Central Dogma Flashcards
What are the structural and catalytic roles of tRNA and rRNA
Transfer RNA brings amino acids to the ribosome during translation
Ribosomal RNA is responsible for the overall structure and catalytic activity (forming covalent peptide bonds)
Base differences between RNA and DNA
RNA uses a different base to thymine - Uracil
Thymine does not have a CH3 group on its carbon ring
Base pairs with adenine just like thymine
A sugar phosphate backbone is still produced
Outline RNA
A linear molecule
composed of FOUR ribonucleotide bases, adenine, cytosine, guanine and uracil
Carries the same information as its DNA template
Not used for long term storage
mRNA is a linear single-stranded molecule
Carries codon information for translation
Bacterial mRNA is used and degraded within minutes
Human mRNA can be used and degraded within days
RNA folding: a linear ribonucleic acid molecule acquires secondary structure through intra molecular interactions
Can base pair with complementary sequences found elsewhere on the same molecule
RNA contains a considerable amount of double helical structure
Folded RNA molecules are often sites of interactions with proteins, dictating splicing of RNA or function
Compare the secondary structure of DNA and RNA
Secondary structure refers to the helices which result from base pairing
DNA tends to form long double helices
RNA tends to form smaller double helices, with shorter regions of homology
RNA also forms more extensive tertiary structures
How is RNA made?
Transcription from a DNA template
RNA Polymerase reads DNA template
Make a single stranded RNA copy of DNA using ribonucleotide bases
Transcription by RNA Polymerase
RNA polymerase moves stepwise along DNA, unwinding the DNA helix in front of it
RNA synthesis happens in the 5’ to 3’ direction
The polymerase adds ribonucleotides one by one to the RNA chain, using an exposed DNA strand as a template. IT DOES NOT REQUIRE A PRIMER
Resulting RNA transcript is a single stranded and complementary to this template strand
The RNA pol displaces newly formed RNA, allowing the two strands of DNA behind it to rewind
A short region of hybrid DNA/RNA helix forms transiently , causing a DNA/RNA helix ‘window’ that moves down the DNA
mRNA carries the same information as DNA but is not used for long term storage and can exit the nucleus.
mRNA is not an identical copy of the DNA segment, because its sequence is complementary to the DNA template
Transcription depends on RNA polymerase and a number of accessory proteins called transcription factors
RNA polymerase begins mRNA synthesis by matching complementary bases to the original DNA strand
The mRNA molecule is elongated and, once the strand is completely synthesised, transcription is terminated.
The newly formed mRNA copies of the gene then serve as blueprints for protein synthesis during process of translation
Functions of 5’ mRNA capping
modifies the 5’ end of RNA transcript-G with a methyl group
Regulates export of mRNA out of the nucleus mRNA is exported in complexes that contain a CAP Binding Complex (CBC) at the 5’ end and RNA binding proteins along the rest of sequence
Required for the efficient translation of the mRNA into protein-The CBC facilitates recognition by the translation initiation machinery
CAP and CBC slows 5’ degradation of mRNA- Blockage of decaPping enzymes to the cap increases the t1/2 of the mRNA
Functions of 3’ mRNA Polyadenylation
3’ end trimmed at a particular sequence and transcript is finished by adding a series of adenines (A) 50-200 nt’s
Poly- A tail increases the t1/2 of the mRNA by protecting it from enzymatic degradation in the cytoplasm
-Poly(A)- binding protein (PABP) binds to poly (A) tracts
- Aids in transcription termination
-protects mRNA from ribonuclease attack
PABP interacts with components of the CAP
- Aids in export of the mRNA from the nucleus
-Promotes the circularisation of eukaryotic mRNAs which in turn simulates translation (circRNAs)
