11.1 Section Objectives – page 281 Section Objectives: Ch. #11.1 • Analyze the structure of DNA • Determine how the structure of DNA enables it to reproduce itself accurately.
Section 11.1 Summary – pages 281 - 287 Although the environment influences how an organism develops, --The genetic information in the molecules of DNA ultimately determines an organism’s traits. --DNA achieves its control by determining the structure of structural proteins and enzymes .
Section 11.1 Summary – pages 281 - 287 • All biological actions depend on proteins called enzymes. • Enzymes control the chemical reactions needed for life. • In the structure of DNA is instructions for making all the proteins for an organism.
Section 11.1 Summary – pages 281 - 287 DNA as the genetic material • In 1952 Alfred Hershey and Martha Chase experimented using radioactively labeled viruses that infect bacteria. • These viruses were made of only protein and DNA.
Section 11.1 Summary – pages 281 - 287 • Hershey/Chase labeled virus DNA with a radioactive isotope for phosphate and the virus protein with an isotope of sulfur. • Following the infection of bacterial cells by the viruses, they showed that DNA, not protein, entered the cells and caused the bacteria to produce new viruses. DNA
Section 11.1 Summary – pages 281 - 287 The structure of nucleotides • DNA is a polymer made of repeating subunits called nucleotides. Nitrogenous base Phosphate group Sugar (deoxyribose) • Nucleotides have three parts: a simple sugar, a phosphate group, and a nitrogenous base.
Section 11.1 Summary – pages 281 - 287 • The simple sugar in DNA, called deoxyribose (dee ahk sih RI bos), gives DNA its name—deoxyribonucleic acid. • The phosphate group is phosphorus surrounded by four oxygen atoms.
Section 11.1 Summary – pages 281 - 287 • A nitrogenous base is a carbon ring structure that contains one or more atoms of nitrogen. • In DNA, there are four possible nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Cytosine (C) Guanine (G) Thymine (T) Adenine (A)
Section 11.1 Summary – pages 281 - 287 • Thus, in DNA there are four possible nucleotides, each containing one of these four bases.
Section 11.1 Summary – pages 281 - 287 • Nucleotides connect to form long chains: -the phosphate group of one nucleotide bonding to the deoxyribose sugar of the next nucleotide. • Phosphate groups and deoxyribose form the backbone of the chain • nitrogenous bases stick out like the teeth of a zipper.
Section 11.1 Summary – pages 281 - 287 • In DNA, the amount of: adenine = thymine guanine = cytosine
Section 11.1 Summary – pages 281 - 287 The structure of DNA • In 1953, James Watson and Francis Crick proposed that DNA is made of two chains of nucleotidesheld together in the middle by nitrogenous bases. • They also proposed that DNA is shaped like a long zipper that is twisted into a coil. Both predictions were true!!
Because DNA is composed of two strands twisted together, its shape is called a double helix.
Section 11.1 Summary – pages 281 - 287 The sequence of nucleotides in DNA is the unique genetic info of an organism. The closer two organisms are related, the more similar their DNA sequences will be. Chromosome
Section 11.1 Summary – pages 281 - 287 Scientists use DNA nucleotide sequences to: • determine evolutionary relationships among organisms • to determine whether two people are related • to identify crime suspects and the bodies of crime victims.
Section 11.1 Summary – pages 281 - 287 Replication of DNA • Before a cell can divide by mitosis or meiosis, it must first make a copy of its chromosomes. • The DNA in the chromosomes is copied in a process called DNA replication.
Section 11.1 Summary – pages 281 - 287 DNA Replication of DNA In replication: • DNA unzips into two separate strands 2. Each old strand (blue) will act as a template for the building of a new strand (red) of DNA Replication Replication
Replication of DNA -each exposed base on the two template strands is paired with a new complementary base to form the two new strands A to T and C to G Pg. 286 Replication
Section 11.1 Summary – pages 281 - 287 • DNA is copied during interphase prior to mitosis and meiosis. • It is important that the new copies are exactly like the original molecules.
Section 1 Check Question 1 What importance did the experiment performed by Alfred Hershey and Martha Chase have in determining what genetic material was? Answer Many scientists believed protein was the genetic material. However, an experiment using radioactively labeled viruses allowed Hershey and Chase to provide convincing evidence that DNA is the genetic material. FL: SC.F.2.4.2
Section 1 Check Question 2 Which of the following is NOT a component of DNA? A. simple sugars B. phosphate groups C. nitrogenous bases D. proteins The answer is D.
Section 1 Check Question 3 Which of the following correctly comprises a complimentary base pair? A. adenine – thymine B. thymine – guanine C. guanine – adenine D. cytosine – thymine The answer is A.