2.5 - What can go wrong with DNA?

Question 1

What is the process of DNA replication?

Answer 1

1. DNA double helix unwinds from one end so that the 2 strands split
2. DNA helicase enzyme makes this happen
3. each strand acts as a template
4. free floating monnucleotids join to each original strand using complementary base pairing
5. mononucleotides are joined together by DNA polymerase enzyme
6. hydrogen bond form between bases on original & new strand
7. new DNA molecule has one strand from orignical DNA & one new strand. both strands are identical

Question 2

What type of replication is DNA replication?

Answer 2

semi-conservative

Question 3

What was the method of Meselson & Stahl’s experiment?

Answer 3

1. Bacterias are initially fed on heavy nitrogen
2. Bacteria are then fed on light nitrogen
3. DNA is extracted and separated by centrifugation after one and two cell cycles
4. DNA from the start shows up as single band of heavy DNA
5. DNA extracted after one cycle of replication shows up as a single band of intermediate DNA
6. DNA extracted after two cycles of replication shows as one band of intermediates and one band of light DNA

Question 4

What were the first 2 results of Meselson & Stahl’s experiment, when they grew the bacteria in separate mediums of N14 & N15?

Answer 4

• 15N is heavy so has a higher density & sinks further down the tube
• 14N is lighter so has a lower density & settle higher up in the tube

Question 5

What did Meselson & Stahl do after growing the bacteria in mediums of N14 & N15 separately?

Answer 5

took a sample of the bacteria growing on N15 & grew it on N14 - allowing it to do one round of DNA replication

Question 6

What the results after Meselson & Stahl grew the N14/N15 hybrid? What did this mean?

Answer 6

a band formed in the middle of the centrifuge in between where the heavy & light bands had previously formed - DNA must have replicated semi-conservatively

Question 7

After the 14/15 band had formed, what did Meselson & Stahl do next? What were their results?

Answer 7

grew another generation of bacteria on the N14 - formed 2 bands, one light band & one 14/15 band

Question 8

Define frameshift

Answer 8

when bases are inserted or deleted causing all of the triplets that follow to be incorrect

Question 9

What are 3 differences between replication of DNA and transcription of DNA?

Answer 9

1. replication involves DNA nucleotides, whereas transcription involves RNA nucleotides
2. replication produces doubled stranded DNA molecules, whereas transcription produces single stranded RNA molecule
3. replication uses DNA polymerase whereas transcription requires RNA polymerase

Question 10

What are the errors in DNA replication called?

Answer 10

point mutations

Question 11

What are the 3 types of mutations called?

Answer 11

1. deletions
2. insertions
3. substitutions

Question 12

What are 2 inherited diseases caused by a gene mutation?

Answer 12

1. sickle cell anaemia
2. cystic fibrosis

Question 13

Which chromosome is the CF gene on?

Answer 13

7

Question 14

What are 2 ways mutations can affect the CFTR protein?

Answer 14

1. ATP cannot bind & open ion channel
2. ion channel is open but Cl cannot move through
3. 3 nucleotides are deleted, which means phenylalanine is not included & protein is not correctly folded

Question 15

What is the mutation called when 3 nucleotides are deleted, which means phenylalanine is not included and the protein is not correctly folded?

Answer 15

DF508