31.3

31.3 Differences Between Prokaryotic and Eukaryotic Cells

Chromosome Structure and Genetic Flow

• Chromosome Shapes:

  • Prokaryotes: Circular chromosomes.

  • Eukaryotes: Linear chromosomes.

• Flow of Genetic Information:

  • DNA → RNA → Protein occurs in both cell types.

  • Separation:

    • Eukaryotes: Transcription occurs in the nucleus; translation in the cytoplasm (allowing regulation of each process).

    • Prokaryotes: Transcription and translation occur concurrently in the cytoplasm (no nuclear membrane).

• Implication: Differences in cell structure impact the timing and regulation of gene expression.

Chromosome Organization

• Definition of Chromosomes:

  • Structures made of DNA and associated proteins, crucial for inheritance during cell division.

  • Provide a way to efficiently package long DNA into cells.

• Size Comparison:

  • E. coli's DNA is 200 times longer than its cell diameter.

  • Human chromosome 1 is 10,000 times longer than an average human cell diameter.

DNA Organization in Prokaryotes

• Single Circular Chromosome:

  • DNA is usually present in one circular chromosome.

  • DNA is supercoiled due to strain from circular structure:

    • Supercoiling allows base pair formation and relieves molecular strain.

• Nucleoid Structure:

  • Supercoiled DNA forms loops in a compact nucleoid structure, anchored by proteins.

Plasmids

• Additional DNA in bacteria, typically circular and replicating independently.

• Plasmids may contain non-essential genes that aid in survival under specific conditions.

DNA Organization in Eukaryotes

• Multiple Linear Chromosomes:

  • Most eukaryotes (including humans) have multiple linear chromosomes.

  • Humans exhibit 23 pairs of chromosomes (46 total), organized by size and sex chromosomes.

• Chromatin Formation:

  • Eukaryotic DNA is packaged with proteins into a DNA-protein complex called chromatin.

  • Chromosomes in eukaryotes are structured and organized for efficient DNA management.