RNA synthesis Flashcards
Main function of transcription and does the language remain the same?
mRNA synthesised in the nucleus and same language of nucleic acids
Main function of translation and does the language remain the same
Protein production from mRNA
Different language form nucleic acid to protein
How many nucleotides are there in the human genome?
3.2 x10^9
How many homologs do chromosomes have and what are they referred to as?
2 and they’re known as paternal and maternal homologs
What is the key function of chromosomes?
To carry genes
What are centromeres made up of and what is there key function?
• Centromere is made up of DNA and key function is to keep the chromosome attached to the spindle fibre during mitosis.
Where are telomeres located and what is there main function?
○ Located at the end of the chromosome
○ Double strand
○ Six base pair repeat
Protects end of chromosome by preventing fusion from neighbouring chromosomes
How many autosomes and sex chromosomes are there?
22 autosomes
1 sex chromosome
What is the intergenic region and what does it contain?
The region of DNA between genes which have no current function
Contains pseudo genes Repetitive DNA
What is a gene and its properties such as size and its affect on phenotype?
- Unit of heredity, contains instructions for an organisms phenotype
- DNA segment containing instructions for making a particular product
- Differ in size
- Differ in number of introns and exons
- Cluster into families
What is the promoter?
a region involved in ensuring RNA polymerase combining for transcription.
What does RNA make and what does it catalyze?
- DNA transcribed into RNA
* Catalyses the formation of phosphodiester bonds
Types of RNA polymerase
- RNA polymerase 1- Most ribosomal RNA
- RNA polymerase 2- Protein coding, microRNA
- RNA polymerase 3- tRNA, 5S rRNA
During RNA synthesis, how many bases are transcribed roughly?
• About 1.25-1.75 kb per min so quite fast
During RNA synthesis, how do polymerases work and the effect on the number of transcripts from a gene simultaneously?
- Many polymerases work on the same gene
* Many transcripts from a gene simultaneously
Why are Transcription factors required?
• Required to initiate or regulate transcription
What does the promoter contain to which RNA polymerase 2 binds to and how many bp is it?
Containts TATA box which is 30 bp.
Transcription(Initiation)
• Eukaryotic promoter regions contain a DNA sequence called the TATA box
• Transcription factor (TFIID ) sub unit, the TBP, recognises the TATA box and binds.
• The binding of TFIID enabled the adjacent binding of TFIIB and TFIIA.
○ TFIIB is responsible for linking RNA polymerase to the complex
○ TFIIA stabilises the complex
• TFIIF is already associated with the RNA polymerase when RNA polymerase binds to the TFIIA-TFIIB-TFIID complex.
• TFIIE and TFIIH both associate with RNA polymerase and initiation is complete.
○ TFIIH breaks apart the double helix at the transcription starting point
○ TFIIH also phosphorylates RNA polymerase II, so it can start transcription.
Transcription(Elongation)
RNA strand gets longer by the addition of nucleotides at the growing 3’ end.
Transcription(Termination)
• When a sequence of DNA, known as a terminator and located after the stop codon, is reached transcription ends
What are untranslated regions and what are they required for?
• Are transcribed but not translated as they’re required for regulation
what is the 5 Primer UTR responsible for?
involved in the regulation of translation
What is the 3 primer UTR responsible for?
regulation of mRNA stability and miRNA binding
RNA processing(Capping)
• Capping:
○ 5’ end becomes modified after 25 nucleotides of RNA have been synthesised.
§ A guanine is added to the 5’ end and an enzyme called methyl transferase, methylates guanine to give rise to 7 methylguanine cap.
□ This cap protect the degradation of mRNA
RNA processing(Polyadenylation)
• Polyadenylation:
○ mRNA is trimmed by an enzyme at the 3’ end
○ The transcript is finished off by a second enzyme that adds repeated Adenine bases to the cut end
○ Poly-A tail is formed making the transcript more stable and protects pre-mRNA from RNAses which digests RNA in the cytoplasm as it moves out the nucleus.
○ The longer the poly-A tail the more stable the RNA is
What is capping and polyadenylation required for?
Required for stability
What is RNA splicing
Removal of introns and joining of exons
Splicing
• Special sequences in a pre-mRNA signal the beginning and the end of an intron
○ Recognised by snRNPs
• At GU we have the 5 primer splicing region
• At AG we have the 3 primer splicing region
• The lariate structure loops to join the branch point as is disposed off leaving the exon which joins the second exon.
What is alternative splicing?
There are splice variables meaning during translation different proteins are synthesised
