DNA Transcription and Translation.txt

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DNA Transcription and Translation.txt
2012-03-14 23:56:36
DNA transcription translation

transcription and translation
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  1. DNA vs Protein as genetic material
    • DNA composed of 4 nucleotides, Protein composed of 20 aas
    • DNA amount constant from cell to cell, protein amounts vary per cell
    • DNA confined to nucleus, proteins throughout cell as enzymes
  2. characteristics of nucleic acids
    • DNA composed of nucleotides, determined in 1800-1900s
    • 3 parts of nucleotide: 5 carbon sugar, phosphate and nitrogenous base
    • nucleotides held together by phosphodiester bonds
  3. Nucleotides
    • composed of Adenine, guanine, cytosine and Uracil
    • A 2 T
    • C 3 G
    • PAG, pure as gold
    • pyrimidines are thymine, cytosine (or uracil)
  4. DNA vs RNA
    • DNA double stranded
    • DNA made of DEoxyribose sugar, phosphate group and nitrogenous base ATG or C
    • RNA single stranded
    • RNA made of RIBOSE sugar, phosphate group and nitrogenous base AUG or C
  5. 1920's Frederick Griffith
    showed component of virulent strain in Diplococcus could transform in non-virulent strains
  6. 1940's Avery, MacLeod & McCarty
    • Destruction of DNA in extracts of heat kills cells
    • These extracts could NOT transform non-virulent cells
    • RNA or protein destruction did not have same effect
  7. 1950's Hershey and Chase
    Confirmed NA heritable material: during phage replication in bacteria, parental DNA transferred to progeny, but NOT parental proteins
  8. Organic Chemistry
    • Nitrogenous base attaches to C #1 of deoxyribose sugar
    • Phosphate group attaches to C #5
    • OH group of carbon 3 involved with phosphodiester bond
  9. Rosalind Franklin and Wilkins
    • Through X Ray diffraction, showed:
    • 1.DNA composed of 2 STRANDS of nucleotides, wound to form helix
    • 2.both strands equally part throughout the molecule
    • 3.helix diameter 20A and periodicities 3.4A and 34A
    • Determined phosphate backbone on outside, with nitrogenous bases on inside
    • Purine pairs w/Pyrimidine
    • sugar phosphate backbone of each strain is antiparallel
  10. Genetic code triplet code
    • degenerate: aa can be coded by more than 1 code
    • unambiguous: each code encodes only 1 type of aa
    • start (AUG) and stop signals (UAA, UGA, UAG)
  11. coding strand
    • non-template strand of DNA
    • IDENTICAL to the RNA that is transcribed
  12. template strand
    • binds DNA and synthesizes complementary RNA strand
    • only this strand is copied
  13. Transcription components
    • RNA polymerase - composed of SIGMA subunit
    • sigma subunit required for INITIATION, not elongation
    • Elongation requires
  14. mRNA processing
    • 5' 7-methyl cap in pro and euk
    • only in euk 3' poly A tail (prevents degredation)
    • only in euk, INTRONS spliced OUT
  15. 2 mechanisms of splicing out INTRONS in eukaryotes
    • 1. self-splicing, aka autocatalytic RNAs
    • removes the introns from rRNA
    • uses active site on intron to do transesterification reaction and release intron
    • 2. splicesome
    • RNA protein complex (snRNP) catalyzes removal of introns from mRNAs
    • bind to active site, recruit more proteins and then cut b/w exon & intron, then fuses exons together
  16. translation process steps
    • 1. initiation: initiation complex forms
    • binding of small ribosomal subunit to mRNA
    • binding of large ribosomal subunit to initiator tRNA
    • 2. elongation
    • reading of mRNA codons and adding of aa to polypeptide chain
    • 3. termination
    • release of polypeptide
    • disassembly of ribosome
  17. Initiation in translation
    • initiation factors 1,2 and 3 bind to small subunit of ribosome when mRNA binds
    • IF3 released once initiator tRNA binds to mRNA codon in P site
    • Large ribosomal subunit binds and IF1 and IF2 release
    • EF-Tu binds to new tRNA now helping to allow entry into A site
  18. Elongation in translation
    • fit of mRNA codon-anticodon tRNA checked by using energy from EF-Tu - GTP bond
    • as more tRNAs attach to A site, PEPTIDYLtransferase (fxn of 28S rRNA) used to form peptide bonds
    • mRNA shifts, through help from EF-G, allowing for A site to be open to allow another tRNA to enter
    • New tRNA enters A site through help from EF-Tu and elongation continues
  19. Roles of peptidyl transferase in translation
    • 1. forms peptide bonds between AAs from tRNA at P site and A site.
    • 2. breaks high energy bonds between AAs and tRNA (this is the energy used for peptide bond)
  20. Termination in translation
    • Release factor binds to A site when STOP codon is encountered
    • These factors also aid in release of polypeptide chain from tRNA at P site
    • RF1 binds to UAA, UAG
    • RF2 binds to UAA, UGA
    • Now Ribosome/mRNA complex disassembles
    • Polypeptide now folds into its conformation, or assisted by chaperonins
  21. Euk vs prok translation
    • Euk mRNA live for hrs, vs. prok mRNA which is minutes
    • 7-methyl cap REQUIRED in euk
    • Kozak recog. seq present in Euk
    • majority of rRNA in euk is associated w/ ROUGH ER, vs. in prok where rRNA is in cytoplasm
  22. Protein folding bindings
    • dependent on sequence of AAs
    • Hydrogen bond formation of R group interaction of each other and environment
    • Post-translational modification occurs, such as addition of phosphate, methyl, sugar, lipid group, formation of disulfide bonds, metal ions
  23. Post-translational modifications
    • N-terminus AA removed or modified
    • AA residues modified
    • Carb. sidechains sometimes attached
    • Polypeptide chains may be trimmed
    • Signal seq. removed
    • Polypeptide chains complexed w/metals
  24. Protein Structure
    • 1. primary: aa sequence (polypeptide chain)
    • 2. 2ndary: A helices and B pleated sheets are specific aas configured together closely
    • 3. tertiary: 3D structure of fully folded protein
    • 4. quaternary: 2 or more polypeptides forming the functional protein (ie: hemoglobin w/its 4 groups)