Cytoskeleton, mitochondria (MP)

Vacuoles and Their Functions

What are Vacuoles?

  • Definition: Membrane-bound organelles responsible for storing substances in a cell.

  • Types of Vacuoles: Different vacuoles have specific functions including:

    • Food Vacuoles

      • Function: Store food within the cell.

      • Example: Found in cells that store food.

    • Contractile Vacuoles

      • Function: Manage intake and release of water, especially in protists (e.g., paramecia).

    • Central Vacuoles

      • Function: Store water, mainly in plant cells; crucial for maintaining turgor pressure.

      • Found in: Primarily in plant cells.

Central Vacuole in Plant Cells

  • Function:

    • Store water.

    • Maintain turgor pressure within the cell.

  • Process:

    • Absorbs water and expands, applying pressure on cell membrane wall.

    • Helps maintain plant cell shape and prevents wilting.

    • Over-absorption of water can cause cell bursting (e.g., when overwatering a plant).

  • Example: A plant’s central vacuole grows as it stores more water, exerting pressure against the cell wall.

Contractile Vacuole in Protists

  • Function: Manage water intake and release primarily in freshwater environments.

  • Process:

    • When a paramecium needs to access nutrients, it releases water from the contractile vacuole to float.

    • It absorbs water to sink back down.

  • Analogy: Functions like a balloon—releasing air decreases size, and absorbing air increases size.

  • Example: In water, paramecium uses contractile vacuole to manage buoyancy.

Cytoskeleton and Its Components

Function of Cytoskeleton

  • Provides structural support to the cell.

  • Protects the cell.

  • Aids in cell locomotion.

Components of the Cytoskeleton

  • Three Main Components:

    • Microfilaments (Actin Filaments): Responsible for cell movement and shape.

    • Microtubules: Involved in transporting materials within the cell.

    • Intermediate Filaments: Maintain structural integrity and anchor cell components.

Monomers and Polymerization

  • Cytoskeletal components consist of monomers that form polymers:

    • Microfilaments:

      • Composed of actin monomers.

      • Polymerize to form microfilaments.

      • Can depolymerize, breaking down into smaller units.

    • Microtubules:

      • Composed of alpha and beta tubulin monomers.

      • Polymerize to form microtubules.

    • Intermediate Filaments:

      • Not true polymers; made from various monomers (e.g., keratin).

      • Do not require specific monomer knowledge for study.

Functions of Each Cytoskeletal Component

  • Intermediate Filaments:

    • Provide structural support.

    • Anchor the nucleus in place.

  • Microfilaments:

    • Enable cell movement.

  • Microtubules:

    • Facilitate material movement inside the cell.

Example of Microtubules in Action

  • Phagocytosis:

    • Cell engulfs material (e.g., bacterium) creating a phagosome.

    • Microtubules guide the phagosome to lysosome for digestion.

Cellular Transport

  • Ongoing Processes:

    • Cells are in constant motion—constructing, demolishing, and transporting.

  • Microtubules Function:

    • Act as tracks for material transportation.

  • Kinesin:

    • A motor protein that transports cargo along microtubules; works like vehicles on a freeway.

    • Highly efficient in converting chemical energy into motion.

Role of Microtubules in Transport

  • Transport cellular components such as organelles, proteins, and DNA along microtubules.

Mitochondria and Chloroplasts (Energy Conversion)

Mitochondria

  • Known as the powerhouse of the cell; converts chemical energy from glucose into ATP via cellular respiration.

Chloroplasts

  • Found in plant cells; responsible for converting light energy into chemical energy (glucose) through photosynthesis.

  • ATP production is essential for both animal and plant cells.

Energy Process in Plants vs. Animals

  • Plants:

    • Can perform both photosynthesis and cellular respiration.

  • Animals:

    • Cannot perform photosynthesis; rely on consuming food for ATP production.

  • Fun Fact: Humans cannot convert sunlight into energy; however, we synthesize Vitamin D from sunlight.

Consumers vs. Producers

Heterotrophs (Consumers)

  • Organisms that cannot make their own food; depend on other organisms for energy.

  • Animals are heterotrophs and must obtain glucose externally.

Autotrophs (Producers)

  • Organisms that produce their own food using energy from external sources (e.g., sunlight).

  • Plants are autotrophs through photosynthesis.

Energy Source for Animals and Plants

  • Animals depend on consuming food for ATP production.

  • Plants produce glucose via photosynthesis and then convert it into ATP.

Chloroplasts and Mitochondria

Dual Membrane Structure

  • Both organelles have a double membrane: an outer and inner membrane essential for energy conversion.

Internal Compartments

  • Chloroplasts: Inner space filled with stroma necessary for photosynthesis.

  • Mitochondria: Contains the matrix, gel-like substance involved in cellular respiration.

Ribosomes and Chromosomes

  • Contain 70S ribosomes similar to bacteria.

  • Both contain circular chromosomes, suggesting their bacterial origin (endosymbiosis).

Endosymbiotic Theory

  • Explains the origin of mitochondria and chloroplasts in eukaryotic cells; suggests ancient prokaryotic cells engulfed bacteria for ATP production, creating a symbiotic relationship.

Evolution of Eukaryotic Cells

  • Complex cells arose through engulfment of bacteria, leading to symbiotic relationships aiding ATP production and evolution of complexity.

Fats and Membranes

Secretory Vesicles

  • Carry molecules to different cell parts—rough ER exports proteins essential for cellular functions.

DNA Replication and Protein Production

  • DNA Polymerase: Replicates DNA in both eukaryotes and prokaryotes.

  • RNA Polymerase: Transcribes DNA into RNA.

Hydrogenation and Fats

  • Hydrogenation adds hydrogen to molecules—producing cis fats (more easily broken down) and trans fats (harder to metabolize).

Microfilaments and Microtubules

  • Play roles in transporting materials for cell division and protein transport processes.

Summary of Organelles

Ribosomes

  • Free ribosome proteins stay within the cell; others on rough ER are exported.

  • Extracellular Matrix: Collagen supports tissues; integrated in cell membrane.

  • Cholesterol: Important for membrane structure and lipid bilayer stability.

  • Contractile Vacuoles: Regulate buoyancy in protists, aiding in movement.