DNA Synthesis

Question 1

Explain the Importance of DNA helix for Semi-conservative replication

Answer 1

• Antiparallel strands allows accurate replication
• Hydrogen bonds between bases - hydrolysed easily
• Base pairing allows accurate replication
• Phospholipid backbone protects from chemical damage to DNA

Question 2

Describe the structure and function of replication origins

Answer 2

• Replication origins are recognised by an initiation complex (group of proteins)
• DNA at replication origin unwinds to form a replication bubble and allows access to the replication machinery

Question 3

What are replication forks?

Answer 3

The position in the replication bubble where DNA unwinds for replication.

Question 4

How many replication origins do bacteria have?

Answer 4

Bacteria have a single replication origin

Question 5

Describe the role of DNA polymerase in DNA replication

Answer 5

• Once the primer has been detected a dNTP (deoxyribose nucleotide triphosphate) is added to the 3’ hydroxyl (OH) group on the template strand
• The 3’ hydroxyl group allows polymerase to start joining the phosphodiester bonds in the 5’ to 3’ of the forming strand

Question 6

Describe the role of Mg 2+ in DNA replication

Answer 6

• Mg 2+ then removes the 2 phosphates from dNTP (deoxyribose nucleotide triphosphate) and the new DNA strand continues to grow
• Mg 2+ makes sure the base is paired correctly

Question 7

How long does the mammalian cell cycle last?

Answer 7

16-24 hours

Question 8

How long does the Bacterial cell cycle last?

Answer 8

20-30 minutes

Question 9

Describe the types of Bacterial DNA polymerase

Answer 9

• I repair
• II repair
• III repair

Question 10

Describe the types DNA polymerase in Eukaryotes

Answer 10

• alpha replication
• beta repair
• gamma mitochondrion
• (Greek E) replication

Question 11

Describe the stages involved in DNA replication

Answer 11

• At the replication origin DNA helical unwinds DNA
• Single stranded binding proteins bind to the newly exposed DNA nucleotides to prevent them from bonding together again
• Topoisomerase prevents DNA from supercoiling
• Primase synthesises primers at both strands
• DNA polymerase builds new strands from the 5’ to 3’ direction it has to bind to new primers separating the lagging strand into fragments (Okazaki fragments)
• primers must be replaced so DNA ligase seals the gaps between Okazaki fragments

Question 12

What enzymes are involved in DNA Synthesis?

Answer 12

• DNA helicase
• DNA polymerase
• Primase
• DNA ligase
• Topoisomerase

Question 13

Describe the structure of Deoxyribose triosphphate

Answer 13

It has the same structure of a nucleotide but it as 3 phosphates instead of 1. It also has any of the 4 bases attached in it.

Question 14

Describe how high fidelity (accuracy) is achieved in DNA replication

Answer 14

• Base pairing in DNA
• Proof-reading by DNA polymerase
• Mismatch repair system - multi enzyme system is highly conserved across species

Question 15

What medical treatments are DNA replication inhibitors used in?

Answer 15

• Antibacterial
• Anti-tumour
• Antiviral