Bmsc 220 Nucleus and Genome

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Scottygo
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Bmsc 220 Nucleus and Genome
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2013-10-14 22:36:57
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Bmsc 220 Nucleus Genome
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Bmsc 220 Nucleus and Genome
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  1. Nucleus is the site of:
    4
    • DNA replication 
    • RNA synthesis (transcription) 
    • RNA processing 
    • ribosome assembly
  2. Where does Protein synth takes place?(translation)
    cytoplasm
  3. nuclear envelope
    • -selective traffic of proteins and RNAs through nuclear pore complexes in the nuclear envelope establishes nuclear composition
    • - RNA out (mostly) 
    • - proteins in (but also back out) 
    • - highly regulated and energy dependent
  4. nuclear pore complex-
    a large macromolecular complex that differs significantly from typical membrane channels and transporters
  5. nuclear lamina
    • •a fibrous mesh that provides structural support located on inside of nuclear membrane
    • •consists of fibrous proteins called lamins (several types), and other proteins.
  6. outer nuclear membrane
    • -phospholipid bilayer that is continuous with the endoplasmic reticulum.
    • -enriched in membrane proteins that bind the cytoskeleton
  7. inner nuclear membrane
    phospholipid bilayer that has proteins that bind the nuclear lamina.
  8. Nucleolus
    site of ribosome assembly
  9. allele
    specifies a specific type of trait, and is one gene copy that is inherited from each parent(but there are many different alleles for any one gene).
  10. Genotype
    the genetic composition of an organism
  11. •Phenotype
    • -Physical representation of genotype
    • -can include biochemical and physiological traits.
  12. linkage groups
    groups of phenotypic traits that are inherited together
  13. chromosomes
    carriers of genes and consist of long DNA molecules and associated proteins
  14. Replication )
    the synthesis of a duplicate copy of a   DNA molecule (DNA polymerase)
  15. Transcription
    the synthesis of an RNA molecule from a DNA template (RNA polymerase)
  16. Translation
    is the synthesis of a polypeptide chain   from an mRNA template (ribosomes)
  17. Semiconservative replication of DNA
    • •semiconservative because one strand of parental DNA is “conserved” (i.e. is one-half of) in each new progeny DNA molecule)
    • •Therefore each new DNA double helix =   1 parent +  1 daughter strand
  18. •RNA polymerases
    enzymes that catalyze the synthesis of RNA from a DNA template
  19. Three major cellular RNAs
    • Messenger RNAs (mRNAs)
    • Ribosomal RNA (rRNA)
    • Transfer RNAs (tRNAs)

    -Other types of regulatory and catalytic RNAs are also present in cells
  20. Messenger RNAs (mRNAs) .
    RNA molecules that serve as templates for protein synthesis
  21. Ribosomal RNA (rRNA)
    is a component of ribosomes.
  22. Transfer RNAs (tRNAs)
    serve as adaptor molecules that align amino acids along the mRNA template.
  23. genetic code
    corresponding information from nucleotide triplets called codons that encode individual amino acids in proteins
  24. Codons
    • -nucleotide triplets that carry meaning
    • -the basic units of the genetic code.

    • 64 codons
    • 1 start(met) AUG
    • 3 stops
  25. Spacer sequences
    long DNA sequences that lie between genes within a chromosome
  26. Exons
    • -segments of protein-coding sequence
    • -Only 10-20% (on average)of a typical gene’s RNA-coding region is the actual protein coding region
    • -~1.2 % of the human genome is exons that actually encode proteins
  27. Introns (or intervening sequences) .
    • -segments of non-protein-coding sequences found between exons
    • -make up the majority of a gene’s RNA-coding
    • -~20% of human genome is introns
  28. RNA splicing
    the joining of exons in a precursor mRNA molecule by cutting out introns
  29. Trends of genome properties between organisms
    -as genome size and gene number increases, % of genome used for protein coding decreases
  30. non-protein coding regions
    -found to encode regulatory RNAs that play important roles in regulation of other genes
  31. •Chromatin
    • - eukaryotic chromosomal DNA complexed with proteins
    • -typically about twice as much protein as DNA.
  32. What does the basic structure of chromatin serve to do?
    • - pack DNA into a small space
    • -total length of human DNA is 2 metres, packed into a 5-10 um nucleus
  33. How is chromosome number related to Genome size?
    It is unrelated?
  34. •Nucleosomes .
    the basic structural units of chromatin, and consist of DNA+histones
  35. •Histones
    • -small proteins containing a high proportion of the basic amino acids, arginine+ and lysine+. 
    • -This facilitates binding to the negatively charged DNA sugar-phosphate backbone.
    •  -H1, H2A, H2B, H3, H4
  36. •Nucleosome core particles
    contain 147 base pairs of DNA wrapped around an octamer consisting of two molecules each of histones H2A, H2B, H3, and H4.
  37. Chromatosome
    166 bp + histone H1
  38. •Euchromatin
    • -decondensed
    • -transcriptionally active interphase chromatin (usually as 10 and 30 nm fibres, or slightly more condensed)
  39. •Heterochromatin
    2 types
    -highly condensed, transcriptionally inactive chromatin, and it contains highly repeated DNA sequences.

    • -Constitutive heterochromatin
    • -Facultative heterochromatin
  40. Constitutive heterochromatin
    contains DNA that is not transcribed in any cell type, such as some DNA sequences at centromeres
  41. Facultative heterochromatin
    -contains DNA sequences that are not transcribed in the cell being examined but may be transcribed in other cell types
  42. •Centromere
    • - is a specialized region of the chromosome that plays a critical role in ensuring the correct distribution of duplicated chromosomes to daughter cells during mitosis
    • -frequently contain repetitive DNA.
    • •Vary in size from 125 bp (S. cerevisiae) to millions of base pairs (humans) with no consensus DNA sequence
  43. centromeric histone H3(CenH3)
    a histone variant within nucleosomes contained in centromeres by all eukaryotes studied to date
  44. •Kinetochore
    • - a protein structure associated with the centromere, to which microtubules bind.
    • -act as a molecular motor during mitosis and meiosis; not associated with centromere during interphase
  45. Telomeres
    • -the sequences at the ends of eukaryotic chromosomes
    • -Critical role in maintaining stability of linear chromosomes
    • -protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes” … become shorter with each cell division
    • -
  46. Telomere DNA sequences
    • DNA sequences of various eukaryotes are similar
    • - repeats of a simple-sequence DNA with clusters of G residues on one strand.
  47. Open-reading frames (ORFs)
    long stretches of nucleotide sequence that can encode polypeptides (no UAA, UGA, UAG) used to identify putative protein-coding genes in genome sequencing projects.
  48. •Mycoplasma genitalium
    propertiess
    size of genome
    lacks what
    • •Simplest present day prokaryote
    • •Second smallest genome of known cells   (580 kbp) with 470 genes
    • •Likely represents the minimal gene set required to maintain a self-replicating organism
    • -Encodes proteins for replication, transcription, translation, membrane transport, and energy metabolism
    • -Lacks many genes for biosynthetic pathways
    • -YET-150 genes still of unknown function
  49. significance of Drosophila in evolution of multicellularity discussion
    -a complex animal, yet has only about twice the number of unique genes found in yeast, a much simpler organism! (1300-6000)
  50. The Human Genome
    how many chromosomes?
    how many genes?
    • 24
    • 20,000-25000
    • -spread over much larger distances/ contain more intronsequence than genes in Drosophila orC. elegans
    • -Share approximately 40% of genes of lower eukaryotes (most involved in basic cellular processes)
  51. Mice, rats, humans:  - ___% of genes in common
    90
  52. Chimps, humans: almost __% identical at the      nucleotide sequence level
    • 99
    • -vary at an average of only 1 nucleotide in 100
  53. Two individual human beings-vary at an average of 1nucleotide in  ____
    1000

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