BIO1204 Lecture - DNA as the Cells Blueprints.pdf

BIO1204 Introduction to Biomedical Science DNA as the Cell’s Blueprint  The material in this lecture and course should be not uploaded or shared on any online platform outside of the University of Southern Queensland....

BIO1204 Introduction to Biomedical Science DNA as the Cell’s Blueprint  The material in this lecture and course should be not uploaded or shared on any online platform outside of the University of Southern Queensland. COMMONWEALTH OF AUSTRALIA Copyright Regulations 1969 WARNING This material has been copied and communicated to you by or on behalf of The University of Southern Queensland pursuant to Part VA of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further copying or communication of this material by you may be the subject of copyright protection under the Act. Do not remove this notice. 2  Acknowledgement of Country In the spirit of reconciliation, the University of Southern Queensland acknowledges the traditional custodians of the lands and waterways where the University is located. Further, we acknowledge the cultural diversity of Aboriginal and Torres Strait Islander peoples and pay respect to Elders past, present and future. 3  Learning Outcomes To be able to: – Describe the structure of DNA, chromosomes & chromatin, including the role of proteins in DNA storage – Significance of chromosomes in the transfer of genetic information – Define the terms: genome, karyotype, haploid/diploid, homologous, sister chromatids , centromeres, kinetochore & telomeres – Explain the cause of human diseases associated with abnormal chromosome structure (resulting in loss/gain of gene/s) & number and the use of cytogenetics to diagnose such abnormalities 4  From Chromosomes to DNA Early researchers worked to determine what carried the message of genes and heredity in the cell. Chromosomes have more protein than DNA by weight. DNA is built of 4 subunits while protein is built of 20 subunits. Experiments in the early 1900’s determined that DNA was the material that carried genes. Subsequent research attempted to determine the DNA structure. 5 B Form DNA - The double helix model (proposed by Watson & Crick, 1953) X-ray diffraction patterns produced by DNA fibres – by Rosalind Franklin and Maurice Wilkins Negative charge (at neutral pH) on the hydrophilic phosphate groups outside of the double helix Hydrophobic bases are within the double helix Overall negative charge useful in lab gel electrophoresis 6 B Form DNA - The double helix model (proposed by Watson & Crick, 1953) Z form DNA… 7  DNA is built of nucleotides A nitrogenous bases Deoxyribose Purines Pyrimidine Phosphate Purine Pyrimidine nucleotide nucleotide 8  DNA is a Double-Stranded Molecule The pentose-phosphate 5’ backbones run in opposite directions Base-pairing 9  Base Pairing – Hydrogen bonds H N H O N H N PURINES PYRIMIDINES Adenine O Thymine H O H N N H N Guanine N H O Cytosine H 10 DNA in the Nucleus & Mitochondria Nuclear DNA Mitochondrial DNA Euglena glacilis cell stained to show DNA 11 Prokaryote & Eukaryote Cells Have Different Strategies of Packaging their DNA 2µ m 10µm 12 DNA Storage in Eukaryotes 700nm metaphase chromatid 13 DNA Usually in Chromatin Form Electron Micrograph Showing 10nm Chromatin Fibres 14  Packaging DNA into Chromatin – Eukaryote Cells https://youtu.be/gbSIBhFwQ4s 15  Packaging DNA – Tertiary Structure Eukaryotic cells  Variable number of chromosomes enclosed within nucleus  Chromosomes are made of chromatin (DNA + proteins)  ~1.8m to ~90mm  Main proteins are histones 16  Histones Proteins that allow chromatin to be condensed –Facilitates replication during mitosis Core histones – H2A, H2B, H3 & H4 –Two of each in a histone octomer Linker histone - H1 “Nucleosome” 17  Packaging DNA Prokaryotic cells (bacteria and archaea)  No nucleus  One large single loop of chromosome  Twisted into a supercoiled state 18 Electron micrograph of folded E. coli chromosome 19 DNA Storage in Prokaryotes 20  DNA Forms Linear, double helixes – Eukaryotes Circular, double-stranded, anti-parallel – Bacteria (prokaryotes) – Mitochondria and chloroplasts – Some viruses (ex: papovavirus) Single stranded – Linear or circular – Some viruses (ex: parvoviruses) – Bacteriophages 21  EUKARYOTES VS PROKARYOTES Double Nuclear Membrane Genome in Cytoplasm Large Genomes (-1011) Small Genomes (104-107) Linear Chromosomes (>1) Circular Chromosome (1) 1000mm 1.5mm Histones & Chromatin No Histones Introns in most genes No Introns Processed RNA Transcripts RNA not Processed (splicing) Compartmentalised Transcription & Translation Transcription (nucleus) & not Separated Translation (cytoplasm) Information in italics to be covered in future lectures… 22  DNA is Packaged into Chromosomes at Start of Mitosis A chromosome is a single unbroken molecule of dsDNA Eg. Human chromosome 13 23 Chromatin to Chromosomes (During prophase) Interphase = G1, S & G2 24  Key Morphological Features of the Metaphase Chromosome Sister chromatids Centromere Kinetochore Telomeres 25  Interphase Chromosomes: Chromatin Euchromatin: Interphase DNA is diffused post-mitosis & consists mostly of transcribed sequence (makes proteins) Heterochromatin: DNA remains condensed (more intense staining) Constitutive: Permanent (centromeres & telomeres) Facultative: Temporary, inducible, groups of tissue specific genes) 26  Centromeres Position of the centromere may be telocentric, acrocentric or metacentric Join sister chromatids together after replication Attach the chromosome (chromatid) to the spindle fibre for movement to cell poles – Must replicate during Metaphase to Anaphase or nondisjunction occurs (separation failure of homologues) Have specific sequences 100-200bp – Similar in different chromosomes of same species 27  Kinetochore >45 proteins Interacts with centromere DNA & microtubules Facilitates chromosome movement during cell division 28  Telomeres Are the termini of the double stranded DNA helix Humans have a 6bp sequence TTAGGG repeated ~1000 times (tandem repeats) –The same hexamer occurs in all vertebrate telomeres –Most other eukaryotes T1-4A0-1G1-8 –The length provides protection from nucleases –Allows replication without loss of genetic material 29  2017 NASA Twin Study Scott Kelly spent 1 year in space while his brother Mark Kelly was home as a control subject. Scott’s telomeres increased significantly in space but shortened again after his return. Gene expression patterns changed with 7% remaining altered after return. Studies included telomeres, biochemistry, immunology, microbiome, DNA/RNA, https://www.nasa.gov/twins-study epigenetics, atherosclerosis, proteins, 30 Ploidy – Number of Chromosome Sets Haploid - one set of chromosomes – The basic genome set – Consists of n chromosomes (in humans n=23) – Most fungi and algae Diploid - two sets of chromosomes – Chromosomes exist in pairs – Cell contains 2n chromosomes – Most animals and plants have 2 copies of each chromosome in each cell Tetraploid – four sets chromosomes – Salmon, ‘domesticated’ crops such as durum wheat 31  Homologous Chromosomes Each pair is similar HOMOLOGOUS in length, centromere They both carry CHROMOSOMES position & staining genes controlling the pattern same inherited trait at the same LOCI (location) Each chromosome consists of 2 genetically identical sister chromatids, as a result of DNA replication SISTER CHROMATIDS prior to cell division 32  Human Genome Spread over 23 different chromosomes – Somatic cells Normal body cells Diploid, 2 copies of each 23 pairs, 46 chromosomes in total 2n, where for humans n = 23 – Gametes Sex cells, ova & sperm Haploid – only one copy of each chromosome 23 chromosomes in total 1n, where for humans n = 23 33 Human Metaphase Chromosome Map Some well known loci: Rhesus = 1p34; ABO = 9q34 Red/Gn = Xq28, SRY = Yp11.3 http:///www.pathology.washington.edu/research/cytopages34 Human female karyotype: 46XX Females have 2 X chromosomes Males have an X and a Y chromosome 35 Human Male Metaphase Karyotype (OLD TECHNOLOGY) 36  Non-invasive Prenatal Testing Utilizes DNA fragments from the baby within the mother’s blood Requires a single blood sample Can be done as early as 10 weeks gestation Tests for chromosomal abnormalities May be subsequently confirmed with invasive diagnostic method https://www.sonicgenetics.com.au/nipt/patients/ https://obgyn-onlinelibrary-wiley-com.ezproxy.usq.edu.au/doi/full/10.1002/pd.5049 37  Chromosomal abnormalities can be detected by cytogenetics technologies 38  Metaphase Chromosomes Can Be Identified with Chromosome Paints ‘Paints’ are chromosome specific DNA probes labelled with fluorescent dyes (NEW TECHNOLOGY) a b Human Chromosome Paints a) Interphase nucleus b) Metaphase Spread c) Karyotype c http://www.chroma.com/resources/index.php 39  Intra-Chromosomal Paints Individual Metaphase chromosome bands may be detected using chromosome paints to specific DNA sequences within chromosomes Allows cytogeneticists to check for chromosomal rearrangements like deletions, inversions & duplications http://www.chroma.com/resources/index.php 40  Human Whole Chromosome Disorders Trisomy – 30% cause spontaneous abortions (miscarriages) – Extra copy of a single chromosome – Only three somatic trisomies come to term Down’s syndrome (extra 21) 1/700 Down’s syndrome showing Edward’s syndrome (extra 18) extra copy of chromosome 1/8,000 21 Patau’s syndrome (extra 13) Visible in both metaphase spreads & interphase 1/20,000 nuclei using FISH 41  Sex Polysomy & Monosomy Kleinfelter’s: male with extra X chromosomes – some secondary characteristics, usually sterile, small testes, enlarged breasts, long limbs, knocked knees & underdeveloped body hair. Mental impairment when more than 2 Xs (eg XXXY etc) Triplo X: – normal appearance, mild mental impairment, usually sterile Double Y: – tend to be tall, disputed association with antisocial behaviour Turner’s: female with single X chromosome – rudimentary ovaries, usually sterile, short, webbed necks, hearing loss, severe cardiovascular abnormalities 42 Tetrasomic for X: Klinefelter Syndrome 43  Klinefelter’s Syndrome Extra Xs – 75% are XXY – XXYY, XXXY, XXXYY, XXXXY, XXXXYY Fertilisation – XY sperm – XX egg 44 Turner’s Syndrome is The Only Viable Human Monosomy Monosomy (10% spontaneous abortions) –missing copy of chromosome X –usually lethal (except 45X - Turner’s) 45 Turner’s Syndrome is The Only Viable Human Monosomy 46 Chromosomal Abnormalities in Cancers Tetrasomy of most chromosomes Chromosomal rearrangements eg. reciprocal translocations 47  Lecture Summary DNA carries the genetic information of the cell and is composed of units of a sugar, phosphate molecule, and a nucleotide base. DNA packaging differs between prokaryotes and eukaryotes. Eukaryotic DNA is tightly organised around proteins called histones to form the structure of a chromosome. The human genome has 23 pairs of chromosomes. Abnormal numbers of chromosomes can lead to death or abnormal development. Modern technologies are able to detect changes in chromosomes. 48  Practice exam questions – Part A 1. Eukaryotic chromosomes have special tandom repeating ends called A. Sister chromatids B. Kinetochore C. Centromere D. Telomere E. Histones 49  Practice exam questions – Part A 1. Eukaryotic chromosomes have special tandom repeating ends called A. Sister chromatids B. Kinetochore C. Centromere D. Telomere E. Histones 50  Practice exam questions – Part B 1. Explain how we can test for abnormal numbers of chromosomes. 2. Describe how DNA is packaged into chromosomes. 51  Any questions? - Post on the StudyDesk forum (if you have question, someone else will too!) - Can also email [email protected] 52 53