DNA, RNA - translation Flashcards
What is the anatomy of eukaryotic mRNA?
cap
- at the 5 prime end
- modified guanine nucleotide is attached = (methylated guanidine)
- identifies the RNA as mRNA and as where the ribosome first binds
untranslated region - after 5 prime cap
- contains sequences which control the rate of translation
coding sequence
- uninterrupted = introns have been removed
untranslated region - at the 3 prime end
- contains sequences which control the stability of mRNA
poly A tail
- adenylation = adenine are added on the end of the chain
- prevents degradation and helps protect mRNA in the export
What is the genetic code? What are the characteristics of the genetic code?
genetic code
- provides the means for the base sequences of mRNAs to encode amino acid sequences in proteins
characteristics
- triplet code = 3 bases code for a single amino acid
- unambiguous = specific triplets code for specific amino acids, they do not code for multiple amino acids
- degenerate = more than one triplet can code for the same amino acid
What are the start and stop codons for eukaryotes?
start
- AUG = methionine = often cleaved off to to form the mature polypeptide
stop
- UAG, UAA, UGA = do not code for an amino acid
What are the characteristics of tRNA?
tRNA
has a clover leaf shape
- is a single strand
- has internal complementary = within the cloverleaf shape, the bases can pair up which causes a double strand region
stem and loop of tRNA
- stem has hydrogen bonds between the bases
- loop has no hydrogen bonds
attachment site for amino acids
is the anti codon
- is complementary to the codons on the mRNA
What are the steps in translation (protein synthesis)
1 - charging of tRNA with amino acids
2 - initiation of polypeptide synthesis
3 - elongation of polypeptide synthesis
4 - termination of polypeptide synthesis
What is the first step in translation?
charging of tRNA with amino acids
an amino acid is attached to a tRNA molecule by amino acyl tRNA transferase
- forms amino acyl tRNA
there are separate specific amino acyl tRNA transferase for each tRNA
- ensures the correct amino acid is linked to the correct tRNA
What is the second step in translation?
initiation of polypeptide synthesis
initiation factors bind at the cap (methylated guanidine)
- RNA is recognised as mRNA due to the 5 prime capping
initiation factors binds the small ribosomal subunit and the initiator tRNA together
initiator tRNA moves alone the mRNA chain until it comes along the start codon
- moves along via the hydrolysis of ATP
- methionine = AUG
once the initiator tRNA find methionine, the initiation factors release
large ribosomal subunit then binds to the small ribosomal subunit
What are the different sites on the ribosomal submits for translation?
ribosome has 3 sites
- E = exit sites where tRNA which is no longer needed is released from
- P = tRNA with existing polypeptide chain is attached
- A= acceptor site where new tRNA joins
What is the third step in translation?
the next amino acyl tRNA recognises the next codon
- binds the anticodon on the tRNA to the codon on the mRNA
methionine is unbound/removed from the first tRNA and a peptide bond forms between the two amino acids
- peptide bond is a type of covalent bond and is formed by peptidyl transferase
ribosome moves alone the mRNA chain
- translocation of mRNA and expulsion of vacant tRNA
What is the fourth/final step in translation?
ribosome continues to translocate down the mRNA until it reaches the stop codon
- stop codon = UAG, UAA, UGA
specific proteins bind at the stop codon
- ensures translation stops
water hydrolysis to form the COOH group of the C terminus end of the polypeptide chain
What is the difference between eukaryotic and prokaryotic protein synthesis?
eukaryotic
- has the cap at the 5 prime end = methylated guanidine
- 5 prime untranslated region is not recognised = only controls the rate of translation
- start codon is methionine = AUG
- ribosome is 80S = has 60S and 40S subunits
prokaryotic
- does not have a cap structure at the 5 prime end
- bacteria ribosomes recognise the untranslated region at the 5 prime end
= called the shine delgarno sequence
= enables initiation of protein synthesis by aligning the ribosome with the start codon (N-formly methionine)
- start codon is N-formly mehtionine = specific for bacteria
- ribosome is 70S = has 50S and 30S subunits
How doe antibiotics work against bacteria?
inhibition of cell wall synthesis impairment of the cell wall inhibition of nucleic acid synthesis inhibition of protein synthesis inhibition of metabolism
Why don’t antibiotics work against viruses?
viruses
- use the protein synthesis machinery of the host cell to make their own proteins = production of viral proteins is not inhibited by antibiotics
have a different structure to bacteria
- no ribosomes
- no cell wall
