Protein Synthesis Part 1
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| Described ribosome couple | Large subunit on top of small subunit and it is inactive. Couple has to be separated to form a monosome, ribosome attaches to the mRNA & is ready to decode info
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| What does the ratio of polysome to monosome reflect? | The activity of protein synthesis. More ribosomes= more protein synthesis
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| Name the four stages of protein synthesis | 1. Aminoacylation 2. Initiation (GTP & ATP) 3. Elongation (GTP) 4. Termination
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| What has to be ensured for all tRNA's | Charged state. Amino acid is esterfied to tRNA. catalyzed by aminoacyl tRNA synthetase
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| Diphthamide | Has a modified histone. Present in EF-2, highly suseptible to inhibition of synthesis by and exotoxin produced by corynebeacterium dipthariae
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| Describe the role of exotoxin | Catalyzes the modification by mono-ADP-ribosylation. Consumes NAD as a substrate by breaking the ribose-nucleotinamide bond. NAD is covalently attached to N
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| Hypusine | It is a composite made up of lysine and spermidine on the other end. Present in eIF-5a. Related to the destruction of pancreatic islets when you have cytokine induced inflammation
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| Selenocysteine | Modified cysteine, found in 15-30 polypeptide chains in Pro and Euk. Selenoproteins play a role in defense against oxidative stress. Encoded by AUG (termination)= insert selenocysteine into selenoproteins
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| What direction is proteins synthesized in? | From N terminus to C terminus. 1st aminoacyl tRNA linking to the 2nd aminoacyl tRNA to form dipeptidyl tRNA then to a 3rd and so forth
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| Describe tRNA features | CCA at 3'. Adaptor molecule, 2 ends are anchoring the AA at the 3' end & at other end there is anticodon loop which interacts with mRNA. 5' loop=di-hydrouridine. 3' loop=T-psuedouridine C loop
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| Feature of psudouracil | Change in Carbon Nitrogen position (RNA editing)
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| Wobble position | Refers to the first base of the anticodon
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| Class I amnioacyl synthetase | tRNA oriented to your right (CCA to right). Synthesase attacks from front to 2' position and need to be moved to 3'
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| Class II aminoacyl synthetase | tRNA has CCA oriented to the left. Synthesase attacks from backside and attaches directly to the 3' position
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| Ribosome of Pro | 70s--30s and 50s subunit. 30s contains 16s which recognizes the initiation codon
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| Ribosome of Euk | 80s--40s and 60s
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| Features of smaller subunits of ribosomes | Have E, P and A sites. First aminoacyl tRNA positions to the P site. Has enzymatic activity called the peptidyl transferase (ribozyme). Organization of small unit allos peptide bond formation.
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| What do Pro mRNA lack that Euk has? | Lacks cap structure, has shine delgarno sequence which is purine rich at 5' UTR (9-16nts) Complementary with 3' end of 16s
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| Describe the mRNA | Has 5' UTR--AUG--coding sequence--termination sequence--3' UTR--3' end
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| AUG | Initiator condon, represents methionine. Recognized by the initiator tRNA. Pro has f-Met-tRNA (formyl group) and Euk has Met tRNA
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| Degeneracy of genetic code | More codons than amino acids
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| Wobble base rules | If you have A or C there is no deviation. G, T or hypoxanthine (I) you have flexibility. I can pair with A, C or U.
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| What step of the process determines the incorporation of amino acids? | The charging of tRNA. cysteinyl-tRNA synthetase results in charge. ATP reacts with AA to form intermediate aminoacyl adenylate then tRNA binds
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| Why would synthetase undergo editing? | To make sure tRNA is right for AA
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| Role of transformylase | Only present in Pro to formylate initiator tRNA
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| Energy used in each step | 1. Aminoacylation: ATP to AMP. 2. Initiation: ATP and extra ATP in Euk for mRNA binding. 3. Elongation: Aminoacyl binding-GTP, tranlocation-GTP. 4. Termination: GTP
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