Organization and Control of Prokaryotic and Eukaryotic Genomes - Part 1

Overview

• Lecture series divided into two parts:
  1. Organization of prokaryotic and eukaryotic genomes
  2. Control of gene expression in prokaryotic and eukaryotic genomes
• Builds on previous chapter: DNA and genomics
  • DNA structure, gene expression, DNA replication

Organization of Prokaryotic and Eukaryotic Genomes

Structure and Organization

• Compare prokaryotic and eukaryotic genomes
• DNA packaging differences

Prokaryotic Genome

• Found in nucleoid region
• No nucleus or membrane-bound organelles
• One circular chromosome
• Supercoiling for DNA compaction
• Genome size smaller than eukaryotic counterparts

Eukaryotic Genome

• Found in nucleus
• Multiple linear chromosomes
• Larger in size with more genes
• Chromosomes have centromeres and telomeres
• DNA packaging involves histones and complex folding
  • Nucleosome -> 10 nm fiber -> 30 nm chromatin fiber -> looped domains -> supercoiling -> metaphase chromosome

DNA Packaging

Prokaryotic Cells

• DNA associates with histone-like proteins
• Form looped domains and supercoiling

Eukaryotic Cells

• DNA associates with histone proteins forming nucleosomes
• Electrostatic interactions hold DNA around histones
• Multiple levels of packaging leading to metaphase chromosomes

Differences in Genome Structure

• Prokaryotes: One circular chromosome, smaller genome, single origin of replication per chromosome, no telomeres/centromeres, lower DNA packing complexity
• Eukaryotes: Multiple linear chromosomes, larger genome, multiple origins of replication, presence of telomeres/centromeres, higher DNA packing complexity with histones and scaffold proteins

Non-coding DNA in Eukaryotes

• Majority of genome is non-coding (~98%)
• Types: Introns, promoters, enhancers, silencers, centromeres, telomeres
• Functions: Regulation of gene expression, chromosome stability

Key Non-coding DNA Structures

• Promoters: Initiate transcription, contain Tata box
• Introns: Non-coding, removed during RNA splicing, allow alternative splicing
• Enhancers/Silencers: Regulate transcription rate, bind specific transcription factors (activators for enhancers, repressors for silencers)
• Terminators: Signal end of transcription, cause RNA polymerase to detach

Alternative Splicing

• One gene can code for multiple proteins
• Mechanism: Introns excised, exons joined in various combinations

Summary and Next Steps

• Covered structure and organization of genomes
• Next: Control of gene expression (Prokaryotic and Eukaryotic)
• Read lecture notes in advance to prepare for upcoming topics