Mark Biodiversity HW. 3.2.2 DNA Structure Lesson 1 Structure of DNA.
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Mark Biodiversity HW 3.2.2 DNA Structure Lesson 1 Structure of DNA 3.2.2 DNA is an information-carrying molecule. Its sequence of bases determines the structure of proteins, including enzymes. Structure of DNA The double-helix structure of DNA, enabling it to act as a stable information- carrying molecule, in terms of the components of DNA nucleotides: deoxyribose, phosphate and the bases adenine, cytosine, guanine and thymine two sugar-phosphate backbones held together by hydrogen bonds between base pairs specific base pairing. Genes and polypeptides A gene occupies a fixed position, called a locus, on a particular strand of DNA. Genes are sections of DNA that contain coded information as a specific sequence of bases. Genes code for polypeptides that determine the nature and development of organisms. The base sequence of a gene can change as a result of a mutation, producing one or more alleles of the same gene. A sequence of three bases, called a triplet, codes for a specific amino acid. The base sequence of a gene determines the amino acid sequence in a polypeptide. In eukaryotes, much of the nuclear DNA does not code for polypeptides. There are, for example, introns within genes and multiple repeats between genes. Differences in base sequences of alleles of a single gene may result in non-functional proteins, including non- functional enzymes. DNA and chromosomes In eukaryotes, DNA is linear and associated with proteins. In prokaryotes, DNA molecules are smaller, circular and are not associated with proteins. Meiosis The importance of meiosis in producing cells which are genetically different. Within this unit, meiosis should be studied only in sufficient detail to show the formation of haploid cells independent segregation of homologous chromosomes. Gametes are genetically different as a result of different combinations of maternal and paternal chromosomes genetic recombination by crossing over. Discovery of DNA How do we know that the unit of inheritance in DNA, and how do we know what it looks like? TIMELINE Use the information on this page to draw a time line In 1865 Gregor Mendel performed the pea plant experiment, selectively choosing the phenotype. In 1875, Strassburger identified Chromosomes. Using Mieschers previous work on nucleic acids, in 1885 Kossel identified the structure of Nucleic Acids. IN 1940, Beadle and Tatum proposed that enzymes decide the genetic sequence. In 1944 Avery and Macleod identified, using viruses, that it is DNA that determines the genetic information. 1950, Chargaff identified the complementary bases of DNA. IN 1952, Hershey and Chase carried on from Avery and Macleods work, confirming that DNA must be genetic information Rosalind Franklin identified DNA molecules using X-ray photography. Watson and Crick, at Oxford University, used this information by Franklin, and work by Wilkins, to contruct the DNA double helix that we still use to this day. STRUCTURE OF DNA Name 2 types of Sugar Molecules DNA and Chromosomes 1.What is DNA? 2.What are genes? 3.What are chromosomes? 4.Where are chromosomes stored? 5.How many chromosomes are there in the human cells? 6.Why is this number important? 7.What is mitosis (asexual reproduction)? 8.What is meiosis (sexual reproduction)? Genes and DNA What is DNA? What is a gene? What is a genotype? What is a phenotype? Function of DNA and Chromosomes Draw a DNA Molecule STRUCTURE OF DNA Introduction to nucleotides Nucleotides are nitrogen-containing organic substances that form the basis of the nucleic acids DNA and RNA. All nucleotides contain the following three groups: In DNA the sugar is deoxyribose, whereas in RNA the sugar is ribose. a phosphate group a pentose sugar a nitrogen- containing base Structure of a Gene Introns Introns and Exons BASES Purine or Pyrimidine ADENINE GUANINE THYMINE (URACIL) CYTOSINE Bases There are five bases, split into two types: adenine (A) and guanine (G) are purine bases. AG TU thymine (T), cytosine (C) and uracil (U) are pyrimidine bases. DNA contains A, G, T and C, whereas RNA contains A, G, U and C. C QUESTION If 19.9 % of the bases in a human are Adenine. What percentage are T,C and G? Joining of Nucleic Acids Have a guess the name of the reaction that joins two nucleic acids together? CONDENSATION REACTION BETWEEN THE PHOSPHATE GROUP AND AN OH GROUP ON THE SUGAR MOLECULE