ABI Bioinformatics Guide 2024
  • INTRODUCTION
    • How to use the guide
  • MOLECULAR BIOLOGY
    • The Cell
      • Cells and Their Organelles
      • Cell Specialisation
      • Quiz 1
    • Biological Molecules
      • Carbohydrates
      • Lipids
      • Nucleic Acids (DNA and RNA)
      • Quiz 2
      • Proteins
      • Catalysis of Biological Reactions
      • Quiz 3
    • Information Flow in the Cell
      • DNA Replication
      • Gene Expression: Transcription
      • Gene Expression: RNA Processing
      • Quiz 4
      • Chromatin and Chromosomes
      • Regulation of Gene Expression
      • Quiz 5
      • The Genetic Code
      • Gene Expression: Translation
    • Cell Cycle and Cell Division
      • Quiz 6
    • Mutations and Variations
      • Point mutations
      • Genotype-Phenotype Interactions
      • Quiz 7
  • PROGRAMMING
    • Python for Genomics
    • R programming (optional)
  • STATISTICS: THEORY
    • Introduction to Probability
      • Conditional Probability
      • Independent Events
    • Random Variables
      • Independent, Dependent and Controlled Variables
    • Data distribution PMF, PDF, CDF
    • Mean, Variance of a Random Variable
    • Some Common Distributions
    • Exploratory Statistics: Mean, Median, Quantiles, Variance/SD
    • Data Visualization
    • Confidence Intervals
    • Comparison tests, p-value, z-score
    • Multiple test correction: Bonferroni, FDR
    • Regression & Correlation
    • Dimentionality Reduction
      • PCA (Principal Component Analysis)
      • t-SNE (t-Distributed Stochastic Neighbor Embedding)
      • UMAP (Uniform Manifold Approximation and Projection)
    • QUIZ
  • STATISTICS & PROGRAMMING
  • BIOINFORMATICS ALGORITHMS
    • Introduction
    • DNA strings and sequencing file formats
    • Read alignment: exact matching
    • Indexing before alignment
    • Read alignment: approximate matching
    • Global and local alignment
  • NGS DATA ANALYSIS & FUNCTIONAL GENOMICS
    • Experimental Techniques
      • Polymerase Chain Reaction
      • Sanger (first generation) Sequencing Technologies
      • Next (second) Generation Sequencing technologies
      • The third generation of sequencing technologies
    • The Linux Command-line
      • Connecting to the Server
      • The Linux Command-Line For Beginners
      • The Bash Terminal
    • File formats, alignment, and genomic features
      • FASTA & FASTQ file formats
      • Basic Unix Commands for Genomics
      • Sequences and Genomic Features Part 1
      • Sequences and Genomic Features Part 2: SAMtools
      • Sequences and Genomic Features Part 3: BEDtools
    • Genetic variations & variant calling
      • Genomic Variations
      • Alignment and variant detection: Practical
      • Integrative Genomics Viewer
      • Variant Calling with GATK
    • RNA Sequencing & Gene expression
      • Gene expression and how we measure it
      • Gene expression quantification and normalization
      • Explorative analysis of gene expression
      • Differential expression analysis with DESeq2
      • Functional enrichment analysis
    • Single-cell Sequencing and Data Analysis
      • scRNA-seq Data Analysis Workflow
      • scRNA-seq Data Visualization Methods
  • FINAL REMARKS
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  1. MOLECULAR BIOLOGY
  2. Information Flow in the Cell

Chromatin and Chromosomes

PreviousQuiz 4NextRegulation of Gene Expression

Last updated 11 months ago

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DNA carrying genetic information is packaged in structures called chromosomes. Bacteria typically have a single chromosome which contains one circular DNA, while eukaryotic genomes are divided into many chromosomes. A eukaryotic chromosome contains a linear DNA molecule associated with numerous proteins classified as histones and non-histone proteins. This complex of DNA and proteins is referred to as chromatin.

Packaging DNA into chromatin fibres achieves a remarkably high level of compaction. For instance, approximately 205 cm of DNA present in every human cell is enclosed within a nucleus about 10 micrometres in diameter.

The primary level of chromatin compaction involves the formation of nucleosomes, which are protein complexes composed of histones. When observed under an electron microscope, chromatin gently extracted from the nuclei resembles beads on a string. Each "bead" represents a nucleosome, around which DNA is wrapped, while the "string" connecting them is linker DNA.

A nucleosome consists of a protein octamer comprising eight histones, each of which has a tail extending from the nucleosome core. These tails undergo various chemical modifications that can alter chromatin structure and regulate gene expression.

Electron microscopy of chromatin. Nucleosomes remind beads on a string Image source: Oak Ridge National Laboratory - ORNL History, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=90681196
Chromatin structure Image source: Darryl Leja, NHGRI - https://medlineplus.gov/genetics/condition/adnp-syndrome/#causes, Public Domain, https://commons.wikimedia.org/w/index.php?curid=130950339