BIO 1A03 McMaster University Test 2 Review Graded A+

BIO 1A03 McMaster University Test 2 Review Graded A+ Translation Cellular components are able to read the genetic message in mRNA and translate the message into specific primary amino acid sequence of a protein How does tRNA structure allow for SPECIFICTY in translation? 1. Plays critical role in ENABLING the translation of the information 2. Each type of tRNA molecule is not identical and can translate a specific codon into a specific amino acid What is the structure of tRNA? - single RNA strand (70-90 nucleotide length) - four double helical segments and three characteristic loops How are the four double helical segments and three loops in tRNA molecules formed? Formed due to the large degree of complementarity along stretches of tRNA which results in many stretches of hydrogen bonding between complementary bases. What are anticodons? In what direction are they conventionally written? Three-base sequence in a transfer RNA molecule base that pairs with a complementary codon in mRNA They are conventionally written in the 3' to 5' direction What is at the 3' end on tRNA? There is a protruding amino acid attachment site made up of CCA nucleotide sequence (terminal "A" is point of attachment for amino acid during tRNA molecule activation) How is the activation of a tRNA molecule with a specific amino acid carried out? Activation is carried out by a family of enzymes called aminoacyl tRNA synthetase True or False; Each enzyme is specific to the type of tRNA and corresponding amino acid it will bind. True - 20 aminoacyl tRNA synthetase How do aminoacyl tRNA synthetases work? The active site of the enzyme recognizes the anticodon end of the tRNA and the region of the amino acid attachment site. Once bound to active site, enzymes catalyze covalent attachment of tRNA molecule to its amino acid (energy from ATP Hydrolysis) Charged tRNA able to deliver amino acids to growing polypeptide chain. What does correct translation require (in terms of codon and anti-codon)? Correct translation requires the correct PAIRING of tRNA anticodon with the appropriate mRNA codon How does codon-anticodon pairing occur? The 5' end of codon (mRNA) will bind with the 3' end of the anticodon (tRNA) What is meant by the term wobble? What does it help to explain? Greater flexibility for base pairing between third nucleotide of a codon and corresponding base of tRNA anticodon Wobble helps explain the redundancy of genetic code When does translation initiation in Eukaryotes occur? In eukaryotes, it occurs when a translational initiation complex forms towards the 5' cap of the mRNA and then scans the mRNA until an AUG start codon is encountered How does translation initiation in Prokaryotes occur? Since there are no 5' caps, translation initiation complex will assemble at one or more ribosome binding sites called Shine-Dalgarno sequences (Located a few bases upstream the translation start codon) What is the unique ability of prokaryotic translation? (think operons) Translation can occur along multiple regions of prokaryotic mRNA sequence - Allows prokaryotes to have specific open reading frames for more than one protein along mRNA Eukaryotic translation initiation requires what components? Two ribosomal subunits mRNA Charged tRNA Initiation factors Initiation factors Bind to 5' cap of mRNA which allows for the recruitment of the small ribosomal subunit Other initiation factors will bind to tRNA that is charged with methionine The partially assembled small subunit and tRNA do what once initiated? They will move along the mRNA in a 5' to 3' direction until AUG is encountered - When this occurs, large ribosomal subunit is able to bind to the rest of the initiation complex using energy from GTP hydrolysis What happens to initiation factors once translation is complete? Initiation factors are released once translation is complete How does translation start in the ribosome (not initiation)? - Methionine located in peptidyl site of ribosome - As the ribosome translates the mRNA, each subsequent charged tRNA enters or binds to aminoacyl (A) site GTP-bound elongation factor Each incoming charged tRNA is delivered in association with these When the correct codon-anticodon pairing is made, GTP is hydrolyzed