Flashcards in L2: Translation Deck (23):
What bond joins amino acids to form the polypeptide protein? And what product is lost?
What give proteins their properties?
Particular side chain structures
What is the structure of an amino acid?
Positive amino group (NH3), C, H, negative carboxyl group (COO) and a side chain group (R)
What two terminuses does a protein show?
An N- terminus end (amino end) and a C- terminus end (carboxyl end)
What is transfer RNA (tRNA)?
Small molecule that
Binds to specific amino acid
Recognises corresponding codon by base pairing
How does the sequence of base pairs in mRNA define the sequence of amino acids in a protein?
By base pairing (G to C, C to G, A to U and T to A)
The genetic code: 3 bases = 1 codon for 1 amino acid
What does a start codon do and what is the codon? What does it code for? Where is it found?
Specifies the start of translation
Codes for methionine
Found at the beginning of protein
What does a stop codon do and give the names of the 3 of them?
Specifies the end of translation
What are the 4 modified bases found in tRNA?
D, Y, T, Ѱ
What shape does tRNA show?
Clover leaf (secondary structure)
Stems where base pairing within molecule occurs
Loops where no base pairing occurs
But folded across so molecule is actually L shaped (tertiary structure)
How does the amino acid bind to the tRNA and to which end?
What does the anticodon in tRNA bind to?
The codon in mRNA
Which enzyme joins the correct amino acid to tRNA (requiring a lot of energy)?
Aminoacyl- tRNA synthase
What takes place at ribosomes?
What do they contain?
What are they made up of?
What do they have?
Contain RNA and protein
2 subunits: large+ small
Binding sites for mRNA and tRNA (EPA sites)
What is the basic mechanism for protein synthesis?
mRNA binds to ribosome
aminoacyl-tRNAs recognise and bind to base triplets in mRNA
Ribosome transfers each new amino acid to the growing polypeptide
Protein is extended from amino terminus to carboxyl terminus
Elongation factor proteins assist the process as well as initiation and release factor proteins
During initiation, what binds to the P site in the small ribosomal subunit?
Methionyl tRNA (eukaryotes)
Formylmethionyl tRNA (bacteria)
What happens after tRNA binds to the ribosome during initiation?
mRNA binds to small subunit (start codon binds to tRNA anticodon)
Large subunit binds
Aminoacyl tRNA for second amino acid binds to site
Protein synthesis proceeds as for normal elongation
What happens during elongation?
Ribosome transfers growing polypeptide from peptide life-tRNA in P site to the new aminoacyl tRNA
Large subunit moves relative to small subunit
Ribosome is reset so next tRNA can bind
Spent tRNA ejected from E site and next aminoacyl tRNA binds
Where does energy for protein synthesis come from?
Hydrolysis of GTP to GDP + phosphate
What does EF-Tu (for bacteria) / EF1 (for eukaryotes) do?
Carries aminoacyl tRNA to ribosome
EF-Tu binds GTP
EF-Tu releases aminoacyl tRNA and hydrolyses GTP to GDP +phosphate
What does EF-G (bac) / EF2 (eu) do?
EF-G/EF2 with bound GTP binds to A site
Resets ribosome ready for next aminoacyl tRNA
When does translation terminate?
At first in-frame stop codon :