Unit 2

Eukaryotic Cells

  • Eukaryotic cells have complex internal structures allowing more sophisticated metabolic functions compared to prokaryotic cells.

  • Key characteristics of eukaryotic cells include:

    • Membrane-bound nucleus housing genetic material.

    • Several membrane-bound organelles.

    • Multiple linear chromosomes (versus single circular chromosomes in prokaryotes).

Organelles and Their Functions

Lysosomes

  • Maintain an acidic pH for cellular waste disposal.

Peroxisomes

  • Carry out oxidation reactions, producing hydrogen peroxide.

  • Critical that they are compartmentalized to avoid cellular damage.

Endomembrane System

  • A group of membranes and organelles working together to modify, package, and transport lipids and proteins, including:

    • Endoplasmic Reticulum (ER)

    • Golgi Apparatus

    • Nuclear Envelope

    • Lysosomes

    • Plasma Membrane

  • Not part of the endomembrane system: mitochondria, chloroplasts, peroxisomes.

Endoplasmic Reticulum (ER)

  • Divided into:

    • Rough ER:

      • Studded with ribosomes for protein synthesis.

      • Newly formed proteins enter the lumen for modification, then packaged into vesicles for the Golgi.

    • Smooth ER:

      • Synthesizes carbohydrates, lipids, and steroid hormones.

      • Detoxifies drugs and toxins.

      • Stores calcium ions.

Golgi Apparatus

  • Functions in storing, tagging, packaging, and distributing lipids and proteins.

  • Faces:

    • Cis face: Receiving side.

    • Trans face: Shipping side.

  • Modifications include adding/removing sugar chains and attaching phosphate groups.

Lysosome

  • Contains digestive enzymes for macromolecule breakdown and cellular recycling.

Vacuoles

  • Large central vacuole in plant cells stores water, waste, and hazardous materials.

  • Enzymes within can break down cellular components.

Mitochondria & Chloroplasts

  • Mitochondria:

    • Energy production through cellular respiration from fuel molecules.

  • Chloroplasts:

    • Photosynthesis to convert sunlight into glucose; thylakoid structures in stacks called grana.

  • Both organelles are involved in energy conversion within the cell.

Plasma Membrane Structure

  • Serves as a semi-permeable barrier, defining the cell's borders and facilitating interactions with the environment.

  • Composed of:

    • Lipids (mainly phospholipids creating the bilayer).

    • Proteins (involved in transport and communication).

    • Carbohydrates (for cell recognition).

  • Phospholipid Structure:

    • Contains a hydrophilic head and two hydrophobic fatty acid tails.

    • Amphipathic nature aids in forming the bilayer, preventing easy passage of polar substances.

Membrane Proteins

  • Integral Membrane Proteins:

    • Span across the membrane; hydrophobic regions anchor them in the bilayer.

  • Peripheral Membrane Proteins:

    • Attaches to the inner or outer surfaces, do not penetrate the lipid bilayer.

Carbohydrates in Membrane

  • Glycoproteins and glycolipids play crucial roles in cell recognition and signaling.

Differences Between Prokaryotes and Eukaryotes

  • Genetic Material:

    • Prokaryotes have circular DNA; eukaryotes have linear DNA.

  • Location of DNA:

    • Prokaryotes: free-floating in cytoplasm; eukaryotes: contained in a nucleus.

  • Organelles:

    • Prokaryotes lack membrane-bound organelles; eukaryotes have numerous such organelles.

  • Size:

    • Prokaryotes: 1-5 micrometers; eukaryotes: 10-700 micrometers.

Extracellular Matrix (ECM) & Cell Wall

ECM

  • Complex meshwork of proteins (primarily collagen) and carbohydrates outside the cell, providing strength and support.

  • Integrins connect ECM to the cell's plasma membrane, aiding in signaling.

Cell Wall

  • Rigid structure surrounding plant cells, primarily composed of cellulose, which offers support and shape.

  • Middle Lamella: A sticky layer helping to hold adjacent plant cell walls together.

Transport Mechanisms

Passive Transport

  • Requires no energy input and occurs along the concentration gradient.

  • Key terms:

    • Concentration Gradient: Differences in concentration across a space.

    • Equilibrium: Equal distribution of particles across a space.

Active Transport

  • Requires energy (ATP) to move substances against the concentration gradient.

  • Involves carrier proteins that undergo conformational change during transport.

Bulk Transport

  • Mechanisms that enclose substances in membrane-bound vesicles for transport, requiring energy.

    • Endocytosis Types:

      • Phagocytosis: Engulfing larger particles.

      • Pinocytosis: Uptake of fluids and small particles.

      • Receptor-mediated endocytosis: Involves specific receptor proteins.

Exocytosis

  • Process of transporting materials out of the cell using vesicles that fuse with the plasma membrane.

Cell Size Limitations

  • Limitations arise as volume increases faster than surface area, impacting the efficiency of transport.

  • Adaptations such as increased surface area help optimize cell function.

Osmosis & Tonicity

  • Osmosis: Movement of water from low to high solute concentration across a semipermeable membrane.

  • Tonicity: Ability of a solution to affect cell volume and shape by altering water movement.

    • Hypotonic solutions cause cells to gain volume, while hypertonic solutions lead to volume loss.