Curtin University Introduction to DNA (PDF)

17/05/2022 How do cells grow, specialise and die? Nucleic acids – DNA & RNA Part 1 of 3 Dr. Arpana Dhar [email protected]...

17/05/2022 How do cells grow, specialise and die? Nucleic acids – DNA & RNA Part 1 of 3 Dr. Arpana Dhar [email protected] 1 WARNING This material has been reproduced and communicated to you by or on behalf of Curtin University in accordance with section 113P of the Copyright Act 1968 (the Act) The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. Do not remove this notice. 2 1  17/05/2022 3 Specific Learning Objectives  Describe the structure and functions of proteins.  Describe the structure of nucleic acids, differentiating between DNA and RNA.  Define the components of a nucleotide.  Differentiate between the nucleotide bases of DNA and RNA.  Explain what the genetic code is and what it is coding for.  Describe the two-step process (transcription & translation) that results in gene expression.  Explain the role of DNA, rRNA, tRNA and mRNA in the production of a protein.  Describe the cell cycle.  Give the details of DNA replication.  Explain what occurs during mitosis and cytokinesis.  Describe how mitosis differs from meiosis. 4 2  17/05/2022 Textbook readings 5 Nucleic acids  First discovered in nuclei of cells, found in all cells  Organic macromolecules (C,H,O,N,P), main information carrying molecules  Polynucleotides – a chain of repeating monomers called nucleotides  Nucleotide A pentose sugar – deoxyribose, ribose A phosphate group A nitrogenous base – adenine, guanine, cytosine, thymine, uracil  Nucleoside – pentose sugar + nitrogenous base  Nucleotide – nucleoside + phosphate group  Sequence of nitrogenous bases carries the information  Two major classes – Deoxyribonucleic Acid (DNA), Ribonucleic Acid (RNA) 6 3  17/05/2022 DNA DNA : Deoxyribonucleic Acid Mainly in nucleus, but also in mitochondria Constitutes the blueprint that codes for protein synthesis Approximately 20,000 – 25, 000 genes in human genome Only 1.5% of DNA is due to genes 98.5% of DNA is non-coding – e.g regulatory sequences, introns, and noncoding DNA – e.g repeat elements 7 8 4  17/05/2022 DNA - structure Watson and Crick (1953) – double helix model Double-stranded polymer - two polynucleotide chains, antiparallel Alternating sugar-phosphate backbone Pentose sugar - deoxyribose Complementary nitrogenous bases form rungs of the ladder adenine - thymine J.D Watson & F.H.C. Crick. guanine - cytosine 1953. Molecular Structure of Nucleic Acids. Nature, 171: 737-38. Nitrogenous bases held together by hydrogen bonds 9 Base pairing rule: A=T C=G 10 5  17/05/2022 Organisation of DNA Double strands of DNA – twisted ladder DNA wrapped around proteins called histones. Histones & DNA bundled together is called chromatin Chromatin twists and condense to form chromosomes Each chromosome contains hundreds to thousands of genes This picture represents a replicated chromosome 11 Quantity of DNA Each somatic human cell nucleus has two copies of each chromosome – one inherited from Mum and the other from Dad. Somatic cells with 46 chromosomes (23 pairs) are said to have the full amount of DNA - diploid The maternal and paternal chromosomes of a pair are called homologous chromosomes (make a “homologous pair) Gametes (sperm and egg) only have 1 chromosome of each homologous pair (have 23 chromosomes), have half the normal amount of DNA - haploid Humans have 22 pairs of autosomal chromosomes and 1 pair of sex chromosomes  Women have 2 X chromosomes (22 + XX)  men have an X and a Y chromosome (22 +XY) When cells are dividing, the chromatin condenses to form chromosomes, is easier to see and can be arranged next to their pair – this kind of map is a karyotype 12 6  17/05/2022 Karyotype A map of chromosomes in a dividing cell Male karyotype (22 autosomes + XY) 13 RNA RNA: Ribo nucleic acid Single stranded polymer, self complementary sequences forms folds, bulges and helices Supports DNA during protein synthesis Found both in the nucleus and cytoplasm Alternating sugar-phosphate backbone Pentose sugar – ribose Nitrogenous bases adenine - uracil guanine - cytosine https://microbenotes.com/rna-properties- structure-types-and-functions/ Three types – mRNA, tRNA, rRNA Different relative sizes, shapes and roles to play in protein synthesis 14 7  17/05/2022 Terminology Genetics - study of heredity Gene – segment of DNA that codes for a protein Allele – alternative form of a gene Genotype – the actual gene (AA, Aa, aa) Phenotype - person’s appearance (blue eyes, brown hair) Dominant and recessive alleles Sex-linked traits: traits affected by genes on sex chromosomes 15 Compendium questions 1. Why do we need proteins in the body? 2. What is a nucleic acid? 3. What are the similarities and differences between DNA and RNA? 4. What is a gene? 5. What is the connection between DNA, RNA and protein synthesis? 6. Describe transcription and translation. 7. What is meant by the terms phenotype and genotype? 8. What is the difference between a chromosome and a chromatid? 9. What are the stages of mitosis? 10. What are the stages of meiosis? 11. Which cell types undergo each type of cell division? 16 8