RNA Flashcards
Tell me the differences between the strucutre of DNA and RNA ?
- RNA contains the pentose sugar of ribose as opposed to the deoxyribose sugar in DNA
- containd Uracil rather than thymine
- single stranded rather than double stranded. this is so it can form well-defined secondary structures
Tell me the 6 types of RNA and their roles
- mRNA: messenger RNA, a template for protein synthesis
- rRNA: ribosomal RNA, major component of ribosomes
- tRNA: transfer RNA, carries amino acids in their activated forms to the ribosome
- snRNA: small nucleuar RNA, participates in RNA splicing
- miRNA: micro RNA, binds to mRNA and inhibits their translation
- siRNA: small interfering RNA, bind to mRNA and promote degradation
How is RNA produced?
Via transcription
What are the different stages of transcription?
- initiation
- elongation
- termination
- processing
What happens in the initiation stage of transcription?
- DNA unwinds and seperates
- RNA polymerase binds to the promoter of the template strand
- RNA synthesis occurs in the 5’–> 3’ direction (antiparallel to the DNA strand)
- RNA forms
RNA polymerase has an subunit and an initiation factor. What are each of these and their role.
Whats a Holoenzyme?
The subunit is called a2ßß’w. This is the subunit of the core enzyme RNA polymerase and is involved in catalytic activity
The initiation factor is σ. This directs the enzymes to the correct initiation sites
Holoenzyme is formed from a combination of enzyme with coenzyme
Whats the start of transcription marked by and what is this?
Promotors, these interact with different transcriptional factors and RNA polymerase to initiate the process
In prokaryotes whats located at position -35 and -10 on the genome when +1 marks the start of RNA and what are these?
In Eukaryotes whats located at position -75 and -25 on the genomes when +1 marks the start of RNA and what are these?
Prokaryotes
Position -35: A consensus sequence (TTGACA)
Position -10: Pribnow box (AT-rich region)
Eukaryotes
Position -75: CAAT box (sometimes present)
Position -25: Hogness box (TATA box)
What occurs in the elongation stage of transcription?
Whats used in this stage in prokaryotes?
- RNA polymerase moves along the template strand, synthesing an RNA molecule
- NTPs (nucleoside triphosphates) are added to the 3; end of RNA
NOTE: in prokaryotes, RNA polymerase is a holoenzyme consisting of a number of subunits including a sigma factor (transcription factor)
Whats are NTPs?
- uses
- what DNA and RNA synthesis use
- why its synthesised within the cell
- building blocks of DNA and RNA
- source of energy for cellular reactions
- involved in signalling pathways
- not absorbed well, so synthesise within the cell
- DNA synthesis uses dNTPs whilst RNA synthesis uses NTPs
What two ways can the termination stage of transcription in prokaryotes occur?
In prokaryotes there are two ways that transcription can be terminated
- Rho-dependant termination
- Rho-independant termination
Tell me about the Rho-dependant termination in prokaryotes?
- it requires a protein known as a Rho factor
- Rho moves along the molecule in the 5’ –> 3’ direction and encourages the dissociation of the DNA template and RNA polymerase
- disrupts the transcriptional complex
Tell me about the Rho-indepedant terminator in prokaryotes?
- a self-annealing hairpin structure is formed
- the hairpin formation causes the RNA polymerase to stall and become unstable
How does termination of transcription occur in eukaroytes?
- terminator signals that are associated with RNA polymerase II are detected and trigger the termination process
- Additional adenine nucleotides are added to the 3’ end od the RNA transcript (a process known as polyadenylation)
Whats polyadenylation?
the addition of a PolyA tail to an mRNA
this tail consisits of multiple AMPs (stretch of RNA which only has adenine bases)
Part of the procee that produces mature mRNA for translation
Whats the biggest difference between DNA-RNA replication in prokaryotes and eukaryotes?
in prokarytoes, transcription and translation occur at the same time
in eukaryotes there is compartmentalisation which means that translation cannot occur until transcription is complete.
What occurs in the processing process of transcription?
- preribosomal RNA is spliced where the introns are removed which then leads to the formation of mature RNA
- normal base pairing rules where thymine is replaced with uracil in RNA