Lesson test: Copying it

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Copying it

1.[2p]
After one round of replication in light medium, Meselson and Stahl saw a single band at intermediate density. Which hypothesis did that rule out?

Conservative replication

Correct

Semiconservative replication

The answer is: Conservative replication

Dispersive replication

The answer is: Conservative replication

Both semiconservative and dispersive

The answer is: Conservative replication

2.[3p]
What did the second generation show?

Two bands, half hybrid and half light, which is what semiconservative copying predicts and dispersive copying does not

Correct

One band at three-quarters light density

The answer is: Two bands, half hybrid and half light, which is what semiconservative copying predicts and dispersive copying does not

One band at fully heavy density

The answer is: Two bands, half hybrid and half light, which is what semiconservative copying predicts and dispersive copying does not

Three bands of equal intensity

The answer is: Two bands, half hybrid and half light, which is what semiconservative copying predicts and dispersive copying does not

3.[3p]
Why does DNA polymerase synthesise only in the 5' to 3' direction?

The energy comes from the incoming nucleotide, so the growing chain needs a free 3' hydroxyl, and this is also what makes proofreading possible

Correct

Because the two strands are antiparallel

The answer is: The energy comes from the incoming nucleotide, so the growing chain needs a free 3' hydroxyl, and this is also what makes proofreading possible

Because RNA primers can only be laid down in that direction

The answer is: The energy comes from the incoming nucleotide, so the growing chain needs a free 3' hydroxyl, and this is also what makes proofreading possible

Because the enzyme cannot bind the 5' end of a template

The answer is: The energy comes from the incoming nucleotide, so the growing chain needs a free 3' hydroxyl, and this is also what makes proofreading possible

4.[1p]
DNA polymerase can begin a new chain from scratch, without a primer.

True

The answer is: False

False

Correct

5.[3p]
E. coli replicates 4,641,652 base pairs from one origin using two forks at 1000 nucleotides per second. How many minutes does one round take?

CorrectNot quite: 38.7

6.[3p]
Match each fidelity mechanism to the improvement it contributes.

Base selection by the polymerase active site
Proofreading by the 3' to 5' exonuclease
Mismatch repair after the fork has passed
All three together

about one error in $10^{5}$
about one error in $10^{9}$
a further factor of about 100
a further factor of 100 to 1000

Show the answer

Base selection by the polymerase active site: about one error in $10^{5}$ Proofreading by the 3' to 5' exonuclease: a further factor of about 100 Mismatch repair after the fork has passed: a further factor of 100 to 1000 All three together: about one error in $10^{9}$

7.[2p]
At $1.2 \times 10^{- 8}$ mutations per base per generation across 6.4 billion base pairs, how many new mutations does a child carry?

CorrectNot quite: 77

8.[3p]
Which are true of telomeres and telomerase?

Select all that apply

The end replication problem arises because the last RNA primer on the lagging strand cannot be replaced

Correct

Telomerase carries its own RNA template and writes DNA from it

Correct

Telomerase is reactivated in around ninety per cent of human cancers

Correct

Circular bacterial chromosomes also require telomeres

The answer is: The end replication problem arises because the last RNA primer on the lagging strand cannot be replaced, Telomerase carries its own RNA template and writes DNA from it, Telomerase is reactivated in around ninety per cent of human cancers

9.[2p]
Why do fluoroquinolone antibiotics and drugs such as etoposide both cause DNA breaks?

They trap a topoisomerase after it has cut the DNA and before it has resealed it

Correct

They cut DNA directly by chemical attack

The answer is: They trap a topoisomerase after it has cut the DNA and before it has resealed it

They prevent helicase from unwinding the helix

The answer is: They trap a topoisomerase after it has cut the DNA and before it has resealed it

They deplete the cell of nucleotides

The answer is: They trap a topoisomerase after it has cut the DNA and before it has resealed it

1.[2p] After one round of replication in light medium, Meselson and Stahl saw a single band at intermediate density. Which hypothesis did that rule out?

2.[3p] What did the second generation show?

3.[3p] Why does DNA polymerase synthesise only in the 5' to 3' direction?

4.[1p] DNA polymerase can begin a new chain from scratch, without a primer.

5.[3p] E. coli replicates 4,641,652 base pairs from one origin using two forks at 1000 nucleotides per second. How many minutes does one round take?

6.[3p] Match each fidelity mechanism to the improvement it contributes.

7.[2p] At 1.2×10-8 mutations per base per generation across 6.4 billion base pairs, how many new mutations does a child carry?

8.[3p] Which are true of telomeres and telomerase?

9.[2p] Why do fluoroquinolone antibiotics and drugs such as etoposide both cause DNA breaks?

1.[2p]
After one round of replication in light medium, Meselson and Stahl saw a single band at intermediate density. Which hypothesis did that rule out?

2.[3p]
What did the second generation show?

3.[3p]
Why does DNA polymerase synthesise only in the 5' to 3' direction?

4.[1p]
DNA polymerase can begin a new chain from scratch, without a primer.

5.[3p]
E. coli replicates 4,641,652 base pairs from one origin using two forks at 1000 nucleotides per second. How many minutes does one round take?

6.[3p]
Match each fidelity mechanism to the improvement it contributes.

7.[2p]
At $1.2 \times 10^{- 8}$ mutations per base per generation across 6.4 billion base pairs, how many new mutations does a child carry?

8.[3p]
Which are true of telomeres and telomerase?

9.[2p]
Why do fluoroquinolone antibiotics and drugs such as etoposide both cause DNA breaks?