DNA V - Transcription | Conjunto de Fichas

Pregunta	Respuesta
Where does protein synthesis occur and what intermediate are synthesised to allow this process to occur? (3)	1. Genes are located in the nucleus, but protein synthesis occurs in the cytoplasm 2.mRNA is needed to allow the genetic information to flow from the nucleus to the cytoplasm. 3.tRNA, rRNA and mRNA are all synthesised for transcription.
What is meant by "Coding strand"? (2)	A DNA strand which has the same base sequence as the synthesised mRNA strand, with Uracil replacing Thymidine Exons
What is meant by "Non-coding strand (2)	The DNA strand which contains sequences of nucleotides that don't code for DNA and isn't translated into an RNA strand. Introns. Is complementary to the mRNA synthesised by the coding strand.
What is RNA Polymerase?	An enzyme that carries out transcription
What is a promoter?	A cis-acting (i.e. affects sequences within the DNA molecule) sequence that signals the start of a gene
What is a terminator?	A DNA sequence that signals the end of the gene by acting as a site where RNA polymerase dissociates from DNA.
Which strand of a DNA molecule can act as the coding strand?	Either side, as long as it's read 5'-3' the designation of coding/non-coding is relative to the strand in which a gene is being transcribed from.
What are the requirements of RNA Polymerase?(3)	1.All four NTPs (remember ribose nucleoside triphosphates, not deoxyribose) 2.A template DNA molecule 3.A promoter (not a primer)
Which NTP releases the most energy when the 2-3 phosphate bond is hydrolysed?	They all release the same amount of energy when dephosphorylated.
How does RNA Polymerisation differ from DNA polymerisation?	They operate the same way, differing only by ribose's additional OH group(2 groups), as opposed to deoxyribose's single OH group. Both involve the addition of an NTP to the 3' end of a nucleotide molecule so synthesis occurs 5'-3'
Describe the first Stage of Transcription (4)	Initiation 1.RNA Polymerase binds to the promoter sequence. 2.DNA strands partially unwind (DNA Helicase+ DNA Gyrase) 3.RNA Synthesis begins
Describe the second Stage of Transcription (3)	Elongation 1.RNA Polymerase moves along the template DNA strand synthesising an RNA copy. 2.Only 15-17bps of DNA are unwound at any given time.
Describe the third Stage of Transcription (2)	Termination RNA Polymerase dissociates from DNA releasing the newly synthesised RNA molecule.
What do promoter sequences signify? (2)	1.Origins of Replication. 2.Boundaries between exons and introns
How is a promoter sequence identified? (2)	By looking for consense sequences, which are "average" sequences found in association with many different genes. They are the origins of replication.
Name 2 common promoter sequences, how the one sequence got its name, and their function (4)	1. 'TTGACA' -35 Hexamer. 2.So named due to its 6 nucleotide sequence and position away from the starting point of transcription (35 nucleotides). 3. 'TATAAT' Pribnow Box. 4.Act as binding sites for RNA Polymerase.
How are different RNA molecules synthesised by E. Coli?	All types of RNA present in E. Coli are synthesised by RNA Polymerase.
How many RNA Polymerase forms exist in E. Coli? What are these forms?(4)	2 forms. 1. The holoenzyme is a hexamer with the subunit structure α2ββ'ωσ. 2.The core enzyme is a pentamer with the subunit structure α2ββ'ω.
What are the functions of these 2 forms?	The holoenzyme carries out initiation but NOT elongation. The core enzyme carries out elongation but NOT initiation.
Draw an annotated diagram showing the organisation and transcription of a simple bacterial protein-coding gene (11)	promoter/gene/coding region/rna polymerase/non-coding strand/coding strand/terminator/mRNA 5'-3'
Describe the initiation of bacterial transcription (5)	1. RNA Polymerase has to bind strongly to the promoter. 2. It binds to the template non-coding strand as this produces an RNA molecule complementary to the coding strand. 3. The holoenzyme is responsible for finding the promoter, however it can't read the subsequent DNA code. 4. Sigma sub-unit dissociates leaving the core enzyme which can read the DNA 5. The core enzyme can't recognise promoter sequences due to its lack of a sigma sub-unit.
Describe the elongation process of bacterial transcription (4)	1. More DNA unwinds due to DNA Helicase, supercoils corrected by DNA Gyrase. 2. More template DNA is available for RNA synthesis, the core enzyme moves along the template strand. 3. The nucleophilic addition of NTPs to the 3'OH of the growing RNA strand is catalysed by RNA Polymerase, leaving NPPi as product. 4. As the enzyme passes along the template strand, the DNA strands behind it start to re-anneal, causing RNA to tail behind the enzyme.
Describe the termination process of bacterial transcription	1. RNA Polymerase encounters a terminator sequence. 2. It dissociates from the DNA molecule 3. The newly synthesised RNA molecule is released.
What essential ion is found at the active site of polymerase enzymes?	Mg2+
What is different about the DNA leaving the active site of a polymerase as opposed to DNA entering the active site?	DNA leaves the active site at a 90' angle in comparison to the angle of its entry point.
How is eukaryotic transcription different to prokaryotic transcription? (5)	1. Eukaryotes have 3 different RNA Polymerases for the transcription of mRNA, tRNA and rRNA. 2. Eukaryotes make a 1' transcript (pre-mRNA) that is processed in the nucleus to form mRNA. 3. In eukaryotes DNA is contained within the nucleus, whereas in prokaryotes DNA isn't contained within a nucleus and is contained with ribosomes within the same compartment. 4. Eukaryotic gene promoters have different nucleotide sequences in comparion to prokaryotic promotoers. 5. Eukaryotic RNA Polymerase can't directly recognise the promoter.
What are the names of the eukaryotic RNA Polymerases and the product they form? (3)	RNA Pol' i - rRNA RNA Pol' ii - mRNA RNA Pol' iii - tRNA
Which type of RNA is the most abundant and which is the most scarce in the cell?	rRNA - abundant mRNA - scarce
Draw a diagram showing the splicing of coding DNA by eukaryotic polymerases	Enhancer/ exon/ splice sites/ gene modded. cap/ 1' transcript cleavage/polyadenylation/ poly A tail RNA splicing Transport and final product
Describe the process of DNA splicing	1. Eukaryotic genes typically have introns and exons, always 1 fewer introns than exons. 2. Capping occurs - the addition of a methylated G cap to the 5' end of the 1' transcript. The cap stabilises the mRNA molecule and is required for translation. 3. Cleavage and polyadenylation occurs, the 3' end of the 1' transcript is cleaved, and a "Poly A tail" of 250A residues is produced. This stabilises the mRNA. 4. RNA splicing - exons are represented in the mRNA, introns are excluded. Exons are spliced together and introns are removed by RNA splicing to generate mRNA.

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