Molecular Machines

Ribosome

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Summary 9

Read this section: Summary, in the Ribosome notes

  1. What does the ribosome do in a cell?

  2. The ribosome's blank checks each codon against the anticodon of the incoming tRNA.

  3. In the bacterial ribosome, the peptide bond is made by blank of the large subunit, not by protein.

  4. No ribosomal protein sits in the catalytic centre. What job do the ribosomal proteins do instead?

  5. A tRNA passes through the ribosome's three binding sites in the order blank.

  6. How many amino acids per second does a ribosome add in E. coli, from slow to fast growth?

  7. The ribosome's error rate is about blank per elongation step.

  8. What did tethering the two ribosomal subunits into one molecule (Ribo-T) show?

  9. What is the status of using ribosomes to make polymers that are not proteins?

How it works 7

Read this section: How it works, in the Ribosome notes

  1. Why does EF-Tu hold the amino-acid end of an incoming tRNA while the anticodon reaches down to the codon?

  2. On the ribosome, what does a correct codon–anticodon pair switch on?

  3. After the ribosome forms a peptide bond, the tRNA blank move on the large subunit while the anticodons stay put, giving hybrid A/P and P/E states.

  4. What carries the ribosome's small subunit into its rotated (ratcheted) state after the peptide bond forms?

  5. What does EF-G·GTP do when it first binds the ribosome after the subunits have rotated?

  6. Why must the ribosome move the mRNA by exactly three nucleotides in each cycle?

  7. Why can't a new protein chain fold into domains inside the ribosome's exit tunnel?

Big picture 6

Read this section: Big picture, in the Ribosome notes

  1. One human HeLa cell holds about blank ribosomes.

  2. About how much protein does a human body build each day?

  3. At the mouse stem-cell rate of 5.6 amino acids per second, about how long would one ribosome take to build titin (34,350 amino acids)?

  4. Where does the analogy of the ribosome as 'a 3D printer that reads a tape' break down?

  5. Many ribosomes read one mRNA at once. Why is 'a factory line' a misleading picture of this?

  6. In mouse L929 cells, how does the number of proteins the proteasome destroys per minute compare with the number ribosomes make?

Evidence 6

Read this section: Evidence, in the Ribosome notes

  1. How did Young and Bremer (1976) measure the ribosome's elongation rate in E. coli?

  2. How did Ingolia and colleagues (2011) measure the elongation rate in mouse embryonic stem cells?

  3. Held in optical tweezers, a single E. coli ribosome advanced along an mRNA hairpin by blank per step.

  4. In Pape and colleagues' (1998) kinetics of tRNA selection on E. coli ribosomes, which two steps were slowest?

  5. In the Haloarcula 50S crystal structure with substrate analogues bound, no protein side-chain atom came closer than blank to the forming peptide bond.

  6. Using a sensitive β-galactosidase reporter in E. coli, how low were most missense error rates that Manickam et al. (2014) measured?

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