Question

1. Protein synthesis requires energy in the form of ATP and GTP.  Two high-energy phosphate bonds (from ATP) fuel the formation of one aminoacyl tRNA.  Formation of the initiation complex requires energy from one GTP.  Delivery of each new tRNA to the Asite requires one GTP.  Termination requires the hydrolysis of one GTP.   Based on this information, the provided table of codons, and your understanding of the processes of Activation, Initiation, Elongation, and Termination, answer the following questions.  

1. How many high energy phosphate bonds are required for the translation of a 100 amino acid polypeptide, starting with mRNA, tRNA, amino acid and all the necessary enzymes.
2. A portion of prokaryotic mRNA has the following base pair sequence: 5’ACAUCUAUGCCACGA3’.  What would happen if the underlined base was mutated to an A.
3. Puromycin is a drug that is an analog of aminoacyl tRNA.  It has an amino group that is capable of forming a peptide bond, but no carboxyl group with which to form another peptide linkage.  What would be the effect of adding puromycin to cultures of bacteria engaged in protein synthesis.  
4. Ribosomes isolated from bacteria grown in heavy medium (¹⁴C ¹⁵N) and from bacteria grown in light (¹²C ¹⁴N) were added to a cell-free in vitro protein synthesis system.  At a later time a sample was removed and 70S ribosomes were analyzed for differing densities.  How many 70S ribosome densities were found and why?
5. How is the methionine residue used for prokaryotic initiation of translation unique – draw it.  

Answer 1

as per guidelines i answer first 4 questions.

a) one molecule of atp can uptake one molecule of amino acid. AMP+ 400Pi = 200 molecules of atp. this amount is activating 200 amino acids. 1 GTP is for initiation and 398 molecules are to form 199 peptide bonds. 300 Nucleotide mrna produce 100 amino acid protein.

b) first of all there is no underline under any base. if one of the amino acid is mutated it is called point mutation. sickle cell Anemia is a example. due to this point mutation wrong amino acid is getting produced. this cause altering in proteins. the genetic expressions are altered due to this. missense mutation and nonsence mutations are two major effects of this pint Mutation.

c) adding of puromycin in the culture medium cause. it cause premature chain Termination during translation. this is mainly taking place in ribosomes. this prevents the translocation of peptidyl - trna from A site to P site. it inhibit peptidyl transferase. erythromycin binds to the 50S ribosomal subunit of bacteria and prevent translocation.

d) as per biochemistry sources, when the ribosomes are isolated from heavy and light medium and measuring the density gradient centrifugation of the 70s ribosomes. we expect 4 bands as a result from density gradient Centrifugation. hybrid of light 30s and 50s of heavy chains and 30s heavy and 50s light are produced.