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