Advanced Molecular Genetics Prepared by Prof Sabah Hassan

Advanced Molecular Genetics Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Chapter 2 DNA: The Genetic Material Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Search for genetic material, is it composed of nucleic acid or protein/DNA or RNA? Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Search for the genetic material Timeline of events: 1890 Weismann - substance in the cell nuclei controls development. 1900 Chromosomes shown to contain hereditary information, later shown to be composed of protein & nucleic acids 1928 Griffith’s Transformation Experiment 1944 Avery’s Transformation Experiment 1953 Hershey-Chase Bacteriophage Experiment 1953 Watson & Crick propose double-helix model of DNA 1956 First demonstration that RNA is viral genetic material Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Frederick Griffith’s Transformation Experiment- 1928 “Transforming principle” demonstrated with Streptococcus pneumoniae Griffith hypothesized that the transforming agent was a “IIIS” protein. But this was only a guess, and Griffith turned out to be wrong. Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Oswald T. Avery’s Transformation Experiment- 1944 Determined that “IIIS” DNA was the genetic material responsible for Griffith’s results (not RNA). Peter J. Russell, i. Genetics: Copyright © Pearson Education, Inc. , publishing as Benjamin Cummings. Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Hershey-Chase Bacteriophage Experiment - 1953 Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Life cycle of virulent T 2 phage Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Hershey-Chase Bacteriophage Experiment - 1953 Alfred Hershey Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Fraenkel-Conrat & Singer - 1957 Demonstrated that RNA is the genetic material of TMV. Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Conclusions about these early experiments Griffith 1928 & Avery 1944: DNA (not RNA) is transforming agent. Hershey-Chase 1953: DNA (not protein) is the genetic material. Gierer & Schramm 1956/Fraenkel-Conrat & Singer 1957: RNA (not protein) is genetic material of some viruses, but no known prokaryotes or eukaryotes use RNA as their genetic material. Alfred Hershey Nobel Prize in Physiology or Medicine 1969 Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Structure of DNA James D. Watson/Francis H. Crick 1953 Double Helix Model of DNA: Six main features Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Nucleotide = monomers that make up DNA and RNA Three components 1. Pentose (5 -carbon) sugar DNA = deoxyribose RNA = ribose (compare 2’ carbons) 2. Nitrogenous base Purines Adenine Guanine Pyrimidines Cytosine Thymine (DNA) Uracil (RNA) 3. Phosphate group attached to 5’ carbon Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

5’ end 3’ end Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Type B-DNA Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Type A, B, and Z conformations of DNA Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

1962: Nobel Prize in Physiology and Medicine James D. Watson Francis H. Crick Maurice H. F. Wilkins What about? Rosalind Franklin Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

RNA possesses uracil (U) instead of thymine (T) A pairs with U and C pairs with G Examples: m. RNA t. RNA r. RNA sn. RNA mi. RNA si. RNA messenger RNA transfer RNA ribosomal RNA small nuclear RNA micro RNA small interfering RNA secondary structure: Yeast Alanine t. RNA Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Organization of DNA/RNA in chromosomes Genome = chromosome or set of chromosomes that contains all the DNA an organism (or organelle) possesses Viral chromosomes TMV 1. single or double-stranded DNA or RNA 2. circular or linear 3. surrounded by proteins T 2 bacteriophage Prokaryotic chromosomes. Most prokaryotes contain one circular chromosome. DNA communicates with the cytoplasm – so it allows direct connection to transcription and translation. Contain only one copy of the gene (haploid). Non-essential genes are stored outside of chromosome – in plasmids. Prokaryotic genome is very compact – contain very little non-coding DNA sequences Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Problem: Measured linearly, the Escherichia coli genome (4. 6 Mb) would be 1, 000 times longer than the E. coli cell. The human genome (3. 4 Gb) would be 2. 3 m long if stretched linearly. Chromosome released from lysed E. coli cell. Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Prokaryotic chromosome structure--solutions: 1. Supercoilin DNA double helix is twisted in space about its own axis, a process is controlled by topoisomerase (enzymes) (occurs in circular and linear DNA molecules) Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Looped domains. 2 Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Eukaryotic chromosome structure Packing of DNA into chromosomes: 1. Level 1 Winding of DNA around histones to create a nucleosome structure. 2. Level 2 Nucleosomes connected by strands of linker DNA like beads on a string. 3. Level 3 into Packaging of nucleosomes Level 4 domains. Formation of looped 1. 30 -nm chromatin fiber. Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Metaphase chromosome depleted of histones maintains its shape with a nonhistone protein scaffold. Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Two other regions of DNA you should know about: • Centromeric DNA (CEN) • Center of chromosome, specialized sequences function with the microtubles and spindle apparatus during mitosis/meiosis. • Telomeric DNA • At extreme ends of the chromosome, maintain stability, and consist of tandem repeats. Play a role in DNA replication and stability of DNA. Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

Repeated DNA: Unique-sequence DNAOften • referred to as single-copy and usually code for genes. Repetitive-sequence DNAMay be • interspersed or clustered and vary in size. SINEsshort interspersed repeated sequences (100 -500 bp) LINEslong interspersed repeated sequences (>5, 000 bp) Microsatellites short tandem repeats <---TTATTATTATTA--> Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 L 2

More about genome size: C value = total amount of DNA in the haploid (1 N) genome Varies widely from species to species and shows no simple relationship to structural or organizational complexity. Examples. C value (bp) T 4 HIV-1 E. Coli Lilium formosanum Zea mays Amoeba proteus Drosophila melanogaster Mus musculus Canis familiaris Equus caballus Homo sapiens Prepared by Prof. Sabah Hassan -Coordination by Prof Sabah Linjawi BIO 702 48, 502 168, 900 9, 750 4, 639, 221 36, 000, 000 5, 000, 000 290, 000, 000 180, 000 3, 454, 200, 000 3, 355, 500, 000 3, 311, 000 3, 400, 000 L 2