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DNA (Key Proteins (telomeres (ends of DNA strands that don't contain…

- - - - reads the mRNA and translates codons into amino acids, which it transfers from the cytoplasm to the growing polypeptide
      - made up of RNA nucleotides with the 3' end being the attachment site for specific amino acids
      - anticodon
        
        opposite end from the attachment site that contains 3 nucleotides that pairs with a specific mRNA codon with a hydrogen bond
      - aminoacyl-tRNA synthetases
        
        enzymes that match up a specific amino acid with a specific tRNA
        
        there are 20 of these, one for each amino acid
        
        attaches the amino acid to the tRNA by hydrolyzing an ATP
      - wobble
        
        flexible base pairing between the tRNA anticodon and mRNA codon
        
        this is why some codons code for the same amino acids even though their 3rd base is a different letter
        
        ex. anticodon "UCU" can pair with codon "AGA" or "AGG" and both code for arginine
    - - consist of small and large subunits in cell's cytoplasm
      - made up of proteins and rRNAs (ribosomal RNAs)
      - facilitate the joining of tRNAs to mRNA
        
        has 3 binding sites for tRNA
        
        A site: holds the tRNA carrying the next amino acid to be added to the chain
        
        P site: holds the tRNA holding the growing polypeptide chain
        
        E site: discharged tRNAs leave the ribosome here
        
        tRNAs move from A to P to E as they hand over their amino acids and the chain to the next tRNA
  - - - start codon (AUG) signals the beginning of translation; codes for methionine
      - small ribosomal subunit binds with the mRNA and the 1st tRNA
        
        once the 1st amino acid is established, the large ribosomal subunit binds to the smaller subunit
    - - mRNA moves through the ribosome as tRNAs add the appropriate amino acids to the growing chain
      - tRNAs move through the 3 sites in the ribosome
      - after an empty tRNA exits, it gets reloaded with its specific amino acid
    - - stop codon (UAG, UAA, or UGA) signals a release factor that acts as a tRNA
      - the release factor adds a water molecule to the tRNA holding the polypeptide, which breaks that bond, releasing the protein
  - - - proteins made in free ribosomes are used in the cytosol
      - proteins made in bound ribosomes (rough ER or to nuclear envelope) end up in endomembrane system or may be secreted from the cell (like insulin)
      - polypeptide synthesis always begins in free ribosomes, so some proteins move the ribosome to the rough ER or nuclear membrane during translation
        
        these proteins contain a signal peptide: sequence of 20 amino acids
        
        signal-recognition particle (SRP) : protein-RNA complex that reads the signal peptide and moves the ribosome to a receptor protein in the ER membrane
- - - - exons exit the nucleus, introns stay inside and dissipate
    - - complex made of proteins and small RNAs that cuts out introns and splices together exons
  - - - genes (DNA template strands) can be transcribed with variations of exons on the pre-mRNA
      - different segments may be treated exons, leading to production of different polypeptides in translation
    - - the different parts of a protein
        
        ex. active site vs. the site that allows the enzyme to bind to the cell membrane
      - different exons can code for different domains
- - - - adenine, thymine, cytosine, guanine
      - A and G are purines=have 2 organic rings
      - C and T are pyrimidines=have one ring
      - A forms 2 hydrogen bonds with T and G forms 3 hydrogen bonds with C
      - bases can be varied in numerous ways and each gene has a unique base sequence
  - - - subunits run in opposite directions (5' and 3' to 3' and 5')
  - - - transformation in bacteria: harmless strain can become pathogenic by ingesting DNA of pathogenic bacteria
      - the DNA in bacteriophages causes infected bacteria to produce more DNA and protein coats (essential for more viruses)
      - Chargaff's Rules
        
        1) DNA base composition varies between species
        
        2) the % of A and T, and C and G are roughly equal for each species
- - - - RNA strand made is complimentary and anti-parallel to the template strand
  - - - pries 2 strands of DNA apart and joins together RNA nucleotides complimentary to DNA template strand
    - - DNA sequence where RNA polymerase attaches and begins transcription
    - - part of DNA that is transcribed into RNA
  - - - start point: DNA nucleotide where RNA polymerase begins transcription; within the promoter
      - transcription factors
        
        collection of proteins that bind to the DNA promoter, which triggers RNA polymerase II to bind to it as well
      - transcription initiation complex
        
        the whole complex of transcription factors and RNA polymerase II bound to the promoter
    - - RNA polymerase untwists the double helix and adds RNA nucleotides to the elongating RNA strand
      - as RNA polymerase moves along DNA template strand, the DNA retwists after that part has been transcribed
    - - once RNA polymerase transcribes the polyadenylation signal sequence in the DNA into AAUAAA in the pre-mRNA, the RNA strand is cut by other proteins in the nucleus
- - - - histones are the protein
        
        histones leave DNA during replication and during transcription
    - - they look like beads on a string
    - - irregular clumps and genetically inactive (can't be replicated in this form)
    - - "true chromatin" more dispersed and loosely packed
      - easier to transcribe DNA in this form