protein synthesis Flashcards
What tRNA is used?
Aminoacyl-tRNA synthetases govern the correct translation of genetic code through loading of tRNAs with correct amino acid
What are ribosomes?
-70S ribonucleoprotein particles made of a small 30S and large 50S subunits
How is triplet code redundant?
-there are 20 amino acids that make up most portiens
-64 possible triplet codons to encode for those (64 possibilities with 4 bases)-so several diff triplet codon sequences can encode from same amino acid
how is triplet code unambiguous?
-each codon can only encode 1 specific amino acid
How does protein synthesis start?
-with initiation of codon AUG which codes for amino acid methionine
What are reading frames?
-specified by the start codon and strength of ribosome binding site
-3 reading frames are possible within a 4 letter encoded triplet decoded sequence
What is aminoacyl-tRNA?
-anticodon is template-recognition site
-amino acid attached to 3’ end
which end is amino acid attached to
3’ end
What is loading/amino-acylation?
-Amino-acylation of tRNA is the process of attachment of amino acids to their corresponding tRNA molecules
How does amino acid attach
It is esterified to the 3’ hydroxyl group of the terminal adenosine of tRNA
What is structure of tRNA
-amino acid attachment site
-extra arm
-anticodon loop
-phosphorylated 5’ terminus
What do tRNAs contain?
-several modified nucleosides
E.g.
* Methylinosine (ml)
* Dihydrouridine (UH2)
* Ribothymidine (T)
* Psuedouridine ()
* Methlguanosine (mG)
* Dimethylguanosine (m2G)
Inosine (I) – part of anticodon
L shaped structure
-This is referred to as the L-shaped structure of tRNA.
-The end of one arm is the anticodon, the other is the CCA stem.
-Intramolecular base-pairing in tRNA assists with its 3-D structure in terms of formation and stability.
Ribosome structure
-RNA/protein hybrid structures
-site of peptide bond formation contains only RNA (yellow) with no protein (red) within
What is aminoacyl tRNA synthesise
-enzymes that attach the amino acids to tRNAs
-highly specific for each amino acid
-need to read anticodon to be able to differentiate between amino acids with similar structures
-have proofreading function to hydrolyse wrongly charged tRNAs
how does amino acid attach to trna
flexible cya arm can move the amino acid between the activation site and the editing site of aminoacyl trna
-if amino acid fits into editing site, it will be removed via hydrolysis
How big is rRNA
-70S
What is it made up of
-50S subunit, 30S subunit
What is secondary structure of rRNA
16s
How is tertiary structure of rRNA determined
-by X-ray crystallography
What is polycistronic mRNA
-an mRNA corresponding to multiple genes whose expression is also controlled by a single promoter and a single terminator.
-occurs in prok
-has multiple translation start sites / ribosome binding sites
-happens in prokaryotic mRNA
-produces several proteins
What is monocistonic mRNA
monocistronic mRNA produces a single protein while polycistronic mRNA produces several proteins that are functionally-related.
-Occurs in euk mRNA
-has single translation start site
-can produce 1 protein
what is polysome
transcription of a segment of E. coli DNA generates mRNA molecules that are immediately translated by multiple ribosomes. a group of ribosomes bound to an mRNA molecule like “beads” on a “thread”. It consists of a complex of an mRNA molecule and two or more ribosomes that act to translate mRNA instructions into polypeptides.
How is translation initiated?
-there is translation initiation site and a region on mRNA which is responsible for binding to ribosomes via interaction of 16S rRNA
