Lecture 4- Structure and Organization of DNA PDF

DNA Organization in Chromosomes. Presented by Dr. Joanne Sadier  Do you know where remains the difference between those people?  Introduction to Genetics  What is the importance of genetics? Genetics Is Important to Individuals, to Society, and to the Study of Biology ...

DNA Organization in Chromosomes. Presented by Dr. Joanne Sadier  Do you know where remains the difference between those people?  Introduction to Genetics  What is the importance of genetics? Genetics Is Important to Individuals, to Society, and to the Study of Biology  Frequency Case 0.200 Odds ratio: 1.26 Control 0.165 1. Eye-catching headline of the form “Gene for…” 2. Highly qualified factual paragraph  Genetic variation  The variant eye color gene discovered in Drosophila is an allele of a gene controlling eye color.  Alleles are defined as alternative forms of a gene. Different alleles may produce differences in the observable features, or phenotype, of an organism.  The set of alleles for a given trait carried by an organism is called the genotype. Thomas Hunt Morgan used the fruit fly, Drosophila melanogaster, to study genetics  Dominant vs. Recessive A dominant allele is expressed even if it is paired with a recessive allele. A recessive allele is only visible when paired with another recessive allele. 7  Hypothetical Chromosomes  Every gene has its place, or locus, on a chromosome  Genotype is the combination of alleles found in an organism  Phenotype is the visible expression of the genotype  Wild-type phenotype is the most common or generally accepted standard  Mutant alleles are usually recessive 1-8 The Search for the Chemical Nature of Genes: DNA or Protein? DNA holds the genetic information  Structure of DNA  Discovery of the Double Helix Launched the Era of Molecular Genetics  The DNA; double helix ▪ Deoxyribonucleic Acid (DNA); the genetic material of all cellular organisms and most viruses. ▪ DNA; the gigantic molecule which is used to encode genetic information for all life on Earth. ▪ DNA responsible for preserving, copying and transmitting information within cells and from generation to generation. ▪ The curving sides of the ladder represent the sugar-phosphate backbone of the two DNA strands; the rings are the base pairs. ▪ Possess antiparallel polarity. ▪ Stabilized by hydrogen bonds between the bases.  Nucleic Acids Nucleic acids are polymers of nucleotides. Two varieties of nucleic acids: DNA (deoxyribonucleic acid) Genetic material that stores information for its own replication and for the sequence of amino acids in proteins RNA (ribonucleic acid) Performs a wide range of functions within cells which include protein synthesis and regulation of gene expression  Figure 1-5 Central Dogma © 2017 Pearson Education, Ltd.  Structure of DNA and RNA Table 3.4 DNA Structure Compared to RNA Structure DNA RNA Sugar Deoxyribose Ribose Adenine, guanine, Adenine, guanine, uracil, Bases thymine, cytosine cytosine Strands Double stranded with Single stranded base pairing Helix Yes No  Structure of a Nucleotide Each nucleotide is composed of three parts: A phosphate group A pentose sugar A nitrogen-containing (nitrogenous) base There are five types of nucleotides found in nucleic acids. DNA contains adenine, guanine, cytosine, and thymine. RNA contains adenine, guanine, cytosine, and uracil.  Nucleotides a. Nucleotide structure b. Deoxyribose versus ribose Nucleotides are joined together by a series of dehydration synthesis reactions to form a linear molecule called a strand, which is a sequence of nucleotides. Structure of DNA and RNA  The backbone of the nucleic acid strand is composed of alternating sugar-phosphate molecules.  DNA is composed of two strands held together by hydrogen bonds between the nitrogen-containing bases. The two strands twist around each other, forming a double helix.  Structure of DNA and RNA The nucleotides may be in any order within a strand but between strands: Adenine (purine) makes hydrogen bonds with thymine (pyrimidine). Cytosine (pyrimidine) makes hydrogen bonds with guanine (purine). The bonding between the nitrogen- containing bases in DNA is referred to as complementary base pairing. The number of 𝐀 + 𝐆 (purines) always equals the number of 𝐓 + 𝐂 (pyrimidines).  Large Amounts of DNA Are Packed into a Cell Things are not that simple Large Amounts of DNA Are Packed into a Cell Eukaryotic chromosome structure Eukaryotic Chromosomes possess centromeres and telomeres  Types of DNA sequences in Eukaryote  Unique Sequence DNA ▪ Protein encoding genes ▪ Gene family  Moderately repetitive DNA( ̴100-300pb) ▪ Tandem repeat sequences ▪ Interspersed repeat sequences (SINE &LINE)  Highly repetitive DNA or satellite DNA(