Chromosomes & DNA Replication

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Created by
Mary Rodriguez :)

Cards (16)

  • In prokaryotes, the DNA is located in the cytoplasm, usually as a single circular ring.
  • Eukaryotes have 1000 times the amount of DNA as prokaryotes and it is located in a nucleus, organized into chromosomes. The number of chromosomes varies from species to species.
  • DNA is coiled around proteins called histones which together, form a spaghetti like molecule called chromatin in non-dividing cells.
  • This coiling of DNA into chromatin allows organization of DNA in the nucleus.
  • When a cell divides, the chromatin coils up even tighter into thick visible chromosomes.
  • DNA replication occurs by the mechanism of base pairing.
  • In eukaryotes, replication begins in many places on the DNA strand where it copies faster. Then it proceeds in both directions until each chromosome is completely copied.
  • The replication fork are the sites where the separation of DNA strands and replications occurs.
  • DNA Helicase (enzyme) binds to DNA and breaks the hydrogen bonds between the two nucleotide strands at the replication form. (Many helicases break the strands at multiple places along the DNA)
  • DNA polymerase (enzyme) adds nucleotides to each of the "template" strands from the original DNA, following the base pairing rules. This produces two new complementary strands of DNA.
  • DNA polymerase also "proof-reads" the nucleotide base pairing for mistakes.
  • Each of the DNA mulecules formed consisted of one new strand of nucleotides and one oringinal strand of nucleotides.

  • The two DNA strands are identical to the original DNA strand and to each other.
  • How does the design of DNA ensure that exact copies are made during replication?
    Complementary base pairing.
  • After DNA replication as occurred (and now there are double the number of chromosomes) What happens to each set of chromosomes?
    The cell divides into 2 cells so that each cell receives a full set of the chromosomes.
  • Mutation is the term given to a complementary strand that doesn't match the sequence of bases in the original strand of DNA.