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MCAT Bio. Chem Ch. 7

QuestionAnswer
Central Dogma of Replication DNA --> RNA --> Proteins
Degenerate code allows: Multiple codons to encode for the same amino acid.
Initiation Codon (Start Codon) AUD
3 Termination Codons (Stop Codons) UGA, UAA, UAG
Redundancy and wobble (third base in codon): Allows mutations to occur without effects in the protein.
Silent Mutations Have no effect on protein synthesis
Nonsense (Truncation) Mutation Produce a premature stop codon
Missense Mutations Produce a codon that codes for a different amino acid
Frameshift Mutation Result from nucleotide addition or deletion and change the reading frame of subsequent codons
RNA Is Structurally Similar To DNA Except: Substitution of a ribose sugar for Deoxyribose. Substitution of Uracil for Thymine. It is single-stranded instead of double-stranded.
Messenger RNA (mRNA) Carries the message from DNA in the nucleus via transcription of the gene, travels into the cytoplasm to be translated.
Transfer RNA (tRNA) Brings in amino acids, recognizes the codon on the mRNA using its anticodon.
Ribosomal RNA (rRNA) Makes up the ribosome, enzymatically active.
Helicase And Topoisomerase: Unwind the DNA double helix
RNA Polymerase II Binds to the TATA box within the promoter region of the gene (25 base pairs upstream from first transcribed base)
hnRNA Synthesized from the DNA template (antisense) strand
Posttranscriptional Modifications Include A 7-methylguanylate triphosphate cap is added to the 5' end. A polyadenosyl (poly-A) tail is added to the 3' end.
Spliceosome Location where splicing is done by snRNA and snRNP's
Introns Are Removed In A: Lariat structure
Exons Are: Ligated together
Polycistronic Genes Genes in which prokaryotic cells can increase the variability of gene products from one transcript (starting transcription in different sites within the gene leads to different gene products)
Alternative Splicing Method in which eukaryotic cells can increase variability of gene products
tRNA Translates the codon into the correct amino acid
Ribosomes Factories where translation or protein synthesis occurs
Initiation (First Stage Of Translation) Occurs when the 30S ribosome attaches to the Shine-Dalgarno sequence and scans for a start codon. It lays down N-formylmethionine in the P site of the ribosome.
Elongation Involves the addition of new aminoacyl-tRNA into the A site of the ribosome and transfer of the growing polypeptide chain from the tRNA in the P site to the tRNA in the A site. The now uncharged tRNA pauses in the E site before exiting the ribosome.
Termination 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.
Initiation, Elongation, And Release Factors Help with each step in recruitment and assembly/disassembly of the ribosome.
Posttranslational Modifications Include: Folding by chaperones. Formation of quaternary structure. Cleavage of proteins or signal sequences. Covalent addition of other biomolecules (phosphorylation, carboxylation, glycosylation, prenylation).
Jacob-Monod Model Of Repressors And Activators Explains how operons work
Operons Inducible or repressible clusters of genes transcribed as a single mRNA.
Inducible Systems (ex: lac operon) Bound by a repressor under normal conditions. They can be turned on by an inducer pulling the repressor from the operator site.
Repressible Systems (ex: 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.
Transcription Factors Search for promoter and enhancer regions in the DNA
Promoters Are within 25 base pairs of the transcription start site
Enhancers Are more than 25 base pairs away from the transcription start site
Modification Of Chromatin Structure: Affects the ability of transcriptional enzymes to access the DNA through histone acetylation (increases accessibility) or DNA methylation (decreases accessibility)
Created by: SamB91