17. Relationship between genes and the phenotype

Question 1

In an error is made during DNA replication how can it be repaired on the spot?

Answer 1

The DNA polymerase can go backwards 3’ to 5’ and cut out an error and replace the base

Question 2

What is a mismatch error in DNA replication?

Answer 2

During DNA replication a nucleotide was mispaired and missed in proofreading

Question 3

How are mismatch errors repaired during DNA replication?

Answer 3

1. The mismatch repair proteins excise the mismatched nucleotide and some adjacent nucleotides
2. DNA polymerase I adds the correct nucleotides
3. DNA ligase repairs the remaining nick

Question 4

What is an excision error?

Answer 4

Where a nucleotide in the DNA is damaged (creating a bubble)

Question 5

How is an excision repaired in DNA replication?

Answer 5

1. The excision repair proteins excise the damaged nucleotide and some adjacent nucleotides
2. DNA polymerase I adds the correct nucleotides by 5’ to 3’ replication of the short strand
3. In the last step DNA ligase repairs the remaining nick

Question 6

What does the polymerase chain reaction do?

Answer 6

PCR mimics DNA replication, but you need to know something about the sequence to design the primers

Question 7

What is the process of PCR?

Answer 7

1. DNA is made single stranded by heating to 95oC
2. Primers complementary to the ends of the region of interest are annealed (3’ end)
3. A DNA polymerase (taq polymerase) adds new bases complementary to the template DNA
4. A sequence of DNA can be amplified millions of types after several PCR cycles

Question 8

What happens if there is a block in a biochemical pathway?

Answer 8

Wherever the block is, the compound prior to that accumulates

Question 9

How does dwarfism arise?

Answer 9

When there is a block in converting tyrosine to thyroxine

Question 10

How does albinism arise?

Answer 10

When there is a block in converting tyrosine to melanin

Question 11

How does phenylketonuria arise?

Answer 11

When there is a block in converting phenylalanine to tyrosine and phenylpyruvic acid is produced

Question 12

What is a prototroph?

Answer 12

Grows on minimal media

Question 13

What is an auxotroph?

Answer 13

Requires a supplement in the medium