Molecular basis of DNA transcription Flashcards
What did the 1944 Avery: DNA as genetic material show
Proved that isolating DNA- pure DNA held the information for converting one bacteria to another
What did the Crick Watson 1953 experiment show
Hypothesis of DNA being double helix
What is “the central dogma of molecular biology”
How information flows between:
gene –> mRNA—> protein
What are the 3 sets of experiments which defined the relationships between nuclear DNA and the protein expression?
A messenger exists that transmits information from the nucleus to the cytoplasm
The genetic code is read in triplets
The amino acid sequence is heavily related to the DNA sequence
Summarise the process of transcription
Using the 3’-5’ strand as a template a complementary mRNA strand is produced
Describe the differences between RNA and DNA
Ribose vs deoxyribose
(At the 2’ for ribose there is a OH whistle for deoxyribose there is a H at the 2’)- THEREFORE THE PHOS BACKBONE IS DIFFERENT
Uracil replaces thymine in RNA
How is RNA synthesised
the template strand = 3’-5’ using complimentary base sequence- the genetic code WILL be the same
RNA polymerase synthesises the RNA strand in the 5’-3’ direction
REQUIRES DNA STRANDS TO SEPARATE
Describe the role of RNA polymerase
The double helix is being unzipped- H bonds between complimentary bases are broken.
Temporary H bonds between one of the strands and the enzyme
What are the 3 main steps of transcription
Initiation
Elongation
Termination
Comment on non coding regions for transcription of Ecoli- helping initiate transcription
Promotor region indicates the region to start code for transcription-
A sigma factor associates with a sequence known as the pribow box “TATAAT”
RNA polymerase binds to the sigma factor
The sigma factor dissociates shortly after the transcription initiation starts
Describe the elongation part of the the prokaryotic transcription
Due to the helicase function of DNA polymerase a transcription bubble is formed due to H bonds temporarily forming between the RNA and DNA nucleotides
The reading of the DNA sequence on the template, allowing for the synthesis of mRNA in the 5’-3’
Describe the termination part of the prokaryotic transmission
Hair pain loop forms- due to the many G-C bonding mRNA folds within itself
This causes the detachment
How is eukaryotic transcription any different?
More complex- more proteins
polymerases
initation factors
elongation factor
helper proteins
ADDITIONAL mRNA PROCESSING
What are exons?
Expressed regions
regions of DNA which are found in mature mRNA
What are introns?
Intervening regions
regions of DNA within a gene unit that are not found in mature mRNA
They do not come for any amino acids in mature protein- as they are not in the RNA sequence
What is splicing
Splicing is the removal. of introns and in doing so converts pre mRNA to mRNA
This is necessary because in eukaryotes, only processed mRNA can be exported form he nucleus and so is available for translation
Some hn RNAs can be spliced in different ways thereby resulting in deferent product from the same gene
Conment on mRNA processing
Capping- for50-2mation of 7-methylguanosine cap at 5’ end
GTP reacts with 5’ end resulting in addition of 5’ phosphate group
Polyadneylation- adding 50-250 adenosine residues at the end of the RNA chain
Protection at both end
Transcriptional Output?
long rRNA (Pol I) mRNA- proteins (Pol II)
miRNA- control amount of mRNA that is translated (Pol Ii)
rRNAs short (Pol III) tRNA (Pol III )
Outline how protein output is regualted
mRNA is degraded- leading to inactive version- this is due to mRNA
Outline how transcription is regulated
TFs - enhancers and repressors
Enhancers
Both of the above make contact with the RNA polymerase
Chromatin structure- where the gene expression depends on the cell type
Methylation
Explain methylation in context of structure
Gene is switched on—> active chromatin—> unmethylated cytosines—-> acetylated histones
Gene is switched off—> inactive chromatin—> methylated cytosines—> deactylated histones PACKED TOGETHER
eg un methylated cell promoters- active
