eco-region

Examples of eco-region in the following topics:

• Abiotic Factors Influencing Plant Growth

  • In terrestrial eco-regions, these are mainly plants, while in aquatic eco-regions, they are mainly algae.

• Transcriptional Enhancers and Repressors

  • In some eukaryotic genes, there are regions that help increase or enhance transcription.
  • These regions, called enhancers, are not necessarily close to the genes they enhance.
  • They can be located upstream of a gene, within the coding region of the gene, downstream of a gene, or may be thousands of nucleotides away.
  • Enhancer regions are binding sequences, or sites, for transcription factors.
  • Transcriptional repressors can bind to promoter or enhancer regions and block transcription.

• Epigenetic Control: Regulating Access to Genes within the Chromosome

  • If DNA encoding a specific gene is to be transcribed into RNA, the nucleosomes surrounding that region of DNA can slide down the DNA to open that specific chromosomal region and allow for the transcriptional machinery (RNA polymerase) to initiate transcription .
  • This occurs within very specific regions called CpG islands.
  • This modification changes how the DNA interacts with proteins, including the histone proteins that control access to the region.
  • Highly-methylated (hypermethylated) DNA regions with deacetylated histones are tightly coiled and transcriptionally inactive.
  • This opens the chromosomal region to allow access for RNA polymerase and other proteins, called transcription factors, to bind to the promoter region, located just upstream of the gene, and initiate transcription.

• Fluid Mosaic Model

  • The hydrophilic regions of the phospholipids tend to form hydrogen bonds with water and other polar molecules on both the exterior and interior of the cell.
  • Integral proteins (some specialized types are called integrins) are, as their name suggests, integrated completely into the membrane structure, and their hydrophobic membrane-spanning regions interact with the hydrophobic region of the the phospholipid bilayer .
  • This type of protein has a hydrophilic region or regions, and one or several mildly hydrophobic regions.
  • This arrangement of regions of the protein tends to orient the protein alongside the phospholipids, with the hydrophobic region of the protein adjacent to the tails of the phospholipids and the hydrophilic region or regions of the protein protruding from the membrane and in contact with the cytosol or extracellular fluid.

• The Promoter and the Transcription Machinery

  • When transcription factors bind to the promoter region, RNA polymerase is placed in an orientation that allows transcription to begin.
  • The promoter region is immediately upstream of the coding sequence.
  • This region can be short (only a few nucleotides in length) or quite long (hundreds of nucleotides long).
  • Within the promoter region, just upstream of the transcriptional start site, resides the TATA box.
  • The region that a particular transcription factor binds to is called the transcription factor binding site.

• Epigenetic Alterations in Cancer

  • In cancer cells, the DNA in the promoter region of silenced genes is methylated on cytosine DNA residues in CpG islands, genomic regions that contain a high frequency of CpG sites, where a cytosine nucleotide occurs next to a guanine nucleotide .
  • Histone proteins that surround that region lack the acetylation modification (the addition of an acetyl group) that is present when the genes are expressed in normal cells.
  • When these modifications occur, the gene present in that chromosomal region is silenced.

• Initiation of Transcription in Prokaryotes

  • At the -10 and -35 regions upstream of the initiation site, there are two promoter consensus sequences, or regions that are similar across all promoters and across various bacterial species.
  • The -10 consensus sequence, called the -10 region, is TATAAT.
  • The A–T-rich -10 region facilitates unwinding of the DNA template; several phosphodiester bonds are made.
  • The σ subunit of prokaryotic RNA polymerase recognizes consensus sequences found in the promoter region upstream of the transcription start sight.

• The trp Operon: A Repressor Operon

  • A DNA sequence that codes for proteins is referred to as the coding region.
  • The five coding regions for the tryptophan biosynthesis enzymes are arranged sequentially on the chromosome in the operon.
  • Just before the coding region is the transcriptional start site.
  • This is the region of DNA to which RNA polymerase binds to initiate transcription.
  • A DNA sequence called the operator sequence is encoded between the promoter region and the first trp-coding gene.

• Genome Evolution

  • Mutation rates differ between species and even between different regions of the genome of a single species .
  • A mutation in a promoter region, enhancer region or a region coding for transcription factors can also result in either a loss of function or and upregulation or downregulation in transcription of that gene.
  • Transposable elements are regions of DNA that can be inserted into the genetic code through one of two mechanisms.
  • The "copy-and-paste" mechanism works by making a genetic copy or copies of a specific region of DNA and inserting these copies elsewhere in the code.
  • This can result in a shift of reading frame, causing the gene to longer code for the expected protein, a premature stop codon or a mutation in the promoter region.

• What constitutes a biome?

  • A biome consists of all the habitats of a community that make up similar ecosystems in a particular region.
  • For example, an ecotone might be a transition region between a grassland and a desert, with species from both.