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Bio Exam II

Gene expression

Flow of genetic info - Crick (1956) - DNA to RNA to Protein - In cells it's unidirectional (goes in one direction)
Originally "1-gene, 1-enzymes" - not all proteins are enzymes -revised to : 1 gene- 1 protein but not all proteins are single polypeptides - revised to 1 gene- 1 polypeptide * still not 100% accurate
Processes - Transcription: DNA to RNA - Translation: RNA to polypeptide ( ribosomes use info in RNA to make polypeptide)
RNA composition and types - ribonucleic acid - DNA: deoxyribose; ATCG, double strand - RNA: ribose; AUCG; single strand
Ribose - contains an -OH where DNA only has an -H ( DNA is more stable)
Uracil - pyrimidine base - used instead of thymine in RNA - same structure as thymine minus on methyl group (-CH3) - Complementary to adenine
3 types of RNA - mRNA: Messenger; encodes AA sequence - rRNA: ribosomal; part of ribosome structure - tRNA: transfer; carries AA's to ribosome during translation
The genetic code - order of amino acids - mechanisms for A,U,C,G - reads 3 bases @ a time - Crick figured it out
Codons - 3 bases= 1 amino acid - 4 bases (AUCG) so there are 64 possible combos
The genetic code -Unambiguous: each codon codes for 1 AA - degenerate: several codons coding for same AA
Genetic Codon - 1 start codon: AUG: starts translation - 3 stop codons: UAA,UGA,UAG: stops translation
Reading Time - codons must be grouped correctly - mutations can result in frame shift ( deletion specifically)
Genetic Code is mostly universal - minor exceptions in some microbes and mitochondria - generally the same across viruses, & cellular life
Transcription (1st part of gene expression) - synthesis of RNA complementary to DNA - 3 stages
Transcription Initiation - DNA is template for RNA synthesis & reads on 3'-5' direction - one strand in transcribed (template strand) ; other strand not transcribed - RNA synthesized in 5'-3' direction
Components of Transcription initiation - Promoter: specific DNA sequence on transcribed strand (promoter region not transcribed) - RNA polymerase: makes new RNA strand; binds promoter; unwinds helix; begins transcription
RNA synthesis ex. Non Transcribed Strand: 5' A-T-G-A-C-T 3' Transcribed "template" Strand: 3' T-A-C-T-G-A 5' RNA: 5' A-U-G-A-C-U 3'
Transcription Elongation - RNA synthesis; anti- parallel to template strand - Uses RNA nucleotide triphosphate
Transcription Termination - specific DNA sequence signals RNA polymerase to stop (not a stop codon) - RNA transcription stops & polymerase falls off - results in completed RNA strand
mRNA modification - only in eukarytoes - transcription to pre-mRNA; not useful for protein synthesis - Add 5' Cap to get out nucleus - Add ploy-A-tail to get out nucleus; provide protection; and ribosome recruitment
RNA Splicing - exons: coding region in pre-mRNA - introns: non-coding region in pre-mRNA - splicing: process of removing introns from pre-mRNA - occurs in nucleus
Translation -mRNA to polypeptide - occurs in ribosomes (cytoplasm or surface of ER)
Components - tRNA; small RNA mol; single strand about 80 nucleotides - 3D structure, intramolecular base-pairing
tRNA function - binds specific AA - brings AA into ribosome - binds correct codon to mRNA - AA can be added to polypeptide
Anti Codon - 3 specific bases on loop of tRNA - complementary to codon on mRNA
Many different tRNA's - all general same shape - each w/ different anti-codon, carries diff. AA - made by aminoacyl-tRNA synthetases
Ribosomes - carries out translation - protein + rRNA
rRNA - ribosomal RNA - transcribed from DNA- not translated into protein
Ribosome function - works as a large enzyme complex - catalyzes reaction b/w mRNA, charged tRNAs, & polypeptides
Translation Initiation - small ribosomal subunit binds mRNA and tRNA- met - moves along mRNA until reaches AUG - initiation factors bring in large subunit (translation initiation complex)
Translation Elongation -repeating cycle - peptide bond formation -translocation - each cycle adds single AA
Translation Termination - stop codon not recognized by tRNA's - recognized by release factors (proteins)- bind to stop codon A site - cannot form new peptide bond - polypeptide released
Translation Termination results in... - release of polypeptide from p-site - release of mRNA - release of last tRNA - dissociation of ribosomal subunits
Created by: tennadeleta.