Genes

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Author:
hellosleepy
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159480
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Genes
Updated:
2013-04-25 10:48:51
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MCAT
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MCAT Biology
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  1. Heterochromatin vs. Euchromatin 
    Heterochromatin: very tightly coiled, not being transcribed  

    Euchromatin: uncoiled, portions of DNA being actively transcribed  
  2. DNA replication is a _____________, ___________, and ___________ process. 
    • 1. Semiconservative
    • 2. Bidirectional - replication proceeds in both directions  
    • 3. Semidiscontinuous - okazi fragments  
  3. First step in DNA replication vs. Transcription 
    DNA replication needs a RNA primer

    Transcription can start with a promoter sequence  
  4. Steps in Replication 
    • 1. Unwinding via Helicase
    • 2. RNA primer notes start of replication site
    • 3. DNA polymerase adds nucleotides while proofreading
    • 4. Primers removed
    • 5. DNA Ligase joins Okazaki fragments  
  5. In which direction is DNA read and synthesized?
    Read from 3'-->5' 

    DNA is synthesized in 5'--->3' as is most everything else  
  6. Location of Replication, Transcription, and Translation  
    Replication: Takes place in the nucleus, mitochondria, and chloroplasts

    Transcription: Takes place in the nucleus and the mitochondria, and chloroplasts 

    Translation: Takes place in the cytoplasm, mitochondira, and chloroplasts  
  7. Trascription - errors
    Error-prone because no proofreading! 

     
  8. Transcription steps
    • 1. Initiation: promoter binding, unzipping of DNA 
    • 2. Elongation: RNA polymerase transcribes template strand
    • 3. Termination: dissociation of promoter and RNA polymerase  
  9. Methods of control at the transcriptional level 
    • 1. Activators and repressors: activation/deactivation of genes 
    • 2. Enhancers and promoters
    • 3. Operons: a sequence of bacterial DNA 
  10. The Lac Operon 
    • Transcriptional regulator
    • Gives a cell the ability to metabolize lactose when glucose is unavailable for metabolism  
  11. Post-transcriptional processing 
    • Modification happens in the nucleus!!! 
    • 1. Addition/deletion of nucleotides
    • 2. Modification of nitrogenous bases
    • 3. 5' cap
    • 4. Poly A Tail  
    • 5. Alternative splicing (exons are spliced together) 
  12. Roles of mRNA, rRNA, and tRNA 
    mRNA: delivers DNA code for translation into protein 

    rRNA: from transcription, combines with ribosome, synthesized in the nucleolus, catalyzes the formation of peptide bonds

    tRNA: collects amino acids in the cytosol, assists in translation, hold anticodon + amino acid complimentary to mRNA codon  
  13. Start Codon
    AUG, also codes for Met 
  14. Stop codons 
    UAG, UAA, UGA

    Do not code for any amino acids  
  15. Steps of Translation
    • 1. mRNA attaches its 5' end to P site 
    • 2. Initiation: large ribosomal subunit joins
    • 3. Elongation: tRNA attaches to A site, translocation to continue translating to protein (req's GTP)
    • 4. Termination: Stop codon is reached

    The P site is where the growing polypeptide chain is found 
  16. Cancer
    • 1. Cells devide indefinitely, immortal 
    • 2. Rapid reproduction, not leaving much time between S phases
  17. Histone complex and properties
    8 Histones + DNA = nucleosome 

    Histones are very basic
  18. Chromatin vs. Chromosomes
    Chromatin is what chromosomes are made of! 

    Chromatin = cotton

    Chromosomes = tee shirt
  19. Homologues
    Two pairs of chromosomes that code for the same trait - but don't necessarily possess the same genes
  20. Interphase 
    G1: cell growth, DNA decondensation, RNA and protein synthesis 

    S: DNA replication mostly

    G2: Duplication of organelles, RNA and protein synthesis  
  21. Prophase of mitosis
    • 1. Chromatin condensation 
    • 2. Centrioles move to opposite ends of the cell
    • 3. Spindle apparatus formation
    • 4. Breakdown of nuclear membrane
  22. Telophase
    • 1. Opposite of prophase
    • 2. Reformation of nuclear membrane
    • 3. Decondensation of chromosomes
    • 4. Formation of 2 daughter nuclei
  23. When does crossing over occur and what is it?
    It's a form of genetic recombination 

    Occurs in Prophase I of meiosis

    Linked genes are more likely to cross over together
  24. When are tetrads seen?
    Starting in prophase I of meiosis I 
  25. Nondisjunction
    Can happen in Anaphase I or II 

    Results when the centromeres unsuccessfully split, so the number of chromosomes in each daughter cell is uneven
  26. Number of gene copies in eukaryotes vs. prokaryotes 
    • Eukaryotes: multiple copies of each gene 
    • Prokaryotes: only one copy of each gene  
  27. Chromosomal Mutations
    Result in structural changes in the chromosomes 

    • 1. Deletions
    • 2. Duplications
    • 3. Translocation
    • 4. Inversion
  28. Transposable elements
    Sequences of DNA flanked by identical nucleotide sequences 

    Method of genetic recombination in somatic cells

    Can re-insert themselves into DNA
  29. Introns are _______ and exons  ______.
    Introns remain IN the nucleus, meaning that they are removed from the primary transcript 

    Exons EXIT the nucleus as a part of the modified mRNA transcript

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