BIOL1110 2022 Lecture 3 - DNA PDF

BIOL1110/BIOX1110 Genes to Organisms DNA: The molecule of heredity Lecture 3 – DNA: The molecule of heredity  Lecture outline Research & pioneering steps that led to the discovery of DNA as the molecule of heredity Contributions of some key players in identifyin...

BIOL1110/BIOX1110 Genes to Organisms DNA: The molecule of heredity Lecture 3 – DNA: The molecule of heredity  Lecture outline Research & pioneering steps that led to the discovery of DNA as the molecule of heredity Contributions of some key players in identifying traits as heritable and in characterising the structure of DNA The structure of DNA Lecture 3 – DNA: The molecule of heredity  Biological information Genetic information must serve two functions: 1) enable the growth, development & function of an organism 2) needs to be passed on from one generation to another Lecture 3 – DNA: The molecule of heredity  Charles Darwin Charles Darwin (1809 - 1882) Voyage of the HMS Beagle around the world ‘On the origin of species’ by means of natural selection (1859) 1) evolution from common ancestor 2) mechanism occurred via natural selection Lecture 3 – DNA: The molecule of heredity Clues for evolution Lecture 3 – DNA: The molecule of heredity  Evolution & natural selection Darwin identified traits in a species as heritable Individuals and species with heritable traits best suited to the environment did better – Natural selection Darwin proposed a process for change (evolution) But, he did not have an explanation of the mechanism behind inheritance Lecture 3 – DNA: The molecule of heredity  Gregor Mendel Gregor Mendel (1822 - 1884) Mendel was an experimentalist who examined the scientific basis of inheritance using plant breeding Worked on peas (started around 1857) – there are many varieties – easy to breed – produce many offspring Lecture 3 – DNA: The molecule of heredity  Mendel’s experiments Mendel identified heritable characters that were masked in the F1 generation Mendel could predict what the ratio of different characters would be These heritable invisible ‘factors’ were later called genes Lecture 3 – DNA: The molecule of heredity  Johann Friedrich Miescher Johann Friedrich Miescher (1844 - 1895) Biologist to first isolate ‘nuclein’ DNA and proteins from nucleus (1869) ‘Nuclein’ contained phosphorus and nitrogen (in a unique ratio) Lecture 3 – DNA: The molecule of heredity  Albrecht Kossel Albrecht Kossel (1853 - 1927) Biochemist who identified the five compounds present in ‘nuclein’ (1885-1901) – Adenine, Cytosine, Guanine, Thymine, Uracil Provided the name DNA – Deoxyribonucleic acid Lecture 3 – DNA: The molecule of heredity  Thomas Morgan Thomas Hunt Morgan (1866 - 1945) In the early 1900’s, Morgan worked on Drosophila melanogaster After multiple years of breeding, he identified variation in a trait – eye colour Lecture 3 – DNA: The molecule of heredity  Morgan’s experiments Morgan found that mating red (female) and white-eyed (male), fly eye colour followed mendelian inheritance 3:1 (red:white) in F2 But… Morgan also noted that all F2 females had red eyes, while 50% of males had red eyes & 50% white eyes Lecture 3 – DNA: The molecule of heredity  Chromosomes & inheritance In the late 1800’s, chromosomes had been discovered Flies have distinct sex chromosomes The link between inheritance of a trait with sex provided evidence for the role of chromosomes in inheritance A specific ‘factor’ is carried on a specific chromosome (eye colour on X chromosome) Lecture 3 – DNA: The molecule of heredity  DNA or proteins? Chromosomes were known to be made of DNA and proteins Which one is the element of heredity? https://www.rsipvision.com/chromosome-classification/ Lecture 3 – DNA: The molecule of heredity  Frederick Griffith Frederick Griffith (1879 - 1941) Bacteriologist developing vaccines Streptococcus pneumoniae Two strains of S. pneumoniae – Pathogenic – Non-pathogenic Lecture 3 – DNA: The molecule of heredity  Griffith’s experiments Griffith demonstrated transformation Suggested that it wasn’t protein, as they would denature with heat Lecture 3 – DNA: The molecule of heredity  Oswald Avery Oswald Avery (1877 - 1955) Bacteriologist interested in the work by Griffith What was the transforming substance? Lecture 3 – DNA: The molecule of heredity  Avery’s experiments Concluded that the transforming substance was DNA  Hershey & Chase Alfred Hershey (1908 – 1997) Martha Chase (1927 - 2003) Worked with bacteriophages Lecture 3 – DNA: The molecule of heredity  Hershey & Chase’s experiments More evidence for DNA as the molecule of inheritance Lecture 3 – DNA: The molecule of heredity  It’s DNA! Identified DNA as the molecule of inheritance It was on chromosomes It contained four nucleotides What was its structure and how was the information packaged? Lecture 3 – DNA: The molecule of heredity  Edwin Chargraff Edwin Chargraff (1905 - 2002) 1) DNA base composition changes with species So DNA was not a tetranucleotide – i.e. AGCTAGCTAGCTAGCT (in equal amounts) 2) Chargraff showed that the amount of A=T, G=C Lecture 3 – DNA: The molecule of heredity  Wilkins & Franklin Maurice Wilkins (1916 - 2004) Rosalind Franklin (1920 - 1958) Used X-ray diffraction to show that DNA: 1) was a long helical rod 2 nm in diameter 2) had regularity in its structure every 0.34 nm and another every 3.4 nm Lecture 3 – DNA: The molecule of heredity  Watson & Crick James Watson (1928 - ….) Francis Crick (1916 - 2004) Used models consistent with all the data to determine the structure of DNA Lecture 3 – DNA: The molecule of heredity  A Nature paper & Nobel Prize “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” - Watson and Crick Nature, 171, 737-8 The Nobel Prize in Physiology or Medicine 1962 was awarded jointly to Francis Harry Compton Crick, James Dewey Watson and Maurice Hugh Frederick Wilkins "for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material” Lecture 3 – DNA: The molecule of heredity  Nucleic acids Polymers consist of multiple repeating subcomponents Nucleotides: repeating subcomponents that exist in a variety of forms rather than repeated monomer subcomponents Polynucleotides: polymers consisting of multiple nucleotides  Three components of nucleotides Phosphate group – links nucleotides together in the polynucleotide chain – phosphodiester bonds Sugar – connects phosphate backbone with base Nitrogenous base – structure identifies nucleotides as guanine, thymine, adenine, cytosine Lecture 3 – DNA: The molecule of heredity  Three components of nucleotides (DNA) Lecture 3 – DNA: The molecule of heredity  Nucleotides and bases Nucleotides are the individual units of DNA - DeoxyriboNucleic Acid A DNA nucleotide is composed of a nitrogenous base, the sugar deoxyribose, and one or more phosphate groups. The four bases in DNA are adenine, thymine, cytosine, and guanine. Adenine and guanine are purines, and cytosine and thymine are pyrimidines. Lecture 3 – DNA: The molecule of heredity  Pyrimidines and Purines Nucleotides come in two varieties Pyrimidines (Thymine & Cytosine) – four-carbon ring connected by nitrogen atoms at the 1 and 3 position Purines (Adenine & Guanine) – pyrimidine ring connected to an imidazole ring; the overall structure is a double ring A binds with T, G binds with C Lecture 3 – DNA: The molecule of heredity Pyrimidines and Purines Lecture 3 – DNA: The molecule of heredity Directionality Lecture 3 – DNA: The molecule of heredity  Direction Lecture 3 – DNA: The molecule of heredity  Directionality Each strand has directionality That is, the 5ʹ to 3ʹ direction of one strand is opposite to the complementary strand, oriented in a 3ʹ to 5ʹ direction Antiparallel: two complementary strands running in opposite directions DNA template strand 3’ AGCCTGAGACTGAATCT 5’ Complementary strand 5’ TCGGACTCTGACTTAGA 3’ The base sequence along one polynucleotide strand can vary considerably BUT the other strand must have a complementary sequence Lecture 3 – DNA: The molecule of heredity Directionality Lecture 3 – DNA: The molecule of heredity  DNA is a double-helix The two strands form a double helix Minor groove Major groove Lecture 3 – DNA: The molecule of heredity  3D & Size Lecture 3 – DNA: The molecule of heredity  Replication of DNA Semiconservative. Lecture 3 – DNA: The molecule of heredity  Replication of DNA Meselson and Stahl experiment Lecture 1 - Introduction to BIOL368 and Scale  Replication of DNA Semiconservative. Lecture 3 – DNA: The molecule of heredity DNA is everywhere Lecture 3 – DNA: The molecule of heredity Lecture 1 - Introduction to BIOL368 and Scale  Lecture summary Appreciation of the steps & people involved in the discovery of DNA as the molecule of heredity DNA is composed of nucleotides Nucleotides are made up of 1) sugar, 2) phosphate group & 3) nitrogenous base Nucleotides are either a purine (A & G) or pyrimidine (T & C) Adenine binds with Thymine (two H-bonds), Guanine binds with Cytosine (three H-bonds) Lecture 3 – DNA: The molecule of heredity  Lecture summary DNA is a double-helix The two strands run in anti-parallel direction DNA has a major and minor grooves DNA is in lots of stuff (even really old stuff) Lecture 3 – DNA: The molecule of heredity