14 minutes

DNA and Cell Reproduction DNA and Cell Reproduction is organized into short-play learning modules, for concise instruction.

1.Mitosis: Chromosome Condensation (1:04) Shows the remarkable packaging of DNA as it condenses into chromosomes.
2.Mitosis: Stages (2:24) Reviews the chromosome patterns seen at different stages of the mitotic cycle.
3.Cytokinesis (00:30) Shows the basic differences between protist, animal and plant cell division.
4.Meiosis (1:00) Shows how chromosome sorting and crossing over introduces new gene combinations into a population, while achieving the reduction of chromosomes to the haploid number.
5.Nucleotide Structure and Bonding (1:26) Illustrates DNA chemistry, the basis for encoding genetic information in molecular structure.
6.Replication Enzymes (1:02) Demonstrates the chemical steps in DNA replication and shows how each step is accomplished by means of an enzyme.
7.Replicating the Leading and Lagging Strands (1:57) Because the two strands of DNA must be replicated in opposite directions, two different replication strategies are used at each replication fork.
8.Topoisomerase and the Twisting Problem (00:43) To prevent tightening of the helix as it is opened, an enzyme nicks the strand and allows it to rotate, relieving tension and permitting the replication fork to advance.
9.Proofreading and Repair (00:53) Damage to DNA is common, but a fleet of repair enzymes races over the DNA and corrects errors.

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