Lecture 9 Flashcards Preview

BMS238 Molecular and Cell Biology > Lecture 9 > Flashcards

Flashcards in Lecture 9 Deck (38)
Loading flashcards...

How can splicing explain how the same gene can produce different proteins when translated

The mRNA transcript can be spliced in different ways which accounts for differences in the proteins produced


What is meant by SnRNPs and what do they consist of

Small nuclear ribonucleo proteins are structures that make up the spliceosome apparatus. They consist of small nuclear RNAs and proteins


Describe the role of rRNAs

Ribosomal RNAs are a major constituent of ribosomes. They are very large and very abundant and catalyse protein synthesis


Polymerase action causes an uncoiling of the DNA that provides a force on the upstream DNA, how is this tension relived

Topoisomerases release the tension by either making single or double stranded breaks in the DNA upstream hence removing some of the coils from the superhelix


What is significant about viruses when it comes to protein synthesis

Viruses break the central dogma of DNA-->RNA-->Protein whereby reverse transcriptase enzymes can make DNA from RNA


Which RNA polymerase transcribes all protein coding genes

RNA Polymerase II


mRNA accounts for the majority of RNA, T or F

F – RNA only accounts for between 3-5% of all RNA


What is meant by the secondary structure of RNAs

Secondary RNA structure refers to the base pairing that occurs within a single RNA strand.


Which end of the mRNA strand is polyadenylated

3’ end


Describe the synthesis of the 5’ cap in eukaryotes

The 5’ cap is present in all eukaryotic mature mRNAs. Its consists of a methyl guanosine trisphosphate cap added to the first nucleotide. The 5’-5’ linkage is unusual and provides stability to the mRNA. The 5’ cap is also required for binding of the eukaryotic initiation factors. The 5’ cap is added when the mRNA is around 20-40 nucleotides long and begins to emerge from RNA polymerase


Specific transcription factors bind close to the promoter region, T or F

F – they bind far away


What is the name given to the machinery that carries our RNA splicing and what does it consist of

Spliceosome – a nuclear complex made up of about 150 proteins and 5 RNAs


What is the role of RNA polymerase I

Transcribes rRNA genes (28S, 18S and 5.8S)


PolyA tails can be up to 200 residues in length, T or F



Explain RNA polymerases role in synthesising the polyA tail

RNA polymerase contains a tail that is highly phosphorylated. The negative charge of these phosphates resembles the RNA backbone negative charge. This serves as a docking point for RNA binding proteins which are held there prior to binding to particular RNA sequences known as polyA signals.


What sequence represents the PolyA signal sequence?



Recall the structure of a mature mRNA from start to finish

Methyl guanosine cap --> 5’ UTR --> START --> Coding Sequence --> 3’ UTR --> PolyA Tail


How many families of tRNAs are there



The tertiary structure of RNA refers to its interactions with other RNAs, T or F

F – tertiary structure is the RNA strands 3D conformation


Give an example of a promoter sequence to which a general transcription factor binds to

TATA box – consisting of a TATAA/TAA/T sequence that lies 30 base pairs upstream of the coding sequence


Which RNA polymerase transcribes all tRNAs, 5S rRNAs and other snRNAs

RNA Polymerase III


What is meant by the primary sequence of RNA

The polyribonucleotide sequence


Splicing is specific to eukaryotic transcription, T or F



What is the role of cleavage stimulating factor and cleavage/polyadenylation specific factor in the synthesis of the PolyA tail?

Cleavage stimulating factor (Cstf) and cleavage/polyadenylation specific factor (CPSF) bind to the negatively charged tail of RNA polymerase II but then jump off when the PolyA signal sequence is detected. They then bind to the polyA signal and cleave the RNA which then allows PolyA polymerase to synthesise a polyA tail


General transcription factors are required for all gene transcription, how do they act

They act to guide RNA polymerase and bind to the promoter sequence


What is significant about non-coding RNAs

Non-coding RNAs serve structural and enzymatic functions, acting more like proteins


Genes can be on either the sense or antisense stands of the DNA but not both, T or F



What is the purpose of the polyA tail

The polyA tail is added as part of the termination process. It acts to maintain the RNA stability and help in mRNA nuclear export and translocation.


What are the key differences between RNA and DNA

RNA replaces thymine with uracil. RNA is also synthesised as a single strand and thus is unstable and rapidly degraded. Finally RNA contains a ribose sugar backbone instead of a deoxyribose sugar. The difference is an -OH group replaces the H bonded to the 2’ carbon in the sugar ring


Which regions of pre-RNA are spliced out but only in eukaryotes