L16: Splicing, Gene Structure, Translation Flashcards
What is alternative splicing and what does it do?
- IT is different splicing patterns and this creates splice variants.
What are splice variants?
- More than one type of protein can be made from a single gene coding for an mRNA.
Describe DNA packaging in bacteria.
- Promoters are unpackaged, hence accessible to RNA polymerase.
- “Default” state is always on
Describe DNA packaging in eukaryotes.
- DNA is packaged tightly and must be un-packaged (decondensed) for the RNA polymerase to access the DNA and start transcription.
What does Eukaryotic RNA processing involve?
- CAP
- polyA
- Splicing
What does the term “mature” or “final” RNA transcript refer to?
- the RNA molecule has been processed and ready to be exported from the nucleus.
Describe the 5’ cap and polyA tail.
- Increases the stability of the mature RNA and protects from degradation
- Helps regulate its translation; more proteins are produced from mRNAs with caps and tails
- Helps the final, mature mRNA transcript leave the nucleus through a nuclear membrane transport protein
What are introns?
- long non-coding sequences that interrupt the coding region of eukaryotic mRNA
What are exons?
- sequences that code for amino acids
What does the coding region begin and end with?
- usually exons!
- introns are located between the exons
- 5’ and 3’ untranslated regions are non-coding regions
What is RNA splicing?
- Introns are removed (spliced) from the mRNA transcript
- Exons can be kept or removed
Where does splicing occur?
- In the nucleus
What are splice junctions?
- Sequences between exons and introns that are cut sites
Are mRNAs always spliced in the same manner?
- Depends on the cell
- Different splicing patterns are called alternative splicing or creating splice variants
Is the triplet code universal?
- It is
- All organisms use this code to translate
What is the significance behind the redundancy of the triplet code
- The code is said to be redundant or degenerate because more than one codon can code for an amino acid
- i.e CGU, CGC, and CGA all code for Arg
What direction is the codon table?
- mRNA 5’ to 3’
Which molecule is the translator of the code
- aminoacyl tRNA synthetase
What must happen in order for translation to occur? (related to tRNAs)
- tRNAs need to have their amino acid attached. This “charges” the tRNA for translation
How many aatRNA synthetases for 20 common amino acids?
20
How many tRNAs for 20 common amino acids?
- Depends, at least 1-2 per amino acid
What is the tRNA called when it is carrying an amino acid?
- aminoacyl tRNA (charged tRNA)
Describe mRNA:tRNA interactions
- hydrogen bonds
What does a mature RNA transcript need to have for translation?
- a sequence where the ribosome will bind
(Shine-Dalgarno sequence or rbs for bacteria and 5’ cap for eukaryotes) - a start codon - the first amino acid is synthesized
- a stop codon - stop translation; doesn’t code for any amino acid
What is the open reading frame?
- the sequence of bases from (and including) the start codon to the stop codon (including)
What sequences does the mRNA transcript contain that are outside the ORF?
5’ UTR (untranslated region)
- location of rbs site (shine Dalgarno sequence) in bac.
- location where 5’ CAP binds in Euk
3’ UTR (untranslated region)
- location of hairpin loop (transcriptional terminator) in bac.
- location of Poly A tail in Euk
What does the start codon set?
- the reading frame
- the codons are read starting at AUG and then in triplets
- does not start at the first base of the mRNA
- the ORF encodes for functional proteins
What happens if there is more than one AUG codon?
- Different amino acids will be produced depending on which start codon is read.
