University:
Eastern Kentucky University
Course:
BIO 111 | Cell and Molecular Biology
Academic year:

2022
Views:

313

Pages:

3
Author:

Charlee Buchanan

Model 2 – DNA Replication Direction of DNA helicase Free Nucleotides DNA helicase 11. Examine Model 2. Number the steps below in order to describe the replication of DNA in a cell. 4 ______ Hydrogen bonds between nucleotides form. 1 ______ Hydrogen bonds between nucleotides break. 2 ______ Strands of DNA separate. 3 ______ Free nucleotides are attracted to exposed bases on the loose strands of DNA. 12. Locate the DNA helicase on Model 2. a. What type of biological molecule is DNA helicase? Protein b. What is the role of DNA helicase in the replication of DNA? Breaking the hydrogen bonds between the nitrogen bases separating the DNA 13. What rule is used to join the free nucleotides to the exposed bases of the DNA? A-->T and C-->G 14. This type of replication is called semi-conservative replication. Considering the meaning of these words (semi—half; conserve—to keep), explain why DNA replication is called semi-conservative. DNA Structure and Replication 3 15. DNA molecules can be tens of thousands of base pairs in length. Mistakes in DNA replication lead to mutations, which may or may not be harmful to an organism. How does semi-conservative replication help prevent mutations during DNA replication? They have checkpoints to make sure the DNA replicated properly. 16. The proportions of the bases are consistent within a species; however they do vary between species. Using the base-pair rules, complete the following table to show the percentage of each type of base in the five different organisms. Organism Human Cow Salmon 4 Percentage of each type of base Adenine 31 28 29 Wheat 27 Yeast 31 Guanine Cytosine 19 19 22 22 21 23 19 21 23 19 Thymine 31 28 29 27 31 Extension Questions Model 3 – Timing of DNA Replication If the chromatin were condensed, replicated chromosomes would be visible. (End of S) S G2 If the chromatin were condensed, homologous chromosomes would be visible. (End of G1) Chromosomes are condensed. Matching sisgter chromatids are connected by a centromere. (Beginning of M) M G1 17. According to Model 3, what term refers to loose DNA inside of a nucleus? Chromatin 18. During what part of the cell cycle is the DNA in a cell’s nucleus replicated? S-phase 19. During what part of the cell cycle is the DNA in a cell condensed into chromosomes? Mitosis (Prophase) 20. Replicated chromosomes are often illustrated as an X shape to match how they look in real life just before cell division. a. According to Model 3, which of the following diagrams correctly show an original set of homologous chromosomes (grey) and their sister chromatids (black)—the replicated portion? b. What structure holds the two sister chromatids together as they prepare for cell division? Centromere DNA Structure and Replication 5