Ch. 18,21 : Gene Expression: The genetic code & Transcription

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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

2

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...

4
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...

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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-...

9
Binding- RNA polymerase binds at DNA promotor site
 

-the transcriber is RNA polymerase

-consists of 2 alpha, beta and beta prime and...

10
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...

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ELONGATION
 

-RNA poly core enzyme (2 alpha,1 beta,1beta prime, prime) reads along the DNA, untwist...

13

TERMINATION- reach termination signal

type 1 of 2:

 

1-Need rho (p) factor

-binds to specific 50-90 base termination sequence

-needs...

14
type 2 of 2:
 

2-Does not need rho (p) factor

-RNA has short complementary sequence to each other...

15

Differences in Eukaryotic Transcription

Protein-protein interactions

 

-Need transcription factors (TF)- must bind to DNA before RNA poly can bind to promoter

-Bind...

16
Elongation (euk.)
 
need special proteins to dissassemble nucleosome in front of RNA poly & reassemble behind...
17
Termination (Euk)
 

-many signals depending on type of RNA poly

-short run of U's

-RNA cleavage:

special...

18
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...

24
Poly (A) tail
 

50-250 nucleotides of A's added to 3' tail

-NOT FROM DNA SEQUENCE-found in termination...

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Introns
 

-intervening sequences within the euk primary transcript absent in mature functional RNA-...

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RNA spliced...
 

removes introns, joins exons (expressed sequences)

-by ribozymes- self-splicing...

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Catalyzed by spliceosome -
 

RNA & protein complex (small nuclear ribonucleoproteins, snRNPs)

-recognizes...

28

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...

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Translation
 

converts nucleotides of a gene into amino acids in a protein in order using genetic code

-almost...

34
(translation) mRNAs are...
 

"read" by ribosome in 3-nucleotide units, termed

(64 possible combinations)

-each...

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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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