Lesson test: The code and the ribosome

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The code and the ribosome

1.[1p]
How many codons are possible with four bases read three at a time?

CorrectNot quite: 64

2.[3p]
Three single-base insertions in the same gene restored function, while one or two destroyed it. What does that show?

The message is read in non-overlapping groups of three from a fixed starting point

Correct

The code is overlapping

The answer is: The message is read in non-overlapping groups of three from a fixed starting point

Insertions are repaired by the cell

The answer is: The message is read in non-overlapping groups of three from a fixed starting point

Each base specifies one amino acid

The answer is: The message is read in non-overlapping groups of three from a fixed starting point

3.[2p]
Nirenberg and Matthaei added polyuridylic acid to a cell-free extract. What was made?

A polypeptide of nothing but phenylalanine

Correct

A polypeptide of nothing but lysine

The answer is: A polypeptide of nothing but phenylalanine

A mixture of all twenty amino acids

The answer is: A polypeptide of nothing but phenylalanine

No polypeptide at all

The answer is: A polypeptide of nothing but phenylalanine

4.[2p]
The genetic code is arranged so that a single base change is disproportionately likely either to be silent or to substitute a chemically similar amino acid.

True

Correct

False

The answer is: True

5.[3p]
Chapeville converted cysteine attached to its own tRNA into alanine, then fed it into a translation system. Where did the alanine appear?

At cysteine codons, because the ribosome reads the anticodon and never inspects the amino acid

Correct

At alanine codons, because the ribosome checks the amino acid

The answer is: At cysteine codons, because the ribosome reads the anticodon and never inspects the amino acid

Nowhere, because the charged tRNA was rejected

The answer is: At cysteine codons, because the ribosome reads the anticodon and never inspects the amino acid

At random positions throughout the protein

The answer is: At cysteine codons, because the ribosome reads the anticodon and never inspects the amino acid

6.[3p]
How does isoleucyl-tRNA synthetase reject valine, which differs by a single methylene group, at one part in forty thousand?

A double sieve: a synthetic site too small for anything larger, and an editing site that hydrolyses anything smaller

Correct

By binding isoleucine forty thousand times more tightly

The answer is: A double sieve: a synthetic site too small for anything larger, and an editing site that hydrolyses anything smaller

By checking the finished protein and removing errors

The answer is: A double sieve: a synthetic site too small for anything larger, and an editing site that hydrolyses anything smaller

By refusing to bind any tRNA until valine has been consumed

The answer is: A double sieve: a synthetic site too small for anything larger, and an editing site that hydrolyses anything smaller

7.[3p]
What did the atomic structures of the ribosome show about its catalytic centre?

There is no protein within about 1.8 nm of it, so the catalyst is RNA

Correct

It is built from three ribosomal proteins acting together

The answer is: There is no protein within about 1.8 nm of it, so the catalyst is RNA

It contains a metal ion cofactor and no macromolecule

The answer is: There is no protein within about 1.8 nm of it, so the catalyst is RNA

It is formed by the transfer RNA rather than by the ribosome

The answer is: There is no protein within about 1.8 nm of it, so the catalyst is RNA

8.[2p]
Each peptide bond costs four high-energy phosphates. How many are needed for a protein of 300 residues?

CorrectNot quite: 1200

9.[3p]
Match each figure of translation to its value.

Bacterial elongation rate
Error rate per codon
Chance of an error in a 300-residue protein
Codons that specify stop

15 to 20 amino acids per second
about one in $10^{4}$
three
about 3 per cent

Show the answer

Bacterial elongation rate: 15 to 20 amino acids per second Error rate per codon: about one in $10^{4}$ Chance of an error in a 300-residue protein: about 3 per cent Codons that specify stop: three

1.[1p] How many codons are possible with four bases read three at a time?

2.[3p] Three single-base insertions in the same gene restored function, while one or two destroyed it. What does that show?

3.[2p] Nirenberg and Matthaei added polyuridylic acid to a cell-free extract. What was made?

4.[2p] The genetic code is arranged so that a single base change is disproportionately likely either to be silent or to substitute a chemically similar amino acid.

5.[3p] Chapeville converted cysteine attached to its own tRNA into alanine, then fed it into a translation system. Where did the alanine appear?

6.[3p] How does isoleucyl-tRNA synthetase reject valine, which differs by a single methylene group, at one part in forty thousand?

7.[3p] What did the atomic structures of the ribosome show about its catalytic centre?

8.[2p] Each peptide bond costs four high-energy phosphates. How many are needed for a protein of 300 residues?

9.[3p] Match each figure of translation to its value.

1.[1p]
How many codons are possible with four bases read three at a time?

2.[3p]
Three single-base insertions in the same gene restored function, while one or two destroyed it. What does that show?

3.[2p]
Nirenberg and Matthaei added polyuridylic acid to a cell-free extract. What was made?

4.[2p]
The genetic code is arranged so that a single base change is disproportionately likely either to be silent or to substitute a chemically similar amino acid.

5.[3p]
Chapeville converted cysteine attached to its own tRNA into alanine, then fed it into a translation system. Where did the alanine appear?

6.[3p]
How does isoleucyl-tRNA synthetase reject valine, which differs by a single methylene group, at one part in forty thousand?

7.[3p]
What did the atomic structures of the ribosome show about its catalytic centre?

8.[2p]
Each peptide bond costs four high-energy phosphates. How many are needed for a protein of 300 residues?

9.[3p]
Match each figure of translation to its value.