4.2 DNA Replication

Question 1

What happens when the body grows or heals itself?

Answer 1

cells divide and each new cell requires an exact copy of the DNA contained in the chromosomes

Question 2

What is DNA replication?

Answer 2

the process of copying one DNA double helix into two identical double helices

Question 3

What does DNA polymerase do in DNA replication?

Answer 3

uses each original strand as a template for the formation of a complementary new strand

Question 4

Why is DNA replication termed semiconservative?

Answer 4

because a new double helix has one conserved old strand and one new strand

Question 5

What does DNA replication result in?

Answer 5

2 DNA helices that are identical to each other and to the original molecule

Question 6

Describe the steps in DNA replication. (5)

Answer 6

1. DNA helicase unwinds and “unzips” the double-stranded DNA by breaking the weak hydrogen bonds between the paired bases
2. new complementary DNA nucleotides (always present in nucleus) fit into place by the process of complementary base pairing, these are positioned and joined by DNA polymerase
3. because the strands of DNA are oriented in an antiparallel configuration and the DNA polymerase may add new nucleotides only to one end of the chain, DNA synthesis occurs in opposite directions.
   LEADING STRAND follows the helicase enzyme while synthesis on the LAGGING STRAND results in the formation of short segments of DNA called OKAZAKI FRAGMENTS
4. to complete replication, enzyme DNA ligase connects the Okazaki fragments and seals any breaks in the sugar-phosphate backbone
5. the two double helix molecules are identical to each other and to the original DNA molecule

Question 7

Why is DNA replication necessary?

Answer 7

when cells divide, each new cell requires a copy of the DNA

cells must make new copies of themselves and replicate their DNA so the organisms can have new cells with healthy DNA when they grow, repair their cells and replace old and damaged cells

Question 8

Summarize DNA replication steps.

Answer 8

1. DNA helicase enzyme separates the DNA strands by breaking the hydrogen bonds between bases.
2. DNA polymerase enzyme catalyzes incorporation of new nucleotides by complementary base pairing.
3. DNA polymerase can only add nucleotides to one end of the growing chain. Therefore, replication is different for each strand. Leading strand synthesis follows the helicase enzyme. Lagging strand synthesis results in formation of Okazaki fragments.
4. DNA ligase connects the Okazaki fragments and seals any breaks in the sugar-phosphate backbone.