Prokaryotic transcription and translation

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What is Transcription?
The process where a single stranded RNA that has a complimentary sequence to template DNA is formed
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What is translation?
the process by which the genetic message carried by messenger RNA directs the synthesis of polypeptides, with the aid of ribosomes etc.
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A key difference between prokaryotic and eukaryotic gene expression
Eukaryotics - transcription happens in the nucleus, translation happens in the cytoplasm. In prokaryotes, they are neither temporally or spatially separated.
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Define prokaryotic cell
A cell who's genetic material is not enclosed by a membrane. Bacteria mostly.
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How many genes does E.coli contain per cell?
c. 4,300
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How do we know gene expression must be controlled in eukaryotes?
Useless genes would have been lost to evolution, so all 4,300 genes are needed. We know that they aren't all being expressed at once, and different genes are needed at different times.
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Two reasons rapid and accurate gene expression is important
survival - the single cell is exposed. Division.
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How can e.coli help us treat infections?
We can determine what genes the e.coli is expressing when it causes an infection such as a UTI. For example, in UTI peptide transport systems and iron acquistion systems are expressed.
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How many RNA polymerases do prokaryotic cells have? How does this differ from eukaryotic cells?
Prokaryotic - One RNA polymerase to make all RNA. Eukaryotics - three nuclear RNA polymerases + one mitochondrial RNA polymerasse
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How many subunits does a prokaryotic RNA polymerase have?
Six - 2a, 1B, 1B', 1w and 1o
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When fully assembled, what is the name of the multisubunit structure?
the holoenzyme
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What has to be lost to make the core polymerase?
o-subunit (sigma)
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What is the structure of the holoenzyme known as? Why?
The crab claw structure - the two B subunits form pincers
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How big are the alpha subunits and what gene encodes them?
329 aa, rpoA gene.
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What are the alpha subunits needed for?
Thought to be needed for assembly of the enzyme and transcriptional regulation
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Beta subunit - size, gene and role
1342 aa, rpoB, role in catalysis
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Beta prime subunit - size, gene and role,.
1407aa, rpoC, can bind to DNA and may have roles in catalysis too.
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omega subunit, size, gene and role.
91 aa, rpoz, important in polymerase assembly and stability. May also restore denatured RNA polymerase to function
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Sigma subunit - size, gene and role.
613aa, there is a range but the most common is sigma 70 from rpoD. Helps the core enzyme recognise the start of genes.
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What are promotor sites?
Areas on DNA where RNA polymerase binds.
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How many promotor sites are there on the E.coli chromasome?
2,000. for 4,300 genes.
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The two common features of promotor regions
-35 sequence which is 6 bases. -10 sequence also known as TATA or Pribnow box.
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What binds to the -35 promotor?
sigma factor domain 4
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what binds to the -10 promotor?
Sigma factor domain 2
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What are the 'consensus' sequences for sigma factor 70? why consensus?
-35 = TTGACA, -10 = TATAAT. There is variation in gap size and sequence.
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Why is it important to have different sigma factors attached to the holoenzyme?
Specialist sigma factors control subsets of genes required under non-routine growth conditions
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An example
os takes over from o7 in stress.
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Why is there an additional binding site for alpha subunit upstream of start site?
Enhances how strong the binding is. Mask other promotor sites to regulate further transcription.
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What is translation?

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the process by which the genetic message carried by messenger RNA directs the synthesis of polypeptides, with the aid of ribosomes etc.

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Card 4

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Card 5

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