Cytoplasm and Organelles Notes

Transport Mechanisms

  • Simple Diffusion

    • Definition: Movement of small, nonpolar molecules across the plasma membrane without any energy input.

    • Direction: High to low concentration.

    • Substances transported: Oxygen, Carbon dioxide, Lipids.

  • Facilitated Diffusion

    • Definition: The process of transporting substances across the membrane with the help of transport proteins.

    • Direction: High to low concentration.

    • Substances transported: Glucose, Ions.

  • Osmosis

    • Definition: Special case of facilitated diffusion specific to water.

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

    • Substances transported: Water molecules.

Membrane Potential

  • Definition: The electric potential difference across a cellular membrane, primarily maintained by the distribution of ions (Na+, K+).

  • Function: Vital for nerve impulse transmission and muscle contraction.

Active Transport

  • Primary Active Transport

    • Definition: The process that uses ATP directly to transport molecules against their concentration gradient.

    • Example: Na+/K+ pump.

  • Secondary Active Transport

    • Definition: Involves the use of energy from the movement of one molecule down its gradient to drive the transport of another molecule against its gradient.

    • Example: Glucose-sodium symporter.

Plasma Membrane Structure

  • Relates to transport processes through:

    • Phospholipid bilayer that allows selective permeability.

    • Integral and peripheral proteins that facilitate transport.

Endocytosis and Exocytosis

  • Endocytosis

    • Function: The process of engulfing material from outside the cell.

    • Direction: Into the cell.

  • Exocytosis

    • Function: The process of expelling materials from the cell.

    • Direction: Out of the cell.

Types of Endocytosis

  • Pinocytosis

    • Definition: Engulfing extracellular fluid and nutrients.

    • Function: Nutrient absorption.

  • Phagocytosis

    • Definition: Engulfing large particles or even other cells.

    • Function: Immune response (e.g., white blood cells).

  • Receptor-Mediated Endocytosis

    • Definition: Specific uptake of molecules based on receptor interactions.

    • Example: Cholesterol uptake through LDL receptors.

Cytoplasm and Cytosol

  • Cytoplasm

    • Definition: All cellular material between plasma membrane and nucleus.

  • Cytosol

    • Definition: Gel-like solution comprised of water and soluble molecules.

  • Inclusions

    • Definition: Insoluble molecules that vary by cell type (e.g., glycogen, pigments).

  • Organelles

    • Definition: Specialized structures with specific functions within the cell.

Cytoplasmic Organelles

  • Membranous Organelles

    • Include Mitochondria, Endoplasmic Reticulum (ER), Golgi Apparatus, Lysosomes, Peroxisomes.

  • Non-Membranous Organelles

    • Include Ribosomes, Cytoskeleton, Centrioles.

Cytoskeleton

  • Structure: A series of flexible protein rods that provide structural support and aid in movements.

  • Components:

    • Microfilaments: Actin filaments aiding cell movement and shape.

    • Intermediate Filaments: Provide tensile strength and resilience.

    • Microtubules: Hollow tubes that assist in cell shape and organelle movement.

Cilia and Flagella

  • Cilia

    • Definition: Whiplike extensions that sweep substances across cell surfaces.

  • Flagella

    • Definition: Longer cellular extensions propelling the whole cell.

  • Both structures derived from microtubules organized by basal bodies.

Ribosomes

  • Structure: Granular organelles made of ribosomal RNA and proteins.

  • Types:

    • Free Ribosomes: Produce proteins that function in the cytoplasm.

    • Membrane-bound Ribosomes: Attached to rough ER and produce proteins meant for export or targeting membranes.

Endomembrane System

  • Definition: A network of membranes that synthesizes, stores, and exports molecules.

  • Components: Rough and Smooth ER, Golgi apparatus, secretory vesicles, lysosomes, nuclear and plasma membranes.

  • Functions:

    • Produces and degrades biological molecules.

    • Detoxifies harmful substances.

Golgi Apparatus

  • Structure: Stacked, flattened membranous sacs.

  • Functions:

    • Modifies, concentrates, and packages proteins and lipids.

    • Packages proteins into secretory, membrane or transport vesicles.

Lysosomes and Peroxisomes

  • Lysosomes

    • Function: Contain enzymes for digesting materials, waste processing, and recycling.

  • Peroxisomes

    • Function: Contain enzymes to detoxify harmful substances (e.g., alcohol).

Ubiquitin and Proteasomes

  • Ubiquitin

    • Function: Marks proteins for degradation, ensuring quality control.

  • Proteasomes

    • Function: Degrade unneeded or damaged proteins into peptides, important for recycling materials.

Mitochondria

  • Definition: Membranous organelles known as the powerhouse of the cell.

  • Function: Generate ATP through aerobic respiration.

  • Structure: Double membrane with inner membrane folds called cristae, which increase surface area for energy production.

  • Key Role: Involved in various metabolic processes, including the citric acid cycle and oxidative phosphorylation.

Cytoskeletal Elements

  • Structure: Composed of a network of protein rods.

    • Microfilaments: Actin filaments providing structure and aiding cell movement.

    • Intermediate Filaments: Provide tensile strength and support against mechanical stress.

    • Microtubules: Hollow tubes that assist with maintaining cell shape, organelle movement, and division.

  • Function: Provide structural support, facilitate movement (both of the cell and within the cell), and aid in cell division.

Centrioles

  • Role in Cilia and Flagella Formation:

    • Centrioles are cylindrical structures composed of microtubules.

    • They organize the microtubule formation required for cilia and flagella, which are cellular extensions involved in movement and sensory functions.

Cilia vs. Microvilli

  • Cilia:

    • Structure: Whiplike extensions constructed from microtubules in a 9+2 arrangement.

    • Function: Move substances across the cell surface (e.g., respiratory tract).

  • Microvilli:

    • Structure: Shorter, finger-like projections that are non-motile and made of actin filaments.

    • Function: Increase the surface area for absorption (e.g., intestinal cells).

Ribosomes, Endoplasmic Reticulum, and Golgi Apparatus

  • Ribosomes:

    • Structure: Granular organelles made of ribosomal RNA and proteins; may be free in the cytoplasm or bound to the rough ER.

    • Function: Synthesize proteins.

  • Endoplasmic Reticulum (ER):

    • Rough ER: Studded with ribosomes; processes and transports proteins.

    • Smooth ER: Lacks ribosomes; synthesizes lipids and detoxifies certain chemicals.

  • Golgi Apparatus:

    • Structure: Stacked, flattened membranous sacs.

    • Function: Modifies, concentrates, and packages proteins and lipids received from the ER into vesicles for secretion or delivery to other organelles.

  • Functional Interrelationships:

    • Ribosomes produce proteins that are processed in the Rough ER; the Golgi modifies these proteins and ships them to their destinations.

Lysosomes vs. Peroxisomes

  • Lysosomes:

    • Function: Contain enzymes for digestion, waste processing, and recycling cellular components.

  • Peroxisomes:

    • Function: Contain enzymes for the detoxification of harmful substances (such as alcohol) and metabolic functions, including the breakdown of fatty acids.

Mitochondria

  • Structure: Membranous organelles with a double membrane; the inner membrane is folded into cristae to increase surface area.

  • Function: Known as the powerhouse of the cell; generate ATP through aerobic respiration, involved in metabolic processes like the citric acid cycle and oxidative phosphorylation.