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Flashcards by J yadonknow, updated more than 1 year ago
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Created by J yadonknow
almost 7 years ago
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| Question | Answer |
| What do promoters used by eukaryotic RNA Pol' ii usually consist of? | A core promoter that may include a TATA box and one or more Upstream Promoter Elements (UPE). |
| What are UPE's? | Sequences of DNA recognised by particular proteins The binding of these proteins to the UPE controls which tissue the gene is switched on in. |
| What happens if you put an unmodified eukaryotic gene in, say, an E. Coli cell? | Transcription won't occur as the promoter sequence won't be recognised by RNA Polymerase. mRNA wouldn't be transcribed as E. Coli wouldn't be able to process the introns. |
| What do eukaryotic promoters used by RNA Pol' ii require? | Accessory proteins called transcription factors |
| What does the core promoter interact with? | General transcription factors |
| What do these GTF recoginse? | The core sequence, often including the sequence of the TATA box. |
| Describe the initiation of transcription in eukaryotic cells | Binding of the GTF TFIID to the core promoter sequence |
| What is TFIID? | A general trancription factor which is a multi-subunit protein that incudes the TATA binding protein (TBP) |
| How is the pre-initiation complex formed? | By further binding of GTFs and RNA Polymerase ii |
| What is essential for the transcription of a gene? | That the pre-initiation complex is formed, if not then the gene will be switched off. That additional transcription factors are also bound to UPEs. |
| What do these transcription factors stimulate? | The formation of the pre-initiation complex May also recruit histone acetylases |
| What is the result of histone acetylase recrutment? | Reduction in the strength of the binding of histones and DNA |
| What do tissues have the properties of? | The genes they express |
| What sort of genes exist in Eu? | Tissue-specific genes i.e. insulin Inducible genes |
| What sort of genes are most prokaryotic genes? | Housekeeping genes |
| What is the purpose of these genes? | Create an essential product and are therefore always transcribed, leads to cell death if not |
| How can gene expression be controlled? | By regulating transcription - x gene regulating translation - x protein regulating RNA processes - x splicing |
| What is the advantage of inducible genes? | They're expressed only when they're needed, so don't waste energy on protein synthesis |
| What does the Lac Operon consist of? | Lac Z Lac Y Lac A |
| What does Lac Z do? | encodes B-Galactosidase which catalyses lactose breakdown GalB1-4Glu |
| What does Lac Y do? | Encodes Galactoside Permease A membrane protein which transports lactose into the E.Coli cell |
| What does Lac A do? | Encodes Galactoside Transacetylase Thought to detoxify other molecules which enter through galactoside permease |
| Draw a sequence of the Lac Operon | P Lac i CAP site P O LZ LY LA |
| Where are lac genes positioned? | Adjacent to one another on the chromosome, with no spaces between them and therefore creates one big mRNA |
| What is the Lac I | Upstream housekeeping gene that encodes the Lac Repressor Protein |
| How is Lac i expressed? | Expressed at very low level, doesn't use much energy and has its own promoter sequence |
| What is the Operator? | Binding site for Catabolite Activator Protein-cAMP complex |
| What does this complex stimulate? | Strong transcription of the Lac Operon |
| What even is an operon? | Long mRNA transcribed from a cluster of several genes |
| Why is this arrangement so energetically favourable? | As you can control transcription of all 3 genes from a single promoter |
| How is the Lac Operon repressed? | When lactose is absent, the LRP which is continually expressed binds to the Operator, and even though RNA Pol can still bind to the promoter it can't unwind the DNA to initiate transcription so the operon is repressed |
| How is the lac operon induced? | When lactose is present in cell, some of it is convert into allolactose, which is similar to lactose except having an GalB1-6Glu Allolactose binds to the LRP, inducing a conformational change so it can no longer bind to the Operator RNA Polymerase is now free to transcribe Lac Z,Y,A. |
| What happens if glucose is present? | Transcription is inefficient because the promoter is weak and therefore a poor binding site RNA Polymerase |
| What makes a weak or strong promoter? | -35 Hexamer and Pribnow Box are both strong promoters, and the more a promoter differs from their TTGACA/TATAAT sequence the less RNA Pol' recognises it |
| Why is the Lac promoter gene quite weak? | As it differs from the ideal promoter in 3 places |
| What are the lac promoter sequences? | TTTACA TATGTT |
| What sort of repression happens as a result of glucose? | Catabolite Repression |
| How does it work? | [cAMP] is indirectly proportional to [C6H12O6] as cAMP is outcompeted, less cAMP-CAP complexes form and don't bind to CAP Site |
| How does the cAMP-CAP complex stimulate strong transcription of the lac operon? | It stimulates binding of RNA Polymerase to the promoter sequence |
| Draw a diagram showing catabolite and LRP repression and a diagram of the lac operon being expressed | Dickbutt |
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