Ch. 18,21 : Gene Expression: The Genetic Code & Transcriptio

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Gene Expressi On﷯﷯﷯ ﷯﷯


 
  
Created Apr 8, 2010
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wa102

 

 
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1
Gene expression -central dogma of molecular bio:
 
the use of info in DNA to direct the production of proteins  -DNA-RNA-protein
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Nuclear env protects  
 
chromo and immature RNA from cytoplasmic enzymes
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Nuclear pores
 
direct continuity between cytoplasm & nucleoplasm -mammalian nucleus ~3,000-4000 pores -eukaryotic...
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Where does replication and trancrption occur? and where does translation occur?
 
-replication and transcription in nucleus, translation in cytosol
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Nuclear pores
 
-Inner & outer membranes nuclear env fuse at nuc pore complex with intricate protein structure -small...
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Transcription occurs in the
 
Nucleus (eukaryotes) Cytosol (prokaryotes
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A cell uses 3 kinds of RNA to make proteins
 
messenger RNA (mRNA) transfer RNA (tRNA) ribosomal RNA (rRNA)
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Overview of Transcription:
 
Binding of RNA polymerase to DNA promoter sequence Initiation of RNA synthesis- base pair...
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Binding- RNA polymerase binds at DNA promotor site
 
-the transcriber is RNA polymerase -consists of 2 alpha, beta and beta prime and sigma...
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Promoter
 
is upstream (neg #), before transcribed sequence/gene- downstream (pos #), no # "0" -specific...
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INITIATION  
 
-link up dNTP's in 5'-3' direction to make RNA strand -RNA-DNA hybrid- complementary base...
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ELONGATION
 
-RNA poly core enzyme (2 alpha,1 beta,1beta prime, prime) reads along the DNA, untwist...
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TERMINATION- reach termination signal type 1 of 2:
 
1-Need rho (p) factor -binds to specific 50-90 base termination sequence -needs...
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type 2 of 2:
 
2-Does not need rho (p) factor -RNA has short complementary sequence to each other & short...
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Differences in Eukaryotic Transcription Protein-protein interactions
 
-Need transcription factors (TF)- must bind to DNA before RNA poly can bind to promoter -Bind...
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Elongation (euk.)
 
need special proteins to dissassemble nucleosome in front of RNA poly & reassemble behind...
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Termination (Euk)
 
-many signals depending on type of RNA poly -short run of U's -RNA cleavage: special AAUAAA...
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Ribosomal RNA
 
-the most abundant (70-80%), most stable RNA in cells- component of ribosomes
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Transfer RNA
 
- 10-20%- critical in protein syn
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Messenger RNA
 
-less than 10%- amino acid sequence
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rRNA
 
-single primary transcript unit with transcribed spacers -150-200 copies in cell -Methylation...
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Methylation
 
addition of methyl groups-protect from enzyme degredation (esp rRNA) then transport to cytosol...
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5' methyl guanine cap
 
to 5' end of pre-mRNA & mRNA -added after initiation of RNA syn -makes RNA more stable...
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Poly (A) tail
 
50-250 nucleotides of A's added to 3' tail -NOT FROM DNA SEQUENCE-found in termination signal -added...
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Introns
 
-intervening sequences within the euk primary transcript absent in mature functional RNA- not...
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RNA spliced...
 
removes introns, joins exons (expressed sequences) -by ribozymes- self-splicing RNA introns -by...
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Catalyzed by spliceosome -
 
RNA & protein complex (small nuclear ribonucleoproteins, snRNPs) -recognizes 5' to 3'...
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Why do eukaryotic genes have introns? 1 of 5
 
-generate numerous diff mRNA's from 1 RNA transcript through alternative RNA-splicing-exon...
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2 of 5
 
-help increase biological complexity increase in gene number (25,000 genes produce 200,000-1...
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3 of 5
 
Evolutionary- hasten evolution of new and potentially useful proteins
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4 of 5
 
each exon codes for diff fct'l regions- protein can fold independently into separate domain
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5 of 5
 
Nucleic acid editing- more 1-100's nucleotides inserted or converted -can inactivate retroviruses -ex....
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Translation
 
converts nucleotides of a gene into amino acids in a protein in order using genetic code -almost...
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(translation) mRNAs are...
 
"read" by ribosome in 3-nucleotide units, termed (64 possible combinations) -each codon codes...
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Exceptions- few slight differences (translation)
 
-In mitochondria, a few bact & unicellular org's -UGA-21st amino acid selenocysteine,...


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