Lecture 7: Translation Flashcards
Know the definition of translation
Translation: the sequence of bases in mRNA specifies the order in which amino acids are added to a polypeptide chain.
Know the factors required for translation
- mRNA
- Initiation factors
- Elongation factors
- release factors
- Aminoacyl tRNA synthetases
- tRNA
- Ribosome (ribsomal RNA + proteins)
Know the structure of the ribosome and describe the three binding sites for tRNAs
complex structure of RNA and protein that bind mRNA and control translation
• Ribosomes consist of a small subunit and a large subunit
• The large subunit of the ribosome contains three binding sites for transfer
RNA (tRNA):
i. A (aminoacyl) site
ii. P (peptidyl) site
iii. E (exit) site
Describe the properties of codons and reading frames
Codon: group of three adjacent nucleotides in an mRNA that code for an amino acid.
Reading frame: region where the ribosome begins reading the sequence of nucleotides.
- The ribosome determines the correct reading frame for the codons.
Compare eukaryotic and prokaryotic ribosomes
Eukaryotic ribosomes are bigger than prokaryotic ribosomes.
Know the structure of tRNA and describe key features of the tRNA molecule
- Translation of the message in mRNA is carried out by tRNA molecules: 70-90 nucleotides long, each with its own self-pairing structure
- clover leaf structure
- phosphate group on 5’
- hydroxyl group on 3’
- Amino acid attachment cite on the A of CAA at the 3’ hydroxyl group.
- anti-codon region at bottom
Know the function of tRNA Synthetase and describe its role in charging tRNAs
Function: connect specific amino acids to specific tRNA molecules
- A tRNA without an amino acid attached is uncharged; a tRNA with an amino acid is attached is charged
Describe the base pairing properties between codons and anti-codons
The first base in the codon in mRNA (5’) pairs with the last base in the anticodon of the tRNA (3’): antiparallel
• Codons specify amino acids according to the genetic code
The codon that initiates translation is AUG: corresponds to the amino acid methionine
Describe the degeneracy of the genetic code and know how to read the codon chart
20 amino acids specified by 64 codons
• Many amino acids are specified by more than one codon: the genetic code is redundant or degenerate
Compare translation initiation in prokaryotes vs eukaryotes
Monocistronic mRNA:
- iniation in eukaryotes is at the 5’ cap, the first AUG is the start codon
Polycistronic mRNA:
- initiation in prokaryotes is at any shine-Delgado sequence. Therefore, mRNA can be a polycistronic mRNA that codes for several peptides.
Describe the process of translation initiation and the role of initiation factors
- Initiation requires Initiation Factors:
i. bind to the 5’ cap of the mRNA
ii. recruit the small subunit of the ribosome
iii. bring up a transfer RNA charged with Methionine - Initiation complex: moves along the mRNA until it reaches the AUG start codon
- When the first AUG codon is reached: i. a large ribosomal subunit joins the complex
ii. initiation factors are released
iii. the next tRNA is ready to join the
ribosome in the A site - Once the tRNA is in the A site, the bond connecting Met to its tRNA is transferred to the amino group of the amino acid in the A site: peptide bond is formed
- The new peptide is now attached to the tRNA in the A site
- Formation of the peptide bond requires proteins in the large subunit, but the rRNA in the large subunit is the catalyst
Describe the process of translation elongation
The ribosome moves one codon farther along the mRNA:
i. tRNA in the E site is ejected
ii. tRNA in the P site is moved to the E site
iii. tRNA in the A site is moved to the P site
iv. A site is open and available for the next tRNA
Describe the process of translation termination and the role of release factors
- Elongation continues until a stop codon is encountered (UAA, UAG, UGA)
- Release Factor protein binds the A site of the ribosome: causes the bond connecting the polypeptide to the tRNA in the P site to break
- The breaking of the bond creates the carboxyl terminus of the polypeptide
