DNA: the thread of life

Transcription

1 DNA: the thread of life Lectured by Chompunuch Virunanon This presentation Partial Fulfillment of the Requirements for the General Biology teaching, Department of Biology Chulalongkorn University Academic Year 2011 Thread of Life" -Mendel's Gene Theory Explained. class only, not for sale 1

2 What are genes? Deoxyribonucleic acid Deoxyribonucleic acid or DNA, is the genetic material that provides the blueprint to produce an individual traits. Each person s DNA id distinct and unique. Even identical twins shows minor difference in their DNA sequence. Likewise, genetics techniques have many important application in biotechnology, are used in criminal justices, forensic, to provide evidence of guilt or innocent. class only, not for sale 2

3 What are SNPs? DNA: genetic material class only, not for sale 3

4 Griffith s experiment explanation: bacerial transformation experiments indicated the existence of biochemical genetic material In 1920, English microbiologist Frederick Griffith, studied a type of bacterium known than Pneumococci and now classified as Streptococcus pneumoniae. Some strains of S. pneumoniae secrete polysaccharide capsule, while other strains do not. S. pneumoniae Griffith s experiments that showed the transformation of bacteria by a transformation principle class only, not for sale 4

5 The Avery, MacLeod and McCarty experiment Biochemical identification of genetic material 1. Information: The genetic material must contain the information necessary to construct an entire organism 2. Replication: The genetic material must be accurately copied. 3. Transmission: After it replicated, the genetic material can be passes from parent to offspring. It also must pass from cell to cell during the process cell division. 4. Variation: difference in genetic material must account for variation within each species and among different species. class only, not for sale 5

6 Eight years after the famous Avery, MacLeod, and McCarty experiment was published, two scientists named Alfred Hershey and Martha Chase performed an entirely different type of genetic experiment. For their experimental system, they selected an extremely small virus called a bacteriophage (or just phage), which only infects bacterial cells. At that time, scientists knew that when these phage infect a bacterial cell, they somehow reprogram the bacterium to transform itself into a factory for producing more phage. They also knew that the phage itself does not enter the bacterium during an infection. Rather, a small amount of material is injected into the bacteria and this material must contain all of the information necessary to build more phages. Thus, this injected substance is the genetic material of the phage T2 bacteriophage class only, not for sale 6

7 Left. Electron Micrograph of bacteriophage T4. Right. Model of phage T4. The phage possesses a genome of linear ds DNA contained within an icosahedral head. The tail consists of a hollow core through which the DNA is injected into the host cell. The tail fibers are involved with recognition of specific viral "receptors" on the bacterial cell surface. class only, not for sale 7

8 Nucleotides contain a phosphate, a sugar and base DNA RNA class only, not for sale 8

9 Levels of DNA structure to create a chromosome Where s DNA locate in cell? class only, not for sale 9

10 The structural characteristics of prokaryotic and viral chromosome An early prediction was that, when DNA isolated from a bacterial or virus is centrifuged, all of the DNA would sediment at the same rate, forming a band in centrifuge tube at the end of the experiment. However, in 1963, Jerome Vinograd obtained an unexpected results. When he centrifuged circular DNA from Polyoma virus, two band were observed. The structural characteristics of prokaryotic and eukaryotic chromosome class only, not for sale 10

11 Prokaryote cell DNA organization DNA Organization In prokaryotes DNA Organization In eukaryotes class only, not for sale 11

12 The structural characteristics of prokaryotic chromosome Bacterial chromosome Electron micrographs of plasmid DNA (relaxed nonsupercoiled DNA) Bacterial chromosome We learned that the DNA of the bacterium Escherichia coli is located in a central region called the nucleoid. If an E. coli cell is lysed gently, the DNA is released in a highly folded state. class only, not for sale 12

13 DNA Supercoiling 1963 observation that polyoma virus DNA preparations had 3 different types of DNA which had uniquely different sedimentation velocities 1965, two are circular, one linear One circular molecule is underwound Negatively supercoiled (more than 10.4 bp/turn of helix) Topoisomers Created by topoisomerases Types I and II His investigations of this finding led to an understanding that circular DNA can exist in a relaxed or supercoiled form. class only, not for sale 13

14 DNA Organization In Eukaryotes DNA protein complex called chromatin Human chromosomes about 19,000 to 73,000 microns in length, total about 2 meters/cell Nucleus about 5-10 microns in diameter Condensation about 10,000X A Microscopists' View of Chromosome Organization Heterochromatin This is the condensed form of chromatin organization. It is seen as dense patches of chromatin. Sometimes it lines the nuclear membrane, however, it is broken by clear areas at the pores so that transport is allowed. Sometimes, the heterochromatin forms a "cartwheel" pattern. Abundant heterochromatin is seen in resting, or reserve cells such as small lymphocytes (memory cells) waiting for exposure to a foreign antigen. Heterochromatin is considered transcriptionally inactive. See Alberts et al, Molecular Biology of the Cell, Garland Publishing, 1994, pages 352 and 353 class only, not for sale 14

15 An important issue in transcription is identifying the right gene Different type of gene Housekeeping genes: encode proteins that are used all the time Other genes are activated only under certain cercumstances eg. lactose operon of Escherichia coli class only, not for sale 15

16 Euchromatin Euchromatin is threadlike, delicate. It is most abundant in active, transcribing cells. Thus, the presence of euchromatin is significant because the regions of DNA to be transcribed or duplicated must uncoil before the genetic code can be read. Chromatin Structure Chromatin proteins subdivided into histones and nonhistones Histones Very high contents of lysine + arginine (20-30%) Amino acid sequences very conserved between species Histone IV differs by one amino acid between pea and cow class only, not for sale 16

17 Chromatin in metaphase The first level of organization you see is a tangle of nm fibers. These are actually coils of the DNA and histones. The figure on the left shows the tangled chromatin fibers in the left panel. Shearing forces can be used to further uncoil and stretch these fibers and the beaded filaments appear. The strands between the beads are segments of double stranded DNA. class only, not for sale 17

18 DNA Condensation DNA duplex 2 nm in diameter Nucleosome string about 11 nm in diameter Nucleosomes form coiled solenoid-shaped fiber with 6 nucleosomes per spiral 30 nm fiber 30 nm fiber then folded/looped to form 300 nm fiber 300 nm fibers coiled/folded to form 700 nm fiber that forms chromatid in meiosis/mitosis Levels of DNA Condensation class only, not for sale 18

19 How DNA and Histones are organized in chromosomes. How can DNA duplicate itself? class only, not for sale 19

20 An overview of DNA replication Meselson and Stahl use density of measurement to in vestigate mechanism of DNA replication Three propose mechanisms for DNA replication class only, not for sale 20

21 DNA replication How gene express? class only, not for sale 21

22 The central dogma of molecular biology Protein include enzymes that catalyze reaction use to make energy Proteins control cellular processes like replication Protein provide channels in the membrane for cell to communicate with each other share metabolites The central dogma class only, not for sale 22

23 Molecular gene expression in prokaryote Vs eukaryote prokaryote Molecular gene expression in prokaryote Vs eukaryote eukaryote class only, not for sale 23

24 How can genetic material transfer from parent to offspring? Thread of Life" -Mendel's Gene Theory Explained. class only, not for sale 24

25 Mendel s law 1. Law of Segregation (The "First Law") The Law of Segregation states that when any individual produces gametes, the copies of a gene separate so that each gamete receives only one copy. A gamete will receive one allele or the other. 2. Law of Independent Assortment (The "Second Law") The Law of Independent Assortment, also known as "Inheritance Law" states that alleles of different genes assort independently of one another during gamete formation. While Mendel's experiments with mixing one trait always resulted in a 3:1 ratio class only, not for sale 25

26 Pedigree Autosomal dominant or recessive???? Pedigree analysis class only, not for sale 26

27 Genetic Technology The first cloned pet: In 2002 is cat!, called CC (for carbon copy) Gene cloning is done to achieve one main goal Producing large amount of DNA or specific gene Expressing the cloned gene to produce the encoded protein class only, not for sale 27

28 Gene cloning class only, not for sale 28