Translation Flashcards
two steps in protein synthesis.
Transcription
Translation
How is the information present in the mature mRNA translated in to a protein?
in mature mRNA bases are grouped into 3 letter codes called codons. Most code for aminoacids.
There are four special codons: one that codes for ‘start’ and three that code for ‘stop’.
Ribosomal RNA (rRNA)
makes up the ribosome. Helps read mRNAs message and assemble proteins.
Transfer RNA (tRNA)
) transfers aminoacids to ribosome that are complementary to the mRNA.
Five different types of RNA, each encoded by different genes:
- mRNA
Messenger RNA, encodes the amino acid sequence of a polypeptide. - tRNA
Transfer RNA, transports amino acids to ribosomes during translation. - rRNA
Ribosomal RNA, forms complexes called ribosomes with protein, the structure on which mRNA is translated. - snRNA =Small nuclear RNA, forms complexes with proteins used in eukaryotic RNA processing (e.g., exon splicing and intron removal).
Micro RNA/small interfering RNA, short ~22 nt RNA sequences that bind to 3’ UTR target mRNAs and result in gene silencing.
Translation begins..
With the binding of the mRNA strand binding to the small ribosomal subunit upstream of the start codon.
The type of aminoacid is determined by the anticodon sequence by the tRNA.
Translation takes place…
- Complementary base-pairing occurs between a codon of the mRNA and the anticodon of the tRNA.
Translation takes place…
- Complementary base-pairing occurs between a codon of the mRNA and the anticodon of the tRNA.
Translation finishes
- Amino acids are brought until the entire mRNA is read.
Each tRNA drops off one amino acid then goes into the cytoplasm to grab another. - The ribosome bonds each amino acid together creating a polypeptide.
Eventually the stop codon is reached and the final amino acid is added.
Translation initiation: more in depth
Initiation begins with a tRNA bearing a modified methionine (met) attached to one of the ribosomal units.
The codon for methionine is a universal “start” codon for “reading” the mRNA strand.
About tRNA
Each cell contains about 60 types of tRNA
70-90 nt long adopt a clover-leaf shape
Each molecule has 3 important features:
Anticodon site with sequence of 3 unpaired bases that is complementary to codon in mRNA
Attachment site to bind a specific amino acid
Recognition site enabling correct aminoacid to bind each tRNA
Forming the initiation complex: binding of amino acyl tRNA
The mRNA where the code for met is located (AUG), binds the small ribosomal unit. AUG is the start code.
The anticodon (UAC) of the tRNA matches the “start” codon on mRNA (AUG).
Translation: more in-depth version
The large ribosomal subunit now binds to the small subunit.
The methionine tRNA binds to the first active site on the ribosome. Translation may now begin.
Translationelongation: in depth version
The second codon in mRNA (GUU) matches the anticodon of a tRNA carrying the amino acid valine (CAA).
The second tRNA binds to the second active site on the large subunit.
A catalytic site on the larger subunit binds the two amino acids together using dehydration synthesis, forming a peptide bond between them.
The first tRNA now detaches and goes of to find another met in the cytoplasm.
The mRNA chain shifts over one codon, placing the second codon (CAU) over the second active site.
A tRNA with an anticodon (GUA) matching the exposed codon (CAU) moves onto the ribosome. This tRNA carries histidine (his).
A new peptide bond forms between val and his on the catalytic site.
The tRNA that carried val will detach and find another val in the cytoplasm.
The mRNA strand will then shift over one more codon.
Translation termination: in depth version
The process continues until the ribosome finds a “stop” codon.
Since there are no tRNA molecules that can recognize these codons, the ribosome recognizes that translation is complete.
The subunits detach from one another, the mRNA is released, and the polypeptide chain moves down the ER for further processing.
The initial met is removed from the polypeptide and the chain is folded into its final 3D shape.
