overall three-dimensional shape of polypeptide supported – result from interactions between amino acid side chains – largely defined by interactions amino acid R groups – structure determined by spatial distribution of hydrophilic and hydrophobic R groups and different types of chemical bonds and interactions – structure usually includes loops or turns in backbone, allows R groups to sit near each other
form of secondary structure – polypeptide folds back and forth on itself, formed pleated sheet – stabilized by hydrogen bonds between carbonyl in one chain and amide in the other across the way – R groups project alternately above and below the plane – amide on one side bonded to carbonyl on other – polypeptide chains run antiparallel (more stable than parallel, which can also occur)
– when AUG codon encountered, ribosomal subunit joins complex, initiation factors released, next tRNA ready to join the ribosome that the tRNA-Met binds with P site and the next tRNA in line comes in at A site – once new tRNA in place, reaction takes place: bond connecting the Met to its tRNA is transferred to amino group of next amino group of next amino acid in line, forming peptide bond – new peptide bond attached to tRNA on A site, ribosome then shifts one codon to right; uncharged tRNA-Met shifts to E site and is released, peptide-bearing tRNA shifts to P site
After translation has been initiated, for how long does elongation go on? 5′-GUACGUCAUGGUAAGAAAGUAAGACCGUCCAAAAAAAAAA-3′
A. Until the ribosome reaches an AUG codon B. Until the ribosome reaches a UAA, UAG, or UGA codon C. Until the ribosome reaches the end of the mRNA D. Until the ribosome reaches the poly(A) tail of the mRNA E. Until the cell runs out of tRNAs
Translation starts at AUG and ends at a stop codon. Use the codon chart below (and on your handout) to determine the amino acid sequence of the polypeptide encoded by this mRNA. 5′-GUACGUCAUGGUAAGAAAGUAAGACCGUCCAAAAAAAAAA-3′
What is the second amino acid in this polypeptide? A. His B. Met C. Tyr D.Val E. None of the above
The template strand of DNA at the beginning of a protein-coding region has the sequence: 5′-TACTGGGATAGCC*AACAT-3′ The “*” indicates the position of a point mutation: a T originally present at this location has been deleted. This deletion will most likely result in _____. A. mRNA codons preceding the mutation will be misread B. mRNA codons following the mutation will be misread C. No change in the polypeptide coded by this gene D. A change in the triplet being recognized as a stop codon
Choose the lane (A-D) on the protein gel below that best represents the expected result: The gene for one of the cell’s lysine tRNAs is mutated such that its wild type anticodon 3′- UUU-5′ is changed to the anticodon 3′-AUU-5′. The mRNA itself is not mutated or changed in any way. 5′-GUACGUCAUGGUAAGAAAGUAAGACCGUCCAAAAAAAAAA-3′ A. Same as wild type B. Band farthest up C. Band farthest down D. No band
Which of the following statements is true about protein synthesis in prokaryotes? A. Extensive RNA processing is required before the prokaryotic transcripts can be translated B. Translation can begin while transcription is still in progress C. Translation does not require ribosomes D. More than one of the above is a true statement
