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2013-04-25 10:48:51

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 

    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