Genomes. Information in genomes are important in maintaining a cell's basic functions:Ability to replicate and make DNAAbility to make new proteinsAbility to obtain and store energy . Genome Organization. Prokaryotes- DNA is circular- single stranded - found in the nucleoid region- or
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1. Major differences between genome organization and gene expression in Prokaryotes and Eukaryotes BIOL 3100: Dr. Furlong and Dr. Clower
2. Genomes Information in genomes are important in maintaining a cell’s basic functions:
Ability to replicate and make DNA
Ability to make new proteins
Ability to obtain and store energy
3. Genome Organization Prokaryotes
- DNA is circular
- single stranded
- found in the nucleoid region
- organized in operons Eukaryotes
DNA is linear
found in the nucleus
has histones The function of theses proteins seems to be the folding and packaging of the DNA into chromosome form
The function of theses proteins seems to be the folding and packaging of the DNA into chromosome form
4. Transcription in Proks The synthesis of a complementary strand of RNA from a DNA template
Enzyme to make transcription unit
Separates DNA and joins RNA nucleotides as they base pair along template
Adds at 3’ end of growing RNA strand (5’?3’ direction)
Determines which template strand will be used
Upstream from transcriptional start site
Where RNA Poly binds during initiation
5. Transcription in Eukaryotes Eukaryotes use specialized RNA polymerase
RNA Polymerase I is located in the nucleolus and transcribes ribosomal RNA (rRNA).
RNA Polymerase II is localized to the nucleus, and transcribes messenger RNA (mRNA) and most small nuclear RNAs (snRNAs).
RNA Polymerase III is localized to the nucleus (and possibly the nucleolar-nucleoplam interface), and transcribes transfer RNA (tRNA) and other small RNAs (including the small 5S rRNA). This allows for the temporal regulation of gene expression through the sequestration of the RNA in the nucleus, and allows for selective transport of RNAs to the cytoplasm, where the ribosomes reside.
This allows for the temporal regulation of gene expression through the sequestration of the RNA in the nucleus, and allows for selective transport of RNAs to the cytoplasm, where the ribosomes reside.
6. Transcription Proks
1. The initiation and termination sites are specific nucleotide sequences on the DNA
The sigma factor allows RNA polymerase to recognize the initiation site (promoter)
The sigma factor is released during elongation
4. RNA polymerase moves down the DNA chain, causing temporary opening of the double helix and transcription of one of the DNA strands
5. When a termination site is reached, chain growth stops
There is a basal transcription complex that uses RNA polymerase II upstream from the transcription site
The core promoter for Pol II contains a TATA Box
TATA binding protein binds and initiates transcription complex assembly at the promoter
Upstream Binding Factor binds the Upstream Control sequence.
UCS recruits and binds a protein complex incorporating TATA Binding Protein and three TBP Associated Factors, called SL1 or TIF-IB. The TBP is forced to bind to a non-sequence specifically.
The TIF-IA complex gets phosphorylated and binds RNAP I
RNAP I binds to the UBF/SL1 complex via TIF-IA complex and transcription starts
Termination is the process of breaking up of the polymerase complex and ending of the RNA strand. In euks using RNA Poly II this termination is very variable (up to 2000 bases), relying on post transcriptional modification.
7. A micrograph of ongoing gene transcription of rRNA illustrating the growing primary transcripts. "Begin" indicates the 5’ end of the DNA, where new RNA synthesis begins; "end" indicates the 3’ end, where the primary transcripts are almost complete.