Structure and properties of RNA Flashcards
Why is RNA less stable than DNA?
Ribose sugar instead of 2-deoxyribose sugar. RNA has a hydroxyl group where DNA has a hydrogen
What are the main features of RNA?
Single-stranded Written in 5' to 3' Shorter than DNA Can form a hairpin structure Carries genetic information
What is the role of the hairpin loop?
Gives stability (so that enzymes have more time)
What are the features of tRNA
3 hairpin loops
Variable loop
Stable due to H bonds
What are the features of mRNA?
Complex but single-stranded
4 major domains
What is transcription?
Synthesis of RNA under the direction of DNA
What is translation?
Actual synthesis of a protein which occurs under the direction of mRNA
What is mRNA?
messenger RNA which encodes the amino acid sequence of a polypeptide
What is tRNA?
Transfer RNA brings amino acids to ribosomes during translations
What is rRNA
Ribosomal RNA. With ribosomal proteins, makes up the ribosomes, the organelles that translate the mRNA
What is sRNA?
Small nuclear RNA. with proteins forms the complex that are used in RNA processing in eukaryotes (not found in prokaryotes)
What 3 sections does a protein containing gene have?
Promotor
Coding sequence
Terminator
How does transcription occur?
- RNA polymerase recognises the promotor and begins transcription (synthesised in a 5’ to 3’ direction
- As the polymerase moves long the template the RNA is released and the DNA helix reforms
- Once the polymerase hits the terminator sequence it stops and the full pre-mRNA transcript is released
How can you work out the mRNA sequence from DNA?
The template strand is used to make the mRNA but you can use the coding strand and swap the Ts for Us
What is the difference between mRNA in prokaryotes and eukaryotes?
In prokaryotes protein-coding is collinear with the translated mRNA. The transcript of the gene is the molecule that is translated into the polypeptide. Whereas in eukaryotes the protein-coding gene is typically NOT COLLINEAR with the translated mRNA. The transcript has to be spliced to remove the introns
How are the ends of pre mRNA modified in transcription?
At the 5’ end a cap is added containing a modified GTP (occurs at the beginning of transcription.)
At the 3’ end a poly(A) tail of 150 or more adenine nucleotides is added.
What is the role of the cap added during transcription?
Used as a recognition signal for ribosomes to bind to the mRNA
What is the role of the poly(A) tail added during transcription?
Stability
How does splicing occur?
- The intron loops out as snRNPs (small nuclear ribonucleoprotein particles, complexes of snRNAs and proteins) bind to form the SPLICESOME
- The intron is removed and the exons are spliced together
- The resulting mature mRNA may then exit the nucleus and be translated in the cytoplasm.
What is tissue specific gene expression?
every cell expresses genes depending on the tissue in which to resides
What are housekeeping genes?
The genes that are expressed in every cell e.g actin for the cytoskeleton