15.3 Flashcards
List the cellular components and molecules involved in translation.
mRNA, tRNA, amino acid, ribosome
Define codon.
o mRNA base triplets
o read in the 5’ to 3’ direction
o specifies one of the 20 AAs to be placed at the corresponding position along a polypeptide
Illustrate the structure and function of tRNAs.
o a distinctive folded structure with three hairpin loops that form the shape of a three-leafed clover
o Transfer amino acids to the growing polypeptide in a ribosome
o Contains anticodon that binds to the codon
Describe the role of aminoacyl-tRNA synthetase in charging tRNA molecules.
o Recognizes only one amino acid but several tRNA
o Adds amino acids to the acceptor stem of tRNA
Describe the structure and function of the ribosomes and identify the tRNA binding sites.
o Structure: made of a large subunit and small subunit. Both enclose around mRNA strand
o Function: site of protein synthesis
o 3 binding sites
3 tRNA binding sites
P site
A site
E site
P site
holds the tRna that carries the growing polypeptide chains & the site where the initiating transfer RNA, carrying formylmethionine, binds to
A site
o the “acceptor” site
o holds the tRNA that carriers the next amino acid to be added to the chain (the site where new amino acids (other than the initial f-Met) enter)
E site
the “exit” site where discharged tRNA leave the ribosome
Explain the process of translation initiation.
o The small ribosomal subunit binds mRNA and a special initiator tRNA unril it reaches the start codon
o Then the large ribosomal subunit binds after
Describe the process of translation elongation including the mRNA codon, tRNA with anticodon and amino acid/growing peptide, and the ribosomes sites.
o Adds amino acids to the C-terminus of the growing peptide chain.
1. matching tRNA anticodon with mRNA codon
2. peptide bond formation
3. translocation of ribosome (moving of the ribosome on the mRNA)
Illustrate how peptide bonds are formed by the ribosome.
Bond forms between the amino group of the new amino acid and the carboxyl group of the growing chain. This breaks the bond between the growing chain and its tRNA
Identify how translation is terminated.
When the ribosome encounters a stop codon which is recognized by the release factor that then releases the polypeptide from the ribosome
Prokaryote gene expression
no introns, several genes may be transcribed into a single mRNA molecule, transcription and translation are coupled because there is no membrane-bound nucleus, begins a AUG preceded by special sequence that binds the ribosome, no modification of mRNA after transcription
Eukaryote gene expression
most genes have introns, one gene per mRNA molecule, transcription in nucleus then mRNA is transported to cytoplasm for translation, being at AUG preceded by 5’ cap that binds the ribosome, a number of modifications while mRNA is in the nucleus and the intron are removed, 5’ cap is added and a ploy-A tail is added
