1)Replication of DNA

Question 1

What kind of replication is used in DNA replication?

Answer 1

Semi-conservative

Question 2

What is DNA?

Answer 2

A unique molecule that can direct its own replication

Question 3

Describe the steps for semi-conservative replication.

Answer 3

Step 1: hydrogen bonds break between the bases, strands separate
Step 2: free nucleotides line up with complementary nucleotides
Step 3: sugar phosphate bonds form, 2 DNA molecules identical to the parent molecule have been formed

Question 4

What is DNA Polymerase?

Answer 4

• adds nucleotides to a growing DNA strand by catalysing the formation of the bond between the sugar of one nucleotide and the phosphate from the next
• can only add 3 nucleotides to the end of a DNA strand

Question 5

What is DNA Ligase?

Answer 5

-joins fragments of DNA together

Question 6

What materials are required for DNA replication?

Answer 6

ATP
Template DNA
Free DNA molecules 
Enzymes: DNA polymerase and DNA ligase
Primers

Question 7

What are primers?

Answer 7

• short sections of RNA nucleotides
• starts off the replication process after the 2 strands unwind
• are added to DNA and the enzyme extends nucleotides from them

Question 8

How are the leading and lagging strand made?

Answer 8

Leading strand: made continuously

Lagging strand: made in fragments, then joined together

Question 9

What are the main steps for copying antiparallel strands?

Answer 9

Step 1: DNA unwound, hydrogen bonds between bases break, DNA is ‘unzipped’

Step 2: 2 replication forks form, opens double strand in opposite directions, bases exposed

Step 3: -leading strand, primer binds to DNA and DNA polymerase adds nucleotides to 3’ end
-DNA polymerase catalyses formation of chemical bond between nucleotides, continues to add nucleotides to 3’ end

Step 4: -lagging strand, primer binds to when exposed DNA, DNA polymerase adds nucleotides to 3’ end

• more DNA exposed, new primer added, DNA polymerase extends new strand until it reaches the previous fragment
• old primer replaced by DNA, enzyme DNA ligase joins fragments together

Question 10

What are the steps for replicating the leading strand?

Answer 10

Step 1: hydrogen bonds break, DNA unzips

Step 2: DNA primer attaches to the start of the piece of DNA being copied

Step 3: DNA polymerase attaches free nucleotides to 3’ end

Step 4: this is a CONTINUOUSLY process till the LEADING STRAND is copied

Question 11

What are the steps for replicating the lagging strand?

Answer 11

Step 1: many primers attach along the strand

Step 2: these are extended by DNA polymerase

Step 3: the fragments are joined by the enzyme LIGASE

Step 4: this is a DISCONTINUOUS process creating the LAGGING STRAND

Question 12

What is the polymerase chain reaction (PCR) and why is it useful?

Answer 12

• used to amplify a DNA sequence of any origin millions of times in a matter of hours
• useful because it is: highly specific, easily automated and capable of amplifying minute amounts of samples

Question 13

What components are needed for the polymerase chain reaction (PCR)?

Answer 13

• buffer (keeps reaction at correct pH)
• nucleotides
• primers (designed and are complementary to the start and end of the sequence to be amplified)
• taq polymerase (enzyme, works at high temps, replaces DNA polymerase)

Question 14

What are the steps for the polymerase chain reaction (PCR)?

Answer 14

Step 1: DNA molecule to be amplified is heated around 95°c, breaking hydrogen bonds between bases

Step 2: the solution is cooled to around 60°c, allows primers to anneal to single strands of DNA

Step 3: the solution is heated to around 72°c, allows extension from primers

Question 15

What are the uses of the polymerase chain reaction (PCR)?

Answer 15

1. Allows amplification of DNA from ancient sources
2. Has forensic applications, minute samples from crime scenes can be amplified from suspects DNA sequences
3. Has medical applications, can diagnose HIV