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Genes & Chromosomes

Genes & Chromosomes. fig. 8.1. A chromosome is a single DNA double helix and contains 100s or 1000s genes. In binary fission, each daughter cell receives a (nearly) exact replica of it. Deoxyribonucleic Acid. Stores information Information to do what?. A Blueprint?.

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Genes & Chromosomes

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  1. Genes & Chromosomes

  2. fig. 8.1 A chromosome is a single DNA double helix and contains 100s or 1000s genes. In binary fission, each daughter cell receives a (nearly) exact replica of it.

  3. Deoxyribonucleic Acid Stores information Information to do what?

  4. A Blueprint? A blueprint gives all of the instructions for how to make something. Genes are more like a list of ingredients. Then, where do the rest of the instructions come from? Genome = the entire set of genes in an organism

  5. The basic unit of measurement is a base pair (bp); E.coli has a 4.6 Mbp genome Each strand of the double helix has some sequence of 4 nucleotides The two strands complement each other Adenine always pairs with thymine Guanine always pairs with cytosine

  6. The two strands are antiparallel and go from 5’ to 3’ The two strands are separate polymers See also fig. 8.3b

  7. DNA Replication Precedes cell division Begins at the origin of replication DNA polymerase (along with other proteins) catalyzes the duplication of DNA DNA replication is considered semiconservative

  8. Each new double helix contains one parental and one new strand Fig. 8.3a

  9. fig. 8.4

  10. Nucleotides are added to the new 3’ end Fig. 8.5

  11. The leading strand is synthesized in a continuous manner The lagging strand is synthesized in fragments, known as Okazaki fragments [synthesis is always 5’ to 3’] DNA ligase catalyzes the filling in of the gaps between Okazaki fragments

  12. Replication can be bidirectional Fig. 8.6

  13. Chromosomes are much longer than the cell They are supercoiled to take up less space They must be uncoiled (partially) during replication DNA gyrase/topoisomerase II catalyzes the coiling and uncoiling (fluoro)quinolone antibiotics inhibit this enzyme

  14. Genome Sizes Human Genome: 3.3 billion bp; ~25000 genes Rice: 430 million bp; ~60000 genes Anopheles mosquito: 278 Mb; 13700 genes Plasmodium: 22.9 Mb; 5268 genes Vibrio cholerae 3.1 - 4Mb ; 3890 Neisseria meningitis 2.2 Mb; 2200 Mycobacterium tuberculosis 4.6 Mb; 4000 Treponema pallidum 1.1 Mb; 1000 genes Helicobacter pylori 1.7 Mb; 1600 genes Deinococcus radiodurans 3.3Mb; 3187 Haemophilus influenzae 1.8Mb; 1700 (middle ear infections) Mycoplasma genitalium 580 kb; 483 genes Viral genomes range from 3.2 kb – 800 kb

  15. Rates of Replication >500 bp/sec in bacteria 50 bp/sec in human cells How long does it take to replicate the entire E.coli genome? What about the human genome? (There are 3600 sec/hr)

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