MBBS 400 Level: The Genome and Cellular Health

Study Notes

The genome encompasses the complete set of genes and genetic material in a cell or organism.
Human genome consists of 23 pairs of chromosomes within cell nuclei and a small DNA molecule in mitochondria.
Encodes approximately 20,000 proteins; protein-coding sequences make up only 1.5% of the total genome.
Up to 80% of the genome consists of non-coding functional sequences that regulate gene expression.
Non-coding sequences include promoter/enhancer regions, non-coding regulatory RNAs, mobile genetic elements, and special structural regions like telomeres.

Over 99.5% of DNA sequences are shared among individuals.
Person-to-person variation is encoded in 75 daltons, with specialized protein transporters influencing ion movement.
Na+/K+ ATPase helps maintain intracellular osmolarity and pH, particularly crucial during cell injury.

Plasma membrane facilitates receptor-mediated and fluid-phase uptake through endocytosis for macromolecules > 1000 daltons.
Endocytosis methods: caveolae-mediated endocytosis, pinocytosis, and receptor-mediated endocytosis.
Defects in receptor-mediated uptake of LDL can lead to familial hypercholesterolemia.

The intracellular cytoskeleton determines cell shape, polarity, trafficking, and motility.
Key cytoskeletal proteins include actin microfilaments, intermediate filaments (e.g., lamin, vimentin), and microtubules.
Cells interact through junctional complexes, including tight junctions, desmosomes (anchoring junctions), and gap junctions.
Gap junctions, formed by connexins, facilitate communication by allowing passage of chemical and electric signals.

All cell constituents are continuously renewed and degraded through the endoplasmic reticulum (ER).
Rough endoplasmic reticulum synthesizes membrane proteins and secretory molecules; smooth ER is involved in lipid synthesis.
ER stress response or unfolded protein response (UPR) can trigger apoptosis.

Lysosomes degrade cellular constituents using acid hydrolases; degradation mechanisms include receptor-mediated endocytosis, autophagy, and phagocytosis.
Proteasomes, known as "cylinders of death," degrade cytosolic and misfolded proteins, regulating macromolecule lifespan.

Often referred to as the "powerhouse" of the cell, containing its own DNA and crucial for oxidative phosphorylation.
Mitochondria have two membranes: an inner membrane folded into cristae containing respiratory chain enzymes and an outer membrane with porin proteins.
Sensitive to certain antibiotics and have short half-lives (1 to 10 days).