Cell Structure and Function

May 30, 2024

Mindmap

Structure and Function of the Cell

Overview

  • Focus on cell structure and functions.
  • Encouragement to watch previous content on study processes.

Nucleus

  • Brain of the cell; central organelle.

Nuclear Envelope

  • Double-layered membrane (outer and inner layer).
  • Outer Layer: Contains ribosomes.
    • DNA β†’ mRNA β†’ mRNA exits via nuclear pores β†’ binds ribosomes.
  • Inner Layer: Contains proteins called lamins.
    • Important for structure, cell division, chromatin interactions.
    • Mutation in lamins causes progeria.

Nuclear Pores

  • Allow transport in and out of the nucleus (ions, proteins, nucleotides).

Nucleolus

  • Site of rRNA synthesis.
    • rrRNA + proteins = ribosomes.

Chromatin

  • Made of DNA + histone proteins.
    • Euchromatin: Loose, more central, active in transcription/replication.
    • Heterochromatin: Tight, closer to nuclear envelope inner membrane.

Nuclear Functions

  • DNA replication, transcription.
    • Types of RNA produced: tRNA, mRNA, rRNA.

Endoplasmic Reticulum

Rough ER

  • Contains ribosomes.
  • Function: Protein synthesis (lysosomal, membrane, secreted proteins).
    • Protein folding and glycosylation (N-type glycosylation).
    • Packs proteins into vesicles for transport to Golgi apparatus.

Smooth ER

  • Lacks ribosomes.
  • Function: Lipid synthesis (fatty acids, phospholipids, cholesterol).
    • Detoxification via CYP450 enzymes.
    • Glycogen to glucose conversion (glucose-6 phosphate metabolism).
    • Calcium storage.

Golgi Apparatus

  • Cis Golgi: Receiving end.
  • Trans Golgi: Shipping end.
  • Function: Modify, package, and sort proteins and lipids.
    • Glycosylation (both N-type and O-type).
    • Phosphorylation (relevant to I-cell disease).
    • Directs modified molecules to lysosomes, membranes, or for secretion.

Cell Membrane

Components

  • Phospholipid Bilayer: Polar heads (hydrophilic) & non-polar tails (hydrophobic).
  • Cholesterol: Controls membrane fluidity.
  • Proteins: Integral and peripheral, have multiple functions (transport, enzymes, linkers).

Functions

  • Acts as selectively permeable barrier.
  • Facilitates specific types of diffusion: simple, facilitated, vesicular transport.

Lysosomes

  • Contain hydrolytic enzymes: Proteases, nucleases, lipases, glucosidases.

Functions

  • Breakdown macromolecules.
  • Autophagy: Recycling old organelles.
  • Autolysis: Breakdown of damaged cells.

Peroxisomes

  • Contain catalase and oxidase enzymes.

Functions

  • Detoxify free radicals (e.g., hydrogen peroxide).
  • Fatty acid oxidation (branches and very long-chain fatty acids).
  • Synthesis of plasmalogens for white matter in the brain.
  • Minor role in alcohol metabolism.

Mitochondria

  • Outer membrane: High permeability.
  • Inner membrane (Cristae): Less permeable.
  • Matrix: Contains mitochondrial DNA.

Functions

  • Site of ATP synthesis (oxidative phosphorylation via electron transport chain).
  • Various metabolic reactions: Krebs cycle, heme synthesis, urea cycle, gluconeogenesis, ketogenesis.

Ribosomes

  • Composed of large (60S) and small (40S) subunits.
  • Made of rRNA and proteins.

Locations

  • Membrane-Bound: On rough ER, involved in protein synthesis (lysosomal, membrane, secreted proteins).
  • Free: In cytosol, synthesize intracellular proteins and enzymes.

Cytoskeleton

Components

  • Microfilaments (Actin): Involved in muscle contraction, cytokinesis, diapedesis, and phagocytosis.
  • Intermediate Filaments: Provide structural support.
    • Anchor cells to cells, cells to extracellular matrix, and organelles within the cell.
  • Microtubules: Made of Ξ±- and Ξ²-tubulin.
    • Intracellular transport via motor proteins (dynein, kinesin).
    • Cell division: Separation of chromatids.
    • Form cell extensions (cilia and flagella).