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Bio 240 Chapter 12 Notes!

by: Izabella Nill Gomez

Bio 240 Chapter 12 Notes! Bio 240

Izabella Nill Gomez
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Hey guys, here the notes from chapter 12! With detailed notes from Dr. Hughes' lecture as well as notes from the textbook, I compiled a delicious combo of 2 in 1 for your enjoyment! These also incl...
General Genetics (Bio 240)
Dr. Hughes
Class Notes
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This 3 page Class Notes was uploaded by Izabella Nill Gomez on Thursday November 5, 2015. The Class Notes belongs to Bio 240 at University of Tennessee - Knoxville taught by Dr. Hughes in Summer 2015. Since its upload, it has received 25 views. For similar materials see General Genetics (Bio 240) in Biology at University of Tennessee - Knoxville.


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Date Created: 11/05/15
Biology 240 Chapter 12 Notes! -Prokaryotic chromosomes lack in associated proteins and have less genetic information. Prokarya can exist as single stranded, double stranded, linear or circular chromosomes and have RNA or DNA as their genetic material. Circularity is not an absolute requirement for virus replication. One thing in common with prokarya and eukarya is the ability to pack long DNA into a small volume. Bacterial chromosomes consist of a double stranded DNa molecules compacted into a nucleoid. Several DNA binding proteins are associated with this, HU and HNS (histone-like structuring) proteins. Small but abundant, these contain high percentages of positiviley charged amino acids functioning to fold and bond DNA. HNS also regulates gene activity in a nonspecific way. Supercoiled DNA: characteristic of closed circular molecules. First observed in polyoma virus in mice. Closed-circular molecules are more compact and sediment more rapidly than linear DNA molecules but have the same molecular weight. Supercoiled shape is caused by higher energy stabilizing the double helix. In most virsues and bacteria, circular closed DNA is slightly underwound. Topoisomers are 2 otherwise identical molecules that differ only in linking number. Enzymes that cut the closed ends of topoisomers are topoisomerases. Topoisomerase I serves to reduce the number of negative supercoils. Topoisomerase II introduces negative supercoils in DNA. This is also found in Eukarya. In both, DNA replication/transcription creates supercoils downstream as the double helix unwinds and becomes accessible to the appropriate enzyme. Polytene chromosomes are found in the salivary glands of flies. Can be seen in the nuclei of interphase cells. Exhibit alternating band pattern, distinctive for each chromosome, called a chromomere. Polytene chromosomes represent paired homologs. Large due to repeated DNA strands. DNA of paired homologs undergo extensive replication ** but no strand separation or cytoplasmic division. Each band represents an individual gene (uncoiled during genetic activity, forming puffs). Puffs illustrate high levels of gene activity (transcription that produces RNA). Bands that don’t turn into puffs have low levels of activity. Lampbrush chromosome resembles brushes (discovered by Flemming). Characteristic of most vertebrate oocytes as well as spermatocytes of some insects (are meiotic chromosomes). Most experimental ones done from amphibian oocytes. Isolated in diplotene stage of prophase I, active directing metabolic activities of the developing cell. Synapsed pairs are held by chiasmata, do not condense and are usually extended. Later in meiosis, they revert to normal length (usually uncoiled). Condensed areas of chromomeres contain lateral loops. Each meiotic chromosome composed of a pair of sister chromatids. Chromatin: decondensed chromosomes, usually present during interphase. While in interphase, Chromatin is dispersed throughout the nucleus. As the cell enters S phase, DNA is replicated and chromatin coils and condenses. Eukaryotic chromatin has a substantial amount of protein associated with chromosomal DNA in all cell cycle phases. Can either be positively charged histones or less positively charged nonhistone proteins. Histones contain large numbers of amino acids lysine, arginine, making possible to bond electrostatically to negative phosphate groups of nucleotides. Histones play an important role in chromatin structure; control regulating diffraction rings. Chromatin is composed of nucleosomes. Formation of nucleosome represents the first level of packing. Characteristic of uncoiled chromatin in stacked nucleosomes from Histone I. In mitotic transition, chromatin is compacted into looped domains; coiled chromatin fibers the constitute the arms of a chromatid. **When present in several levels of compaction within the chromatin fiber, DNA inaccessible to the interaction with other DNA binding proteins. To accommodate DNA protein interactions, chromatin must change structure (chromatin remodeling). To allow replication and gene expression, chromatin must relax and expose DNA to the proteins. There are unstructured histone tails that are not packed into histone domains with nucleosomes, but protrude from it. Other make connections with other nucleosomes. Provide potential targets along the chromatin fiber for a variety of chemical modificators that may be linked to genetic function. Acetylation for enzyme histone acetyltransferase involves the addition of an acetyl group to the positively charged amino group on the side chain of lysine and neutralizes the positive charge. High levels of acetylation remodel chromatin fiber to increase the regions of active genes and decreases inactive regions. Methylation/phosphorylation, resulting from enzymes methyltransferase and kinase. Added to lysine and arginine, involving unfolding and condensation during and after DNA replication. Methylation within nucleosomes often correlated with gene activity in eukarya; methylation of cytosine within polynucleotides of DNA forms 5-methyl cytosine, negatively correlated with gene activity (methylation can have a positive or negative effect). Euchromatin: parts of the chromosome that is uncoiled. Heterochromatin: parts of the chromosome that remain condensed. Heterochromatin are generally inactive because they lack genes or contain genes that are expressed. Heterochromatin replicates later during the S phase of the cell cycle than euchromatin. Ex: telomere, centromere---help maintain structural stability. In some cases, characteristic to genetic material of eukarya, whole chromosomes can be heterochromatic (inactivated X chromosomes Barr body). If some heterochromatic areas are translocated to new site, genetically active sites may become inert if adjacent to the heterochromatin; position effect. Chromosome bonding techniques stain chromosomes to make them distinguishable from one another. C-bonding refers to staining of only centromeric regions of mitotic chromosomes (specific area of heterochromatin). G-bonds produced by staining technique that runs along the length of each chromosome. Involves digestion of mitotic chromosomes with trypsin enzyme. Reflect heterozygosity and complexity of chromosome. Repetitive DNA: functional genes present in more than one copy (multiple-copy genes), satellite DNA (only in eukarya): makes up a variable proportion of DNA (differs slightly in density), short and repetitive, located in heterochromatic regions, flanking centromeres. -Separation of homologs during mitosis/meiosis depends on centromeres, primary constrictions along eukaryotic chromosomes. Repetitive DNA within is critical to role (CEN Region). DNA binds a platform of proteins including the kinetochore that binds to microtubules of spindle fiber during division. Each centromere serves identical function (most DNA sequences are almost identical). Alphoid family mainly found in centromere regions and is transcribed into RNA that ultimately serves a kinetochore function. Moderately repetitive DNA: most characteristic for tandem repeats or noncoding sequences. Ex: variable number tandem repeats (VNTRs) dispersed throughout the genome, known better as minisatellites. Allows for DNA fingerprinting for forensic study. Microsatellites or short tandem repeats (STRs) are also dispersed throughout genome and vary among individuals. Serve as molecular markers. Transposable sequences: mobile, can potentially move to different locations in the genome; much of human genome is comprised of these. Short interspersed elements are a set of closely related sequences, Alu family, sometimes transcribed into RNA, although the role is not clear. Long interspersed elements have sequences from the R1 family (retrotransposons). There is a large amount of DNA that appears to be noncoding; pseudogenes represent evolutionary vestiges of duplicated copies of genes that have undergone significant mutational alteration. Usually not transcribed. **Only a very small part of the genome actually codes for proteins. Possible Exam Questions: 1. The term “satellite DNA” refers to: highly repetitive DNA in Eukaryotes, DNA fraction that separates from the bulk of the DNA during centrifugation, and DNA in the heterochromatic centromere regions of eukaryotes 2. In contrast with euchromatin, heterochromatin contains more genes and is earlier replicating: False


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