Lecture 10 Flashcards
translation
polymerization of amino acids into polypeptide chains
what does translation require?
-amino acids
-mRNA
ribosomes
-tRNA
transfer RNAs
- adapt genetic information present as specific triplet codons in mRNA to corresponding amino acids
- tRNA anticodons complements mRNA
- carry corresponding amino acids
ribsosomes
- have an essential role in expression of genetic information
- consists of ribosomal proteins and ribomsomal RNAs
- consists of large and small subunits
size of ribsosomes
- 70S in prokaryotes
- 80S in eukaryotes
tRNAs
- small in size and very stable
- 75-90 nucleotides
- transcribed from DNA tRNA genes
- contain posttranscriptionally modified bases
- have a cloverleaf structure
aminoacylation
- tRNA charging
- before translation can proceed, tRNA molecules must be chemically linked to respective amino acids
aminoacyl tRNA synthetase
enzyme that catalyzes aminoacylation
- 20 different kinds for each amino acid
- highly specific and only recognize for its respective amino acid
what are the three steps of mRNA translation?
initiation, elongation, and termination
what does initiation require?
- small and large ribosomal subunits
- mRNA molecule
- GTP
- charged initiator tRNA
- Mg2+
- initiation factors
what are the initiation factors?
- IF1 = blocks A-site
- IF2 = GTPase
- IF3 = inhibits small subunit binding
Shine-Dalgarno sequence
-precedes AUG start codon in bacteria and base-pairs with region on 16S rRNA of 30S small subunit, facilitating initiation
initiation complex
-small ribosomal subunit and initiation factors
termination
signaled by stop codons at the A site
-codons do not specify for an amino acid
FTP-dependent release factors
stimulates hydrolysis of polypeptide from peptidyl tRNA released from translation complex