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Biochemistry Ch. 7 - RNA and the Genetic Code
MCAT
17
Biochemistry
Undergraduate 3
03/23/2016

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Term
What codons code for the start and stop of translation? What happens when each of those codons are read?
Definition
AUG codes for methionine which is the start codon for translation. UAA, UAG, UGA are all stop codons which make the polypeptide strand terminate elongation
Term
What is degeneracy/redundancy and why is it important?
Definition
Degeneracy/redundancy means that almost all amino acids have more than one codon that specifies them. This is important because it allows for mistakes to be made while still maintaining the correct amino acid sequence. This is most commonly seen in the 3rd nucleotide of a codon, also called the wobble position.
Term
silent, nonsense and missense mutations
Definition
no effect, premature stop codon and a codon that codes for a different amino acid
Term
helicase
Definition
unwinds double helix
Term
RNA polymerase II
Definition
  • main polymerase in transcribing DNA
  • binds to the TATA box within the promoter region of the gene
Term
heterogenous nuclear RNA
Definition
primary transcript before modifications
Term
What occurs during posttranscriptional processing?
Definition
  • splicing: removes introns and ligates exons together
  • 5' cap: a 7-methylguanylate triphosphate cap is placed at the 5' end of the transcript
  • 3' Poly-A tail: protects end of RNA from degradation
Term
spliceosome
Definition
made up of small nuclear RNAs (snRNA) and small nuclear ribonucleoproteins (snRNPs, 'snurps'); recognizes splice sites and forms lariate that excise the introns
Term
What are the three stages of translation?
Definition
  • initiation¬†
  • elongation
  • termination
Term
translation: initiation
Definition
  • small ribosomal subunit binds to the mRNA (Shine-Dalgarno sequence in prokaryoates, 5' cap in eukaryotes)
  • the small ribosomal subunit scans for a start codon
  • it lays down N-formylmethionine in prokaryotes and methionine in eukaryotes at the P site
  • the large subunit then binds the small subunit
Term
translation: elongation
Definition
  • a new aminoacyl-tRNA is added into the A site
  • the growing polypeptide is transferred from the tRNA in the P site to the tRNA in the A site
  • the uncharged tRNA pauses in teh E site before exiting the ribosome
  • the tRNA in the A site is moved to the P site and it starts over
Term
translation: termination
Definition
occurs when the codon in the A site is a stop codon; release factor places a water molecule on the polypeptide chain and thus releases the protein
Term
posttranslational modifications
Definition
  • folding by chaperones
  • formation of quaternary structure
  • cleavage of proteins or signal sequences
  • covalent addition of other biomolecules (phosphorylation, carboxylation, glycosylation, prenylation)
Term
operon
Definition
an inducible or repressible cluster of genes transcribed as a single mRNA
Term
inducible systems
Definition
lac operon; bonded to a repressor under normal conditions; they can be turned on by an inducer pulling the repressor from the operator site
Term
repressible systems
Definition
trp operon; transcribed under normal conditions; they can be turned off by a corepressor coupling with the repressor and the binding of this complex to the operator site
Term
What are controls on gene expression in eukaryotes?
Definition
  • transcription factors: search for promoter and enhancers regions the DNA
  • promoters: contain upstream elements that affect how much a gene is transcribed
  • enhancers: up or downstream of promoter and amplifies transcription
  • histones: acetylated histones allow for easier access to DNA; DNA wrapped in histones can't be accessed
  • methylation of DNA: methylation is often linked with silencing gene expression
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