridging the gap. The gap is repaired by DNA polymerase I and DNA ligase UvrB is expelled. Figure 14.2 Nucleotide excision repair in E. coli. UvrA loads UvrB onto damaged DNA...

Relaxed Control In Gene Expression

Recombinant (constructed in vitro from parts of naturally occurring plasmids) Encode bacteriocins (proteins which kill or inhibit growth of other bacteria, e.g. agrocins and colicins). Also encode immunity functions so that the host cell is not destroyed. Killer plasmids in yeast are analogous None Catabolic heavy metals) Usually antibiotic resistance used as dominant selectable marker (q.v. plasmid vectors) Enables host to cause disease. Specifically refers to those plasmids encoding direct...

Mobile Genetic Elements

Fundamental concepts and definitions * Mobile genetic elements are segments of DNA able to move from site to site in the genome, or between genomes in the same cell. Found in both prokaryotes and eukaryotes, they are a diverse group differing in structure, mechanism of mobilization, distribution, freedom of movement and level of autonomy. The mobility of some elements has a clear cellular function, but most are believed to be selfish DNA or accidentally mobilized DNA. In higher eukaryotes, a...

Nucleosomes

Nucleosomes are the fundamental units of chromatin. They are found in all eukaryotes with the exception of the dinoflagellates and are conserved In structure. When nuclei are lysed in a low salt solution, the chromatin decondenses and nucleosomes can be observed resembling beads on a string. The relationship between DNA and the nucleosome can be investigated using nucleases Figure 3.1 . Limiting digestion of decondensed chromatin separates the nucleosomes into short...

Bs

Figure 4,1 Aneuploidy in the gametes caused by nondisjunction. 1 Homologous chromosome pairs tail to segregate at first meiotic division primary nondisjunction . 2 Chromatids fail to segregate at second meiotic division secondary nondisjunction . the dosage of genes which escape inactivation and effects occurring early in development before X-inactivation takes place. Disomy for the Y-chrornosome has little phenotypic impact, and the behavioral abnormalities which have been associated with this...