Eukaryotic Genes Vs Prokaryotic Flashcards
What is it called when prokaryotic mrna has clustered genes on it and codes for many proteins involved in same processes?
Polycistronic
Eukaryotic mrna is monocistronic. What does that mean
Each gene is seperate on mrna. It has its own promoter and terminator
How does the polycistronic and monocistronic organisation affect genetics
In prokaryotes, if one promoter is damaged or lost many genes will not be transcribed due to clustered
In eukaryotes only the gene associated affected
What are transcription promoters
Nucleotide sequences on 5’ end which allows transcription factors and therefore rna polymerase to bind
In prokaryotes, the sigma factor recognises a conserved sequence on promoter region. How does this allow transcription
The sigma factor then binds and allows the positioning of rna polymerase to initiate transcription
What does the mix of rna polymerase and sigma factor in prokaryotes represent
A holo enzyme
There are 3 rna polymerase in eukaryotes vs 1 in prokaryotes. Name and explain what they transcribe
Rna pol 1- transcribes rrna genes
Rna pol 2- transcribes all protein coding genes
Rna pol 3- transcribes tRNA,rRNA, other non coding rnas
What is rna polymerase 2 promoter comprised of
Repeating sequences /motifs such as the TATA box- TATATATATATATA sequence
What binds to the tata box in eukaryotic promoter site to initiate rna polymerase 2
The transcription factor 2D complex
Which then recruits rna polymerase 2
What is the terminator sequence in eukaryotes and what happens
AAUAAA
Rna at this point is cut by endonucleases from the dna
How is gene expression altered in prokaryotes using sigma factors
Sigma factors have ability to direct rna polymerase to specific genes. By using alternative sigma factors, they recognise different sequences and so could affect whether gene is transcribed or not.
What would a mutation to sigma factor do
Affect expression of all the sets of genes it regulates (eg in a cluster)
How do eukaryotes alter gene expression using many different transcription factors
The TFs bind to the motifs in the promoter region which influences ability for rna polymerase to bind
These regulate each promoter/gene. More is needed for transcription than just the TATA box and tf 2D complex
How would you analyse patters of transcription
Isolate mrna from different organisms and replicate them
The mrna is labelled with eg fluorescent dye
The mrna are then hybridised and analysed in a microarray - dna in genes spotted on a slide
When do changes in gene expression occur
Diseases like cancer
Different tissues = different genes expressed
During development different genes expressed
Splicing removes introns in between exons. Explain the structure of an intron which allows splicing
Before intron and after intron there are conserved sequences
These are splice sites
The splice site after intron usually has pyrimidines such as A or G
What are splice sites for (conserved sequences)
They define where introns are and recruit the spliceosome
What cuts dna in splicing
Spliceosome
Do protein genes only encode for 1 protein? Why not?
No - due to alternative splicing
Due to alternative splicing and alternative promoters, mrna can have many different versions. What are these called
The transcriptome
After transcriptomes undergo post translational modifications, what are all the proteins called
The proteome
Which base does translation always start at
Methionine
What is an open reading frame
The sequence of bases translated from the start to stop codon
What does the small subunit do
Reads and recognises the start codon at mrna (start of orf) - AUG
Pairs trna to complementary codon
What does the large subunit do
House the PEPTIDYL TRANSFERASE CENTRE (synthesis of protein)
How are ORF identified in prokaryotes in translation
Each gene in a cluster has its own shine dalgarno sequence before the AUG start. This is recognised by the small subunit via base pairing
How does the small subunit recognise the shine dalgarno sequence
Through base pairing - complementary sequence
Why would a mutation of the shine dalgarno sequence only affect 1 gene is the prokaryotes are polycistronic
Each gene has its own ORF. Independent translation of all of them
When Is a poly A tail added to eukaryotic mrna?
After mrna is cut by endonucleases at the terminator region in transcription
What is the importance of the poly A tail on mrna
It increases its stability
What is the 5’ cap on eukaryotic mrna for
It allows the small subunit to bind in translation
In eukaryotic translation, after the small subunit binds to the cap, which sequence later in the mrna is recognised by small subunit
The Kozak consensus sequence (before the AUG)
Where does translation start in eukaryotes
The kozak consensus sequence
Why does transcription affect translation in prokaryotes but not eukaryotes
In prokaryotes they are paired. Translation occurs whilst mrna could still be getting transcribed from dna
In eukaryotes, the mrna is cut and has to transport to the cytoplasm where translation occurs- they are seperate processes
