Week 2 A - Genome organisation

Genome Organization Course Notes

Course Information

  • Course: BI2BMG4 Molecular Genetics

  • Instructor: Eva Kevei

  • Contact: e.g.kevei@reading.ac.uk

  • Institution: University of Reading

Reference Text

  • Title: Lewin's Genes XII, 6th Edition

  • Authors: Benjamin A. Pierce, Jocelyn E. Krebs, Elliott S. Goldstein, Stephen T. Kilpatrick

Outline of Key Topics

  1. Genome Size and Packaging

    • Explore how different organisms manage their genome size and the biological significance of protective mechanisms for DNA integrity against damage and degradation.

    • Genomes can differ greatly in size. For example, the human genome contains approximately 3 billion base pairs, while some species like the Amoeba dubia have significantly larger genomes due to polyploidy.

    • Protective mechanisms include DNA repair systems that fix damage caused by environmental factors such as UV light and chemicals.

  2. Nucleosome Structure

    • Discuss the fundamental components of nucleosomes, including the core histone octamer and how DNA is organized around it, emphasizing the importance of nucleosomal arrangement for genome accessibility.

    • Each nucleosome consists of approximately 147 base pairs of DNA wrapped around a histone octamer made of H2A, H2B, H3, and H4 histones.

    • The linker DNA between nucleosomes can play a role in gene regulation by influencing chromatin structure.

  3. Histones and Their Modifications

    • Examine various types of post-translational modifications such as methylation and acetylation, and their role in determining the functional state of chromatin, correlating these modifications with gene expression trends.

    • Other modifications, including phosphorylation and ubiquitination, also affect chromatin and gene expression. Histone acetylation typically correlates with gene activation, while methylation has a dual role depending on the context and specific residues modified.

  4. Chromatin

    • Differentiate between euchromatin and heterochromatin, including their structural and functional properties, and the implications of their dynamic nature in gene regulation and expression.

    • Euchromatin is less densely packed and generally accessible for transcription, while heterochromatin is tightly packed and usually transcriptionally inactive.

  5. Chromosomes

    • Analyze the structure and behavior of chromosomes during cell division, alongside the mechanisms by which they maintain integrity and genetic fidelity.

    • Chromosomes undergo significant structural changes during mitosis and meiosis, including condensation and segregation, which are critical for successful cell division.

  6. 3D Genome Organization

    • Comprehend the principles of spatial localization of genes within the nucleus and how this organization affects chromatin structure and gene regulation, highlighting the significance in cellular functions.

    • Techniques such as Hi-C are used to study the 3D structure of genomes, revealing how distant gene regions may interact within the nucleus.

  7. Role of Chromatin and Chromosome Organization in Disease

    • Investigate the connections between chromatin structure, gene expression dysregulation, and various diseases, focusing on cancer and genetic disorders.

    • Abnormal chromatin modifications and structural changes can lead to the misregulation of genes associated with cell growth and differentiation, playing a significant role in oncogenesis.

Learning Outcomes

  • Demonstrate an understanding of how large genomes are managed through various cellular mechanisms, including replication, repair, and packaging, ensuring DNA stability and integrity.

  • Attain knowledge regarding the precise composition and structural organization of nucleosomes, including their packaging into higher-order chromatin structures and implications for gene expression.

  • Gain awareness of the impact of histone modifications, including how different patterns can alter gene expression profiles and ChIP-seq techniques for analyzing modifications.

  • Effectively distinguish between euchromatin, which is transcriptionally active, and heterochromatin, which is typically silent, and understand their functional roles in various biological contexts.

  • Comprehend the necessity and methodologies for studying 3D genome organization, including the role this plays in the regulation of genes and chromatin architecture.

Multilayer Concepts

  • Viral Genomes

    • Explore the diverse structural characteristics and lengths of viral genomes, highlighting examples from families like Poxviridae and Adenoviridae, emphasizing their unique packaging mechanisms and implications for infection.

    • Viral genomes can be linear or circular, single-stranded or double-stranded, which influences how they replicate and how viral proteins are expressed.

  • Bacterial Genome Organization

    • Understand the distinct features of bacterial genome structure, primarily comprised of a single circular chromosome, the role of supercoiling, and the function of nucleoid-associated proteins in maintaining cellular organization and regulating gene expression.

    • Many bacteria also contain plasmids, which are small circular DNA molecules that can carry genes beneficial for survival, such as antibiotic resistance.

  • Eukaryotic Genome Packaging Strategies

    • Discuss the complexity of eukaryotic genomes housed within the nucleus, emphasizing mechanisms of organization into nucleosomes, chromatin, and chromosomes, and their roles in gene accessibility and transcription.

    • Eukaryotic cells utilize a variety of histone variants and proteins that aid in the dynamic regulation of chromatin structures.

Advanced Concepts and Techniques

  • Single-cell Micrococcal Nuclease Sequencing (scMNase-seq)

    • Examine the methodologies employed in analyzing nucleosome positioning and chromatin accessibility to gain insights into the regulatory mechanisms of gene expression.

    • Techniques such as ATAC-seq provide complementary insights by identifying accessible chromatin regions across different cell types.

  • Interplay of Histone Readers and Modifications

    • Explore how specific histone modifications serve as signals for histone readers, influencing chromatin structure and gene expression control across various biological contexts.

    • The functioning of histone readers is pivotal in the recruitment of additional proteins necessary for chromatin remodeling and transcriptional activation.

Supplementary Resources

  • Links to videos for further understanding of DNA structure and supercoiling.

  • Recommended extra readings focused on nucleosome positioning and chromatin architecture to reinforce concepts learned during the course.

  • Case studies illustrating the impact of chromatin modifications in specific diseases, providing practical examples of molecular genetics in action.