Structure and Function of the Cell

Introduction

• Discussion on the structure and function of the cell.
• Encouragement to watch previous videos for study techniques.
• Overview of upcoming topics: Nucleus, ER, Golgi Apparatus, Cell Membrane, Lysosomes, Peroxisomes, Mitochondria, Ribosomes, Cytoskeleton.

Nucleus

• Nuclear Envelope
  • Double-layered structure.
  • Outer layer: Contains ribosomes for mRNA transport.
  • Inner layer: Contains lamins for structure and division.
  • Disorders: Lamin mutations cause progerias.
• Nuclear Pores
  • Allow transport of ions, proteins, and nucleotides between the cytoplasm and nucleus.
• Nucleolus
  • Site of rRNA synthesis.
  • Produces ribosomes by combining rRNA with proteins.
• Chromatin
  • Made of DNA and histone proteins.
  • Types: Euchromatin (loose, DNA expression), Heterochromatin (tight, structural).
• Functions
  • DNA replication and transcription.
  • RNA types: tRNA, mRNA, rRNA.

Endoplasmic Reticulum (ER)

• Rough ER
  • Contains ribosomes.
  • Functions: Protein synthesis, folding, glycosylation (N-type), and packaging for Golgi apparatus.
• Smooth ER
  • No ribosomes.
  • Functions: Lipid synthesis, detoxification (CYP450 enzymes), glucose 6-phosphate metabolism, calcium storage.

Golgi Apparatus

• Structure
  • Cis face: Receives vesicles from ER.
  • Trans face: Ships modified proteins and lipids.
• Functions
  • Modifies proteins through glycosylation (O-type) and phosphorylation.
  • Packages proteins for lysosomes, membranes, or excretion.

Cell Membrane

• Structure
  • Phospholipid bilayer: Polar heads (hydrophilic), fatty acid tails (hydrophobic).
  • Cholesterol: Regulates fluidity.
  • Proteins: Integral and peripheral for transport and enzymatic functions.
• Functions
  • Acts as a barrier with selective permeability.
  • Transport processes: Simple diffusion, facilitated diffusion, vesicular transport.

Lysosomes

• Functions
  • Contain hydrolytic enzymes (proteases, nucleases, lipases, glucosidases).
  • Breakdown of macromolecules.
  • Autophagy: Recycling of organelles.
  • Autolysis: Destruction of damaged cells.

Peroxisomes

• Enzymes
  • Catalase, oxidase, other metabolic enzymes.
• Functions
  • Breakdown of hydrogen peroxide into water and oxygen.
  • Fatty acid metabolism (alpha and beta oxidation).
  • Lipid and cholesterol synthesis (plasmalogen for brain white matter).
  • Ethanol metabolism.

Mitochondria

• Structure
  • Outer membrane: Smooth and permeable.
  • Inner membrane: Cristae, less permeable.
  • Matrix: Contains DNA.
• Functions
  • ATP synthesis via oxidative phosphorylation and electron transport chain.
  • Krebs cycle, heme synthesis, urea cycle, gluconeogenesis, ketogenesis.

Ribosomes

• Structure
  • Large (60S) and small (40S) subunits.
• Functions
  • Site of protein synthesis (translation).
  • Membrane-bound (for lysosomes, membranes) vs. cytosolic (for internal enzymes).

Cytoskeleton

• Microfilaments (Actin)
  • Functions: Muscle contraction, cytokinesis, diapedesis, phagocytosis.
• Intermediate Filaments
  • Functions: Anchor cells to each other, extracellular matrix, and organelles.
• Microtubules
  • Functions: Intracellular transport, cell division (chromatid separation), cilia and flagella formation.

Conclusion

• Summary of cell structure and function.
• Encouragement to follow the study and preparation process for mastery.