Cell Biology: Chromatin and Genome Structure

Smooth Endoplasmic Reticulum

• Lacks ribosomes, distinguishing it from rough ER, and primarily involved in lipid synthesis.
• Higher pH of cytosol can inactivate certain contents, a safety measure for cell function.

Lysosomal Storage Diseases

• Tay-Sachs Disease

  • Caused by the absence of hexosaminidase A.
  • Results in the accumulation of gangliosides, affecting neurological function.

• Mucopolysaccharidosis

  • Caused by absence of beta-glucuronidase.
  • Leads to the accumulation of glycosaminoglycans, impacting cellular processes.

Membrane Proteins

• Composed of proteins (55%) with types including:

  • Integral Proteins

    • Embedded in or traverse the membrane, forming structural channels or pores.

  • Peripheral Proteins

    • Located on either side of the membrane; function as enzymes or assist in transport processes.

• Functions of Membrane Proteins

  • Acts as adhesion molecules for cell communication.
  • Integral proteins serve as receptors with a high affinity for specific ligands, initiating cell signaling.
  • Ligands aggregate and cause invagination, leading to the formation of endosomes and vesicles.

Lysosomes

• Known as the cell's digestive system, containing hydrolytic enzymes collectively called acid hydrolases.
• Operate efficiently within an acidic environment, crucial for breaking down biomolecules.
• Plasma membrane is a phospholipid bilayer derived from the Golgi apparatus.

Phagocytosis

• Refers to the process of "cell eating."
  • Involves pseudopodia formation, enclosing molecules in vacuoles, and fusing membranes to form phagosomes.
  • Endosomes direct the fate of internalized molecules for recycling or degradation.

Clathrin-Mediated Endocytosis

• Adaptor proteins recruit clathrin, helping select cargo for endocytosis.
• Clathrin forms coated pits on the membrane, which bud off to create vesicles.
• Dynamin facilitates the final detachment of vesicles from the plasma membrane.

Chromatin and Nucleus

• Heterochromatin

  • Densely packed and typically inactive in gene expression.

• Chromosomes

  • Highly organized chromatin structure, condensed during cell division.

• Nucleosomes

  • The fundamental unit of chromatin, containing segments of DNA.

Genome and Genes

• Genome encompasses all genetic material, including coding and non-coding regions.
• Genes are specific DNA sequences that summon the production of proteins.

Endoplasmic Reticulum

• Acts as the cell's factory with two distinct regions:

  • Rough Endoplasmic Reticulum (RER)

    • Characterized by ribosomes, focuses on protein synthesis.
    • Ribosomes consist of ribosomal RNA (rRNA) and proteins, specifically the 60s and 40s subunits.

  • Lipid Synthesis

    • Smooth ER involved in the biosynthesis of lipids and metabolic processes.

Acidic Environment of Lysosomes

• Optimal pH for acid hydrolases is around 5, while the cytosol's pH hovers around 7.4, emphasizing the importance of compartmentalization in cellular functions.

This quiz covers key concepts related to the structure and organization of chromatin, including heterochromatin, nucleosomes, and chromosomes. It also explores the structure of the genome and the plasma membrane of organelles such as lysosomes. Test your understanding of these fundamental cellular components.