yacomine_essential biology 3.4 & 7.2 dna replication (hl only)_3211

Essential Biology 03.4 & 7.2: DNA Replication (Core and AHL)

Resources: http://sciencevideos.wordpress.com/bis-ib-diploma-programme-biology/02-the-double-helix/dna-replication/

1. State during which phase of the cell cycle DNA replication occurs. DNA replication occurs in the S-phase of interphase.

2. State the function of DNA replication. DNA replication copies all of the DNA in all of the chromosomes so each daughter cell made through mitosis has a full set of DNA

3. Which of the following is the end product of DNA replication in a human somatic cell?A. 23 chromosomesB. 46 chromosomesC. 23 pairs of chromosomesD. 23 pairs of sister chromatids

Answer: C

4. Describe how mitosis ensures that each new daughter cell is identical (mitosis review). Mitosis ensures that each new daughter cell is identical by aligning at the equator during metaphase and using spindle fibers to separate chromatids during anaphase.

5. Distinguish between initiation of DNA replication in prokaryotes and eukaryotes, with regard to origin of initiation and direction of replication:

Prokaryotes EukaryotesInitiation Single origin, Many points of origin

Direction Bi-directional, around the DNA loop. One direction, along the strand

6. Explain ‘DNA replication occurs in a 5’ to 3’ direction’.

Stephen Taylor Bandung International School http://sciencevideos.wordpress.com

http://sciencevideos.wordpress.com/

http://sciencevideos.wordpress.com/bis-ib-diploma-programme-biology/02-the-double-helix/dna-replication/

http://sciencevideos.wordpress.com/bis-ib-diploma-programme-biology/02-the-double-helix/dna-replication/


This means that the DNA replication starts at the 5’ end of the strand and the 3’ attaches to the next 5’ part of the strand, and the process continues.

Work through some of the animations on the presentation and blog before completing the following questions.

7. Explain the process of DNA Replication (focusing on prokaryotes):

i. DNA Helicase unwinds and unzips the DNA double helix:DNA Polymerase creates complimentary strands.

ii. Distinguish between the lead strand and the lagging strand. The lead strand’s replication is continuous and simpler. The lagging strand’s replication ‘leapfrogs’, and is more complex because it is moving in the opposite direction as the DNA Helicase. RNA primers mark positions.

iii. Explain the role of DNA polymerase on lead strand replication:DNA polymerase puts nucleotides at the end of the complementary strands.




iv. Explain the importance of complementary base pairing in conserving the base-sequence during DNA Replication. The importance of complementary base pairing is that if there is a single mistake, there will either be a mutation, which could strengthen the cell (or cause cancer) or kill the cell.

v. Explain the process of DNA replication on the lagging strand, with reference to RNA primase, primers, DNA polymerase III, Okazaki fragments, DNA polymerase I and DNA ligase. RNA primase places RNA primers, which marks the initiation of DNA polymerase, which attaches to an RNA primer and replicates the DNA in a 5’ to 3’ direction. When it approaches another RNA primer, the DNA polymerase will detach itself from the previous primer and leap over to the new one, and start replicating again. DNA polymerase I then removes the RNA primers. Finally, the Okazaki fragments (the fragments of the DNA strand which the DNA is replicated onto) are joined together with the help of DNA Ligase.




vi. Summarize the roles of the enzymes of DNA Replication:

Enzyme Function

DNA Helicase Unzips and unwinds the DNA double helix and breaks the hydrogen bonds that connect the nitrogenous bases.

DNA Polymerase III Attaches nucleotides in a 5’ to 3’ direction.

RNA Primase Leaves RNA Primase on the lag strand.

DNA Polymerase I Removes RNA primers.

DNA Ligase Puts Okazaki fragments together.

8. Some biochemists are making a mixture of enzymes for DNA replication in the lab. In each of these cases, something was missing from the mixture. For each situation, deduce which one enzyme was missing, with a reason:

a. The DNA produced came out as lots of short sections of DNA, a few hundred base-pairs long, rather than one continuous strand. The DNA Ligase was missing, as it puts the Okazaki fragments together to form a continuous strand.

b. Only the lead strand was replicated.




RNA Primase was missing because it needs to put the RNA primers on the strand to tell the DNA Polymerase to put DNA on the strand.

c. No DNA was replicated. The original DNA remained untouched. The DNA Helicase was missing because it unzips the DNA double helix so that DNA replication can occur.

9. Explain why DNA replication is considered ‘semi-conservative’.

Unwind Unzip Replicate New strands


New strands contain the originalParental strand and one

Copied (complementary) strands

Complementary strand

Parental strand


yacomine_essential biology 3.4 & 7.2 dna replication (hl only)_3211

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