Translation Flashcards
What is the meaning of the “genetic code”?
The 64 triplets of nucleotides in mRNA that makes he codons used in translation. Each triplet encodes for a specific one of the 20 aminoacids, except for the three “stop codons”
What is a codon?
The series of three nucleotides that can be read and translated into a specific amino acid.
Describe the characteristics of a codon
3 nucleotides
Non overlapping
Codes for specific amino acid
What is a reading frame?
Each codon has to be read in triplets of nucleotides, which makes out the frame that it is read
3 possible reading frames
What is an open reading frame?
The part of a reading frame that has the ability to be translated
A continous stretch of codons that contains a start codon (always AUG=methionine) and a stop codon (UAA, UAG, UGA)
What does it mean that the genetic code is universal and degenerate?
Is common for almost all living organisms (the same 4 nucleotides)
Many triplets code for the same amino acid, the difference mostly in the last/third position
What is an anticodon?
The three pairs of nucleotides in the tRNA that base pairs/corresponds to the codon in mRNA
What is a ribosome?
The unit of rRNA and proteins that is reading the mRNA and translate it into proteins
What is the characteristics of a ribosome?
Composed of one large and one small subunit
The small ribosomal subunit reads the mRNA
The large ribosomal subunit joins the amino acids into a protein
What is tRNA.
transfer RNA is the link between mRNA and the amino acid sequence of proteins.
It carries the amino acid to the ribosome during translation
What are the characteristics of tRNA?
Clover-leaf like secondary structure
The aminoacid arm carries the amino acid by its carboxylgroup to the A residue of at the 3’ end of tRNA
The anticodon arm contains the anticodon
What are the five stages of protein synthesis?
Amino acid activation Initiation Elongation Termination Folding and processing
Describe stage 1 in protein synthesis
Amino acid activation:
Cytosolic
The enzyme aminoacyl-tRNA synthesase help amino acid to bind to their corresponding tRNA and activates it.
Ensures appropriate placement in the growing peptide
Makes out the second genetic code
Describe stage 2 in protein synthesis
Initiation
AUG initiation codon
Amino terminus
Carbonyl terminus
Amino terminal in AUG/methionine residues fMet
Is not a normal tRNAmet
Step 1:
30S ribosomal subunit + shine dalgarno sequence
Step 2:
3 sites of binding A P E sites
The P site is the only site where fMet-tRNA can bind
Step 3:
50S ribosomal subunit-70S subunit (initiation complex, contains mRNA and fMet-tRNA)
Not in eukaryotes
Describe stage 3 in protein synthesis
Elongation
1. Binding of an incoming aminoacyl-tRNA at A site
2. Peptide bond formation, 2 aa is bound in A and P sites by their tRNAs
Peptidyl transferase activity
3. Translocation, ribosome moves one codon forward the 3’ end of mRNA the dipeptyl -tRNA moves to P and empty tRNA to E (exit)-site
