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DNA

DNA. http:// www.youtube.com / watch?feature = player_detailpage&v =M4zHVRLXkgw. Chapter 12- DNA. Section 12.1 Within the cell, DNA must be capable of: Storing Copying Transmitting the genetic information. Before a cell divides, it must make a complete copy of every one of its genes.

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DNA

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  1. DNA http://www.youtube.com/watch?feature=player_detailpage&v=M4zHVRLXkgw

  2. Chapter 12- DNA Section 12.1 Within the cell, DNA must be capable of: Storing Copying Transmitting the genetic information

  3. Before a cell divides, it must make a complete copy of every one of its genes. Genes are transmitted from one generation to the next. DNA molecules must be carefully sorted and passed along during cell division.

  4. Section 12. 2 DNA stands for Deoxyribonucleic acid and is a molecule. DNA is a nucleic acid made up of nucleotides joined into long strands or chains by covalent bonds.

  5. Nucleic acids are made up of smaller subunits, linked together to form long chains. • Nucleotides are the building blocks of nucleic acids. • Nucleotides are made up of three basic components: • A 5-carbon sugar called deoxyribose • A phosphate group • A nitrogenous base.

  6. DNA has four kinds of nitrogenous bases: Adenine (A) Guanine (G) Cytosine (C) Thymine (T)

  7. Chargaff’s Rule A=T G=C Look at the table on page 345 of your book. What do you notice about the numbers?

  8. Franklin’s X-Rays (pg. 346) The X-shaped pattern shows that the strands in DNA are twisted around each other like the coils of a spring, a shape known as a helix. DNA is made of a double helix! Watson and Crick They built a model of DNA, which was a double helix. Two strands of nucleotide sequences were wound around each other.

  9. The Double Helix Model The double-helix model explains Chargaff’s rule of base pairing and how the two strands of DNA are held together. This model can tell us how DNA can function as a carrier of genetic information! The two strands run in OPPOSITE directions- they are antiparallel and come together at the center of the molecule.

  10. Hydrogen Bonding Hydrogen bonds form between nitrogenous bases. Question: Are hydrogen bonds strong or weak?

  11. Hydrogen bonds are weak chemical forces. Question: Why is this important that these bonds are weak?

  12. BONDING If these bonds did not separate, DNA could not be replicated! Bonds form between certain base pairs! Adenine pairs withThymine Guanine pairs with Cytosine This perfect fit is called base pairing!

  13. Section 12.3- DNA Replication Before a cell can divide, the DNA must first be copied. Each base on one strand pairs with one base on the opposite strand. These strands are said to be complimentary! What does that mean?

  14. Mrs. Wald’s Favorite Science Guy! http://www.youtube.com/watch?v=8kK2zwjRV0M

  15. Replication Before a cell divides, it duplicates its DNA in a copying process called REPLICATION. During replication, the DNA molecule separates into two strands and then produces two new complementary strands following the rules of base pairing. Each DNA molecule resulting from replication has one original strand and one new strand.

  16. Base pairing activity!!!

  17. Why are enzymes important? DNA replication is carried out by enzymes! The hydrogen bond between base pairs is broken and the two strands of the molecule unwind. DNA polymerase is an enzyme that joins individual nucleotides to produce a new strand of DNA. DNA polymerase proofreads each new DNA strand.

  18. Let’s take a look at figure 12-8 on page 351.

  19. DNA at the tips of chromosomes are known as telomeres. A special enzyme called telomerase helps to prevent genes from being damaged or lost during replication. DNA replication occurs during the S phase of the cell cycle. What does the S stand for?

  20. Prokaryotic DNA Replication The cells of most prokaryotes have a singe, circular DNA molecule in the cytoplasm, containing nearly all the cell’s genetic information. In prokaryotes, DNA replication does not start until regulatory proteins bind to a single starting point on the chromosome. Replication in most prokaryotic cells starts from a single point and proceeds in two directions until the entire chromosome is copied. http://www.youtube.com/watch?v=HBwyNrkYnp0

  21. Eukaryotic DNA Replication Eukaryotic chromosomes are BIGGER than those of prokaryotes. Replication may begin at dozens or even hundreds of places on the DNA molecule, proceeding in both directions until each chromosome is completely copied! Damaged regions of DNA are sometimes replicated, resulting in changes to DNA base sequences that may alter certain genes.

  22. The two copies of DNA produced by replication in each chromosome remain closely associated until the cell enters prophase of mitosis. In prophase the chromosomes condense and become visible!

  23. During anaphase, these two chromatids will separate from each other, producing two cells, each with a complete set of genes coded in DNA.

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