DNA Replication

Question 1

what is replication?

Answer 1

Replication occurs before cell division because the new, daughter cell will also need a complete copy of cellular DNA.

Question 2

what is the purpose of DNA?

Answer 2

• make enzymes
• the proteins build the cell structures
• the DNA controls which enzymes are made and the enzymes determine what reactions take place
• the structures and reactions in the cell determine what sort of a cell it is and what its function is

Question 3

What is step unwiding in DNA replication?

Answer 3

1) unwiding/ seperation of DNA strands

• begins at origins of replication
• two strands open forming replication forks (y shaped region)
• new strands grow at the forks
• DnA helicase: enzyme which catalyzes the unwinding and seperation (breaking H-Bonds) of the Parental double helix

Question 4

What is replication in DNA replication?

Answer 4

2) replication/ initaiation

• as the DNA strands open at the origin, replication bubbles form
• prokaryotes (bacteria) have a single bubble
• Eukaryotic chromosones have many bubbles

Question 5

What is initiation in DNA replication?

Answer 5

initiation

• initiation does not start at one end of the double helix strand and finish at the other end
• There are particular sequences in the DNA molecule at which replication is initiated. These are called origins of replication.
• These are targeted as the origin points for unzipping DNA to start replication.
• DNA helicase attaches at these origin points, unzipping and unwinding the DNA by breaking the hydrogen bond holding the two DNA strands together.
• The unzipped DNA forms a replication fork which moves apart (in teo directions), forming a replication bubble.

Question 6

what is the first step in DNA replication?

Answer 6

unwinding/ separation, replication, initiation

Question 7

What is the priming in DNA replication?

Answer 7

• RNA primers (enzyme): before new DnA strands can form, there must be small preexisting primers (rNA) presnt to addition of new nucleotides 9DNA polymerase).
• The leading Strand froms from the midd;e of the fork. DNA polymerase adds nucleotides to the 3’ end, allowing continous etension of the complementary DNA molecule (it leads the way).

Question 8

What is step 2 of DNA replication?

Answer 8

Priming

Question 9

what is step 3 of DNA replication?

Answer 9

Syntheis of DNA strands?

Question 10

What is the synthesis in DNA replication?

Answer 10

Synthesis of New DNA strands

• The lesding strand is synthesised as a single strand from the point of origin toward tghe opening replication fork
• leading strand: syntheised as a single polymer in the 5’ to 3’ direction
• dna polymerase can only synthesise dna in one direction by adding nucleotides to the 3’ prime end of the template DNA

Question 11

What is step four of DNA replication?

Answer 11

4) DNa replication: leading & lagging strand identificationm

• strand synthesis proceeds smoothly as the replication for unzips
• strand syntheis away from the replication fork (Okazaki fragments): joined by DNA ligase.

Question 12

What is step five of DNA replication?

Answer 12

• NDA polymerase initially makes about 1 in 10,000 base pairing errors
• Enzymes proofread and correct these mistakes
• The new error rate for DNA that has been proofread is 1 in 1 billion base pairing errors.

Question 13

What is step six of DNA replication?

Answer 13

• Chemicals and UV radiation damage DNA in our body cells
• Cells must consistently repair DAMAGED DNA`
• Excision repair occurs when any of over 50 repair enzymes remove damaged parts of DNA
• DNA polymerase and DNA ligase replace and bond the new nucleotides together.