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BIO130H1 (167)

Chromosomes and Genomes

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John Coleman

Chapter Four: DNA, Chromosomes, and Genomes (pp 195-263) Required readings: pp 202-206, pp 208-218 Chromosomal DNA and its packaging in the chromatic fiber - DNAs most important function is to carry genes, including the informations about when, in what type of a cell and in what quantity proteins and RNA molecules are to be made - Genomes of eukaryotes are divided into chromosomes - Genes are arranged on chromosomes - There is a specialized DNA sequences that are required for a chromosome to be accurately duplicated and passed on from one generation to the next - DNA packaging if all the DNA was laid out end to end it would reach approximately 2 meters - DNA packaging is done by specialized proteins that bind to and fold the DNA - This generates a series of coils and loops that provide increasingly higher levels of organization, preventing DNA from becoming an unmanageable tangle - Even though DNA is tightly folded, it is compacted in a way to keeps it available to the many enzymes in the cell that replicate it, repair it and use its genes to produce RNA molecules an proteins 1. Eukaryotic DNA is packaged into a set of chromosomes - In eucaryotes the DNA in the nucleus is divided between a set of different chromosomes - Each chromosome consists of a single, long DNA molecule associated with proteins that fold and pack the fine DNA thread into a more compact structure - Chromosome is a structure composed of very long DNA molecule and associated PRs that carries some or all of the hereditary information of an organism; esp evident in animal and plant cells undergoing mitosis and meiosis, during which each chromosome becomes condensed into a compact rod-like structure visible under the light microscope - The DNA and protein complex is called chromatin - Chromosomes are also associated with many proteins and RNAs, which are required for gene expression, DNA replication and repair - Bacteria carry their genes on a single DNA molecule, which is often circular - This DNA is also associated with proteins that package and condense it, but they are different from eucaryotes - Although often called the bacterial chromosomes, it does not have the same structure as eucaryotes - With exception of a few cells, almost each human cell contains two copies of each chromosome, one inherited from the father and one from the mother www.notesolution.com
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