PowerPoint 3b - The Cell copy

Overview of Cell Structures

• This section provides critical information about the structures and functions of various cell types, particularly focusing on prokaryotic and eukaryotic cells, and their respective membranes and walls.

Cell Membrane and Selective Permeability

• Plasma Membrane

  • All cells are surrounded by a plasma or cell membrane controlling entry and exit of molecules.

  • Selective permeability regulates which molecules can transport in/out, differing from semi-permeability that primarily relates to cell walls.

Phospholipid Structure

• Phospholipids

  • Comprised of:

    • Hydrophilic head: Contains phosphate group + modifier attached to glycerol.

    • Hydrophobic tails: Two fatty acid chains (saturated/unsaturated).

Phospholipid Bilayer Formation

• Phospholipids form a bilayer with hydrophilic heads facing outward toward aqueous solutions and hydrophobic tails facing inward, away from water, providing cell membrane structure.

Membrane Proteins

• Integral Membrane Proteins

  • Amphipathic proteins span the plasma membrane, possessing both hydrophilic and hydrophobic regions affecting orientation and function.

• Peripheral Proteins

  • Associated with membrane surface, often glycoproteins, involved in cell recognition and attachment.

Fluid Mosaic Model

• 1972 Model by Singer and Nicolson

  • Describes membrane as a fluid structure with a mosaic of various proteins embedded.

• Molecule Movement

  • Phospholipids and proteins exhibit lateral movement, contributing to membrane fluidity.

Membrane Properties

• Features:

  • Flexible, self-sealing, able to fuse with other membranes (ex: vesicles).

Membrane Differences in Organisms

• Archaea vs Bacteria

  • Archaeal membranes contain ether linkages; stable, varying permeabilities; may have lipid monolayers.

  • Bacterial membranes feature ester linkages with branched/unbranched fatty acids influencing rigidity and permeability.

Cell Wall Structures

• Bacterial Cell Wall

  • Primarily composed of peptidoglycan (alternating NAG and NAM subunits) strengthened by peptide bridges.

  • Gram-Negative Bacteria: Thin peptidoglycan layer, surrounded by an outer membrane containing LPS (lipopolysaccharides).

  • Gram-Positive Bacteria: Thick peptidoglycan layer reinforced with teichoic acids for rigidity.

Glycocalyx

• A gelatinous layer (sugar coat) outside cell walls, aiding in adherence and protection against desiccation, can form capsules or slime layers.

Biofilms

• Mixed microbial communities providing protection and aiding in nutrient capture; they exhibit different behavior compared to free-living bacteria.

Cytoskeleton

• Cytoskeletal Components: Microfilaments, intermediate filaments, microtubules; essential for cell shape, movement, and organelle anchoring.

Eukaryotic Cell Structures

• Nucleus: Contains nuclear envelope, pores, and nucleoplasm; where ribosome subunits are synthesized and assembled.

• Endomembrane System: Includes components from the nuclear envelope to the plasma membrane, facilitating material transport throughout the cell.

Organelles in Eukaryotic Cells

• Mitochondria: Site for aerobic respiration, featuring a double membrane with cristae and matrix.

• Chloroplasts: Involved in photosynthesis, containing thylakoid membranes stacked in grana.

Cellular Transport Mechanisms

• Passive Transport: Movement across membranes without energy, including diffusion and osmosis.

• Active Transport: Requires energy to move substances against their concentration gradient.

Eukaryotic Extracellular Matrix (ECM)

• Composed of carbohydrates/proteins, serving critical functions in structural support and communication.