Cell Structure and Function Lecture Notes

Introduction

• Discussing the structure and function of a cell.
• Previous video on study and preparation methods for creating content.
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Nucleus

Components

• Nuclear Envelope: Double-layered (outer and inner layers).
  • Outer Layer: Contains ribosomes which translate mRNA into proteins.
  • Inner Layer: Contains lamins important for nuclear structure and cell division. Mutations can lead to disorders like progerias.
• Nuclear Pores: Allow transport between the nucleus and cytoplasm.
• Nucleolus: Site of rRNA synthesis and ribosome assembly.
• Chromatin: Made up of DNA and histone proteins.
  • Euchromatin: Loose, active in DNA transcription/replication.
  • Heterochromatin: Tight, located near the nuclear envelope.

Functions

• DNA Replication: Creating more DNA.
• Transcription: Creating RNA (tRNA, mRNA, rRNA).

Endoplasmic Reticulum (ER)

Rough ER (RER)

• Structure: Contains ribosomes on its surface.
• Function: Protein synthesis, folding, and glycosylation (N-type).
  • Produces proteins for lysosomes, organelles, cell membrane, and secretion.
  • Protein Folding: Ensures correct protein function.
  • Glycosylation: Addition of sugar residues to proteins.
• Packaging: Proteins are packaged into vesicles and sent to the Golgi apparatus.

Smooth ER (SER)

• Structure: Lacks ribosomes.
• Function: Lipid synthesis (fatty acids, phospholipids, cholesterol), detoxification (CYP450 enzymes), glucose-6-phosphate metabolism, and calcium storage.

Golgi Apparatus

• Cis Golgi: Receives vesicles from RER and SER.
• Function: Modifies proteins and lipids (glycosylation, phosphorylation), packages them into vesicles.
• Trans Golgi: Sends vesicles to lysosomes, cell membrane, or for secretion.

Cell Membrane

• Phospholipid Bilayer: Hydrophilic heads (polar) and hydrophobic tails (non-polar).
• Cholesterol: Regulates membrane fluidity.
  • More cholesterol = less fluidity, less cholesterol = more fluidity.
• Proteins: Integral and peripheral proteins for transport, enzymes, and cell linking.
• Functions: Acts as a barrier, involved in diffusion (simple, facilitated) and vesicular transport.

Lysosomes

• Hydrolytic Enzymes: Proteases, nucleases, lipases, glucosidases for breaking down macromolecules.
• Functions:
  • Breakdown of macromolecules
  • Autophagy: Recycling worn-out organelles.
  • Autolysis: Breakdown of damaged cells.

Peroxisomes

• Enzymes: Catalase, oxidase, and other metabolic enzymes.
• Functions:
  • Detoxification: Breakdown of hydrogen peroxide into water and oxygen.
  • Fatty Acid Oxidation: Breakdown of fatty acids into acetyl-CoA.
  • Lipid and Cholesterol Synthesis: Including plasmalogen for brain white matter.
  • Ethanol Metabolism.

Mitochondria

• Structure: Outer membrane (smooth, high permeability), inner membrane (folded, less permeable), and matrix (contains mitochondrial DNA).
• Function: ATP synthesis via oxidative phosphorylation (electron transport chain).
  • Metabolic pathways: Krebs cycle, heme synthesis, urea cycle, gluconeogenesis, ketogenesis.
  • Contains mitochondrial DNA (maternal origin).

Ribosomes

• Structure: Large (60S) and small (40S) subunits.
• Components: rRNA and proteins.
• Types: Membrane-bound (RER) and cytosolic (free in cytoplasm).
• Function: Protein synthesis (translation).
  • RER Ribosomes: Make lysosomal, membrane, and secreted proteins.
  • Cytosolic Ribosomes: Make cytosolic proteins (e.g., enzymes).

Cytoskeleton

Microfilaments (Actin)

• Functions:
  • Muscle contraction (with myosin).
  • Cytokinesis: Constriction ring formation during cell division.
  • Diapedesis: Movement of white blood cells.
  • Phagocytosis: Engulfing pathogens.

Intermediate Filaments

• Functions: Provide tensile strength and structural support.
  • Anchor cells to extracellular matrix and to each other.
  • Anchor organelles within cells.

Microtubules

• Functions:
  • Intracellular transport: Using motor proteins (dynein, kinesin) and requiring ATP.
  • Cell division: Separate chromatids during mitosis.
  • Cell extensions: Form base of cilia and flagella for movement.

Conclusion

• Summary of cell structure and function.
• Encouragement to follow the study process and engage with the content.
• Gratitude expressed to viewers.