Lesson test: Reading it out

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Reading it out

1.[3p]
Brenner, Jacob and Meselson found that new phage RNA associated with pre-existing heavy ribosomes. What did that establish?

Ribosomes are generic readers and the specificity lies in the message

Correct

Each ribosome is specialised for one protein

The answer is: Ribosomes are generic readers and the specificity lies in the message

Phage DNA is translated directly without an intermediate

The answer is: Ribosomes are generic readers and the specificity lies in the message

Ribosomes are made afresh for each new protein

The answer is: Ribosomes are generic readers and the specificity lies in the message

2.[3p]
Why does DNA use thymine when RNA uses uracil?

Cytosine deaminates spontaneously to uracil, so any uracil found in DNA can be recognised as damage and removed

Correct

Thymine forms three hydrogen bonds with adenine and uracil forms two

The answer is: Cytosine deaminates spontaneously to uracil, so any uracil found in DNA can be recognised as damage and removed

Uracil cannot be synthesised in the nucleus

The answer is: Cytosine deaminates spontaneously to uracil, so any uracil found in DNA can be recognised as damage and removed

Thymine is cheaper to make than uracil

The answer is: Cytosine deaminates spontaneously to uracil, so any uracil found in DNA can be recognised as damage and removed

3.[1p]
RNA polymerase proofreads as carefully as DNA polymerase does.

True

The answer is: False

False

Correct

4.[2p]
What is a sigma factor, and why is it detachable?

A subunit that recognises the promoter and then releases, so a cell can redirect transcription by swapping which one is loaded

Correct

A subunit that catalyses bond formation and is reused

The answer is: A subunit that recognises the promoter and then releases, so a cell can redirect transcription by swapping which one is loaded

A protein that degrades unwanted messages

The answer is: A subunit that recognises the promoter and then releases, so a cell can redirect transcription by swapping which one is loaded

A repressor that blocks the operator

The answer is: A subunit that recognises the promoter and then releases, so a cell can redirect transcription by swapping which one is loaded

5.[2p]
A bacterial message has a half-life of five minutes. What fraction remains thirty minutes after transcription stops? Give a decimal.

CorrectNot quite: 0.016

6.[3p]
Roberts and Sharp hybridised a mature adenovirus mRNA to its gene and looked at it under an electron microscope. What did they see?

Loops of unpaired DNA, showing that stretches of the gene are absent from the message

Correct

A simple continuous double-stranded line

The answer is: Loops of unpaired DNA, showing that stretches of the gene are absent from the message

Two separate hybrids of equal length

The answer is: Loops of unpaired DNA, showing that stretches of the gene are absent from the message

No hybrid at all

The answer is: Loops of unpaired DNA, showing that stretches of the gene are absent from the message

7.[3p]
Match each modification of a eukaryotic transcript to its purpose.

The 5' cap
The poly(A) tail
Splicing
Export through the nuclear pore

removes introns and joins exons
protects the 3' end and sets the message's lifetime
acts as a quality control gate
protects that end and marks it for ribosome loading

Show the answer

The 5' cap: protects that end and marks it for ribosome loading The poly(A) tail: protects the 3' end and sets the message's lifetime Splicing: removes introns and joins exons Export through the nuclear pore: acts as a quality control gate

8.[2p]
The Dscam gene of the fruit fly offers 12, 48, 33 and 2 alternatives at four positions. How many distinct messages can it produce?

CorrectNot quite: 38016

9.[2p]
Which are given as advantages of having genes interrupted by introns?

Select all that apply

Alternative splicing lets one gene specify several proteins

Correct

Splicing choices can themselves be regulated

Correct

Recombination within introns can shuffle protein modules between genes

Correct

Introns reduce the energetic cost of transcription

The answer is: Alternative splicing lets one gene specify several proteins, Splicing choices can themselves be regulated, Recombination within introns can shuffle protein modules between genes

1.[3p] Brenner, Jacob and Meselson found that new phage RNA associated with pre-existing heavy ribosomes. What did that establish?

2.[3p] Why does DNA use thymine when RNA uses uracil?

3.[1p] RNA polymerase proofreads as carefully as DNA polymerase does.

4.[2p] What is a sigma factor, and why is it detachable?

5.[2p] A bacterial message has a half-life of five minutes. What fraction remains thirty minutes after transcription stops? Give a decimal.

6.[3p] Roberts and Sharp hybridised a mature adenovirus mRNA to its gene and looked at it under an electron microscope. What did they see?

7.[3p] Match each modification of a eukaryotic transcript to its purpose.

8.[2p] The Dscam gene of the fruit fly offers 12, 48, 33 and 2 alternatives at four positions. How many distinct messages can it produce?

9.[2p] Which are given as advantages of having genes interrupted by introns?

1.[3p]
Brenner, Jacob and Meselson found that new phage RNA associated with pre-existing heavy ribosomes. What did that establish?

2.[3p]
Why does DNA use thymine when RNA uses uracil?

3.[1p]
RNA polymerase proofreads as carefully as DNA polymerase does.

4.[2p]
What is a sigma factor, and why is it detachable?

5.[2p]
A bacterial message has a half-life of five minutes. What fraction remains thirty minutes after transcription stops? Give a decimal.

6.[3p]
Roberts and Sharp hybridised a mature adenovirus mRNA to its gene and looked at it under an electron microscope. What did they see?

7.[3p]
Match each modification of a eukaryotic transcript to its purpose.

8.[2p]
The Dscam gene of the fruit fly offers 12, 48, 33 and 2 alternatives at four positions. How many distinct messages can it produce?

9.[2p]
Which are given as advantages of having genes interrupted by introns?