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Biology 9 Review

Biology 9 Review. DNA Structure and Replication. Genetic Material. You resemble your parents because you have copies of chromosomes from each. Chromosomes are each made up of many genes .

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Biology 9 Review

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  1. Biology 9 Review DNA Structure and Replication

  2. Genetic Material • You resemble your parents because you have copies of chromosomes from each. Chromosomes are each made up of many genes. • Experiments by multiple scientists led to the discovery that DNA is the material in cells that stores genetic information. • Frederick Griffith discovered transformation in cells. Transformation is a change in a genotype caused when cells take up foreign genetic material. • Oswald Avery discovered that DNA is the material responsible for transformation. • Alfred Hershey and Martha Chase DNAis the material that passes down heredity information

  3. Genetic Material • Watson and Crick, two researchers at Cambridge University, determined that a DNA molecule is a double helix; two strands twisted around each other like a winding staircase. • Each strand of DNA is made of linked nucleotides; the subunits that make up DNA.

  4. Each nucleotide has three parts; • a phosphate group, • a five carbon sugar molecule, • and a nitrogen containing base. • The nucleotides link by a weak hydrogen bond.

  5. The five-carbon sugar molecule in the backbone is called deoxyribose. Deoxyribose is the D in DNA. DNA’s full name is deoxyribosenucleicacid • While the sugar molecule and phosphate group that make up the backbone spirals are the same for each nucleotide molecule, the nitrogen bases will be one of four types.

  6. The four nitrogen bases • may be one of the following four • Adenine • Guanine • Cytosine • Thymine

  7. In 1949, Erwin Chagraff discovered that the amount of adenine always equaled the amount of thymine. • Also, the amount of guanine always equaled the amount of cytosine. • Watson and Crick soon after discovered that a purine on one strand of DNA is always paired with a pyrimide on the opposite strand.

  8. We call these pairings base-pairs. • Each rung of the ladder of the staircase design is made up of one of these base-pairs. • Watson and Crick discovered as well that these pairings of the four nitrogen bases are always inspecific base-pairs.

  9. Adenine always pairs with thymine. • Guanine always pairs with cytosine. • We call these two groupings complementary base-pairs

  10. Adenine + thymine. • Guanine +cytosine. • = complementary base-pairs

  11. The process of making an exact copy of DNA is called replication. • Step 1: • Before DNA replication can begin, the double helix unwinds in the first step separating the two strands. • DNA helicasesopen the double helix by breaking the weak hydrogen bonds that linked the nitrogen base-pairs (the rungs of the DNA ladder). • Like opening a zipper, the two sides are unzipped, separating the pairs of complementary bases.

  12. Step 2: • Once the strands are separated, additional proteins attach to each strand, holding them apart and preventing them from returning to their previous double-helix shape. • These areas where the double-helix separates are called replication forks because of their Y shape.

  13. Step 3: • At the replication fork, enzymes known as DNA polymerasesadd nucleotides to the exposed bases, according to the base-pairing rules • (adenine always links to thymine and guanine always links to cytosine). • As the DNA polymerases move along, two new full double-helixes form.

  14. Step 4: • Once the DNA polymerases have begun adding nucleotides to a growing double-helix, the process continues until all of the DNA has been copied. • Than the polymerases receive a signal to detach and we are left with a two new strands of identical DNA. • Replication is complete, each strand identical to the original strand.

  15. In the course of DNA replication, errors sometimes occur and the wrong nucleotide is added to the strand. • A “proofreading” function watches for this in the process and makes corrections before the replication goes farther.

  16. The process checks to make sure the correct nucleotide was added and does not proceed until this is verified. • If is senses a mistake, it backs up, replaces the incorrect nucleotide with the proper one, and only than continues on with replication. • The proofreading reduces mistakes to about one error per 1 billion nucleotides.

  17. Replication does not begin at one end of the DNA molecule and end at the other. • The circular DNA molecules of prokaryotes usually have two replication forks that begin at a single point. • The replication forks move away from each other until they meet on the opposite side of the DNA circle.

  18. In eukaryote cells, each chromosome contains a single long strand of DNA. The length presents a challenge. • To solve this and speed up replication, eukaryote cells replicate in about 100 sections. • Each section has it’s own start and end point. With these 100 replication forks working in sync; the replication takes 8 hours instead of 33 days.

  19. Computer Lab: Review • After completing worksheet Bio_9_Review, go to the computer lab and use the internet to research the following questions and answer them with short two paragraph mini-report. DO NOT CUT, PASTE, OR COPY: USE YOUR OWN WORDS • How are DNA replication and mutations tied together.

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